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tramp trampver User Manual
**************************

This file documents tramp trampver, a remote file editing package for Emacs.

tramp stands for ``Transparent Remote (file) Access, Multiple Protocol''.  This package provides remote file editing, similar to Ange FTP.

The difference is that Ange FTP uses FTP to transfer files between the local and the remote host, whereas tramp uses a combination of rsh and rcp or other work-alike programs, such as ssh/scp.

You can find the latest version of this document on the web at https://www.gnu.org/software/tramp/.

There is a mailing list for tramp, available at tramp-bug-report-address, and archived at the tramp Mail Archive (https://lists.gnu.org/r/tramp-devel/).

Copyright © 1999--2020 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being ``A GNU Manual'', and with the Back-Cover Texts as in (a) below.  A copy of the license is included in the section entitled ``GNU Free Documentation License''.

     (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and modify this GNU manual.''

An overview of tramp
********************

tramp is for transparently accessing remote files from within Emacs.  tramp enables an easy, convenient, and consistent interface to remote files as if they are local files.  tramp's transparency extends to editing, version control, and dired.

tramp can access remote hosts using any number of access methods, such as rsh, rlogin, telnet, and related programs.  If these programs can successfully pass ASCII characters, tramp can use them. tramp does not require or mandate 8-bit clean connections.

tramp's most common access method is through ssh, a more secure alternative to ftp and other older access methods.

tramp on MS Windows operating systems is integrated with the PuTTY package, and uses the plink program.

tramp mostly operates transparently in the background using the connection programs.  As long as these programs enable remote login and can use the terminal, tramp can adapt them for seamless and transparent access.

tramp temporarily transfers a remote file's contents to the local host editing and related operations.  tramp can also transfer files between hosts using standard Emacs interfaces, a benefit of direct integration of tramp in Emacs.

tramp can transfer files using any number of available host programs for remote files, such as rcp, scp, rsync or (under MS Windows) pscp.  tramp provides easy ways to specify these programs and customize them to specific files, hosts, or access methods.

For faster small-size file transfers, tramp supports encoded transfers directly through the shell using mimencode or uuencode provided such tools are available on the remote host.

tramp behind the scenes
.......................

Accessing a remote file through tramp entails a series of actions, many of which are transparent to the user.  Yet some actions may require user response (such as entering passwords or completing file names).  One typical scenario, opening a file on a remote host, is presented here to illustrate the steps involved:

C-x C-f to initiate find-file, enter part of the tramp file name, then hit TAB for completion.  If this is the first time connection to that host, here's what happens:

  * tramp invokes telnet HOST or rsh HOST
     -l USER and establishes an external process to connect to the remote host.  tramp communicates with the process through an Emacs buffer, which also shows output from the remote host.

  * The remote host may prompt for a login name (for telnet, for example) in the buffer.  If on the other hand, the login name was included in the file name portion, tramp sends the login name followed by a newline.

  * The remote host may then prompt for a password or pass phrase (for rsh or for telnet).  tramp displays the password prompt in the minibuffer.  tramp then sends whatever is entered to the remote host, followed by a newline.

  * tramp now waits for either the shell prompt or a failed login message.

     If tramp does not receive any messages within a timeout period (a minute, for example), then tramp responds with an error message about not finding the remote shell prompt.  If any messages from the remote host, tramp displays them in the buffer.

     For any login failed message from the remote host, tramp aborts the login attempt, and repeats the login steps again.

  * Upon successful login and tramp recognizes the shell prompt from the remote host, tramp prepares the shell environment by turning off echoing, setting shell prompt, and other housekeeping chores.

     Note that for the remote shell, tramp invokes /bin/sh.  The remote host must recognize exec /bin/sh and execute the appropriate shell.  This shell must support Bourne shell syntax.

  * tramp executes cd and ls commands to find which files exist on the remote host.  tramp sometimes uses echo with globbing.  tramp checks if a file or directory is writable with test.  After each command, tramp parses the output from the remote host for completing the next operation.

  * After remote file name completion, tramp transfers the file contents from the remote host.

     For inline transfers, tramp sends a command, such as mimencode -b /path/to/remote/file, waits until the output has accumulated in the buffer, decodes that output to produce the file's contents.

     For external transfers, tramp sends a command as follows:

          rcp user@host:/path/to/remote/file /tmp/tramp.4711

     tramp reads the local temporary file /tmp/tramp.4711 into a buffer, and then deletes the temporary file.

  * Edit, modify, change the buffer contents as normal, and then save the buffer with C-x C-s.

  * tramp transfers the buffer contents to the remote host in a reverse of the process using the appropriate inline or external program.

I hope this has provided you with a basic overview of what happens behind the scenes when you open a file with tramp.

Obtaining tramp
***************

tramp is included as part of Emacs (since Emacs 22.1).

tramp is also freely packaged for download on the Internet at https://ftp.gnu.org/gnu/tramp/.  The version number of tramp can be obtained by the variable tramp-version. For released tramp versions, this is a three-number string like ``2.4.2''.

A tramp release, which is packaged with Emacs, could differ slightly from the corresponding standalone release.  This is because it isn't always possible to synchronize release dates between Emacs and tramp.  Such version numbers have the Emacs version number as suffix, like ``2.3.5.26.3''.  This means tramp 2.3.5 as integrated in Emacs 26.3.  A complete list of tramp versions packaged with Emacs can be retrieved by

     (assoc 'Tramp customize-package-emacs-version-alist)

tramp is also available as GNU ELPA (https://elpa.gnu.org) package.  Besides the standalone releases, further minor version of tramp will appear on GNU ELPA, until the next tramp release appears.  These minor versions have a four-number string, like ``2.4.2.1''.

tramp development versions are available on Git servers. Development versions contain new and incomplete features.  The development version of tramp is always the version number of the next release, plus the suffix ``-pre'', like ``2.4.3-pre''.

One way to obtain tramp from Git server is to visit the Savannah project page at the following URL and then clicking on the Git link in the navigation bar at the top.

https://savannah.gnu.org/projects/tramp/

Another way is to follow the terminal session below:

     $ cd ~/emacs
     $ git clone git://git.savannah.gnu.org/tramp.git

From behind a firewall:

     $ git config --global http.proxy http://user:pwd@proxy.server.com:8080
     $ git clone https://git.savannah.gnu.org/r/tramp.git

tramp developers:

     $ git clone login@git.sv.gnu.org:/srv/git/tramp.git

After one of the above commands, ~/emacs/tramp will containing the latest version of tramp.

To fetch updates from the repository, use git pull:

     $ cd ~/emacs/tramp
     $ git pull

Run autoconf as follows to generate an up-to-date configure script:

     $ cd ~/emacs/tramp
     $ autoconf

See the file INSTALL in that directory for further information how to install tramp.

Short introduction how to use tramp
***********************************

tramp extends the Emacs file name syntax by a remote component.  A remote file name looks always like method,user@host,/path/to/file.

You can use remote files exactly like ordinary files, that means you could open a file or directory by C-x C-f method,user@host,/path/to/file RET, edit the file, and save it.  You can also mix local files and remote files in file operations with two arguments, like copy-file or rename-file.  And finally, you can run even processes on a remote host, when the buffer you call the process from has a remote default-directory.

File name syntax
================

Remote file names are prepended by the method, user and host parts.  All of them, and also the local file name part, are optional, in case of a missing part a default value is assumed. The default value for an empty local file name part is the remote user's home directory.  The shortest remote file name is -,,, therefore.  The - notation for the default host is used for syntactical reasons, Default Host.

The method part describes the connection method used to reach the remote host, see below.

The user part is the user name for accessing the remote host. For the smb method, this could also require a domain name, in this case it is written as user%domain.

The host part must be a host name which could be resolved on your local host.  It could be a short host name, a fully qualified domain name, an IPv4 or IPv6 address, File name syntax.  Some connection methods support also a notation of the port to be used, in this case it is written as host#port.

Using ssh and plink
===================

If your local host runs an SSH client, and the remote host runs an SSH server, the simplest remote file name is ssh,user@host,/path/to/file.  The remote file name ssh,, opens a remote connection to yourself on the local host, and is taken often for testing tramp.

On MS Windows, PuTTY is often used as SSH client.  Its plink method can be used there to open a connection to a remote host running an ssh server: plink,user@host,/path/to/file.

Using su, sudo and sg
=====================

Sometimes, it is necessary to work on your local host under different permissions.  For this, you could use the su or sudo connection method.  Both methods use root as default user name and the return value of (system-name) as default host name. Therefore, it is convenient to open a file as sudo,,/path/to/file.

The method sg stands for ``switch group''; the changed group must be used here as user name.  The default host name is the same.

Combining ssh or plink with su or sudo
======================================

If the su or sudo option shall be performed on another host, it could be comnbined with a leading ssh or plink option.  That means, tramp connects first to the other host with non-administrative credentials, and changes to administrative credentials on that host afterwards.  In a simple case, the syntax looks like prefixsshpostfixhopuser@host|sudopostfixhoppostfix/path/to/file. See Ad-hoc multi-hops.

Using sudoedit
==============

The sudoedit method is similar to the sudo method. However, it is a different implementation: it does not keep an open session running in the background.  This is for security reasons; on the backside this method is less performant than the sudo method, it is restricted to the localhost only, and it does not support external processes.

Using smbclient
===============

In order to access a remote MS Windows host or Samba server, the smbclient client is used.  The remote file name syntax is smb,user%domain@host,/path/to/file.  The first part of the local file name is the share exported by the remote host, path in this example.

Using GVFS-based methods
========================

On systems, which have installed GVFS (the GNOME Virtual File System), its offered methods could be used by tramp.  Examples are sftp,user@host,/path/to/file, afp,user@host,/path/to/file (accessing Apple's AFP file system), dav,user@host,/path/to/file and davs,user@host,/path/to/file (for WebDAV shares).

Using GNOME Online Accounts based methods
=========================================

GVFS-based methods include also GNOME Online Accounts, which support the Files service.  These are the Google Drive file system, and the OwnCloud/NextCloud file system.  The file name syntax is here always gdrive,john.doe@gmail.com,/path/to/file (john.doe@gmail.com stands here for your Google Drive account), or nextcloud,user@host#8081,/path/to/file (8081 stands for the port number) for OwnCloud/NextCloud files.

Using Android
=============

An Android device, which is connected via USB to your local host, can be accessed via the adb command.  No user or host name is needed.  The file name syntax is adb,,/path/to/file.

Using rclone
============

A convenient way to access system storages is the rclone program.  If you have configured a storage in rclone under a name storage (for example), you could access it via the remote file name syntax rclone,storage,/path/to/file.  User names are not needed.

Configuring tramp
*****************

tramp is initially configured to use the scp program to connect to the remote host.  Just type C-x C-f and then enter file name scp,user@host,/path/to/file.  For details, see Default Method, see Default User, see Default Host.

For problems related to the behavior of the remote shell, see Remote shell setup.

For changing the connection type and file access method from the defaults to one of several other options, see Connection types.

Note that some user options described in these examples are not auto loaded by Emacs.  All examples require tramp is installed and loaded:

     (customize-set-variable 'tramp-verbose 6 "Enable remote command traces")

For functions used to configure tramp, the following clause might be used in your init file:

     (with-eval-after-load 'tramp (tramp-change-syntax 'simplified))

Types of connections to remote hosts
====================================

Inline method and external method are the two basic types of access methods.  While they both use the same remote shell access programs, such as rsh, ssh, or telnet, they differ in the file access methods.  Choosing the right method becomes important for editing files, transferring large files, or operating on a large number of files.

The performance of the external methods is generally better than that of the inline methods, at least for large files.  This is caused by the need to encode and decode the data when transferring inline.

The one exception to this rule are the scp-based access methods.  While these methods do see better performance when actually transferring files, the overhead of the cryptographic negotiation at startup may drown out the improvement in file transfer times.

External methods should be configured such a way that they don't require a password (with ssh-agent, or such alike).  Modern scp implementations offer options to reuse existing ssh connections, which will be enabled by default if available.  If it isn't possible, you should consider Password handling, otherwise you will be prompted for a password every copy action.

Inline methods
==============

Inline methods use the same login connection to transfer file contents.  Inline methods are quick and easy for small files.  They depend on the availability of suitable encoding and decoding programs on the remote host.  For local source and destination, tramp may use built-in equivalents of such programs in Emacs.

Inline methods can work in situations where an external transfer program is unavailable.  Inline methods also work when transferring files between different user identities on the same host.

tramp checks the remote host for the availability and usability of one of the commands defined in tramp-remote-coding-commands.  tramp uses the first reliable command it finds.  tramp's search path can be customized, see Remote programs.

In case none of the commands are unavailable, tramp first transfers a small Perl program to the remote host, and then tries that program for encoding and decoding.

