Monit Tricks

Recently I had a chance to do a little monit foo with a co-worker for a rather interesting project that we will hopefully be sending off into the intertubes.

For one part of this project, I got the chance to get my hands dirty with my old friend monit. Monit, for those that don’t know, is a UNIX system administrators dream.

Here’s a brief run down of what monit can do from the web site:

Monit can start a process if it does not run, restart a process if it does not respond and stop a process if it uses too much resources. You can use Monit to monitor files, directories and filesystems for changes, such as timestamp changes, checksum changes or size changes. You can also monitor remote hosts; Monit can ping a remote host and can check TCP/IP port connections and server protocols. Monit is controlled via an easy to use control file based on a free-format, token-oriented syntax. Monit logs to syslog or to its own log file and notifies you about error conditions and recovery status via customizable alert.

So…with that little bit of unnecessary advertising going on. What was I trying to do? It was pretty simple really. Monitor a process, if it is not running, restart it. However, there was a twist that I hadn’t done before. It needed to restart as a particular user. My past experience had always been monitoring applications such as a ssh server or smtp server. I hadn’t gone down the path of monitoring an application that a user could start. But if you are doing anything like a kiosk, this type of functionality might come in handy for you.

The solution is ridiculously simple. All you need to do is add an “as” line to the start portion of your script. Here’s an example I found online:

start program = "/etc/init.d/tomcat start"
              as uid nobody and gid nobody
        stop program  = "/etc/init.d/tomcat stop"
              # You can also use id numbers instead and write:
              as uid 99 and with gid 99

I’m sure I’m not the only one that has run into this so I figured I would help spread the word on a very obvious and probably overlooked monit feature.

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