OpenRC is a dependency-based init system that initially maintained compatibility with sysvinit (/sbin/init) and, beginning with OpenRC 0.25, provided its own. OpenRC was written by Gentoo developers and it is designed to be used by other distributions and BSD systems.
OpenRC service packages are named
package_name-openrc and, when installed, are normally available in
OpenRC provides features such as hardware initiated initscripts or cgroups support.
/etc/rc.conf is the global OpenRC configuration file.
OpenRC can be used with one of several network managers or even with none, see
/etc/conf.d/net for examples of static or dynamic network configuration. The netifrc package provides a collection of modules for configuring and managing network interfaces via individual, per-interface scripts located in the /etc/init.d/ directory. Its presence is not mandatory or it can be left unused in favour of another network manager.
Changing the default dependencies of init scripts might be needed to fit more complex setups. See
/etc/rc.conf for how to change the default behavior; notice the rc_depend_strict option. In addition, the following networking examples show how flexible OpenRC can be.
OpenRC reads the kernel command-line used at boot time, and will start the runlevel specified by the softlevel parameter if provided, instead of default. For instance, you can choose whether to boot into the default, nonetwork or single-user runlevels with the following example grub.conf configuration:
/boot/grub/grub.conf title=Regular start-up kernel (hd0,0)/boot/vmlinuz-linux root=/dev/sda3 title=Start without networking kernel (hd0,0)/boot/vmlinuz-linux root=/dev/sda3 softlevel=nonetwork title=Single-user mode kernel (hd0,0)/boot/vmlinuz-linux root=/dev/sda3 softlevel=single
OpenRC uses runlevels in very much the same way as sysvinit (or BSD init). At any given time the system is in one of the defined runlevels. There are three internal runlevels and four user defined runlevels.
boot: Starts all system-necessary services for other runlevels
default: Used for day-to-day-operations
nonetwork: Used when no network connectivity is required
single: Single-user mode
The system can switch to a runlevel with the openrc <runlevel> command, e.g.:
OpenRC can be controlled and configured using openrc, rc-service, rc-update and rc-status commands.
# rc-update add service runlevel # rc-update del service runlevel
# rc-service service start # rc-service service restart # rc-service service stop
Use rc-update show -v to display all available init scripts and their their current runlevel (if they have been added to one):
# rc-update show -v
Running rc-update or rc-update show will display only the init scripts that have been added to a runlevel.
OpenRC runlevels are directories living in
/etc/runlevels to create additional runlevels is enough to issue:
# install -d /etc/runlevels/$runlevel
It is possible to manage variants using rc-update -s. An example for using stacked runlevels on laptop to group networking services based on location is at OpenRC/StackedRunlevel.
OpenRC monitors and can be triggered by external events, such as new hardware from udev. See OpenRC/Event Driven for details.
OpenRC can return the state of services to the runlevel's setting state, provide stateful init scripts and automatic respawning. If one issues openrc as root (for default runlevel), crashed services will start and manually launched services will stop. To prevent the latter you can run openrc -n (--not-stop)
By default openrc will attempt just to start crashed services, not restart. This сontrolled by rc_crashed_stop (default NO) and rc_crashed_start (default YES) options in
OpenRC has extended cgroups support. See OpenRC/CGroups for details.
OpenRC doesn't execute
/etc/rc.local by default; instead, it executes scripts from
/etc/local.d ending in .start when local service starts and .stop when it stops. To mimic the good old
rc.local behaviour, create
/etc/rc.local/rc.local.start with the following and make it executable with chmod +x:
: # /etc/local.d/rc.local.start [ -e /etc/rc.local ] && /etc/rc.local
Make sure that the local service is enabled. The scripts in
/etc/local.d are executed in lexical order and the example above assumes
/etc/rc.local has got execute permissions.
The SSH service must come up with the internal network, for instance eth0 and never wlan0.
Override the net dependency from
/etc/init.d/sshd, and refine it to depend on net.eth0:
/etc/conf.d/sshd rc_need="!net net.eth0"
The SSH service must start with eth0 (not wlan0) in "default" runlevel, but in "office" runlevel it must start with wlan0 (not eth0).
Make additional symlinks to sshd with the network interface names:
# ln -s sshd /etc/init.d/sshd.eth0 # ln -s sshd /etc/init.d/sshd.wlan0
Settings are read from
# cp /etc/conf.d/sshd /etc/conf.d/sshd.eth0 # cp /etc/conf.d/sshd /etc/conf.d/sshd.wlan0
Add the dependencies:
# echo 'rc_need="!net net.eth0"' >> /etc/conf.d/sshd.eth0 # echo 'rc_need="!net net.wlan0"' >> /etc/conf.d/sshd.wlan0
In this example net.eth0 and net.wlan0 read their settings from
/etc/conf.d/net.office, depending on the active runlevel. Add all runscripts to the different runlevels:
# rc-update add sshd.eth0 default # rc-update add sshd.wlan0 office # rc-update add net.eth0 default office # rc-update add net.wlan0 default office
To switch between "default" runlevel and "office" runlevel without rebooting the computer, change to "nonetwork" runlevel in between. The network interfaces will be stopped this way, and re-read their runlevel specific configuration. This works best when "nonetwork" is a stacked runlevel in both the "default" and "office" runlevels, and the display manager and other non-network services are added to the "nonetwork" runlevel only.
default runlevel <---> nonetwork runlevel <---> office runlevel
# rc nonetwork && rc office # rc nonetwork && rc default