This is an old revision of the document!
Table of Contents
Runit
Introduction
runit is a UNIX init scheme with service supervision. It is a cross-platform Unix init scheme with service supervision, a replacement for sysvinit, and other init schemes and supervision that are used with the traditional init. runit is compatible with djb's daemontools.
In Unix-based computer operating systems, init (short for initialization) is the first process started during booting of the computer system. Init is a daemon process that continues running until the system is shut down. Slackware comes with its own legacy init (/sbin/init) from the sysvinit package, that used to be included in almost all other major Linux distributions.
The init daemon (or its replacement) is characterised by Process ID 1 (PID 1).
To read on the benefits of runit, see here: http://smarden.org/runit/benefits.html
* Unless otherwise stated, all commands in this article are to be run by root.
Use runit with traditional init (sysvinit)
runit is not provided by Slackware, but a SlackBuild is maintained on https://slackbuilds.org/. It does not have any dependencies.
As we do not want yet to replace init with runit, run the slackbuild with CONFIG=no:
CONFIG=no ./runit.SlackBuild
Then install the resulting package and proceed as follows:
mkdir /etc/runit/ /service/ cp -a /usr/doc/runit-*/etc/2 /etc/runit/ /sbin/runsvdir-start &
Starting via rc.local
For a typical Slackware-stlyle service, you can edit /etc/rc.d/rc.local
file
if [ -x /sbin/runsvdir-start ]; then /sbin/runsvdir-start & fi
and then edit write /etc/rc.d/rc.local_shutdown
#!/bin/sh RUNIT=x$( /sbin/pidof runsvdir ) if [ "$RUNIT" != x ]; then kill $RUNIT fi
Then give rc.local_shutdown
executive permission:
chmod +x /etc/rc.d/rc.local_shutdown
and reboot
Starting via inittab (supervised)
Remove the entries in /etc/rc.d/rc.local
and /etc/rc.d/rc.local_shutdown
described above.
Edit /etc/inittab
cat >>/etc/inittab <<EOT SV:123456:respawn:/sbin/runsvdir-start EOT
and tell init to re-read its configuration, e.g.:
init q
or reboot
How to replace init with runit
runit provides runit-init
which can be used to boot up the system.
If you followed the previous chapter, then stop runsvdir and reverse all the changes that you made on your system.
So, remove the last line from /etc/inittab
rm -rf /etc/runit /service
And reboot:
shutdown -r now
Also, it is best to re-build and re-install runit
This time, when running slackbuild, do pass not any value for CONFIG, or set it to yes:
unset CONFIG sh runit.SlackBuild
and upgrade with the resulting runit package.
Disable services that are already provided by the traditional init:
cd /service/ rm *
Create a new TTY service for runit:
cd /etc/sv/ cp -ar agetty-tty1/ agetty-tty8/ sed -i 's/tty1/tty8/g' agetty-tty8/* ln -s /etc/sv/agetty-tty8 /service
Start runit's stage 2 for testing:
/etc/runit/2 &
And check that the agetty is running, by logging in as an unprivileged user (not as root!)
CTRL+ALT+F8
If this has been successful, then reverse the last intervention:
kill $( pidof runsvdir ) rm /service/agetty-tty8 rm -rf /etc/sv/agetty-tty8 for N in {1..6}; do ln -s /etc/sv/agetty-tty${N} /service done
Then, to boot in runit, reboot and enter init=/sbin/runit-init
in the Lilo prompt. To do this, hit the tab key when you are presented with the Lilo menu as shown in Images 1 and 2 below.
Image 1.: Hit the Tab key on the Lilo Menu before the counter times out.
Image 2: Add init=/sbin/runit-init in the OS Selection Prompt
Confirm that runit has taken PID 1:
ps -o comm= -p 1 runit
If you do not have a multi boot system, you may append the init selection in /etc/lilo.conf
For example:
append="vt.default_utf8=0 init=/sbin/runit-init"
Then run lilo:
lilo -v
Or just replace /sbin/init
with /sbin/runit-init
like this:
cp /sbin/init /sbin/init.sysv cp /sbin/runit-init /sbin/init
However, with the last alternative, be warned that if you had booted with the original init, the system may refuse to reboot, therefore boot from runit-init first.
Startup and Shutdown
The bsd style init scripts provided by Slackware are used to bring up the system.