To increase transfer speeds for large text files, use compression before encoding.  The user option tramp-inline-compress-start-size specifies the file size for such optimization.  This feature depends on the availability and usability of one of the commands defined in tramp-inline-compress-commands.

rsh

     rsh is an option for connecting to hosts within local networks since rsh is not as secure as other methods.

ssh

     ssh is a more secure option than others to connect to a remote host.

     ssh can also take extra parameters as port numbers.  For example, a host on port 42 is specified as host#42 (the real host name, a hash sign, then a port number).  It is the same as passing -p 42 to the ssh command.

telnet

     Connecting to a remote host with telnet is as insecure as the rsh method.

su

     Instead of connecting to a remote host, su program allows editing as another user.  The host can be either localhost or the host returned by the function (system-name).  See Multi-hops for an exception to this behavior.

sudo

     Similar to su method, sudo uses sudo. sudo must have sufficient rights to start a shell.

     For security reasons, a sudo connection is disabled after a predefined timeout (5 minutes per default).  This can be changed, see Predefined connection information.

doas

     This method is used on OpenBSD like the sudo command.  Like the sudo method, a doas connection is disabled after a predefined timeout.

sg

     The sg program allows editing as different group.  The host can be either localhost or the host returned by the function (system-name).  The user name must be specified, but it denotes a group name.  See Multi-hops for an exception to this behavior.

sshx

     Works like ssh but without the extra authentication prompts. sshx uses ssh -t -t HOST -l USER /bin/sh to open a connection with a ``standard'' login shell.  It supports changing the remote login shell /bin/sh.

     Note that sshx does not bypass authentication questions.  For example, if the host key of the remote host is not known, sshx will still ask ``Are you sure you want to continue connecting?''.  tramp cannot handle such questions. Connections will have to be setup where logins can proceed without such questions.

     sshx is useful for MS Windows users when ssh triggers an error about allocating a pseudo tty.  This happens due to missing shell prompts that confuses tramp.

     sshx supports the -p argument.

krlogin

     This method is also similar to ssh.  It uses the krlogin -x command only for remote host login.

ksu

     This is another method from the Kerberos suite.  It behaves like su.

plink

     plink method is for MS Windows users with the PuTTY implementation of SSH.  It uses plink -ssh to log in to the remote host.  It supports changing the remote login shell /bin/sh.

     Check the Share SSH connections if possible control for that session.

     plink method supports the -P argument.

plinkx

     Another method using PuTTY on MS Windows with session names instead of host names.  plinkx calls plink -load SESSION -t.  User names and port numbers must be defined in the session.  It supports changing the remote login shell /bin/sh.

     Check the Share SSH connections if possible control for that session.

External methods
================

External methods operate over multiple channels, using the remote shell connection for some actions while delegating file transfers to an external transfer program.

External methods save on the overhead of encoding and decoding of inline methods.

Since external methods have the overhead of opening a new channel, files smaller than tramp-copy-size-limit still use inline methods.

rcp

     This method uses the rsh and rcp commands to connect to the remote host and transfer files.  This is the fastest access method available.

     The alternative method remcp uses the remsh and rcp commands.

scp

     Using a combination of ssh to connect and scp to transfer is the most secure.  While the performance is good, it is slower than the inline methods for smaller files.  Though there is no overhead of encoding and decoding of the inline methods, scp's cryptographic handshake negates those speed gains.

     ssh-based methods support -p feature for specifying port numbers.  For example, host#42 passes -p 42 in the argument list to ssh, and -P 42 in the argument list to scp.

rsync

     ssh command to connect in combination with rsync command to transfer is similar to the scp method.

     rsync performs much better than scp when transferring files that exist on both hosts.  However, this advantage is lost if the file exists only on one side of the connection.

     This method supports the -p argument.

scpx

     scpx is useful to avoid login shell questions.  It is similar in performance to scp.  scpx uses ssh -t -t HOST -l USER /bin/sh to open a connection.  It supports changing the remote login shell /bin/sh.

     scpx is useful for MS Windows users when ssh triggers an error about allocating a pseudo tty.  This happens due to missing shell prompts that confuses tramp.

     This method supports the -p argument.

pscp

psftp

     These methods are similar to scp or sftp, but they use the plink command to connect to the remote host, and they use pscp or psftp for transferring the files. These programs are part of PuTTY, an SSH implementation for MS Windows.

     They support changing the remote login shell /bin/sh.

     Check the Share SSH connections if possible control for that session.

     These methods support the -P argument.

fcp

     This method is similar to scp, but uses fsh to connect and fcp to transfer files.  fsh/fcp, a front-end for ssh, reuse ssh session by submitting several commands.  This avoids the startup overhead due to scp's secure connection.  Inline methods have similar benefits.

     The command used for this connection is: fsh HOST -l USER /bin/sh -i

     fsh has no inline method since the multiplexing it offers is not useful for tramp.  fsh connects to remote host and tramp keeps that one connection open.

nc

     Using telnet to connect and nc to transfer files is sometimes the only combination suitable for accessing routers or NAS hosts.  These dumb devices have severely restricted local shells, such as the busybox and do not host any other encode or decode programs.

sudoedit

     The sudoedit method allows to edit a file as a different user on the local host.  You could regard this as tramp's implementation of the sudoedit.  Contrary to the sudo method, all magic file name functions are implemented by single sudo ...  commands.  The purpose is to make editing such a file as secure as possible; there must be no session running in the Emacs background which could be attacked from inside Emacs.

     Consequently, external processes are not implemented.

     The host name of such remote file names must represent the local host. Since the default value is already proper, it is recommended not to use any host name in the remote file name, like sudoedit,,/path/to/file or sudoedit,user@,/path/to/file.

     Like the sudo method, a sudoedit password expires after a predefined timeout.

ftp

     When tramp uses ftp, it forwards requests to whatever ftp program is specified by Ange FTP.  This external program must be capable of servicing requests from tramp.

smb

     This non-native tramp method connects via the Server Message Block (SMB) networking protocol to hosts running file servers that are typically based on Samba or MS Windows.

     Using smbclient requires a few tweaks when working with tramp:

     The first directory in the localname must be a share name on the remote host.

     Since some SMB share names end in the $ character, tramp must use $$ when specifying those shares to avoid environment variable substitutions.

     When tramp is not specific about the share name or uses the generic remote directory /, smbclient returns all available shares.

     Since SMB authentication is based on each SMB share, tramp prompts for a password even when accessing a different share on the same SMB host.  This prompting can be suppressed by Password handling.

     To accommodate user name/domain name syntax required by MS Windows authorization, tramp provides for an extended syntax in user%domain format (where user is the user name, % is the percent symbol, and domain is the MS Windows domain name).  An example:

          smb,daniel%BIZARRE@melancholia,/daniel$$/.emacs

     where user daniel connects as a domain user to the SMB host melancholia in the MS Windows domain BIZARRE to edit .emacs located in the home directory (share daniel$).

     Alternatively, for local WINS users (as opposed to domain users), substitute the domain name with the name of the local host in UPPERCASE as shown here:

          smb,daniel%MELANCHOLIA@melancholia,/daniel$$/.emacs

     where user daniel connects as local user to the SMB host melancholia in the local domain MELANCHOLIA to edit .emacs located in the home directory (share daniel$).

     The domain name and user name are optional for smbclient authentication.  When user name is not specified, smbclient uses the anonymous user (without prompting for password).  This behavior is unlike other tramp methods, where local user name is substituted.

     The smb method is unavailable if Emacs is run under a local user authentication context in MS Windows.  However such users can still access remote files using UNC file names instead of tramp:

          //melancholia/daniel$$/.emacs

     UNC file name specification does not allow the specification of a different user name for authentication like the smbclient can.

adb

     This method uses Android Debug Bridge program for accessing Android devices.  The Android Debug Bridge must be installed locally for tramp to work.  Some GNU/Linux distributions provide Android Debug Bridge as an installation package.  Alternatively, the program is installed as part of the Android SDK.  tramp finds the adb program either via the PATH environment variable or the absolute path set in the user option tramp-adb-program.

     tramp connects to Android devices with adb only when the user option tramp-adb-connect-if-not-connected is not nil.  Otherwise, the connection must be established outside Emacs.

     tramp does not require a host name part of the remote file name when a single Android device is connected to adb. tramp instead uses adb,, as the default name. adb devices shows available host names.

     adb method normally does not need user name to authenticate on the Android device because it runs under the adbd process.  But when a user name is specified, however, tramp applies an su in the syntax.  When authentication does not succeed, especially on un-rooted Android devices, tramp displays login errors.

     For Android devices connected through TCP/IP, a port number can be specified using device#42 host name syntax or tramp can use the default value as declared in adb command.  Port numbers are not applicable to Android devices connected through USB.

rclone

     The program rclone allows to access different system storages in the cloud, see https://rclone.org/ for a list of supported systems.  If the rclone program isn't found in your PATH environment variable, you can tell tramp its absolute path via the user option tramp-rclone-program.

     A system storage must be configured via the rclone config command, outside Emacs.  If you have configured a storage in rclone under a name storage (for example), you could access it via the remote file name

          rclone,storage,/path/to/file

     User names are part of the rclone configuration, and not needed in the remote file name.  If a user name is contained in the remote file name, it is ignored.

     Internally, tramp mounts the remote system storage at location /tmp/tramp.rclone.storage, with storage being the name of the configured system storage.

     Optional flags to the different rclone operations could be passed as connection property, see Predefined connection information.  Supported properties are "mount-args", "copyto-args" and "moveto-args".

     Access via rclone is slow.  If you have an alternative method for accessing the system storage, you shall prefer this. GVFS-based methods for example, methods gdrive and nextcloud.

     Note: The rclone method is experimental, don't use it in production systems!

GVFS-based external methods
===========================

GVFS is the virtual file system for the GNOME Desktop, https://en.wikipedia.org/wiki/GVFS.  Remote files on GVFS are mounted locally through FUSE and tramp uses this locally mounted directory internally.

Emacs uses the D-Bus mechanism to communicate with GVFS. Emacs must have the message bus system, D-Bus integration active, see D-Bus (dbus).

afp

     This method is for connecting to remote hosts with the Apple Filing Protocol for accessing files on macOS volumes.  tramp access syntax requires a leading volume (share) name, for example: afp,user@host,/volume.

dav

davs

     dav method provides access to WebDAV files and directories based on standard protocols, such as HTTP.  davs does the same but with SSL encryption.  Both methods support the port numbers.

     Paths being part of the WebDAV volume to be mounted by GVFS, as it is common for OwnCloud or NextCloud file names, are not supported by these methods.  See method nextcloud for handling them.

gdrive

     Via the gdrive method it is possible to access your Google Drive online storage.  User and host name of the remote file name are your email address of the Google Drive credentials, like gdrive,john.doe@gmail.com,/.  These credentials must be populated in your Online Accounts application outside Emacs.

     Since Google Drive uses cryptic blob file names internally, tramp works with the display-name of the files.  This could produce unexpected behavior in case two files in the same directory have the same display-name, such a situation must be avoided.

nextcloud

     As the name indicates, the method nextcloud allows you to access OwnCloud or NextCloud hosted files and directories.  Like the gdrive method, your credentials must be populated in your Online Accounts application outside Emacs. The method supports port numbers.

sftp

     This method uses sftp in order to securely access remote hosts.  sftp is a more secure option for connecting to hosts that for security reasons refuse ssh connections.

 -- User Option: tramp-gvfs-methods
     This user option is a list of external methods for GVFS. By default, this list includes afp, dav, davs, gdrive, nextcloud and sftp. Other methods to include are ftp, http, https and smb.  These methods are not intended to be used directly as GVFS-based method.  Instead, they are added here for the benefit of Archive file names.

     If you want to use GVFS-based ftp or smb methods, you must add them to tramp-gvfs-methods, and you must disable the corresponding Tramp package by setting tramp-ftp-method or tramp-smb-method to nil, respectively:

          (add-to-list 'tramp-gvfs-methods "ftp")
          (customize-set-variable 'tramp-ftp-method nil)

Selecting a default method
==========================

In a remote file name, the use of a default method is indicated by the pseudo method -, File name syntax.

 -- User Option: tramp-default-method
     Default method is for transferring files.  The user option tramp-default-method sets it.  tramp uses this user option to determine the default method for remote file names that do not have one specified.

          (customize-set-variable 'tramp-default-method "ssh")

 -- User Option: tramp-default-method-alist
     Default methods for transferring files can be customized for specific user and host combinations through the user option tramp-default-method-alist.

     For example, the following two lines specify to use the ssh method for all user names matching john and the rsync method for all host names matching lily.  The third line specifies to use the su method for the user root on the host localhost.

          (add-to-list 'tramp-default-method-alist '("" "john" "ssh"))
          (add-to-list 'tramp-default-method-alist '("lily" "" "rsync"))
          (add-to-list 'tramp-default-method-alist
                       '("\\`localhost\\'" "\\`root\\'" "su"))

External methods performance faster for large files.  see Inline methods.  see External methods.

Choosing the access method also depends on the security environment. For example, rsh and telnet methods that use clear text password transfers are inappropriate for over the Internet connections.  Secure remote connections should use ssh that provide encryption.

