Ubuntu Manpage: tsocks - Library for intercepting outgoing network connections and redirecting them

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=/lib/libtsocks.so

       C Shell -

       setenv LD_PRELOAD=/lib/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 ~/.tsocks.conf and if that file cannot be
accessed, 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@progsoc.uts.edu.au)

COPYRIGHT

       Copyright 2000 Shaun Clowes

       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@yggdrasil.com (Adam J. Richter) and can be had from ftp.yggdrasil.com
       pub/dist/pkg