tsocks (8) - Linux Manuals

tsocks: Library for intercepting outgoing network connections and

Command to display tsocks manual in Linux: $ man 8 tsocks

NAME

tsocks - Library for intercepting outgoing network connections and redirecting them through a SOCKS server.

SYNOPSIS

Set LD_PRELOAD to load the library then use applications as normal

The syntax to force preload of the library for different shells is specified below:
Bash, Ksh and Bourne shell -

export LD_PRELOAD=libtsocks.so

C Shell -

setenv LD_PRELOAD=libtsocks.so

This process can be automated (for Bash, Bourne and Korn shell users) for a single command or for all commands in a shell session by using the tsocks(1) script

You can also setup tsocks in such a way that all processes automatically use it, a very useful configuration. For more information on this configuration see the CAVEATS section of this manual page.

DESCRIPTION

tsocks is a library to allow transparent SOCKS proxying. It wraps the normal connect() function. When a connection is attempted, it consults the configuration file (which is defined at configure time but defaults to /etc/tsocks.conf) and determines if the IP address specified is local. If it is not, the library redirects the connection to a SOCKS server specified in the configuration file. It then negotiates that connection with the SOCKS server and passes the connection back to the calling program.

tsocks is designed for use in machines which are firewalled from then internet. It avoids the need to recompile applications like lynx or telnet so they can use SOCKS to reach the internet. It behaves much like the SOCKSified TCP/IP stacks seen on other platforms.

ARGUMENTS

Most arguments to tsocks are provided in the configuration file (the location of which is defined at configure time by the --with-conf=<file> argument but defaults to /etc/tsocks.conf). The structure of this file is documented in tsocks.conf(8)

Some configuration options can be specified at run time using environment variables as follows:

TSOCKS_CONF_FILE: This environment variable overrides the default location of the tsocks configuration file. This variable is not honored if the program tsocks is embedded in is setuid. In addition this environment variable can be compiled out of tsocks with the --disable-envconf argument to configure at build time
TSOCKS_DEBUG: This environment variable sets the level of debug output that should be generated by tsocks (debug output is generated in the form of output to standard error). If this variable is not present by default the logging level is set to 0 which indicates that only error messages should be output. Setting it to higher values will cause tsocks to generate more messages describing what it is doing. If set to -1 tsocks will output absolutely no error or debugging messages. This is only needed if tsocks output interferes with a program it is embedded in. Message output can be permanently compiled out of tsocks by specifying the --disable-debug option to configure at build time
TSOCKS_DEBUG_FILE: This option can be used to redirect the tsocks output (which would normally be sent to standard error) to a file. This variable is not honored if the program tsocks is embedded in is setuid. For programs where tsocks output interferes with normal operation this option is generally better than disabling messages (with TSOCKS_DEBUG = -1)
TSOCKS_USERNAME: This environment variable can be used to specify the username to be used when version 5 SOCKS servers request username/password authentication. This overrides the default username that can be specified in the configuration file using 'default_user', see tsocks.conf(8) for more information. This variable is ignored for version 4 SOCKS servers.
TSOCKS_PASSWORD: This environment variable can be used to specify the password to be used when version 5 SOCKS servers request username/password authentication. This overrides the default password that can be specified in the configuration file using 'default_pass', see tsocks.conf(8) for more information. This variable is ignored for version 4 SOCKS servers.

DNS ISSUES

tsocks will normally not be able to send DNS queries through a SOCKS server since SOCKS V4 works on TCP and DNS normally uses UDP. Version 1.5 and up do however provide a method to force DNS lookups to use TCP, which then makes them proxyable. This option can only enabled at compile time, please consult the INSTALL file for more information.

ERRORS

tsocks will generate error messages and print them to stderr when there are problems with the configuration file or the SOCKS negotiation with the server if the TSOCKS_DEBUG environment variable is not set to -1 or and --disable-debug was not specified at compile time. This output may cause some problems with programs that redirect standard error.

CAVEATS

tsocks will not in the above configuration be able to provide SOCKS proxying to setuid applications or applications that are not run from a shell. You can force all applications to LD_PRELOAD the library by placing the path to libtsocks in /etc/ld.so.preload. Please make sure you correctly enter the full path to the library in this file if you do this. If you get it wrong, you will be UNABLE TO DO ANYTHING with the machine and will have to boot it with a rescue disk and remove the file (or try the saveme program, see the INSTALL file for more info). THIS IS A ***WARNING***, please be careful. Also be sure the library is in the root filesystem as all hell will break loose if the directory it is in is not available at boot time.

BUGS

tsocks can only proxy outgoing TCP connections

tsocks does NOT work correctly with asynchronous sockets (though it does work with non blocking sockets). This bug would be very difficult to fix and there appears to be no demand for it (I know of no major application that uses asynchronous sockets)

tsocks is NOT fully RFC compliant in its implementation of version 5 of SOCKS, it only supports the 'username and password' or 'no authentication' authentication methods. The RFC specifies GSSAPI must be supported by any compliant implementation. I haven't done this, anyone want to help?

tsocks can force the libc resolver to use TCP for name queries, if it does this it does it regardless of whether or not the DNS to be queried is local or not. This introduces overhead and should only be used when needed.

tsocks uses ELF dynamic loader features to intercept dynamic function calls from programs in which it is embedded. As a result, it cannot trace the actions of statically linked executables, non-ELF executables, or executables that make system calls directly with the system call trap or through the syscall() routine.

FILES

/etc/tsocks.conf - default tsocks configuration file

AUTHOR

Shaun Clowes (delius [at] progsoc.uts.edu.au)

COPYRIGHT

tsocks and its documentation may be freely copied under the terms and conditions of version 2 of the GNU General Public License, as published by the Free Software Foundation (Cambridge, Massachusetts, United States of America).

This documentation is based on the documentation for logwrites, another shared library interceptor. One line of code from it was used in tsocks and a lot of the documentation :) logwrites is by adam [at] yggdrasil.com (Adam J. Richter) and can be had from ftp.yggdrasil.com pub/dist/pkg