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NOTE: I am running Red Hat 6.7

I have a service that is configured with the Linux init system to start a process as a service when the machine boots. This was done by doing this one-time configuration from the command line:

ln -snf /home/me/bin/my_service /etc/init.d/my_service
chkconfig --add my_service
chkconfig --level 235 my_service on

When the OS reboots, the service starts as expected.

I ALSO need the service to be restarted if the service (my_service) crashes. From what I've read, all I need to do is add an entry to /etc/inittab that looks like this:

mysvc:235:respawn:/home/me/bin/my_service_starter

Where my_service_starter looks like:

#!/bin/bash
/home/me/bin/my_service start

My understanding is that when the init system detects that my_service is not running, it will attempt to restart it by running "my_service_starter".

However this does not seem to be working.

I need to understand how to tell the Linux init system to restart my service when the service crashes.

StvnBrkdll
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2 Answers2

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Given an entry like:

mysvc:235:respawn:/home/me/bin/my_service_starter

Then inittab will:

  1. call /home/me/bin/my_service_starter
  2. which will call /home/me/bin/my_service start
  3. ...and then exit, so init will thing your service has failed
  4. so init will call /home/me/bin/my_service_starter again

...and so forth, which will result in init deciding that your script is respawning too fast, after which it will ignore it completely.

A process started by inittab is not expected to exit. If you really want to use inittab to maintain your service, you could remove /etc/init.d/my_service, and then in /etc/inittab you would have something like:

mysvc:235:respawn:/home/me/bin/my_service

And you would need to ensure that my_service runs in the foreground (some programs automatically daemonize by default, although these will often have some sort of --run-in-foreground flag).

If you upgrade to CentOS 7 or something else with systemd, this all becomes easier.

You can also investigate "third-party" process supervisors like "supervisord" or "runit" that you could use for process monitoring/restarting on CentOS 6.

Update

As mangotang points out, and I forgot, RHEL 6 actually shipped with upstart, even though it used almost exclusively SysV-style init scripts. So a better solution would be to create an upstart service instead. There are some reasonable getting-started docs here.

Matthieu
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larsks
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  • Part of what is unclear to me is: does Red Hat 6.7 use the System V init (which uses inittab), or does it use Upstart? This info seems to suggest that Red Hat 6.7 uses Upstart: http://searchenterpriselinux.techtarget.com/tip/RHEL-6-ditches-System-V-init-for-Upstart-What-Linux-admins-need-to-know Does upstart also use the inittab file? – StvnBrkdll Sep 09 '16 at 15:30
  • Actually, RHEL 6 uses *both*. So you could actually write an upstart service to accomplish the same thing. I always forget that upstart support was there, because it was largely unused and has since gone away in RHEL 7. – larsks Sep 09 '16 at 15:33
  • At the top of my RHEL 6's inittab file, it says: `# inittab is only used by upstart for the default runlevel. # # ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.` I am wondering if this means that I can't expect the inittab stuff to work, and must use upstart? – StvnBrkdll Sep 09 '16 at 15:48
  • Also: after making sure that my service's script runs in the foreground, and rebooting, my service does not start. Guessing that this must mean the inittab does not work the way I expected with RHEL 6.7. I'll have to give upstart a try. – StvnBrkdll Sep 09 '16 at 15:55
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On RHEL 6.X, at top of the /etc/inittab file it says:

# inittab is only used by upstart for the default runlevel. 
# 
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM

RHEL 6.X uses Upstart instead of the System V init system. See the man pages for initctl(8) and initctl(5), or ask Google about Upstart.

StvnBrkdll
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