Initially the single user script /etc/rc.d/rc.S
runs. If set in the default runlevel 3, it follows it with /etc/rc.d/rc.M
. In runit the initialisation script is located in /etc/runit/1
for all runlevels. By default /etc/runit/2
is restricted to the TTY services.
The script /etc/rc.d/rc.6
is the rebooting script for the traditional init, while /etc/rc.d/rc.0
(symlinked to the former) is the halting script. In runit, these scripts are called by /etc/runit/3
Note that the shutdown command provided by sysvinit package will not work in runit. To reboot you enter
/sbin/runit-init 6
and to halt enter
/sbin/runit-init 0
A convenient script is provided with the configuration files which is placed in /usr/sbin/shutdown
that determines whether the system has booted with the traditional init or runit and then calls the relevant command accordingly.
The halt
, reboot
and poweroff
commands provided by the sysvinit package would still work with runit.
Desktop Environments call /sbin/shutdown
so they will not work until you move this file and symlink it to /usr/sbin/shutdown
mv /sbin/shutdown /sbin/shutdown.sysv ln -s /usr/sbin/shutdown /sbin/shutdown
However consider that shutdown would not work for the original init.
runsv
Although runit may replace init as the PID 1 daemon, there is not much benefit unless other services are migrated from Slackware's BSD style to runsv(8). While this is not a complicated task, some familiarisation with runit's characteristics is recommended and makes the task easier. This short example should help illustrate runsv to new users.
Make an arbitrary directory under /etc/sv/
mkdir /etc/sv/example/
As a non-priviliged user (say user bob), create some directories:
mkdir -p /home/bob/runit/logs
Then edit a /home/bob/runit/service.sh
script that simulates a (finicky) service in a convenient directory; say
#!/bin/bash echo "Started service..." for i in {1..10} do echo "Doing stuff..." sleep 1 done echo "Oh no I crashed..." >&2 exit 1
Give it executable permission:
chmod +x /home/bob/runit/service.sh
Run it to check and appreciate its execution:
/home/bob/runit/service.sh
Log in back as root and edit a file called /etc/sv/example/run
and give it executable permissions:
#!/bin/sh -e exec 2>&1 exec chpst -u bob /home/bob/runit/service.sh
chmod +x /etc/sv/example/run
Note the exec in the last line, it tells the shell that interprets the script to replace itself with the service daemon
Naturally edit as necessary.
Create another directory:
mkdir /etc/sv/example/log/
and edit another file under it, also called /etc/sv/example/log/run
#!/bin/sh exec chpst -u bob svlogd -tt /home/bob/runit/logs
Give it executable permission:
chmod +x /etc/sv/example/log/run
Run the service to ensure that it works:
/etc/sv/example/run
Finally, we are ready to deploy the service. Create a symbolic link in /service
to our staging location.
ln -s /etc/sv/example /service
Watch how your “service” works, crashes, but it is recovered by runit:
As your non-privilged user:
tail -f /home/bob/runit/logs/current
Hit CTRL+C to exit.
Finally, login back as root and let bob take the ownership of the whole /etc/sv/example/
directory:
chown -R bob.users /etc/sv/example/
Now bob can manage this service with the sv
command. Note that in most cases, services should belong to root, and only to root.
Managing Services with sv
To see the status of a supervised service use sv s <service_name>
, for example,
sv s example
returns
run: example: (pid 42) 1587s
To see the status of all services, use
sv s /service/*
Stop/Start/Restart
Start a service
sv u example
Stop a service
sv d example
Restart a service
sv t example
Each of these is a shortcut, for 'up', 'down', and 'terminate', respectively. Only the first letter of each word is recognised.
More verbose forms of the above:
sv start example sv stop example sv restart example
Each of these will also return the status of the service upon exit.
Enabling a service
Service directories are placed under /etc/sv/
. To enable a service in the current runlevel, create a symlink from it to /service
.
ln -s /etc/sv/example /service/
Once a service is linked it will always start on boot and restart if it stops (unless this is disabled).
Disabling a service
To disable a service in the current runlevel remove the symlink to its service directory from /service
.
rm /service/example
Removing the symlink will also stop the service.
Check out the sv man page to see additional options.
man sv
If you do not want a service to start upon bootup, or when enabled, just touch an empty file called down
in the appropriate service directory.
touch /etc/sv/service/down
Dependencies
Dependencies of service are supported by starting the dependent run script as follows:
#!/bin/sh sv start dependent-service || exit 1 . . exec ...
