Executing Remote Commands on Demand with SSH

A nice feature of SSH is that it is capable of logging in and executing single commands on a remote system. You just have to place the remote command, enclosed in quotes, at the end of the ssh command of the local server. In the example below, a user on server Smallfry who needs to know the version of the kernel running on server Bigboy (192.168.1.100) remotely runs the uname -a command. The command returns the version of 2.6.8-1.521 and the server's name, Bigboy:

     [root@smallfry tmp]# ssh 192.168.1.100 "uname -a"
     root@192.168.1.100's password:
     Linux bigboy 2.6.8-1.521 #1 Mon Aug 16 09:01:18 EDT 2004 i686 i686
     i386 GNU/Linux
     [root@smallfry tmp]#

This feature can be very useful. You can combine it with password-free login, explained later in this chapter, to get the status of a remote server whenever you need it. More comprehensive monitoring may best be left to such purpose built programs as MRTG, which is covered in Chapter 22, "Monitoring Server Performance."