Which method to use?
--------------------

tramp provides maximum number of choices for maximum flexibility.  Choosing which method depends on the hosts, clients, network speeds, and the security context.

Start by using an inline method.

External methods might be more efficient for large files, but most tramp users edit small files more often than large files.

Enable compression, tramp-inline-compress-start-size, for a performance boost for large files.

Since ssh has become the most common method of remote host access and it has the most reasonable security protocols, use ssh method.  Typical ssh usage to edit the /etc/motd file on the otherhost:

     C-x C-f ssh,root@otherhost,/etc/motd RET

If ssh is unavailable for whatever reason, look for other obvious options.  For MS Windows, try the plink method.  For Kerberos, try krlogin.

For editing local files as su or sudo methods, try the shortened syntax of root:

     C-x C-f su,,/etc/motd RET

For editing large files, scp is faster than ssh. pscp is faster than plink.  But this speed improvement is not always true.

Selecting a default user
========================

 -- User Option: tramp-default-user
     A tramp file name can omit the user name part since tramp substitutes the currently logged-in user name.  However this substitution can be overridden with tramp-default-user. For example:

          (customize-set-variable 'tramp-default-user "root")

 -- User Option: tramp-default-user-alist
     Instead of a single default user, tramp-default-user-alist allows multiple default user values based on access method or host name combinations.  The alist can hold multiple values.  For example, to use the john as the default user for the domain somewhere.else only:

          (add-to-list 'tramp-default-user-alist
                       '("ssh" ".*\\.somewhere\\.else\\'" "john"))

     A Caution: tramp will override any default user specified in the configuration files outside Emacs, such as ~/.ssh/config. To stop tramp from applying the default value, set the corresponding alist entry to nil:

          (add-to-list 'tramp-default-user-alist
                       '("ssh" "\\`here\\.somewhere\\.else\\'" nil))

     The last entry in tramp-default-user-alist should be reserved for catch-all or most often used login.

          (add-to-list 'tramp-default-user-alist
                       '(nil nil "jonas") t)

Selecting a default host
========================

 -- User Option: tramp-default-host
     When host name is omitted, tramp substitutes the value from the tramp-default-host user option.  It is initially populated with the local host name where Emacs is running.  The default method, default user and default host can be overridden as follows:

          (custom-set-variables
           '(tramp-default-method "ssh")
           '(tramp-default-user "john")
           '(tramp-default-host "target"))

     With all defaults set, -,, will connect tramp to John's home directory on target via ssh.

 -- User Option: tramp-default-host-alist
     Instead of a single default host, tramp-default-host-alist allows multiple default host values based on access method or user name combinations.  The alist can hold multiple values.  While tramp-default-host is sufficient in most cases, some methods, like adb, require defaults overwritten.

Connecting to a remote host using multiple hops
===============================================

Multi-hops are methods to reach hosts behind firewalls or to reach the outside world from inside a bastion host.  With multi-hops, tramp can negotiate these hops with the appropriate user/host authentication at each hop.  All methods until now have been the single hop kind, where the start and end points of the connection did not have intermediate check points.

 -- User Option: tramp-default-proxies-alist
     tramp-default-proxies-alist specifies proxy hosts to pass through.  This user option is list of triples consisting of (HOST USER PROXY).

     The first match is the proxy host through which passes the file name and the target host matching USER@HOST.  HOST and USER are regular expressions or nil, interpreted as a regular expression which always matches.

     PROXY is a literal tramp file name whose local name part is ignored, and the method and user name parts are optional.

     The method must be an inline method (see Inline methods).  If PROXY is nil, no additional hop is required reaching USER@HOST.

     For example, to pass through the host bastion.your.domain as user bird to reach remote hosts outside the local domain:

          (add-to-list 'tramp-default-proxies-alist
                       '("\\." nil "ssh,bird@bastion.your.domain,"))
          (add-to-list 'tramp-default-proxies-alist
                       '("\\.your\\.domain\\'" nil nil))

     Note: add-to-list adds elements at the beginning of a list.  Therefore, most relevant rules must come last in the list.

     Proxy hosts can be cascaded in the alist.  If there is another host called jump.your.domain, which is the only host allowed to connect to bastion.your.domain, then:

          (add-to-list 'tramp-default-proxies-alist
                       '("\\`bastion\\.your\\.domain\\'"
                         "\\`bird\\'"
                         "ssh,jump.your.domain,"))

     PROXY can take patterns %h or %u for HOST or USER respectively.  Ports or domains, if they are part of a hop file name, are not expanded by those patterns.

     To login as root on remote hosts in the domain your.domain, but login as root is disabled for non-local access, then use this alist entry:

          (add-to-list 'tramp-default-proxies-alist
                       '("\\.your\\.domain\\'" "\\`root\\'" "ssh,%h,"))

     Opening sudo,randomhost.your.domain, first connects to randomhost.your.domain via ssh under your account name, and then performs sudo -u root on that host.

     It is key for the sudo method in the above example to be applied on the host after reaching it and not on the local host. tramp checks therefore, that the host name for such hops matches the host name of the previous hop.

     HOST, USER and PROXY can also take Lisp forms.  These forms when evaluated must return either a string or nil.

     To generalize (from the previous example): For all hosts, except my local one, first connect via ssh, and then apply sudo -u root:

          (add-to-list 'tramp-default-proxies-alist
                       '(nil "\\`root\\'" "ssh,%h,"))
          (add-to-list 'tramp-default-proxies-alist
                       '((regexp-quote (system-name)) nil nil))

Passing through hops involves dealing with restricted shells, such as rbash.  If tramp is made aware, then it would use them for proxies only.

 -- User Option: tramp-restricted-shell-hosts-alist
     An alist of regular expressions of hosts running restricted shells, such as rbash.  tramp will then use them only as proxies.

     To specify the bastion host from the example above as running a restricted shell:

          (add-to-list 'tramp-restricted-shell-hosts-alist
                       "\\`bastion\\.your\\.domain\\'")

Passing firewalls
=================

Sometimes, it is not possible to reach a remote host directly.  A firewall might be in the way, which could be passed via a proxy server.

Both ssh and PuTTY support such proxy settings, using an HTTP tunnel via the CONNECT command (conforming to RFC 2616, 2817 specifications).  Proxy servers using HTTP 1.1 or later protocol support this command.

Tunneling with ssh
------------------

With ssh, you could use the ProxyCommand entry in ~/.ssh/config:

     Host host.other.domain
          ProxyCommand nc -X connect -x proxy.your.domain:3128 %h %p

nc is BSD's netcat program, which establishes HTTP tunnels. Any other program with such a feature could be used as well.

In the example, opening ssh,host.your.domain, passes the HTTP proxy server proxy.your.domain on port 3128.

Tunneling with PuTTY
--------------------

PuTTY does not need an external program, HTTP tunnel support is built-in.  In the PuTTY config program, create a session for host.your.domain.  In the Connection/Data entry, select the HTTP option, and add proxy.your.domain as Proxy hostname, and 3128 as Port.

Opening plinkx,host.your.domain, passes the HTTP proxy server proxy.your.domain on port 3128.

Using Non-Standard Methods
==========================

The tramp-methods variable currently has an exhaustive list of predefined methods.  Any part of this list can be modified with more suitable settings.  Refer to the Lisp documentation of that variable, accessible with C-h v tramp-methods RET.

In the ELPA archives, there are several examples of such extensions. They can be installed with Emacs' Package Manager.  This includes

docker-tramp
     Integration for Docker containers.  A container is accessed via docker,user@container,/path/to/file, where user is the (optional) user that you want to use, and container is the id or name of the container.

kubernetes-tramp
     Integration for Docker containers deployed in a Kubernetes cluster. It is derived from docker-tramp.  A container is accessed via kubectl,user@container,/path/to/file, user and container have the same meaning as in docker-tramp.

lxc-tramp
     Integration for LXC containers.  A container is accessed via lxc,container,/path/to/file, container has the same meaning as in docker-tramp.  A user specification is ignored.

lxd-tramp
     Integration for LXD containers.  A container is accessed via lxd,user@container,/path/to/file, user and container have the same meaning as in docker-tramp.

magit-tramp
     Browsing git repositories with magit.  A versioned file is accessed via git,rev@root-dir,/path/to/file. rev is a git revision, and root-dir is a virtual host name for the root directory, specified in magit-tramp-hosts-alist.

tramp-hdfs
     Access of a hadoop/hdfs file system.  A file is accessed via hdfs,user@node,/path/to/file, where user is the user that you want to use, and node is the name of the hadoop server.

vagrant-tramp
     Convenience method to access vagrant boxes.  It is often used in multi-hop file names like prefixvagrantpostfixhopbox|sudopostfixhopboxpostfix/path/to/file, where box is the name of the vagrant box.

Selecting config files for user/host name completion
====================================================

tramp-completion-function-alist uses predefined files for user and host name completion (see File name completion).  For each method, it keeps a set of configuration files and a function that can parse that file.  Each entry in tramp-completion-function-alist is of the form (METHOD PAIR1 PAIR2 ...).

Each PAIR is composed of (FUNCTION FILE). FUNCTION is responsible for extracting user names and host names from FILE for completion.  There are two functions which access this variable:

 -- Function: tramp-get-completion-function method
     This function returns the list of completion functions for METHOD.

     Example:

          (tramp-get-completion-function "rsh")

               => ((tramp-parse-rhosts "/etc/hosts.equiv")
                   (tramp-parse-rhosts "~/.rhosts"))

 -- Function: tramp-set-completion-function method function-list
     This function sets FUNCTION-LIST as list of completion functions for METHOD.

     Example:

          (tramp-set-completion-function "ssh"
           '((tramp-parse-sconfig "/etc/ssh_config")
             (tramp-parse-sconfig "~/.ssh/config")))

               => ((tramp-parse-sconfig "/etc/ssh_config")
                   (tramp-parse-sconfig "~/.ssh/config"))

The following predefined functions parsing configuration files exist:

tramp-parse-rhosts

     This function parses files which are syntactical equivalent to ~/.rhosts.  It returns both host names and user names, if specified.

tramp-parse-shosts

     This function parses files which are syntactical equivalent to ~/.ssh/known_hosts.  Since there are no user names specified in such files, it can return host names only.

tramp-parse-sconfig

     This function returns the host nicknames defined by Host entries in ~/.ssh/config style files.

tramp-parse-shostkeys

     SSH2 parsing of directories /etc/ssh2/hostkeys/* and ~/ssh2/hostkeys/*.  Hosts are coded in file names hostkey_PORTNUMBER_HOST-NAME.pub.  User names are always nil.

tramp-parse-sknownhosts

     Another SSH2 style parsing of directories like /etc/ssh2/knownhosts/* and ~/ssh2/knownhosts/*.  This case, hosts names are coded in file names HOST-NAME.ALGORITHM.pub.  User names are always nil.

tramp-parse-hosts

     A function dedicated to /etc/hosts for host names.

tramp-parse-passwd

     A function which parses /etc/passwd for user names.

tramp-parse-etc-group

     A function which parses /etc/group for group names.

tramp-parse-netrc

     A function which parses ~/.netrc and ~/.authinfo-style files.

To keep a custom file with custom data in a custom structure, a custom function has to be provided.  This function must meet the following conventions:

 -- Function: my-tramp-parse file
     FILE must be either a file on the host, or nil.  The function must return a list of (USER HOST), which are taken as candidates for completion for user and host names.

     Example:

          (my-tramp-parse "~/.my-tramp-hosts")

               => ((nil "toto") ("daniel" "melancholia"))

Reusing passwords for several connections
=========================================

To avoid repeated prompts for passwords, consider native caching mechanisms, such as ssh-agent for ssh-like methods, or pageant for plink-like methods.

tramp offers alternatives when native solutions cannot meet the need.

Using an authentication file
----------------------------

The package auth-source.el, originally developed for No Gnus, reads passwords from different sources, see auth-source (auth).  The default authentication file is ~/.authinfo.gpg, but this can be changed via the user option auth-sources.

A typical entry in the authentication file:

     machine melancholia port scp login daniel password geheim

The port can take any tramp method (see Inline methods, see External methods).  Omitting port values matches all tramp methods.  Domain and ports, as used in tramp file name syntax, must be appended to the machine and login items:

     machine melancholia#4711 port davs login daniel%BIZARRE password geheim

If there doesn't exist a proper entry, the password is read interactively.  After successful login (verification of the password), it is offered to save a corresponding entry for further use by auth-source backends which support this.  This could be changed by setting the user option auth-source-save-behavior to nil.

Set auth-source-debug to t to debug messages.

Note that auth-source.el is not used for ftp connections, because tramp passes the work to Ange FTP.  If you want, for example, use your ~/.authinfo.gpg authentication file, you must customize ange-ftp-netrc-filename:

     (customize-set-variable 'ange-ftp-netrc-filename "~/.authinfo.gpg")

Caching passwords
-----------------

tramp can cache passwords as entered and reuse when needed for the same user or host name independent of the access method.

password-cache-expiry sets the duration (in seconds) the passwords are remembered.  Passwords are never saved permanently nor can they extend beyond the lifetime of the current Emacs session.  Set password-cache-expiry to nil to disable expiration.

