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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).