Mapping a filesystem into the main tree


  11..  PPuurrppoossee

  At this point, we are trying to logically connect a filesystem (a
  local partition or a server volume) with the directory tree. The
  filesystem can be located anywhere.

  The following situation is not uncommon:


  +o  You have a large directory, say /home/jack, which is getting bigger
     and bigger.

  +o  You are out of disk space.

  +o  You buy a second hard drive, create a single partition on it
     (/dev/hdb1 for example).

  +o  You rename /home/jack to /home/jack.backup

  +o  You map /dev/hdb1 to /home/jack.

  +o  You copy /home/jack.backup to /home/jack.

  After that, you may delete /home/jack.backup. You get the same logical
  file layout, but now have space on the first drive and a lot of space
  for /home/jack to grow on the second.


  22..  TTaasskk

  To achieve the connection, you have to:


  1. Select a hard drive partition.

  2. Identify the type of filesystem. _E_x_t_2 for _L_i_n_u_x and _U_m_s_d_o_s for DOS
     drives.

  3. Pick a mount point. It can be any directory or subdirectory.


  33..  GGeenneerraall ooppttiioonnss

  The general options are not needed most of the time. They allow for
  increased flexibility and security.


  +o  Read-only

     It is possible to protect a partition from writing. Even the
     superuser won't be able to write there. This is seldom used on a
     normal hard drive partition though.

  +o  User mountable

     This is generally used with the following option, and is useful for
     removable media. It allows anyone to activate the connection at any
     time. Normally, only root (the superuser) can establish a mount.

  +o  Do not mount at boot time

     Especially useful for removable media, it prevents the system from
     trying to establish a mount at boot time.
  +o  No program allowed to execute

     This is a security feature, which is especially useful for
     removable media. If you set the user mountable option on a
     removable media, it allows any user to come and install a set of
     files, specifically setup, to give him full access to your system
     (administrator privileges).  This option would prevent this
     situation from occurring.

  +o  No special device file support

     This is a security feature.

     Special devices are generally created with proper access rights in
     the /dev directory. They may be created in other places too, with
     the mknod command. This feature prevents mounting media with
     special devices created with relaxed security. Such devices would
     defeat all security on the system.

  +o  No setuid programs allowed

     This is yet another security feature. It is a compromise between
     full access and the above option (no execution allowed).

     If you set this option, the system will deny privileged programs
     their special rights. A privileged program is one that switches the
     user to another identity while it is running (generally root).
     This allows the user to do special tasks that only the supervisor
     can do.

  +o  User quota enabled

     This flag tells the kernel to enable quota accounting on the
     filesystem. Quota accounting maintains, for each user in real time,
     the amount of disk space used and the amount of files and
     directories they own. Limits may be imposed on some or all users.

     This is controlled separately for each file system. The file
     quota.user is created in the root of the filesystem (linuxconf will
     create it for you if you activate this feature). The utility
     quotacheck is run to initialize the file with the current state of
     the filesystem. The kernel, from now on, will silently update this
     for each user account.

     This is useful for preventing a single user from filling the disk.

  +o  Group quota enabled

     This is the same feature as user quota enabled, but for groups. The
     group quotas hold the sum of the quotas of all file members of the
     group. A file quota.group is created when this feature is enabled
     and the utility quotacheck is used to initialize the file.

     While a user may be under his personal quota limit, the quota of
     his group may be over its limit. The user will be prevented from
     creating new files and/or growing them.


  44..  ((UU))MMss--DDOOSS  aanndd HHppffss  (( OOSS//22 )) ooppttiioonnss


  44..11..  SSeeccuurriittyy ffeeaattuurreess

  Both _M_s_-_D_O_S and _O_S_/_2 are single-user operating systems.  Their
  respective filesystems lack most of the features expected in a multi-
  user operating system like _L_i_n_u_x.
  For one, there is no file ownership. This means that when a _D_O_S hard
  drive is mounted into the _L_i_n_u_x filesystem tree, files will be
  available to every user on the machine.

  Keep in mind that _L_i_n_u_x is a multi-user system. It is fairly easy to
  create user accounts on your system for co-workers so they can share
  your CPU or system resources. It would be unpleasant to find out later
  that everyone has access to every personal file you have in your _D_O_S
  partitions.

  _L_i_n_u_x offers a neat solution to this. You can logically apply an
  ownership and permission flag to all files and directories on _D_O_S
  partitions. No special data is written to the partitions. It is simply
  a presentation mode used by _L_i_n_u_x.

  Here are the options you can control


  +o  Default user ID

     You can assign one owner to all files and directories in the
     filesystem. The default owner is root.

  +o  Default group ID

     You can assign one group to all files and directories in the file
     system. The default group is root.

  +o  Default permissions

     You can selectively turn on or off every one of the nine _U_N_I_X style
     permission bits. Permission bits are expressed as three groups of
     three bits each. Each group has the following layout:


  +o  Read access

  +o  Write access

  +o  Execute access


     The groups are


  +o  Owner permission bits

  +o  Group permission bits

  +o  Other users (not the owner and not a member of the group)
     permission bits.


     These bits are expressed in octal notation. A "one" indicates that
     the corresponding permission is off. For example a value of 007,
     enable full access to the owner and the group but disable all
     access for other users. A value of 022 provides full access to the
     owner, but disables writing for all other users.


  44..22..  TTrraannssllaattiioonn mmooddee


  Text files are stored in a slightly different format on _M_s_-_D_O_S and
  _O_S_/_2, compared to _U_N_I_X and _L_i_n_u_x. The difference lies in the way end-
  of-file is identified.
  _M_s_-_D_O_S uses a sequence of two characters, an ASCII Carriage-return
  followed by an ASCII Line Feed.  _U_N_I_X use only a single Line Feed.

  The Ms-DOS, Umsdos and Hpfs file-systems share one option to make life
  easier when sharing files on a hard drive between _L_i_n_u_x and _M_s_-_D_O_S or
  _O_S_/_2.

  Here are the modes available:


  +o  binary -        This means no translation at all.

  +o  auto - The translation will be activated on all files except those
     with a special extension.

     Here are the known binary extensions:


  +o  Program code

     APP BIN COM DLL DRV EXE LIB OBJ OVL OVR PIF SYS

  +o  Common archivers

     ARC ARJ DEB GZ  LHA LZH TAR TAZ TGZ TPZ TZ  TZP Z   ZIP ZOO

  +o  Graphics

     BMP GIF GL  JPG PCX TIF

  +o  TeX

     DVI GF PK PXL TFM VF


  +o  text

     The translation will be done on all files. This option should be
     used with care.

  Once a translation mode is selected, it is done both at read and write
  times. This makes it nearly transparent to _L_i_n_u_x applications.

  Please note that the current trend is towards flexible utilities
  (editors) which can handle both formats instead of using a filesystem
  trick like this one.


  55..  OOtthheerr ooppttiioonnss

  New filesystems and filesystem features do appear once in a while.
  These filesystems may have options unknown to _L_i_n_u_x_c_o_n_f.

  To cope with this, there is an extra option line. Normally filesystem
  options are a group of keyword/value pairs, separated by a comma.



                       opt1=val,opt2=none,opt3,opt4=2







  66..  CCoommmmeenntt

  You can write anything you want here, including an explanation about
  the option combination you have selected.