Runlevels
If you installed the slackbuild configuration files, you have two runlevels: default and single. The current runlevel is default. You can verify by looking under /etc/runit/runsvdir/,
you will see that /etc/runit/runsvdir/current
is a symbolic link /etc/runit/runsvdir/default/
.
Change runlevel to another runlevel; single:
runsvchdir single
You will see that /etc/runit/runsvdir/current
is now symlinked to /etc/runit/runsvdir/single
and /etc/runit/runsvdir/previous
is symlinked to /etc/runsvdir/default
. If you reboot, you will boot again on the default runlevel as you have this entry in /etc/runit/2
runsvchdir default >/dev/null
You can create any other runlevel and name them as you like. To start, you can copy an existing runlevel directory and modify as you wish.
cp -ar /etc/runit/runsvdir/default /etc/runit/runsvdir/custom/
You can edit the runsvdir line of /etc/runit/2
to your requirements.
Run scripts
Only one executable can be called for a service (the last line) and it must be called by the exec
command. There are some generic runit run scripts on the Internet and on other Linux distributions. Also, other Slackers may post them on publicly available repositories. The author of this article has placed his here: https://gitlab.com/chrisabela/runit_scripts_for_slackware
Another set of installable run scripts are available at SBo. (currently pending)
In direct contrast to Slackware's BSD style service scripts, runit run scripts must not must run in the foreground, otherwise runit would think that they have crashed and restart them.
For some services, this may not be possible, but there are workarounds. You can forcefully terminate them by ending the run script like this:
sv d service_name
Or you can use the pause
command to keep the service alive. pause
is a trivial command that will simply not exit, until it is killed (akin to tail -f /dev/null). A SlackBuild for pause
is available at SBo. Then end the run script with:
exec chpst -b service_name pause
Migrating Services
It is suggested that services are migrated from stage 2 (which are still under the Slackware's BSD init scheme) to stage 3 carefully. Start from the bottom of /etc/rc.d/rc.M
and work up. This means that you should start with any entries under /etc/rc.d/rc.local
Then continue for /etc/rc.d/rc.S
Proceed with other services to benefit's from runit features. Note that for some services, such as atd
and crond
, you would need to edit /etc/rc.d/rc.M
as they are hard-coded.
Let's take the popular NetworkManager
service as an example. According to the permission of /etc/rc.d/rc.networkmanager
this script is called by /etc/rc.d/rc.M
The latter is called by /etc/runit/2
(stage 2).
Stop the service:
/etc/rc.d/rc.networkmanager stop
Disable it:
chmod -x /etc/rc.d/rc.networkmanager
Create a suitable directory for runit
mkdir /etc/sv/networkmanager/
Write a runit run script: /etc/sv/networkmanager/run
#!/bin/sh prefix=/usr exec_prefix=/usr sbindir=${exec_prefix}/sbin NETWORKMANAGER_BIN=${sbindir}/NetworkManager export XDG_CACHE_HOME=/root/.cache exec $NETWORKMANAGER_BIN -n > /dev/null 2>&1
Symlink the /etc/sv/networkmanager
directory to /service
to enable under current runlevel and it will start in a few seconds:
ln -s /etc/sv/networkmanager /service
If run exits and /etc/sv/<service name>/finish
exists (typically when the service is switched off), runsv
runs finish
if it has executable permission.
It is stuggested to let udev
under runit's stage 2, but you can setup its monitoring for stage 3.
Using runit-init with other init scripts
OpenRC
Here runit-init
is used for booting, which then transfers control to the OpenRC for things like mounting the filesystem, loading modules, running udev, etc.
It requires a working OpenRC system. Check the openrc page for instructions.
The level 1 runit service uses the OpenRC boot
and sysinit
runlevels.
The gentoo wiki has more information, and runit-init-openrc details how to install and set it up.
void-runit
Here the scripts provided by the void-runit project are used to mount the filesystem, load modules, etc.
Currently this is the most independent way to setup runit.
Sources
3. https://en.wikipedia.org/wiki/Init
4. https://voidlinux.org/usage/runit/
5. https://www.youtube.com/watch?v=jiBlIhFxNJo
6. http://kchard.github.io/runit-quickstart/
7. https://www.slackbook.org/beta/
8. https://gitlab.com/chrisabela/runit_scripts_for_slackware
9. https://wiki.gentoo.org/wiki/Runit
10. https://github.com/void-linux/void-runit
- Written for Slackware 14.2 in December 2018
- Originally written by Chris Abela