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Introduction to fsh

Remote command execution via a cryptographically strong method such as lsh or ssh is often painfully slow. The biggest problem is that the client and the server perform a lot of complex calculations during connection establishment.

fsh uses lsh or ssh to establish a secure tunnel to the remote system. This takes as long as a normal connection establishment, but once the tunnel is established, fsh can reuse it to start new sessions on the remote system almost instantaneously. You get the security of ssh and the speed of rsh.

There are three programs at work. fshd establish a tunnel to the remote system. It can use lsh, ssh or even rsh to establish it. It will start in.fshd on the remote system. You can start fshd manually, or allow fsh to do it automatically on an as-needed basis.

in.fshd receives commands such as "create a new session running the command gcc foo.c, and call it session 3" or "send the following data to standard input of session 5" via the tunnel. You would normally not interact directly with in.fshd.

fsh is a drop-in replacement for rsh. It connects to the local fshd using a unix domain socket that is protected so that only the users that started fshd can connect to it. It uses fshd to forward a request to in.fshd, which will in turn start the requested program.

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