[linux] linux execute command remotely

how do I execute command/script on a remote linux box? say I want to do service tomcat start on box b from box a.

If you don't want to deal with security and want to make it as exposed (aka "convenient") as possible for short term, and|or don't have ssh/telnet or key generation on all your hosts, you can can hack a one-liner together with netcat. Write a command to your target computer's port over the network and it will run it. Then you can block access to that port to a few "trusted" users or wrap it in a script that only allows certain commands to run. And use a low privilege user.

on the server

mkfifo /tmp/netfifo; nc -lk 4201 0</tmp/netfifo | bash -e &>/tmp/netfifo

This one liner reads whatever string you send into that port and pipes it into bash to be executed. stderr & stdout are dumped back into netfifo and sent back to the connecting host via nc.

on the client

To run a command remotely: echo "ls" | nc HOST 4201

I think this article explains well:

Running Commands on a Remote Linux / UNIX Host

Google is your best friend ;-)

 ssh user@machine 'bash -s' < local_script.sh

or you can just

 ssh user@machine "remote command to run"