Set password-cache to nil to disable password caching.

Reusing connection related information
======================================

For faster initial connection times, tramp stores previous connection properties in a file specified by the user option tramp-persistency-file-name.

The default file name for tramp-persistency-file-name is ~/.emacs.d/tramp.

tramp reads this file during Emacs startup, and writes to it when exiting Emacs.  Delete this file for tramp to recreate a new one on next Emacs startup.

Set tramp-persistency-file-name to nil to disable storing connections persistently.

When tramp detects a change in the operating system version in a remote host (via the command uname -sr), it flushes all connection related information for that host and creates a new entry.

Setting own connection related information
==========================================

For more precise customization, parameters specified by tramp-methods can be overwritten manually.

Set tramp-connection-properties to manually override tramp-methods.  Properties in this list are in the form (REGEXP PROPERTY VALUE).  REGEXP matches remote file names.  Use nil to match all. PROPERTY is the property's name, and VALUE is the property's value.

PROPERTY is any method specific parameter contained in tramp-methods.  The parameter key in tramp-methods is a symbol name tramp-<foo>.  To overwrite that property, use the string "<foo>" for PROPERTY.  For example, this changes the remote shell:

     (add-to-list 'tramp-connection-properties
                  (list (regexp-quote "ssh,user@randomhost.your.domain,")
                        "remote-shell" "/bin/ksh"))

     (add-to-list 'tramp-connection-properties
                  (list (regexp-quote "ssh,user@randomhost.your.domain,")
                        "remote-shell-login" '("-")))

The parameters tramp-remote-shell and tramp-remote-shell-login in tramp-methods now have new values for the remote host.

PROPERTY could also be any property found in tramp-persistency-file-name.

Relevant connection properties to override
------------------------------------------

Not all connection properties need to be changed.  The most relevant properties are listed here:

  * "login-program"

     The property "login-program" keeps the program to be called in order to connect the remote host.  Sometimes, the program might have another name on your host, or it is located on another path.  In this case, you can overwrite the default value, which is special for every connection method.  It is used in all connection methods of tramp-sh.el.

  * "login-args"

     "login-args" specifies a list of lists of arguments to pass to "login-program".  Read the docstring of tramp-methods how to construct these lists.

  * "remote-shell"

     This property tells Tramp which remote shell to apply on the remote host.  It is used in all connection methods of tramp-sh.el. The default value is "/bin/sh".

  * "remote-shell-login"

     A property to be used in conjunction with "remote-shell".  It specifies, which shell argument triggers a login shell.  Its default value is "-l", but some shells, like ksh, prefer "-".

  * "session-timeout"

     All tramp-sh.el based methods accept the property "session-timeout".  This is the time (in seconds) after a connection is disabled for security reasons, and must be reestablished.  A value of nil disables this feature.  Most of the methods do not set this property except the sudo and doas methods, which use predefined values.

  * "tmpdir"

     The temporary directory on the remote host.  If not specified, the default value is "/data/local/tmp" for the adb method, "/C$/Temp" for the smb method, and "/tmp" otherwise.

  * "posix"

     Connections using the smb method check, whether the remote host supports posix commands.  If the remote host runs Samba, it confirms this capability.  However, some very old Samba versions have errors in their implementation.  In order to suppress the posix commands for those hosts, the property "posix" shall be set to nil.

     The default value of this property is t (not specified in tramp-methods).  If the remote host runs native MS Windows, there is no effect of this property.

  * "mount-args"
     "copyto-args"

     "moveto-args"

     These properties keep optional flags to the different rclone operations.  Their default value is nil.

How tramp finds and uses programs on the remote host
====================================================

tramp requires access to and rights to several commands on remote hosts: ls, test, find and cat.

Besides there are other required programs for Inline methods and External methods of connection.

To improve performance and accuracy of remote file access, tramp uses perl (or perl5) and grep when available.

 -- User Option: tramp-remote-path
     tramp-remote-path specifies which remote directory paths tramp can search for Remote programs.

     tramp uses standard defaults, such as /bin and /usr/bin, which are reasonable for most hosts.  To accommodate differences in hosts and paths, for example, /bin:/usr/bin on Debian GNU/Linux or /usr/xpg4/bin:/usr/ccs/bin:/usr/bin:/opt/SUNWspro/bin on Solaris, tramp queries the remote host with getconf
     PATH and updates the symbol tramp-default-remote-path.

     For instances where hosts keep obscure locations for paths for security reasons, manually add such paths to local .emacs as shown below for tramp to use when connecting.

          (add-to-list 'tramp-remote-path "/usr/local/perl/bin")

     Another way to find the remote path is to use the path assigned to the remote user by the remote host.  tramp does not normally retain this remote path after login.  However, tramp-own-remote-path preserves the path value, which can be used to update tramp-remote-path.

          (add-to-list 'tramp-remote-path 'tramp-own-remote-path)

     Note that this works only if your remote /bin/sh shell supports the login argument -l.

Starting with Emacs 26, tramp-remote-path can be set per host via connection-local variables, see Connection Variables (emacs). You could define your own search directories like this:

     (connection-local-set-profile-variables 'remote-path-with-bin
        '((tramp-remote-path . ("~/bin" tramp-default-remote-path))))

     (connection-local-set-profile-variables 'remote-path-with-apply-pub-bin
        '((tramp-remote-path . ("/appli/pub/bin" tramp-default-remote-path))))

     (connection-local-set-profiles
        '(:application tramp :machine "randomhost") 'remote-path-with-bin)

     (connection-local-set-profiles
        '(:application tramp :user "anotheruser" :machine "anotherhost")
          'remote-path-with-apply-pub-bin)

When remote search paths are changed, local tramp caches must be recomputed.  To force tramp to recompute afresh, call M-x tramp-cleanup-this-connection RET or friends (see Cleanup remote connections).

Remote shell setup hints
========================

Changing the default remote or local shell
------------------------------------------

Per default, tramp uses the command /bin/sh for starting a shell on the remote host.  This can be changed by setting the connection property "remote-shell", see Predefined connection information.  If you want, for example, use /usr/bin/zsh on a remote host, you might apply

     (add-to-list 'tramp-connection-properties
                  (list (regexp-quote "ssh,user@host,")
                        "remote-shell" "/usr/bin/zsh"))

This works only for connection methods which allow to override the remote login shell, like sshx or plink.  See Inline methods and External methods for connection methods which support this.

This approach has also the advantage, that settings in tramp-sh-extra-args will be applied.  For zsh, the trouble with the shell prompt due to set zle options will be avoided.

Similar problems can happen with the local shell Tramp uses to create a process.  Per default, it uses the command /bin/sh for this, which could also be a link to another shell.  In order to overwrite this, you might apply

     (customize-set-variable 'tramp-encoding-shell "/usr/bin/zsh")

This uses also the settings in tramp-sh-extra-args.

Other remote shell setup hints
------------------------------

tramp checks for the availability of standard programs in the usual locations.  Common tactics include successively trying test -e, /usr/bin/test -e, and /bin/test -e.  ls -d is another approach.  But these approaches do not help with these new login patterns.

When tramp encounters two-factor logins or additional challenge questions, such as entering birth date or security code or passphrase, tramp needs a few more configuration steps to accommodate them.

The difference between a password prompt and a passphrase prompt is that the password for completing the login while the passphrase is for authorizing access to local authentication information, such as the ssh key.

There is no one configuration to accommodate all the variations in login security, especially not the exotic ones.  However, tramp provides a few tweaks to address the most common ones.

tramp-shell-prompt-pattern

     tramp-shell-prompt-pattern is for remote login shell prompt, which may not be the same as the local login shell prompt, shell-prompt-pattern.  Since most hosts use identical prompts, tramp sets a similar default value for both prompts.

tramp-password-prompt-regexp

tramp-wrong-passwd-regexp

     tramp uses tramp-password-prompt-regexp to distinguish between prompts for passwords and prompts for passphrases. By default, tramp-password-prompt-regexp handles the detection in English language environments.  See a localization example below:

          (customize-set-variable
           'tramp-password-prompt-regexp
            (concat
             "^.*"
             (regexp-opt
              '("passphrase" "Passphrase"
                ;; English
                "password" "Password"
                ;; Deutsch
                "passwort" "Passwort"
                ;; Français
                "mot de passe" "Mot de passe")
              t)
             ".*:\0? *"))

     Similar localization may be necessary for handling wrong password prompts, for which tramp uses tramp-wrong-passwd-regexp.

tramp-terminal-type

     tramp uses the user option tramp-terminal-type to set the remote environment variable TERM for the shells it runs. Per default, it is "dumb", but this could be changed.  A dumb terminal is best suited to run the background sessions of tramp.  However, running interactive remote shells might require a different setting.  This could be achieved by tweaking the TERM environment variable in process-environment.

          (let ((process-environment
                 (cons "TERM=xterm-256color" process-environment)))
            (shell))

Determining a tramp session

     Sometimes, it is needed to identify whether a shell runs under tramp control.  The setting of environment variable TERM will help:

          if test "$TERM" = "dumb"; then
             ...
          fi

     Another possibility is to check the environment variable INSIDE_EMACS.  Like for all subprocesses of Emacs, this is set to the version of the parent Emacs process, see Interactive Shell (emacs).  tramp adds its own package version to this string, which could be used for further tests in an inferior shell.  The string of that environment variable looks always like

          echo $INSIDE_EMACS
          => 26.2,tramp:2.3.4

tset and other questions

     To suppress inappropriate prompts for terminal type, tramp sets the TERM environment variable before the remote login process begins via the user option tramp-terminal-type (see above).  This will silence common tset related prompts.

     tramp's strategy for handling such prompts (commonly triggered from login scripts on remote hosts) is to set the environment variables so that no prompts interrupt the shell initialization process.

     An alternative approach is to configure tramp with strings that can identify such questions using tramp-actions-before-shell.  Example:

          (defconst my-tramp-prompt-regexp
            (concat (regexp-opt '("Enter the birth date of your mother:") t)
                    "\\s-*")
            "Regular expression matching my login prompt question.")

          (defun my-tramp-action (proc vec)
            "Enter \"19000101\" in order to give a correct answer."
            (save-window-excursion
              (with-current-buffer (tramp-get-connection-buffer vec)
                (tramp-message vec 6 "\n%s" (buffer-string))
                (tramp-send-string vec "19000101"))))

          (add-to-list 'tramp-actions-before-shell
                       '(my-tramp-prompt-regexp my-tramp-action))

Conflicting names for users and variables in .profile

     When a user name is the same as a variable name in a local file, such as .profile, then tramp may send incorrect values for environment variables.  To avoid incorrect values, change the local variable name to something different from the user name.  For example, if the user name is FRUMPLE, then change the variable name to FRUMPLE_DIR.

Non-Bourne commands in .profile

     When the remote host's .profile is also used for shells other than Bourne shell, then some incompatible syntaxes for commands in .profile may trigger errors in Bourne shell on the host and may not complete client's tramp connections.

     One example of a Bourne shell incompatible syntax in .profile: using export FOO=bar instead of FOO=bar; export
     FOO.  After remote login, tramp will trigger an error during its execution of /bin/sh on the remote host because Bourne shell does not recognize the export command as entered in .profile.

     Likewise, (~) character in paths will cause errors because Bourne shell does not do (~) character expansions.

     One approach to avoiding these incompatibilities is to make all commands in ~/.shrc and ~/.profile Bourne shell compatible so tramp can complete connections to that remote. To accommodate using non-Bourne shells on that remote, use other shell-specific config files.  For example, bash can use ~/.bash_profile and ignore .profile.

Interactive shell prompt

     tramp redefines the remote shell prompt internally for robust parsing.  This redefinition affects the looks of a prompt in an interactive remote shell through commands, such as M-x shell RET.  Such prompts, however, can be reset to something more readable and recognizable using these environment variables.

     tramp sets the INSIDE_EMACS environment variable in the startup script file ~/.emacs_SHELLNAME.

     SHELLNAME is bash or equivalent shell names.  Change it by setting the environment variable ESHELL in the .emacs as follows:

          (setenv "ESHELL" "bash")

     Then re-set the prompt string in ~/.emacs_SHELLNAME as follows:

          # Reset the prompt for remote tramp shells.
          if [ "${INSIDE_EMACS/*tramp*/tramp}" == "tramp" ] ; then
             PS1="[\u@\h \w]$ "
          fi

     See Interactive Shell (emacs).

busybox / nc

     tramp's nc method uses the nc command to install and execute a listener as follows (see tramp-methods):

          $ nc -l -p 42

     The above command-line syntax has changed with busybox versions.  If nc refuses the -p parameter, then overwrite as follows:

          (add-to-list
           'tramp-connection-properties
           `(,(regexp-quote "192.168.0.1")
             "remote-copy-args" (("-l") ("%r"))))

     where 192.168.0.1 is the remote host IP address (see Predefined connection information).

