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_ _ _ _ _ _
| (_) |__ | | _____ ___ _ __ __ _| (_)_ _____
| | | '_ \| |/ / _ \/ _ \ '_ \ / _` | | \ \ / / _ \
| | | |_) | < __/ __/ |_) | (_| | | |\ V / __/
|_|_|_.__/|_|\_\___|\___| .__/ \__,_|_|_| \_/ \___|
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(C) Fabio Busatto <fabio.busatto@gmail.com>
1. OVERVIEW
Many systems provide the ability to keep tcp connections alive, so they
aren't reset by peers or by routers because of inactivity.
Even if this feature is present, only a few programs correctly implement
the code to use it. If your favourite foo-client is not written with
support for tcp keepalive, you'll continue to see your connection reset.
libkeepalive library provides a way to enable tcp keepalive support in
any program that uses shared libraries (e.g.: glibc shared object) to
perform network operations. Using the preload method, you will be able to
intercept normal program execution and to inject the code needed to enable
the keepalive routines, everything done without modifying the original
binary file and with no need to gain root privileges.
2. OBTAINING SOFTWARE
Latest version of libkeepalive is available on
http://libkeepalive.sourceforge.net/#download.
3. BUILDING BINARIES
Just run make (use gmake if your default make is another one).
4. INSTALLING
Simply copy libkeepalive.so in some cool directory (/usr/lib, or ~/lib if
you're not so elite to have root privileges).
If you want to enable keepalive in suid programs too, you have to copy
libkeepalive.so in /lib or /usr/lib and suid it (according to ld.so
manpage). In any other scenarios the library will not work with suid
binaries.
5. USER CONFIGURATION
libkeepalive will do its job if you set the environment variable LD_PRELOAD
to the path of libkeepalive.so shared library before executing the target
program. You must specify the full path of the library if ld.so cannot is
not able to find it. You can also set the variable in your startup script
(i.e.: ~/.profile), depending from your shell.
For informations about setting environment variables, refer to your shell
documentation.
6. SYSTEM-WIDE CONFIGURATION
Host administrators may want to impose the use of libkeepalive to all their
users and all daemons loaded by the system startup process.
Adding the full path of the libkeepalive.so dynamic library to
/etc/ld.so.preload you obtain the same result as the LD_PRELOAD variable is
always set, forcing the use indipendently from the environment.
7. DISABLING FOR A SPECIFIC EXECUTION
If you need to disable the action of libkeepalive for a single job, or if
your admin set the ld.so.preload, you can set the KEEPALIVE environment
variable to "off", inhibiting the library even if it will be loaded.
8. TUNING KEEPALIVE PARAMETERS
You can change the keepalive parameters using environment variables or via
sysctl/procfs.
env sysctl
KEEPCNT <=> net.ipv4.tcp_keepalive_probes
KEEPIDLE <=> net.ipv4.tcp_keepalive_time
KEEPINTVL <=> net.ipv4.tcp_keepalive_intvl
DON'T FORGET to configure your system-specific parameters for keepalive!
Many times, defaults are not what you need and you have to change your
settings (see your system documentation for this).
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