runit - a UNIX init scheme with service supervision

Benefits
How to replace init
How to use runit with current init
How to use dietlibc
Frequently asked questions

The runit program
The runit-init program

The sv program

The runsvdir program
The runsvchdir program
The runsv program

The svlogd program

The chpst program
The utmpset program

The program runit is intended to run as Unix process no 1, it is automatically started by the runit-init /sbin/init-replacement if this is started by the kernel.

runit performs the system's booting, running and shutting down in three stages:

Stage 1:
runit starts /lib/init/start and waits for it to terminate. The system's one time initialization tasks are done here. /lib/init/start has full control over /dev/console to be able to start an emergency shell in case the one time initialization tasks fail.
Stage 2:
runit starts /lib/init/run which should not return until the system is going to halt or reboot; if it crashes, it will be restarted. Normally, /lib/init/run runs runsvdir. In Stage 2 runit optionally handles the INT signal (ctrl-alt-del keyboard request on Linux/i386).
Stage 3:
If runit is told to halt or reboot the system, or Stage 2 returns without errors, it terminates Stage 2 if it is running, and runs /lib/init/stop. The systems tasks to shutdown and halt or reboot are done here.

The program runit-init is intended to replace /sbin/init. The command init 0 tells runit to halt the system, and init 6 to reboot. Runlevels are handled through the runsvdir and runsvchdir programs. Service dependencies are resolved automatically.

runit is optimized for reliability and small size. The amount of code in process no 1 should be minimal.

See How to install runit for installing runit, and How to replace init for configuring runit to run as process no 1. See How to use with current init if you want to use runit without replacing the current init scheme. Please read the list of Frequently asked questions with answers.

If runit on Linux is compiled and linked with the dietlibc, it yields in a statically linked runit binary of 8.5k size and this ps axuw output on my system:

 USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
 root         1  0.0  0.0    20   16 ?        S     2002   0:02 runit

I recommend doing this; for instructions, see How to use dietlibc.

runit in use: I replaced sysvinit successfully with runit on several server systems and a laptop running Debian/GNU Linux sarge, woody, and potato. Here is an example:

 # strings /proc/1/exe |grep Id
 $Id: runit.c,v 1.7 2002/02/13 09:59:52 pape Exp $
 # uptime
  11:59:13 up 365 days, 23:22,  3 users,  load average: 0.01, 0.02, 0.00
 # ps axuw |head -n20
 USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
 root         1  0.0  0.0    20   16 ?        S     2002   0:07 runit
 root         2  0.0  0.0     0    0 ?        SW    2002   0:00 [keventd]
 root         3  0.0  0.0     0    0 ?        SWN   2002   0:51 [ksoftirqd_CPU0]
 root         4  0.0  0.0     0    0 ?        SW    2002 144:38 [kswapd]
 root         5  0.0  0.0     0    0 ?        SW    2002   0:08 [bdflush]
 root         6  0.0  0.0     0    0 ?        SW    2002   7:24 [kupdated]
 root       168  0.0  0.0  1652  168 ?        S     2002   0:27 /usr/sbin/cron
 root       174  0.0  0.0    36   24 ?        S     2002   1:06 runsvdir /var/service log: ...............................................................................................
 root       176  0.0  0.0    20   20 ?        S     2002   0:00 runsv qmail-send
 root       177  0.0  0.0    20   20 ?        S     2002   0:00 runsv getty-5
 root       178  0.0  0.0    20   20 ?        S     2002   0:00 runsv getty-4
 root       179  0.0  0.0    20   20 ?        S     2002   0:00 runsv getty-3
 root       180  0.0  0.0    20   20 ?        S     2002   0:00 runsv getty-2
 root       182  0.0  0.0    20   20 ?        S     2002   0:00 runsv socklog-unix
 root       183  0.0  0.0  1256    4 tty5     S     2002   0:00 /sbin/getty 38400 tty5 linux
 root       184  0.0  0.0  1256    4 tty3     S     2002   0:00 getty 38400 tty3 linux
 root       185  0.0  0.0    20   20 ?        S     2002   0:00 runsv socklog-klog
 root       186  0.0  0.0    20   20 ?        S     2002   0:00 runsv ssh
 root       187  0.0  0.0  1256    4 tty4     S     2002   0:00 getty 38400 tty4 linux
 # pstree
 runit-+-bdflush
       |-cron
       |-gcache
       |-keventd
       |-ksoftirqd_CPU0
       |-kswapd
       |-kupdated
       `-runsvdir-+-runsv-+-multilog
                  |       `-qmail-send-+-qmail-clean
                  |                    |-qmail-lspawn
                  |                    `-qmail-rspawn---qmail-remote
                  |-4*[runsv---getty]
                  |-2*[runsv-+-multilog]
                  |          `-socklog]
                  |-runsv-+-multilog
                  |       `-sshd-+-sshd---sshd---bash---bash---pstree
                  |              `-sshd---sshd---rsync
                  |-runsv---clockspeed
                  |-runsv-+-dnscache
                  |       `-multilog
                  |-runsv---apache-ssl-+-9*[apache-ssl]
                  |                    |-gcache
                  |                    `-4*[multilog]
                  |-7*[runsv-+-multilog]
                  |          `-tcpserver]
                  |-4*[runsv-+-multilog]
                  |          `-tinydns]
                  |-runsv---uncat
                  |-2*[runsv-+-multilog]
                  |          `-tcpsvd]
                  |-runsv-+-svlogd
                  |       `-tcpsvd-+-smtpfront-qmail
                  |                `-smtpfront-qmail---qmail-queue
                  `-runsv-+-svlogd
                          `-tcpsvd---bincimap-up---bincimapd