Android shell setup hints
=========================

tramp uses the adb method to access Android devices. Android devices provide a restricted shell access through an USB connection.  The local host must have the adb program installed.  Usually, it is sufficient to open the file adb,,/.  Then you can navigate in the filesystem via dired.

Alternatively, applications such as Termux or SSHDroid that run sshd process on the Android device can accept any ssh-based methods provided these settings are adjusted:

  * sh must be specified for remote shell since Android devices do not provide /bin/sh.  sh will then invoke whatever shell is installed on the device with this setting:

          (add-to-list 'tramp-connection-properties
          	     (list (regexp-quote "192.168.0.26") "remote-shell" "sh"))

     where 192.168.0.26 is the Android device's IP address. (see Predefined connection information).

  * tramp requires preserving PATH environment variable from user settings.  Android devices prefer /system/xbin path over /system/bin.  Both of these are set as follows:

          (add-to-list 'tramp-remote-path 'tramp-own-remote-path)
          (add-to-list 'tramp-remote-path "/system/xbin")

  * When the Android device is not rooted, specify a writable directory for temporary files:

          (add-to-list 'tramp-remote-process-environment "TMPDIR=$HOME")

  * Open a remote connection with the command C-x C-f ssh,192.168.0.26#2222, RET, where sshd is listening on port 2222.

     To add a corresponding entry to the ~/.ssh/config file (recommended), use this:

          Host android
               HostName 192.168.0.26
               User root
               Port 2222

     To use the host name android instead of the IP address shown in the previous example, fix the connection properties as follows:

          (add-to-list 'tramp-connection-properties
          	     (list (regexp-quote "android") "remote-shell" "sh"))

     Open a remote connection with a more concise command C-x C-f ssh,android, RET.

Auto-save and Backup configuration
==================================

To avoid tramp from saving backup files owned by root to locations accessible to others, default backup settings in backup-directory-alist have to be altered.

Here's a scenario where files could be inadvertently exposed.  Emacs by default writes backup files to the same directory as the original files unless changed to another location, such as ~/.emacs.d/backups/.  Such a directory will also be used by default by tramp when using, say, a restricted file su,root@localhost,/etc/secretfile.  The backup file of the secretfile is now owned by the user logged in from tramp and not root.

When backup-directory-alist is nil (the default), such problems do not occur.

To ``turn off'' the backup feature for remote files and stop tramp from saving to the backup directory, use this:

     (add-to-list 'backup-directory-alist
                  (cons tramp-file-name-regexp nil))

Disabling backups can be targeted to just the su and sudo methods:

     (setq backup-enable-predicate
           (lambda (name)
             (and (normal-backup-enable-predicate name)
                  (not
                   (let ((method (file-remote-p name 'method)))
                     (when (stringp method)
                       (member method '("su" "sudo"))))))))

Another option is to create better backup file naming with user and host names prefixed to the file name.  For example, transforming /etc/secretfile to ~/.emacs.d/backups/!su:root@localhost:!etc!secretfile, set the tramp user option tramp-backup-directory-alist from the existing user option backup-directory-alist.

Then tramp backs up to a file name that is transformed with a prefix consisting of the DIRECTORY name.  This file name prefixing happens only when the DIRECTORY is an absolute local file name.

Example:

     (add-to-list 'backup-directory-alist
                  (cons "." "~/.emacs.d/backups/"))
     (customize-set-variable
      'tramp-backup-directory-alist backup-directory-alist)

The backup file name of su,root@localhost,/etc/secretfile would be

Just as for backup files, similar issues of file naming affect auto-saving remote files.  Auto-saved files are saved in the directory specified by the user option auto-save-file-name-transforms. By default this is set to the local temporary directory.  But in some versions of Debian GNU/Linux, this points to the source directory where the Emacs was compiled.  Reset such values to a valid directory.

Set auto-save-file-name-transforms to nil to save auto-saved files to the same directory as the original file.

Alternatively, set the user option tramp-auto-save-directory to direct all auto saves to that location.

Issues with Cygwin ssh
======================

This section is incomplete.  Please share your solutions.

Cygwin's ssh works only with a Cygwin version of Emacs.  To check for compatibility: type M-x eshell RET, and start ssh test.host RET.  Incompatibilities trigger this message:

     Pseudo-terminal will not be allocated because stdin is not a terminal.

Some older versions of Cygwin's ssh work with the sshx access method.  Consult Cygwin's FAQ at https://cygwin.com/faq/ for details.

On the Emacs Wiki (https://www.emacswiki.org/emacs/SshWithNTEmacs) it is explained how to use the helper program fakecygpty to fix this problem.

When using the scpx access method, Emacs may call scp with MS Windows file naming, such as c:/foo.  But the version of scp that is installed with Cygwin does not know about MS Windows file naming, which causes it to incorrectly look for a host named c.

A workaround: write a wrapper script for scp to convert Windows file names to Cygwin file names.

When using the ssh-agent on MS Windows for password-less interaction, ssh methods depend on the environment variable SSH_AUTH_SOCK.  But this variable is not set when Emacs is started from a Desktop shortcut and authentication fails.

One workaround is to use an MS Windows based SSH Agent, such as Pageant.  It is part of the Putty Suite of tools.

The fallback is to start Emacs from a shell.

Using tramp
***********

tramp operates transparently, accessing remote files as if they are local.  However, tramp employs a formalized remote file naming syntax to perform its functions transparently.  This syntax consists of many parts specifying access methods, authentication, host names, and file names.  Ange FTP uses a similar syntax.

Unlike opening local files in Emacs, which are instantaneous, opening remote files in tramp is slower at first.  Sometimes there is a noticeable delay before the prompts for passwords or authentication appear in the minibuffer.  Hitting RET or other keys during this gap will be processed by Emacs.  This type-ahead facility is a feature of Emacs that may cause missed prompts when using tramp.

tramp file name conventions
===========================

method,host,/path/to/file opens file /PATH/TO/FILE on the remote host HOST, using the method METHOD.

prefixsshpostfixhopmelancholiapostfix.emacs
     For the file .emacs located in the home directory, on the host melancholia, using method ssh.

prefixsshpostfixhopmelancholia.danann.netpostfix.emacs
     For the file .emacs specified using the fully qualified domain name of the host.

prefixsshpostfixhopmelancholiapostfix~/.emacs
     For the file .emacs specified using the ~, which is expanded.

prefixsshpostfixhopmelancholiapostfix~daniel/.emacs
     For the file .emacs located in daniel's home directory on the host, melancholia.  The ~<user> construct is expanded to the home directory of that user on the remote host.

prefixsshpostfixhopmelancholiapostfix/etc/squid.conf
     For the file /etc/squid.conf on the host melancholia.

HOST can take IPv4 or IPv6 address, as in ssh,127.0.0.1,.emacs or ssh,ipv6prefix::1ipv6postfix,.emacs.

By default, tramp will use the current local user name as the remote user name for log in to the remote host.  Specifying a different name using the proper syntax will override this default behavior:

     method,user@host,path/to/file

ssh,daniel@melancholia,.emacs is for file .emacs in daniel's home directory on the host, melancholia, accessing via method ssh.

For specifying port numbers, affix #<port> to the host name.  For example: ssh,daniel@melancholia#42,.emacs.

All method, user name, host name, port number and local name parts are optional, see Default Method, see Default User, see Default Host.

File name completion
====================

tramp can complete the following tramp file name components: method names, user names, host names, and file names located on remote hosts.  User name and host name completion is activated only, if file name completion has one of the styles basic, emacs21, or emacs22. See Completion Styles (emacs).

For example, type C-x C-f prefixwithspace s TAB, tramp completion choices show up as

       sbin/
       prefixhopscppostfix
       prefixhopscpxpostfix
       prefixhopsftppostfix
       prefixhopsgpostfix

       prefixhopsmbpostfix
       srv/
       prefixhopsshpostfix
       prefixhopsshxpostfix
       prefixhopsupostfix

       prefixhopsudopostfix
       sys/

prefixhopsshpostfixhop is a possible completion for the respective method, and sbin/ stands for the directory /sbin on your local host.

Type s h postfixhop for the minibuffer completion to prefixsshpostfixhop.  Typing TAB shows host names tramp extracts from ~/.ssh/config file, for example.

       prefixhopsshpostfixhop127.0.0.1postfix
       prefixhopsshpostfixhop192.168.0.1postfix

       prefixhopsshpostfixhopipv6prefix::1ipv6postfixpostfix
       prefixhopsshpostfixhoplocalhostpostfix

       prefixhopsshpostfixhopmelancholia.danann.netpostfix
       prefixhopsshpostfixhopmelancholiapostfix

Choose a host from the above list and then continue to complete file names on that host.

When the configuration (see Customizing Completion) includes user names, then the completion lists will account for the user names as well.

Results from auth-sources search (see Using an authentication file) are added to the completion candidates.  This search could be annoying, for example due to a passphrase request of the ~/.authinfo.gpg authentication file.  The user option tramp-completion-use-auth-sources controls, whether such a search is performed during completion.

Remote hosts previously visited or hosts whose connections are kept persistently (see Connection caching) will be included in the completion lists.

After remote host name completion comes completion of file names on the remote host.  It works the same as with local host file completion except that killing with double-slash // kills only the file name part of the tramp file name syntax.  A triple-slash stands for the default behavior. See Minibuffer File (emacs).

Example:

     C-x C-f ssh,melancholia,/usr/local/bin//etc TAB
          -| ssh,melancholia,/etc

     C-x C-f ssh,melancholia,//etc TAB
          -| ssh,melancholia,/etc

     C-x C-f ssh,melancholia,/usr/local/bin///etc TAB
          -| /etc

During file name completion, remote directory contents are re-read regularly to account for any changes in the filesystem that may affect the completion candidates.  Such re-reads can account for changes to the file system by applications outside Emacs (see Connection caching).

 -- User Option: tramp-completion-reread-directory-timeout
     The timeout is number of seconds since last remote command for rereading remote directory contents.  A value of 0 re-reads immediately during file name completion, nil uses cached directory contents.

Declaring multiple hops in the file name
========================================

tramp file name syntax can accommodate ad-hoc specification of multiple proxies without using tramp-default-proxies-alist configuration setup (see Multi-hops).

Each proxy is specified using the same syntax as the remote host specification minus the file name part.  Each hop is separated by a |.  Chain the proxies from the starting host to the destination remote host name and file name.  For example, hopping over a single proxy bird@bastion to a remote file on you@remotehost:

     C-x C-f prefixsshpostfixhopbird@bastion|sshpostfixhopyou@remotehostpostfix/path RET

Each involved method must be an inline method (see Inline methods).

tramp adds the ad-hoc definitions on the fly to tramp-default-proxies-alist and is available for re-use during that Emacs session.  Subsequent tramp connections to the same remote host can then use the shortcut form: ssh,you@remotehost,/path.  Ad-hoc definitions are removed from tramp-default-proxies-alist via the command M-x tramp-cleanup-all-connections RET (see Cleanup remote connections).

 -- User Option: tramp-save-ad-hoc-proxies
     For ad-hoc definitions to be saved automatically in tramp-default-proxies-alist for future Emacs sessions, set tramp-save-ad-hoc-proxies to non-nil.

          (customize-set-variable 'tramp-save-ad-hoc-proxies t)

Ad-hoc proxies can take patterns %h or %u like in tramp-default-proxies-alist.  The following file name expands to user root on host remotehost, starting with an ssh session on host remotehost: prefixsshpostfixhop%h|supostfixhopremotehostpostfix.

On the other hand, if a trailing hop does not specifiy a host name, the host name of the previous hop is reused. Therefore, the following file name is equivalent to the previous example: prefixsshpostfixhopremotehost|supostfixhoppostfix.

Integration with other Emacs packages
=====================================

tramp supports starting new running processes on the remote host for discovering remote file names.  Emacs packages on the remote host need no specific modifications for tramp's use.

This type of integration does not work with the ftp method, and does not support the pty association as specified in start-file-process.

process-file and start-file-process work on the remote host when the variable default-directory is remote:

     (let ((default-directory "/ssh:remote.host:"))
       (start-file-process "grep" (get-buffer-create "*grep*")
                           "/bin/sh" "-c" "grep -e tramp *"))

Remote processes do not apply to GVFS (see GVFS-based methods) because the remote file system is mounted on the local host and tramp just accesses by changing the default-directory.

tramp starts a remote process when a command is executed in a remote file or directory buffer.  As of now, these packages have been integrated to work with tramp: compile.el (commands like compile and grep) and gud.el (gdb or perldb).

For tramp to find the command on the remote, it must be accessible through the default search path as setup by tramp upon first connection.  Alternatively, use an absolute path or extend tramp-remote-path (see Remote programs):

     (add-to-list 'tramp-remote-path "~/bin")
     (add-to-list 'tramp-remote-path "/appli/pub/bin")

Customize user option tramp-remote-process-environment to suit the remote program's environment for the remote host. tramp-remote-process-environment is a list of strings structured similar to process-environment, where each element is a string of the form ENVVARNAME=VALUE.

