Replacing init with runit on Debian GNU/Linux

This is based mostly on the ​notes on replacing init with runit written by the runit developers.

Install the needed Debian runit packages:

# aptitude install runit runit-services runit-run

The runit-run program is the one that actually replaces /sbin/init with /sbin/runit-init:

proton:~ 0# ls -al /sbin/init*
lrwxrwxrwx 1 root root    10 2007-12-21 18:40 /sbin/init -> runit-init
-rwxr-xr-x 1 root root 32652 2007-01-30 17:27 /sbin/init.sysv
proton:~ 0# 

runit-init is what will now start on boot and handle starting services. It also emulates many of the commands that could be passed to init. The configuration directory for runit-init is /etc/runit:

proton:~ 0# ls -al /etc/runit/
total 10
drwxr-xr-x  3 root root 1024 2007-12-21 18:41 .
drwxr-xr-x 51 root root 4096 2007-12-21 18:41 ..
-rwxr-xr-x  1 root root  188 2006-11-04 14:33 1
-rwxr-xr-x  1 root root  576 2006-11-04 14:33 2
-rwxr-xr-x  1 root root  239 2006-11-04 14:33 3
-rwxr-xr-x  1 root root  209 2006-11-04 14:33 ctrlaltdel
drwxr-xr-x  4 root root 1024 2007-12-21 18:40 runsvdir
proton:~ 0# ls -al /etc/runit/runsvdir/
total 4
drwxr-xr-x 4 root root 1024 2007-12-21 18:40 .
drwxr-xr-x 3 root root 1024 2007-12-21 18:41 ..
lrwxrwxrwx 1 root root    7 2007-12-21 18:40 current -> default
drwxr-xr-x 2 root root 1024 2007-12-21 18:41 default
drwxr-xr-x 2 root root 1024 2007-12-21 18:40 single
proton:~ 0#

The main service directory is /var/service (which is a link to /etc/runit/runsvdir/current, which is a link to either /etc/runit/runsvdir/default or /etc/runit/runsvdir/single, for default or single user mode, i think):

proton:~ 0# ls -al /var/service/
total 2
drwxr-xr-x 2 root root 1024 2007-12-21 18:41 .
drwxr-xr-x 4 root root 1024 2007-12-21 18:40 ..
lrwxrwxrwx 1 root root   15 2007-12-21 18:40 getty-1 -> /etc/sv/getty-1
lrwxrwxrwx 1 root root   15 2007-12-21 18:40 getty-2 -> /etc/sv/getty-2
lrwxrwxrwx 1 root root   15 2007-12-21 18:40 getty-3 -> /etc/sv/getty-3
lrwxrwxrwx 1 root root   15 2007-12-21 18:40 getty-4 -> /etc/sv/getty-4
lrwxrwxrwx 1 root root   15 2007-12-21 18:40 getty-5 -> /etc/sv/getty-5
lrwxrwxrwx 1 root root   20 2007-12-21 18:41 socklog-klog -> /etc/sv/socklog-klog
lrwxrwxrwx 1 root root   20 2007-12-21 18:41 socklog-unix -> /etc/sv/socklog-unix
proton:~ 0# 

These service directories start the gettys, and the main system log daemons. The next thing to do make service directories for the rest of the services that we want handled by runit. This is where runit-services comes in. runit-services provides service directories for a bunch of standard services, all located in /etc/sv:

proton:~ 0# ls /etc/sv/
apache    dhcp     getty-2  nfs-kernel-server  socklog-inet       socklog-unix
chrony    exim     getty-3  portmap            socklog-klog       squid
cron      gdm      getty-4  postfix            socklog-notify     ssh
dhclient  getty-1  getty-5  README             socklog-ucspi-tcp  xdm
proton:~ 0# 

/etc/sv/README gives a good intro on how to get these services started. I'm going to start by getting the cron service working:

proton:~ 0# /etc/init.d/cron stop
Stopping periodic command scheduler: crond.
proton:~ 0# dpkg-divert --add /etc/init.d/cron
Adding `local diversion of /etc/init.d/cron to /etc/init.d/cron.distrib'
proton:~ 0# mv /etc/init.d/cron /etc/init.d/cron.distrib
proton:~ 0# ln -s /usr/bin/sv /etc/init.d/cron
proton:~ 0# ln -s /etc/sv/cron /var/service/
proton:~ 0# sv status cron
run: cron: (pid 2033) 2s
proton:~ 0#

That was simple. Now ssh:

proton:~ 0# /etc/init.d/ssh stop
Stopping OpenBSD Secure Shell server: sshd.
proton:~ 0# dpkg-divert --add /etc/init.d/ssh
Adding `local diversion of /etc/init.d/ssh to /etc/init.d/ssh.distrib'
proton:~ 0# mv /etc/init.d/ssh /etc/init.d/ssh.distrib
proton:~ 0# ln -s /usr/bin/sv /etc/init.d/ssh
proton:~ 0# ln -s /etc/sv/ssh/
log/       run        supervise  
proton:~ 0# ln -s /etc/sv/ssh /var/service
proton:~ 0# sv status ssh
run: ssh: (pid 2059) 2s; run: log: (pid 2057) 2s
proton:~ 0# 

An important one to me, which does not have an included service dir, is a serial console. So I went ahead and wrote one:

proton:~ 0# ls -al /etc/sv/getty-S0/
total 4
drwxr-xr-x  2 root root 1024 2007-12-21 19:32 .
drwxr-xr-x 26 root root 1024 2007-12-21 19:26 ..
-rwxr-xr-x  1 root root   32 2007-12-21 19:27 finish
-rwxr-xr-x  1 root root   43 2007-12-21 19:30 run
lrwxrwxrwx  1 root root   20 2007-12-21 19:32 supervise -> /var/run/sv.getty-S0
proton:~ 0# cat /etc/sv/getty-S0/run 
#!/bin/sh
exec getty -L ttyS0 115200 vt102
proton:~ 0# cat /etc/sv/getty-S0/finish
#!/bin/sh
exec utmpset -w ttyS0
proton:~ 0# 

Finally, reboot your system:

/sbin/init.sysv 6