TSOCKS(8)TSOCKS(8)NAMEtsocks - 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=/usr/local/lib/tsocks/libtsocks.so
C Shell -
setenv LD_PRELOAD=/usr/local/lib/tsocks/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 automati‐
cally use it, a very useful configuration. For more information on this
configuration see the CAVEATS section of this manual page.
DESCRIPTIONtsocks 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 /usr/local/etc/tsocks.conf) and determines if the IP address speci‐
fied 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
/usr/local/etc/tsocks.conf). The structure of this file is documented
in tsocks.conf(8)
Some configuration options can be specified at run time using environ‐
ment variables as follows:
TSOCKS_CONFFILE
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 envi‐
ronment variable can be compiled out of tsocks with the --dis‐
able-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 -1tsocks will output absolutely no
error or debugging messages. This is only needed if tsocks out‐
put 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 vari‐
able 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 mes‐
sages (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 com‐
pile 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
Linuxspecific: 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.
BUGStsocks 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 authentica‐
tion' authentication methods. The RFC specifies GSSAPI must be sup‐
ported 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 executa‐
bles, or executables that make system calls directly with the system
call trap or through the syscall() routine.
FILES
/usr/local/etc/tsocks.conf - default tsocks configuration file
SEE ALSOtsocks.conf(5)tsocks(1)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
Shaun ClowesTSOCKS(8)