To avoid any conflicts with local host environment variables set through local configuration files, such as ~/.profile, use ENVVARNAME= to unset them for the remote environment.

Use add-to-list to add entries:

     (add-to-list 'tramp-remote-process-environment "JAVA_HOME=/opt/java")

Modifying or deleting already existing values in the tramp-remote-process-environment list may not be feasible on restricted remote hosts.  For example, some system administrators disallow changing HISTORY environment variable.  To accommodate such restrictions when using tramp, fix the tramp-remote-process-environment by the following code in the local .emacs file:

     (let ((process-environment tramp-remote-process-environment))
       (setenv "HISTORY" nil)
       (setq tramp-remote-process-environment process-environment))

Setting the ENV environment variable instructs some shells to read an initialization file.  Per default, tramp has disabled this.  You could overwrite this behavior by evaluating

     (let ((process-environment tramp-remote-process-environment))
       (setenv "ENV" "$HOME/.profile")
       (setq tramp-remote-process-environment process-environment))

In addition to tramp-remote-process-environment, you can set environment variables for individual remote process calls by let-binding process-environment.  tramp applies any entries not present in the global default value of process-environment (overriding tramp-remote-process-environment settings, if they conflict). For example:

     (let ((process-environment (cons "HGPLAIN=1" process-environment)))
       (process-file ...))

Let-binding in this way works regardless of whether the process to be called is local or remote, since tramp would add just the HGPLAIN setting and local processes would take whole value of process-environment along with the new value of HGPLAIN.

For integrating other Emacs packages so tramp can execute remotely, please file a bug report.  See Bug Reports.

Running remote programs that create local X11 windows
-----------------------------------------------------

To allow a remote program to create an X11 window on the local host, set the DISPLAY environment variable for the remote host as follows in the local .emacs file:

     (add-to-list 'tramp-remote-process-environment
                  (format "DISPLAY=%s" (getenv "DISPLAY")))

(getenv "DISPLAY") should return a recognizable name for the local host that the remote host can redirect X11 window interactions.  If querying for a recognizable name is not possible for whatever reason, then replace (getenv "DISPLAY") with a hard-coded, fixed name.  Note that using :0 for X11 display name here will not work as expected.

An alternate approach is specify ForwardX11 yes or ForwardX11Trusted yes in ~/.ssh/config on the local host.

Running shell on a remote host
------------------------------

Set explicit-shell-file-name to the appropriate shell name when using tramp between two hosts with different operating systems, such as windows-nt and gnu/linux.  This option ensures the correct name of the remote shell program.

When explicit-shell-file-name is equal to nil, calling shell interactively will prompt for a shell name.

Starting with Emacs 26, you could use connection-local variables for setting different values of explicit-shell-file-name for different remote hosts. See Connection Variables (emacs).

     (connection-local-set-profile-variables
       'remote-bash
       '((explicit-shell-file-name . "/bin/bash")
         (explicit-bash-args . ("-i"))))

     (connection-local-set-profile-variables
       'remote-ksh
       '((explicit-shell-file-name . "/bin/ksh")
         (explicit-ksh-args . ("-i"))))

     (connection-local-set-profiles
       '(:application tramp :protocol "ssh" :machine "localhost")
       'remote-bash)

     (connection-local-set-profiles
       `(:application tramp :protocol "sudo"
         :user "root" :machine ,(system-name))
       'remote-ksh)

Running shell-command on a remote host
--------------------------------------

shell-command executes commands synchronously or asynchronously on remote hosts and displays output in buffers on the local host.  Example:

     C-x C-f sudo,, RET
     M-& tail -f /var/log/syslog.log RET

tail command outputs continuously to the local buffer, *Async Shell Command*

M-x auto-revert-tail-mode RET runs similarly showing continuous output.

shell-command uses the variables shell-file-name and shell-command-switch in order to determine which shell to run. For remote hosts, their default values are /bin/sh and -c, respectively (except for the adb method, which uses /system/bin/sh).  Like the variables in the previous section, these variables can be changed via connection-local variables.

If Emacs supports the variable async-shell-command-width (since Emacs 27.1), tramp cares about its value for asynchronous shell commands.  It specifies the number of display columns for command output.  For synchronous shell commands, a similar effect can be achieved by adding the environment variable COLUMNS to tramp-remote-process-environment.

Running eshell on a remote host
-------------------------------

tramp is integrated into eshell.el, which enables interactive eshell sessions on remote hosts at the command prompt. You must add the module eshell-tramp to eshell-modules-list.  Here's a sample interaction after opening M-x eshell RET on a remote host:

     ~ $ cd sudo,,/etc RET
     sudo,root@host,/etc $ hostname RET
     host
     sudo,root@host,/etc $ id RET
     uid=0(root) gid=0(root) groups=0(root)
     sudo,root@host,/etc $ find-file shadow RET
     #<buffer shadow>
     sudo,root@host,/etc $

eshell added custom su and sudo commands that set the default directory correctly for the *eshell* buffer. tramp silently updates tramp-default-proxies-alist with an entry for this directory (see Multi-hops):

     ~ $ cd ssh,user@remotehost,/etc RET
     ssh,user@remotehost,/etc $ find-file shadow RET
     File is not readable: ssh,user@remotehost,/etc/shadow
     ssh,user@remotehost,/etc $ sudo find-file shadow RET
     #<buffer shadow>

     ssh,user@remotehost,/etc $ su - RET
     su,root@remotehost,/root $ id RET
     uid=0(root) gid=0(root) groups=0(root)
     su,root@remotehost,/root $

Running a debugger on a remote host
-----------------------------------

gud.el provides a unified interface to symbolic debuggers (Debuggers (emacs)). tramp can run debug on remote hosts by calling gdb with a remote file name:

     M-x gdb RET
     Run gdb (like this): gdb -i=mi ssh,host,~/myprog RET

Since the remote gdb and gdb-inferior processes do not belong to the same process group on the remote host, there will be a warning, which can be ignored:

     &"warning: GDB: Failed to set controlling terminal: Operation not permitted\n"

As consequence, there will be restrictions in I/O of the process to be debugged.

Relative file names are based on the remote default directory.  When myprog.pl exists in ssh,host,/home/user, valid calls include:

     M-x perldb RET
     Run perldb (like this): perl -d myprog.pl RET

Just the local part of a remote file name, such as perl -d /home/user/myprog.pl, is not possible.

Arguments of the program to be debugged must be literal, can take relative or absolute paths, but not remote paths.

Running remote processes on MS Windows hosts
--------------------------------------------

winexe runs processes on a remote MS Windows host, and tramp can use it for process-file and start-file-process.

tramp-smb-winexe-program specifies the local winexe command.  Powershell V2.0 on the remote host is required to run processes triggered from tramp.

explicit-shell-file-name and explicit-*-args have to be set properly so M-x shell RET can open a proper remote shell on a MS Windows host.  To open cmd, set it as follows:

     (setq explicit-shell-file-name "cmd"
           explicit-cmd-args '("/q"))

To open powershell as a remote shell, use this:

     (setq explicit-shell-file-name "powershell"
           explicit-powershell-args '("-file" "-"))

Cleanup remote connections
==========================

tramp provides several ways to flush remote connections.

 -- Command: tramp-cleanup-connection vec &optional keep-debug keep-password
     This command flushes all connection related objects.  VEC is the internal representation of a remote connection.  When called interactively, this command lists active remote connections in the minibuffer.  Each connection is of the format method,user@host,.

     Flushing remote connections also cleans the password cache (see Password handling), file cache, connection cache (see Connection caching), and recentf cache (see File Conveniences (emacs)).  It also deletes session timers (see Predefined connection information) and connection buffers.

     If KEEP-DEBUG is non-nil, the debug buffer is kept.  A non-nil KEEP-PASSWORD preserves the password cache.

 -- Command: tramp-cleanup-this-connection
     Flushes the current buffer's remote connection objects, the same as in tramp-cleanup-connection.

 -- Command: tramp-cleanup-all-connections
     Flushes all active remote connection objects, the same as in tramp-cleanup-connection.  This command removes also ad-hoc proxy definitions (see Ad-hoc multi-hops).

 -- Command: tramp-cleanup-all-buffers
     Just as for tramp-cleanup-all-connections, all remote connections and ad-hoc proxy definition are cleaned up in addition to killing all buffers related to remote connections.

Renaming remote files
=====================

Sometimes, it is desirable to safe file contents of buffers visiting a given remote host.  This could happen for example, if the local host changes its network integration, and the remote host is not reachable anymore.

 -- Command: tramp-rename-files source target
     Replace in all buffers the visiting file name from SOURCE to TARGET.  SOURCE is a remote directory name, which could contain also a localname part.  TARGET is the directory name SOURCE is replaced with.  Often, TARGET is a remote directory name on another host, but it can also be a local directory name.  If TARGET has no local part, the local part from SOURCE is used.

     If TARGET is nil, it is selected according to the first match in tramp-default-rename-alist.  If called interactively, this match is offered as initial value for selection.

     On all buffers, which have a buffer-file-name matching SOURCE, this name is modified by replacing SOURCE with TARGET.  This is applied by calling set-visited-file-name.  The new buffer-file-name is prompted for modification in the minibuffer.  The buffers are marked modified, and must be saved explicitly.

     If user option tramp-confirm-rename-file-names is nil, changing the file name happens without confirmation.  This requires a matching entry in tramp-default-rename-alist.

     Remote buffers related to the remote connection identified by SOURCE, which are not visiting files, or which are visiting files not matching SOURCE, are not modified.

     Interactively, TARGET is selected from tramp-default-rename-alist without confirmation if the prefix argument is non-nil.

     The remote connection identified by SOURCE is flushed by tramp-cleanup-connection.

 -- Command: tramp-rename-these-files target
     Replace visiting file names to TARGET.  The current buffer must be related to a remote connection.  In all buffers, which are visiting a file with the same directory name, the buffer file name is changed.

     Interactively, TARGET is selected from tramp-default-rename-alist without confirmation if the prefix argument is non-nil.

 -- User Option: tramp-default-rename-alist
     The default target for renaming remote buffer file names.  This is an alist of cons cells (source . target).  The first matching item specifies the target to be applied for renaming buffer file names from source via tramp-rename-files.  source is a regular expressions, which matches a remote file name.  target must be a directory name, which could be remote (including remote directories Tramp infers by default, such as method,user@host,).

     target can contain the patterns %m, %u or %h, which are replaced by the method name, user name or host name of source when calling tramp-rename-files.

     source could also be a Lisp form, which will be evaluated.  The result must be a string or nil, which is interpreted as a regular expression which always matches.

     Example entries:

          ("ssh,badhost,/path/to/dir/"
           . "ssh,goodhost,/path/to/another/dir/")

     would trigger renaming of buffer file names on badhost to goodhost, including changing the directory name.

          ("ssh,.+\\\\.company\\\\.org," . "prefixsshpostfixhopmulti.hop|sshpostfixhop%hpostfix")

     routes all connections to a host in company.org via ssh,multi.hop,, which might be useful when using Emacs outside the company network.

          (nil . "~/saved-files/%m:%u@%h/")

     saves all remote files locally, with a directory name including method name, user name and host name of the remote connection.

 -- User Option: tramp-confirm-rename-file-names
     Whether renaming a buffer file name by tramp-rename-files or tramp-rename-these-files must be confirmed.

Archive file names
==================

tramp offers also transparent access to files inside file archives.  This is possible only on hosts which have installed GVFS (the GNOME Virtual File System), GVFS-based methods.  Internally, file archives are mounted via the GVFS archive method.

A file archive is a regular file of kind /path/to/dir/file.EXT. The extension .EXT identifies the type of the file archive.  A file inside a file archive, called archive file name, has the name /path/to/dir/file.EXT/dir/file.

Most of the magic file name operations (elisp), are implemented for archive file names, exceptions are all operations which write into a file archive, and process related operations.  Therefore, functions like

     (copy-file "/path/to/dir/file.tar/dir/file" "/somewhere/else")

work out of the box.  This is also true for file name completion, and for libraries like dired or ediff, which accept archive file names as well.

