tsocks For Linux

tsocks provides transparent network access through a SOCKS version 4 or 5 proxy (usually on a firewall).

SOCKS servers are a form of proxy that are commonly used in firewalled LAN environments to allow access between networks, and often to the Internet. The problem is that most applications don't know how to gain access through SOCKS servers. This means that network based applications that don't understand SOCKS are very limited in networks they can reach. An example of this is simple 'telnet'.

tsocks' role is to allow these non SOCKS aware applications (e.g telnet, ssh, ftp etc) to use SOCKS without any modification. It does this by intercepting the calls that applications make to establish network connections and negotating them through a SOCKS server as necessary. If you're on a network firewalled from the internet with a SOCKS server for outside access, telnet can't use this server and thus can't telnet out to the Internet., sou you cannot get out.

tsocks is based on the 'shared library interceptor' concept. Through use of the LD_PRELOAD environment variable or the /etc/ld.so.preload file tsocks is automatically loaded into the process space of every executed program. From there it overrides the normal connect() function by providing its own. Thus when an application calls connect() to establish a TCP connection it instead passes control to tsocks. tsocks determines if the connection needs to be made via a SOCKS server (by checking /etc/tsocks.conf) and negotiates the connection if so (through use of the real connect() function )