Simple daemon with start-stop-daemon and runit

[1]

PDF [1] (to print)

Org [2] (source)

Creating a daemon with almost zero effort.

start-stop-daemon

The example with the start-stop-daemon uses Gentoo OpenRC as root.

The simplest daemon we can create is a while loop:

echo '#!/bin/sh' > whiledaemon.sh
echo 'while true; do true; done' >> whiledaemon.sh
chmod +x whiledaemon.sh

Now we start it as daemon

start-stop-daemon --pidfile whiledaemon.pid \
--make-pidfile --background ./whiledaemon.sh

Top shows that it is running:

top | grep whiledaemon.sh

We stop it using the pidfile:

start-stop-daemon --pidfile whiledaemon.pid \
--stop ./whiledaemon.sh

That’s it.

Hint: To add cgroups support on a Gentoo [3] install, open /etc/rc.conf and uncomment
rc_controller_cgroups="YES"
Then in the initscript you can set the other variables described below that line. Thanks for this hint goes to Luca Barbato [4]!

If you want to ensure that the daemon keeps running without checking a PID file (which might in some corner cases fail because a new process claims the same PID), we can use runsvdir [5] from runit.

daemon with runit

Minimal examples for runit daemons - first as unpriviledged user, then as root.

runit as simple user

Create a script which dies

echo '#!/usr/bin/env python\nfor i in range(100): a = i*i' >/tmp/foo.py
chmod +x /tmp/foo.py

Create the daemon folder

mkdir -p ~/.local/run/runit_services/python
ln -sf /tmp/foo.py ~/.local/run/runit_services/python/run

Run the daemon via runsvdir

runsvdir ~/.local/run/runit_services

Manage it with sv (part of runit)

# stop the running daemon
SVDIR=~/.local/run/runit_services/ sv stop python
# start the service (it shows as `run` in top)
SVDIR=~/.local/run/runit_services/ sv start python

runit as root

Minimal working example for setting up runit as root - like a sysadmin might do it.

echo '#!/usr/bin/env python\nfor i in range(100): a = i*i' >/tmp/foo.py &&
    chmod +x /tmp/foo.py &&
    mkdir -p /run/arne_service/python &&
    printf '#!/bin/sh\nexec /tmp/foo.py' >/run/arne_service/python/run &&
    chmod +x /run/arne_service/python/run &&
    chown -R arne /run/arne_service &&
    su - arne -c 'runsvdir /run/arne_service'

Or without bash indirection (giving up some flexibility we don’t need here)

echo '#!/usr/bin/env python\nfor i in range(100): a = i*i' >/tmp/foo.py && 
    chmod +x /tmp/foo.py &&
    mkdir -p /run/arne_service/python &&
    ln -s /tmp/foo.py /run/arne_service/python/run &&
    chown -R arne /run/arne_service &&
    su - arne -c 'runsvdir /run/arne_service'

Anhang	Größe
2015-04-15-Mi-simple-daemon-openrc.org [2]	2.92 KB
2015-04-15-Mi-simple-daemon-openrc.pdf [1]	152.99 KB

Simple daemon with start-stop-daemon and runit

Table of Contents

start-stop-daemon

daemon with runit

runit as simple user

runit as root