CODEWITHSUNDEEP
linuxbashprocessdaemon
din2
din2

Reputation: 195

Start process if dead

What I'm trying to do is to start a process if not started. Here is what I try

#!/bin/bash
pid=`ps ax | grep app | grep -v grep | wc -l`
  if [ $pid = 0 ]
then
 /etc/init.d/app start
fi

The problem is that the line

/etc/init.d/app start

is not executed. What is wrong here ? I know that I can you daemontools but I like the "bash" approach.

Upvotes: 0

Views: 3369

Answers (4)

KurzedMetal
KurzedMetal

Reputation: 12946

I can't check on my servers right now, but Debian use start-stop-daemon to load services, it seems the right tool to use for your task, since it keeps track of your background process by PID and not just matching a name in the process list (which can do too).

Upvotes: 0

sorpigal
sorpigal

Reputation: 26086

If you have GNU ps this is easy and doesn't require any craziness.

if ! ps -C app >/dev/null ; then
     /etc/init.d/app start
fi

You just need to be careful that the app you pass to ps is the actual process name.

Upvotes: 0

ghoti
ghoti

Reputation: 46826

You can avoid the double grep by turning your keyword into a regex that doesn't match itself. And you can use grep -c instead of counting with wc. In your script, you could try:

pcount=`ps ax | grep -c "[a]pp"`

Alternately, use the actual pid instead of the process count:

#!/bin/bash

pid=`ps ax | awk '/[a]pp/{print $1}'`

if ! ps "$pid" >/dev/null; then
  /etc/init.d/app start
fi

Note that this is still a very bad way to handle restarts of a service. You should see if app maintains its own pid file, perhaps somewhere in /var/run/, then test the contents of that.

#!/bin/sh
if [ -f /var/run/app.pid ]; then
  if ps `cat /var/run/app.pid` >/dev/null; then
    /etc/init.d/app start
  fi
else
  /etc/init.d/app start
fi

Or even better, launch app using daemontools runit or upstart or something equivalent that will take care of these things for you.

Upvotes: 2

Eugen Rieck
Eugen Rieck

Reputation: 65264

Take a look at the == operator.

Best may be something like

pid=`ps ax | grep app | grep -v grep`
test -z "$pid" && /etc/init.d/app start

Upvotes: 3

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