File archives are identified by the file name extension .EXT. Since GVFS uses internally the library libarchive(3), all suffixes, which are accepted by this library, work also for archive file names.  Accepted suffixes are listed in the constant tramp-archive-suffixes.  They are

  * .7z --- 7-Zip archives

  * .apk --- Android package kits

  * .ar --- UNIX archiver formats

  * .cab, .CAB --- Microsoft Windows cabinets

  * .cpio --- CPIO archives

  * .deb --- Debian packages

  * .depot --- HP-UX SD depots

  * .exe --- Self extracting Microsoft Windows EXE files

  * .iso --- ISO 9660 images

  * .jar --- Java archives

  * .lzh, .LZH --- Microsoft Windows compressed LHA archives

  * .msu, .MSU --- Microsoft Windows Update packages

  * .mtree --- BSD mtree format

  * .odb, .odf, .odg, .odp, .ods, .odt --- OpenDocument formats

  * .pax --- Posix archives

  * .rar --- RAR archives

  * .rpm --- Red Hat packages

  * .shar --- Shell archives

  * .tar, .tbz, .tgz, .tlz, .txz, .tzst --- (Compressed) tape archives

  * .warc --- Web archives

  * .xar --- macOS XAR archives

  * .xpi --- XPInstall Mozilla addons

  * .xps --- Open XML Paper Specification (OpenXPS) documents

  * .zip, .ZIP --- ZIP archives

File archives could also be compressed, identified by an additional compression suffix.  Valid compression suffixes are listed in the constant tramp-archive-compression-suffixes.  They are .bz2, .gz, .lrz, .lz, .lz4, .lzma, .lzo, .uu, .xz, .Z, and .zst.  A valid archive file name would be /path/to/dir/file.tar.gz/dir/file.  Even several suffixes in a row are possible, like /path/to/dir/file.tar.gz.uu/dir/file.

An archive file name could be a remote file name, as in /ftp:anonymous@ftp.gnu.org:/gnu/tramp/tramp-2.3.2.tar.gz/INSTALL. Since all file operations are mapped internally to GVFS operations, remote file names supported by tramp-gvfs perform better, because no local copy of the file archive must be downloaded first.  For example, /sftp:user@host:... performs better than the similar /scp:user@host:....  See the constant tramp-archive-all-gvfs-methods for a complete list of tramp-gvfs supported method names.

If url-handler-mode is enabled, archives could be visited via URLs, like https://ftp.gnu.org/gnu/tramp/tramp-2.3.2.tar.gz/INSTALL.  This allows complex file operations like

     (progn
       (url-handler-mode 1)
       (ediff-directories
        "https://ftp.gnu.org/gnu/tramp/tramp-2.3.1.tar.gz/tramp-2.3.1"
        "https://ftp.gnu.org/gnu/tramp/tramp-2.3.2.tar.gz/tramp-2.3.2" ""))

It is even possible to access file archives in file archives, as

     (progn
       (url-handler-mode 1)
       (find-file
        "http://ftp.debian.org/debian/pool/main/c/coreutils/coreutils_8.28-1_amd64.deb/control.tar.gz/control"))

In order to disable file archives, you could add the following form to your init file:

     (customize-set-variable 'tramp-archive-enabled nil)

Reporting Bugs and Problems
***************************

tramp's development team is actively engaged in solving bugs and problems and looks to feature requests and suggestions.

tramp's mailing list is the place for more advice and information on working with tramp, solving problems, discussing, and general discussions about tramp.

tramp's mailing list is moderated but even non-subscribers can post for moderator approval.  Sometimes this approval step may take as long as 48 hours due to public holidays.

tramp-bug-report-address is the mailing list. Messages sent to this address go to all the subscribers.  This is not the address to send subscription requests to.

To subscribe to the mailing list, visit: the tramp Mail Subscription Page (https://lists.gnu.org/mailman/listinfo/tramp-devel/).

Check if the bug or problem is already addressed in see Frequently Asked Questions.

Run M-x tramp-bug RET to generate a buffer with details of the system along with the details of the tramp installation. Please include these details with the bug report.

The bug report must describe in as excruciating detail as possible the steps required to reproduce the problem.  These details must include the setup of the remote host and any special or unique conditions that exist.

Include a minimal test case that reproduces the problem.  This will help the development team find the best solution and avoid unrelated detours.

To exclude cache-related problems, flush all caches before running the test, Cleanup remote connections.  Alternatively, and often better for analysis, reproduce the problem in a clean Emacs session started with emacs -Q.  Then, tramp does not load the persistency file (see Connection caching), and it does not use passwords from auth-source.el (see Password handling).

When including tramp's messages in the bug report, increase the verbosity level to 6 (see Traces) in the ~/.emacs file before repeating steps to the bug.  Include the contents of the *tramp/foo* and *debug tramp/foo* buffers with the bug report.  Both buffers could contain non-ASCII characters which are relevant for analysis, append the buffers as attachments to the bug report.  This is also needed in order to avoid line breaks during mail transfer.

Note that a verbosity level greater than 6 is not necessary at this stage.  Also note that a verbosity level of 6 or greater, the contents of files and directories will be included in the debug buffer.  Passwords typed in tramp will never be included there.

Frequently Asked Questions
**************************

  * Where is the latest tramp?

     tramp is available at the GNU URL:

     https://ftp.gnu.org/gnu/tramp/

     tramp's GNU project page is located here:

     https://savannah.gnu.org/projects/tramp/

  * Which systems does it work on?

     The package works successfully on Emacs 24, Emacs 25, Emacs 26, and Emacs 27.

     While Unix and Unix-like systems are the primary remote targets, tramp has equal success connecting to other platforms, such as MS Windows 7/8/10.

  * How to speed up tramp?

     tramp does many things in the background, some of which depends on network speeds, response speeds of remote hosts, and authentication delays.  During these operations, tramp's responsiveness slows down.  Some suggestions within the scope of tramp's settings include:

     Use an external method, such as scp, which are faster than internal methods.

     Keep the file tramp-persistency-file-name, which is where tramp caches remote information about hosts and files.  Caching is enabled by default.  Don't disable it.

     Set remote-file-name-inhibit-cache to nil if remote files are not independently updated outside tramp's control. That cache cleanup will be necessary if the remote directories or files are updated independent of tramp.

     Set tramp-completion-reread-directory-timeout to nil to speed up completions, File name completion.

     Disable version control to avoid delays:

          (setq vc-ignore-dir-regexp
                (format "\\(%s\\)\\|\\(%s\\)"
                        vc-ignore-dir-regexp
                        tramp-file-name-regexp))

     If this is too radical, because you want to use version control remotely, trim vc-handled-backends to just those you care about, for example:

          (setq vc-handled-backends '(SVN Git))

     Disable excessive traces.  Set tramp-verbose to 3 or lower, default being 3.  Increase trace levels temporarily when hunting for bugs.

  * tramp does not connect to the remote host

     Three main reasons for why tramp does not connect to the remote host:

       - Unknown characters in the prompt

          tramp needs a clean recognizable prompt on the remote host for accurate parsing.  Shell prompts that contain escape sequences for coloring cause parsing problems.  Remote shell setup for customizing prompt detection using regular expressions.

          To check if the remote host's prompt is being recognized, use this test: switch to tramp connection buffer *tramp/foo*, put the cursor at the top of the buffer, and then apply the following expression:

               M-: (re-search-forward (concat tramp-shell-prompt-pattern "$")) RET

          If the cursor has not moved to the prompt at the bottom of the buffer, then tramp has failed to recognize the prompt.

          When using zsh on remote hosts, disable zsh line editor because zsh uses left-hand side and right-hand side prompts in parallel.  Add the following line to ~/.zshrc:

               [[ $TERM == "dumb" ]] && unsetopt zle && PS1='$ ' && return

          This uses the default value of tramp-terminal-type, "dumb", as value of the TERM environment variable.  If you want to use another value for TERM, change tramp-terminal-type and this line accordingly.

          Alternatively, you could set the remote login shell explicitly.  See Remote shell setup for discussion of this technique,

          When using fish shell on remote hosts, disable fancy formatting by adding the following to ~/.config/fish/config.fish:

               function fish_prompt
                 if test $TERM = "dumb"
                    echo "\$ "
                 else
                    ...
                 end
               end

          When using WinSSHD on remote hosts, tramp does not recognize the strange prompt settings.

          A similar problem exist with the iTerm2 shell integration, which sends proprietary escape codes when starting a shell.  This can be suppressed by changing the respective integration snippet in your ~/.profile like this:

               [ $TERM = "dumb" ] || \
               test -e "${HOME}/.iterm2_shell_integration.bash" && \
               source "${HOME}/.iterm2_shell_integration.bash"

          And finally, bash's readline should not use key bindings like C-j to commands.  Disable this in your ~/.inputrc:

               $if term=dumb
               # Don't bind Control-J or it messes up tramp.
               $else
               "\C-j": next-history
               $endif

       - Echoed characters after login

          tramp suppresses echos from remote hosts with the stty -echo command.  But sometimes it is too late to suppress welcome messages from the remote host containing harmful control characters.  Using sshx or scpx methods can avoid this problem because they allocate a pseudo tty.  See Inline methods.

       - tramp stops transferring strings longer than 500 characters

          Set tramp-chunksize to 500 to get around this problem, which is related to faulty implementation of process-send-string on HP-UX, FreeBSD and Tru64 Unix systems.  Consult the documentation for tramp-chunksize to see when this is necessary.

          Set file-precious-flag to t for files accessed by tramp so the file contents are checked using checksum by first saving to a temporary file. see Saving Buffers (elisp).

               (add-hook
                'find-file-hook
                (lambda ()
                  (when (file-remote-p default-directory)
                    (set (make-local-variable 'file-precious-flag) t))))

  * tramp fails in a chrooted environment

     When connecting to a local host, tramp uses some internal optimizations.  They fail, when there is a chrooted environment.  In order to disable those optimizations, set user option tramp-local-host-regexp to nil.

  * tramp does not recognize if a ssh session hangs

     ssh sessions on the local host hang when the network is down.  tramp cannot safely detect such hangs.  The network configuration for ssh can be configured to kill such hangs with the following command in the ~/.ssh/config:

          Host *
               ServerAliveInterval 5

  * tramp does not use default ssh ControlPath

     tramp overwrites ControlPath settings when initiating ssh sessions.  tramp does this to fend off a stall if a master session opened outside the Emacs session is no longer open.  That is why tramp prompts for the password again even if there is an ssh already open.

     Some ssh versions support a ControlPersist option, which allows you to set the ControlPath provided the variable tramp-ssh-controlmaster-options is customized as follows:

          (customize-set-variable
           'tramp-ssh-controlmaster-options
           (concat
             "-o ControlPath=/tmp/ssh-ControlPath-%%r@%%h:%%p "
             "-o ControlMaster=auto -o ControlPersist=yes"))

     Note how "%r", "%h" and "%p" must be encoded as "%%r", "%%h" and "%%p".

     If the ~/.ssh/config is configured appropriately for the above behavior, then any changes to ssh can be suppressed with this nil setting:

          (customize-set-variable 'tramp-use-ssh-controlmaster-options nil)

  * On multi-hop connections, tramp does not use ssh ControlMaster

     In order to use the ControlMaster option, tramp must check whether the ssh client supports this option.  This is only possible on the local host, for the first hop.  tramp does not use this option on proxy hosts.

     If you want to use this option also for the other hops, you must configure ~/.ssh/config on the proxy host:

          Host *
               ControlMaster	auto
               ControlPath	tramp.%C
               ControlPersist	no

     Check man ssh_config whether these options are supported on your proxy host.

  * File name completion does not work with tramp

     ANSI escape sequences from the remote shell may cause errors in tramp's parsing of remote buffers.

     To test if this is the case, open a remote shell and check if the output of ls is in color.

     To disable ANSI escape sequences from the remote hosts, disable --color=yes or --color=auto in the remote host's .bashrc or .profile.  Turn this alias on and off to see if file name completion works.

  * File name completion does not work in directories with large number of files

     This may be related to globbing, which is the use of shell's ability to expand wild card specifications, such as *.c.  For directories with large number of files, globbing might exceed the shell's limit on length of command lines and hang.  tramp uses globbing.

     To test if globbing hangs, open a shell on the remote host and then run ls -d * ..?* > /dev/null.

     When testing, ensure the remote shell is the same shell (/bin/sh, ksh or bash), that tramp uses when connecting to that host.

  * How to get notified after tramp completes file transfers?

     Make Emacs beep after reading from or writing to the remote host with the following code in ~/.emacs.

          (defadvice tramp-handle-write-region
            (after tramp-write-beep-advice activate)
            "Make tramp beep after writing a file."
            (interactive)
            (beep))

          (defadvice tramp-handle-do-copy-or-rename-file
            (after tramp-copy-beep-advice activate)
            "Make tramp beep after copying a file."
            (interactive)
            (beep))

          (defadvice tramp-handle-insert-file-contents
            (after tramp-insert-beep-advice activate)
            "Make tramp beep after inserting a file."
            (interactive)
            (beep))

  * How to get a Visual Warning when working with root privileges? Host indication in the mode line?

     Install tramp-theme from GNU ELPA via Emacs' Package Manager. Enable it via M-x load-theme RET tramp RET.  Further customization is explained in user option tramp-theme-face-remapping-alist.

  * Remote host does not understand default options for directory listing

     Emacs computes the dired options based on the local host but if the remote host cannot understand the same ls command, then set them with a hook as follows:

          (add-hook
           'dired-before-readin-hook
           (lambda ()
             (when (file-remote-p default-directory)
               (setq dired-actual-switches "-al"))))

  * Why is ~/.sh_history on the remote host growing?

