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I'm looking for a standard way or best practice to keep a daemon started by an init.d shell script alive.

Or even better, is there a way to keep it alive directly from /etc/init.d?

Specifically, I have a daemon called dtnd with and infinite loop that looks for unexpected ended process, if there are any, the daemon wake up them again. Also, I use the start-stop-daemon tool in order to let the precess by run from a given system user.

I want to run this dtnd daemon from startup. In order to achieve this behavior I created a init.d script that "wraps" the dtnd file using start, stop and status commands.

I have 2 questions that I will like to solve:

  1. Is there a way to achieve keeping alive some process from init.d shell script. Is an standard/best way practice?

  2. It's recommended to keep a process alive with infinite loop? I guess it's better to use some command like respawn to achieve that. It's correct?

I know about the existance of the respawn command. I think that's what I need but I don't understand the workflow between /etc/init.d/ and /etc/init. Can anyone help me?

Note that I don't have inittab neither upstart (I'm only allowed to use /etc/init, /etc/init.d, cron and system tools as start-stop-daemon. I mean, only the default tools)

Thank you so much for your time!

adriantunez
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5 Answers5

15

Debian will eventually have systemd, so this is the way to do it on a Linux system which uses systemd (and many do already; you might consider switching distributions).

Systemd can handle keeping the service alive for you automatically; no other tools are required. Simply make sure that Restart=always is set in the service file's [Service] section.

# vi /etc/systemd/system/dtnd.service

[Service]
Restart=always
#...everything else...

Several other options are available as well, for more complex scenarios.

Michael Hampton
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5

You could add it to /etc/inittab with respawn:

d1:2345:respawn:/path/to/your/first_daemon arg1 arg2
d2:2345:respawn:/path/to/your/second_daemon arg1 arg2

It's a dirty hack, but I've used it succesfully in the past on older sysv-init systems.

Gajus
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Dennis Kaarsemaker
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2

Well, that is one of the main reason, why debian is moving to systemd.

sysvinit (/etc/init.d) is not able to detect, if a service is down/not responding. This means you have to monitor these services and escalate if a service won’t do his job anymore.

probably the easiest thing to do would be to migrate to another daemonhandler like systemd (default in RHEL7, will be default in next debian and ubuntu lts), upstart (default in RHEL6, Ubuntu 12.04 and 14.04), daemontools (like mentioned, develloped by djb) or something else.

doing the job of keeping a service alive will be PITA in sysvinit.

janaurka
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1

Best practice is to ensure that your daemons DO NOT STOP in the first place.

Failing that you might want to have a look at DJB's daemontools

symcbean
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1

The standard approach for me is to use the Monit utility for this.

I can't quite tell from your description if you've written something like Monit and are trying to make sure it's running, or if you need something to watch the daemon you've created.

ewwhite
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