Writing Init Scripts: Difference between revisions
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=== restart === | === restart === |
Revision as of 11:14, 3 December 2018
This material is work-in-progress ... Do not follow instructions here until this notice is removed. |
Introduction
Alpine Linux uses the OpenRC init system to start services. Don't confuse OpenRC init with our system init (the first process that is executed aka pid 1). Many of the current init.d script found in Alpine Linux are taken from Gentoo. If you want to save time you could search Gentoo's repository for an existing initscript for your service. You can also check Gentoo's wiki for some additional OpenRC information.
NOTE: OpenRC recently added documentation on how to write proper Init scripts. Make sure you read it!
If you cannot find an init.d script from Gentoo, or you just want to start to write your own init.d scripts, we provide you with some basic information on how to write simple OpenRC init scripts.
Primary information about the OpenRC format can be found in the OpenRC man page openrc-run.
apk add openrc-doc man
man openrc-run
Minimal Templates
Every init.d script you write needs to start with a shebang like:
#!/sbin/openrc-run
Services relying on OpenRC exclusively
#!/sbin/openrc-run command="/path/to/command"
Services supervised by s6
Notes:
- Install and configure the
s6-scan
service to start on system boot - Exclude
start()
,stop()
andstatus()
functions in order for s6 supervision to work reliably. OpenRC has built-in equivalent functions which invoke the necessary s6 commands. - Include a
depend()
stanza to ensure that thes6-svscan
service is already running. - Add a
start_pre()
stanza to symlink the service directory into the scan directory, because the/etc/init.d/bootmisc
scripts cleans out the/run
directory on system boot.
#!/sbin/openrc-run name="foo" supervisor="s6" s6_service_path="${RC_SVCDIR}/s6-scan/${name}" depend() { need s6-svscan } start_pre() { if [ ! -L "${RC_SVC_DIR}/s6-scan/${name}" ]; then ln -s "/path/to/${name}/service/dir" "${RC_SVCDIR}/s6-scan/${name}" fi }
The rest of the below basic example could be omitted, but that would most probably leave you with an non working initd script.
Basic example
#!/sbin/openrc-run name=$RC_SVCNAME cfgfile="/etc/$RC_SVCNAME/$RC_SVCNAME.conf" command="/usr/bin/my_daemon" command_args="--my-daemon-args" command_user="my_system_user" pidfile="/run/$RC_SVCNAME/$RC_SVCNAME.pid" start_stop_daemon_args="--args-for-start-stop-daemon" command_background="yes" depend() { need net } start_pre() { checkpath --directory --owner $command_user:$command_user --mode 0775 \ /run/$RC_SVCNAME /var/log/$RC_SVCNAME }
start, stop, restart functions
OpenRC defined a few basic functions ie: start, stop, restart. These functions are defined by default but can be overwritten by defining your own set of functions. This is generally only necessary if you want to do something special which is not provided by the default start/stop/restart implementations.
start
start() { ebegin "Starting mydaemon" start-stop-daemon --start \ --exec /usr/sbin/mydaemon \ --pidfile /var/run/mydaemon.pid \ -- \ --args-for-mydaemon eend $? }
restart
Daemon, Forking, Logging
TODO...