     Due to the remote shell saving tilde expansions triggered by tramp, the history file is probably growing rapidly. tramp can suppress this behavior with the user option tramp-histfile-override.  When set to t, environment variable HISTFILE is unset, and environment variables HISTFILESIZE and HISTSIZE are set to 0.  Don't use this with bash 5.0.0.  There is a bug in bash which lets bash die.

     Alternatively, tramp-histfile-override could be a string. Environment variable HISTFILE is set to this file name then.  Be careful when setting to /dev/null; this might result in undesired results when using bash as remote shell.

     Another approach is to disable tramp's handling of the HISTFILE at all by setting tramp-histfile-override to nil.  In this case, saving history could be turned off by putting this shell code in .bashrc or .kshrc:

          if [ -f $HOME/.sh_history ] ; then
             /bin/rm $HOME/.sh_history
          fi
          if [ "${HISTFILE-unset}" != "unset" ] ; then
             unset HISTFILE
          fi
          if [ "${HISTSIZE-unset}" != "unset" ] ; then
             unset HISTSIZE
          fi

     For ssh-based method, add the following line to your ~/.ssh/environment:

          HISTFILE=/dev/null

  * How to shorten long file names when typing in tramp?

     Adapt several of these approaches to reduce typing.  If the full name is ssh,news@news.my.domain,/opt/news/etc, then:

      1. Use simplified syntax:

          If you always apply the default method (see Default Method), you could use the simplified tramp syntax (see Change file name syntax):

               (customize-set-variable 'tramp-default-method "ssh")
               (tramp-change-syntax 'simplified)

          The reduced typing: C-x C-f
          prefixnews@news.my.domainpostfix/opt/news/etc
          RET.

      2. Use default values for method name and user name:

          You can define default methods and user names for hosts, (see Default Method, see Default User):

               (custom-set-variables
                '(tramp-default-method "ssh")
                '(tramp-default-user "news"))

          The reduced typing: C-x C-f -,news.my.domain,/opt/news/etc RET.

          Note that there are some useful shortcuts already.  Accessing your local host as root user, is possible just by C-x C-f su,, RET.

      3. Use configuration options of the access method:

          Programs used for access methods already offer powerful configurations (see Customizing Completion).  For ssh, configure the file ~/.ssh/config:

               Host xy
                    HostName news.my.domain
                    User news

          The reduced typing: C-x C-f ssh,xy,/opt/news/etc RET.

          Depending on the number of files in the directories, host names completion can further reduce key strokes: C-x C-f
          prefixsshpostfixhopx TAB.

      4. Use environment variables to expand long strings

          For long file names, set up environment variables that are expanded in the minibuffer.  Environment variables are set either outside Emacs or inside Emacs with Lisp:

               (setenv "xy" "ssh,news@news.my.domain,/opt/news/etc/")

          The reduced typing: C-x C-f $xy RET.

          Note that file name cannot be edited here because the environment variables are not expanded during editing in the minibuffer.

      5. Define own keys:

          Redefine another key sequence in Emacs for C-x C-f:

               (global-set-key
                [(control x) (control y)]
                (lambda ()
                  (interactive)
                  (find-file
                   (read-file-name
                    "Find tramp file: "
                    "ssh,news@news.my.domain,/opt/news/etc/"))))

          Simply typing C-x C-y would prepare minibuffer editing of file name.

          See the Emacs Wiki (https://www.emacswiki.org/emacs/TrampMode) for a more comprehensive example.

      6. Define own abbreviation (1):

          Abbreviation list expansion can be used to reduce typing long file names:

               (add-to-list
                'directory-abbrev-alist
                '("^/xy" . "ssh,news@news.my.domain,/opt/news/etc/"))

          The reduced typing: C-x C-f /xy RET.

          Note that file name cannot be edited here because the abbreviations are not expanded during editing in the minibuffer. Furthermore, the abbreviation is not expanded during TAB completion.

      7. Define own abbreviation (2):

          The abbrev-mode gives additional flexibility for editing in the minibuffer:

               (define-abbrev-table 'my-tramp-abbrev-table
                 '(("xy" "ssh,news@news.my.domain,/opt/news/etc/")))

               (add-hook
                'minibuffer-setup-hook
                (lambda ()
                  (abbrev-mode 1)
                  (setq local-abbrev-table my-tramp-abbrev-table)))

               (defadvice minibuffer-complete
                 (before my-minibuffer-complete activate)
                 (expand-abbrev))

               ;; If you use partial-completion-mode
               (defadvice PC-do-completion
                 (before my-PC-do-completion activate)
                 (expand-abbrev))

          The reduced typing: C-x C-f xy TAB.

          The minibuffer expands for further editing.

      8. Use bookmarks:

          Use bookmarks to save tramp file names. see Bookmarks (emacs).

          Upon visiting a location with tramp, save it as a bookmark with menu-bar edit bookmarks set.

          To revisit that bookmark: menu-bar edit bookmarks jump.

      9. Use recent files:

          recentf remembers visited places. see File Conveniences (emacs).

          Keep remote file names in the recent list without have to check for their accessibility through remote access:

               (recentf-mode 1)

          Reaching recently opened files: menu-bar file Open Recent.

      10. Use filecache:

          Since filecache remembers visited places, add the remote directory to the cache:

               (with-eval-after-load 'filecache
                 (file-cache-add-directory
                   "ssh,news@news.my.domain,/opt/news/etc/"))

          Then use directory completion in the minibuffer with C-x C-f C-TAB.

      11. Use bbdb:

          bbdb has a built-in feature for Ange FTP files, which also works for tramp file names. see Storing FTP sites in the BBDB (bbdb).

          Load bbdb in Emacs:

               (require 'bbdb)
               (bbdb-initialize)

          Create a BBDB entry with M-x bbdb-create-ftp-site RET. Then specify a method and user name where needed.  Examples:

               M-x bbdb-create-ftp-site RET
               Ftp Site: news.my.domain RET
               Ftp Directory: /opt/news/etc/ RET
               Ftp Username: sshpostfixhopnews RET
               Company: RET
               Additional Comments: RET

          In BBDB buffer, access an entry by pressing the key F.

     Thanks to tramp users for contributing to these recipes.

  * Why saved multi-hop file names do not work in a new Emacs session?

     When saving ad-hoc multi-hop tramp file names (see Ad-hoc multi-hops) via bookmarks, recent files, filecache, bbdb, or another package, use the full ad-hoc file name including all hops, like ssh,bird@bastion|sshpostfixhopnews.my.domain,/opt/news/etc.

     Alternatively, when saving abbreviated multi-hop file names ssh,news@news.my.domain,/opt/news/etc, the user option tramp-save-ad-hoc-proxies must be set non-nil value.

  * How to connect to a remote Emacs session using tramp?

     Configure Emacs Client (see Emacs Server (emacs)).

     Then on the remote host, start the Emacs Server:

          (require 'server)
          (setq server-host (system-name)
                server-use-tcp t)
          (server-start)

     If (system-name) of the remote host cannot be resolved on the local host, use IP address instead.

     Copy from the remote host the resulting file ~/.emacs.d/server/server to the local host, to the same location.

     Then start Emacs Client from the command line:

          emacsclient ssh,user@host,/file/to/edit

     user and host refer to the local host.

     To make Emacs Client an editor for other programs, use a wrapper script emacsclient.sh:

          #!/bin/sh
          emacsclient ssh,$(whoami)@$(hostname --fqdn),$1

     Then change the environment variable EDITOR to point to the wrapper script:

          export EDITOR=/path/to/emacsclient.sh

  * How to determine whether a buffer is remote?

     The buffer-local variable default-directory tells this.  If the form (file-remote-p default-directory) returns non-nil, the buffer is remote.  See the optional arguments of file-remote-p for determining details of the remote connection.

  * How to save files when a remote host isn't reachable anymore?

     If the local machine Emacs is running on changes its network integration, remote hosts could become unreachable.  This happens for example, if the local machine is moved between your office and your home without restarting Emacs.

     In such cases, the command tramp-rename-files can be used to alter remote buffers’ method, host, and/or directory names.  This permits saving their contents in the same location via another network path, or somewhere else entirely (including locally).  see Renaming remote files.

  * How to disable other packages from calling tramp?

     There are packages that call tramp without the user ever entering a remote file name.  Even without applying a remote file syntax, some packages enable tramp on their own.  How can users disable such features.

       - ido.el

          Disable tramp file name completion:

               (customize-set-variable 'ido-enable-tramp-completion nil)

       - rlogin.el

          Disable remote directory tracking mode:

               (rlogin-directory-tracking-mode -1)

  * How to disable tramp?

       - To keep Ange FTP as default the remote files access package, set this in .emacs:

               (customize-set-variable 'tramp-default-method "ftp")

          If you want to enable Ange FTP's syntax, add the following form:

               (tramp-change-syntax 'simplified)

       - To disable both tramp (and Ange FTP), set tramp-mode to nil in .emacs.  Note, that we don't use customize-set-variable, in order to avoid loading tramp.

               (setq tramp-mode nil)

       - To deactivate tramp for some look-alike remote file names, set tramp-ignored-file-name-regexp to a proper regexp in .emacs.  Note, that we don't use customize-set-variable, in order to avoid loading tramp.

               (setq tramp-ignored-file-name-regexp "\\`/ssh:example\\.com:")

          This is needed, if you mount for example a virtual file system on your local host's root directory as /ssh:example.com:.

       - To unload tramp, type M-x tramp-unload-tramp RET. Unloading tramp resets Ange FTP plugins also.

How file names, directories and localnames are mangled and managed
******************************************************************

Splitting a localname into its component parts
==============================================

tramp package redefines lisp functions file-name-directory and file-name-nondirectory to accommodate the unique file naming syntax that tramp requires.

The replacements dissect the file name, use the original handler for the localname, take that result, and then re-build the tramp file name.  By relying on the original handlers for localnames, tramp benefits from platform specific hacks to the original handlers.

Integrating with external Lisp packages
=======================================

File name completion.
---------------------

Sometimes, it is not convenient to open a new connection to a remote host, including entering the password and alike.  For example, this is nasty for packages providing file name completion.  Such a package could signal to tramp, that they don't want it to establish a new connection.  Use the variable non-essential temporarily and bind it to non-nil value.

     (let ((non-essential t))
       ...)

File attributes cache.
----------------------

Keeping a local cache of remote file attributes in sync with the remote host is a time-consuming operation.  Flushing and re-querying these attributes can tax tramp to a grinding halt on busy remote servers.

To get around these types of slow-downs in tramp's responsiveness, set the process-file-side-effects to nil to stop tramp from flushing the cache.  This is helpful in situations where callers to process-file know there are no file attribute changes.  The let-bind form to accomplish this:

     (let (process-file-side-effects)
       ...)

For asynchronous processes, tramp uses a process sentinel to flush file attributes cache.  When callers to start-file-process know beforehand no file attribute changes are expected, then the process sentinel should be set to the default state.  In cases where the caller defines its own process sentinel, tramp's process sentinel is overwritten.  The caller can still flush the file attributes cache in its process sentinel with this code:

     (unless (memq (process-status proc) '(run open))
       (dired-uncache remote-directory))

Since tramp traverses subdirectories starting with the root-directory, it is most likely sufficient to make the default-directory of the process buffer as the root directory.

How to Customize Traces
***********************

tramp messages are raised with verbosity levels ranging from 0 to 10.  tramp does not display all messages; only those with a verbosity level less than or equal to tramp-verbose.

The verbosity levels are

 0  silent (no tramp messages at all)

 1  errors

 2  warnings

 3  connection to remote hosts (default verbosity)

 4  activities

 5  internal

 6  sent and received strings

 7  file caching

 8  connection properties

 9  test commands

10  traces (huge)

With tramp-verbose greater than or equal to 4, messages are also written to a tramp debug buffer.  Such debug buffers are essential to bug and problem analyses.  For tramp bug reports, set the tramp-verbose level to 6 (see Bug Reports).

The debug buffer is in Outline Mode (emacs). In this buffer, messages can be filtered by their level.  To see messages up to verbosity level 5, enter C-u 6 C-c C-q. Other navigation keys are described in Outline Visibility (emacs).

tramp handles errors internally.  But to get a Lisp backtrace, both the error and the signal have to be set as follows:

     (setq debug-on-error t
           debug-on-signal t)

If tramp-verbose is greater than or equal to 10, Lisp backtraces are also added to the tramp debug buffer in case of errors.

To enable stepping through tramp function call traces, they have to be specifically enabled as shown in this code:

     (require 'trace)
     (dolist (elt (all-completions "tramp-" obarray 'functionp))
       (trace-function-background (intern elt)))
     (untrace-function 'tramp-read-passwd)

The buffer *trace-output* contains the output from the function call traces.  Disable tramp-read-passwd to stop password strings from being written to *trace-output*.

GNU Free Documentation License
******************************

     [file doclicense.texi not included]