OpenRC
Alpine Linux uses openrc for its init system. Refer to the excellent guide working with OpenRC from Alpine Linux documentation project to learn the basics.
Quick-Start Information
The following commands are available to manage the init system:
- Basics:
# rc-update add <service> <runlevel>
# rc-update del <service> <runlevel>
# rc-service <service> <start stop restart> # ⇔ /etc/init.d/service <start stop restart>
- To check services and their set runlevels:
rc-status
- To change to a different runlevel:
# openrc <runlevel>
- Reboot/Halt/Poweroff: (And their equivalent from traditional GNU/Linux systems)
# reboot # ⇔ shutdown now -r
# halt # ⇔ shutdown now -H
# poweroff # ⇔ shutdown now -P
Available Runlevels
The available runlevels are:
- default - Used if no runlevel is specified. (This is generally the runlevel you want to add services to.)
- hotplugged
- manual
The special runlevels are:
- sysinit - Brings up system specific stuff such as
/dev,/procand optionally/sysfor Linux based systems. It also mounts/lib/rc/init.das a ramdisk using tmpfs where available unless/is mounted rw at boot.rcuses/lib/rc/init.dto hold state information about the services it runs. sysinit always runs when the host first starts and should not be run again. - boot - Generally the only services you should add to the boot runlevel are those which deal with the mounting of filesystems, set the initial state of attached peripherals and logging. Hotplugged services are added to the boot runlevel by the system. All services in the boot and sysinit runlevels are automatically included in all other runlevels except for those listed here.
- single - Stops all services except for those in the sysinit runlevel.
- reboot - Changes to the shutdown runlevel and then reboots the host.
- shutdown - Changes to the shutdown runlevel and then halts the host.
Preventing slow services from delaying boot
Services that take a while to start will block the boot process until they complete. E.g.: iwd and networking might delay startup of an interactive system rather than start in the background.
This can be remedied as per Patrycja's blog post titled OpenRC: Start services after login prompt. This solution makes use of stacked runlevels.
- Create a custom runlevel (name is “async” here, but it doesn’t matter)
# mkdir /etc/runlevels/async
- Add default as a stacked runlevel
# rc-update add -s default async
- Remove slow services from default and add them to async
# rc-update del chronyd
# rc-update add chronyd async
- Add changing of runlevel to async by adding the line ::once:/sbin/openrc async to /etc/inittab file:
Contents of /etc/inittab
After rebooting, services from async will start separately. This change does not affect other services that start from Default runlevel and they may still block agetty from running due to the wait label.
cgroups v2
Since openrc 0.51 cgroups v2, or "unified", is the default.
You can enable hybrid cgroups v1 & v2 by editing /etc/rc.conf and setting rc_cgroup_mode="hybrid".
Then you should run
# rc-service cgroups start
to take effect
and
# rc-update add cgroups
to auto mount the cgroup filesystem on boot