runit - a UNIX init scheme with service supervision

See here for the current stable release 1.0.x of runit.

How to install runit
Upgrading from previous versions of runit

Benefits
How to replace init
How to use runit with current init
How to use dietlibc

Runlevels
Service dependencies
A collection of run scripts

The runit program
The runit-init program

The runsvdir program
The runsvchdir program
The runsv program
The runsvstat program
The runsvctrl program

The svlogd program

The svwaitdown program
The svwaitup program

The chpst program
The utmpset program

runit is a daemontools alike replacement for sysvinit and other init schemes. runit runs on GNU/Linux, *BSD, MacOSX, Solaris, and can easily be adapted to other Unix operating systems. If runit runs for you on any other operating system, please let me know.

Warning: Replacing sysvinit or init can cause the system's boot to fail. Make sure you are able to recover and repair your system, for example if you run a boot loader, it should be able to pass init=/bin/sh to the kernel.

runit is discussed on the <supervision@list.skarnet.org> mailing list. To subscribe send an empty email to <supervision-subscribe@list.skarnet.org>.

Mailing list archives are available at skarnet.org, and gmane.org.

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 /etc/runit/1 and waits for it to terminate. The system's one time initialization tasks are done here. /etc/runit/1 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 /etc/runit/2 which should not return until the system is going to halt or reboot; if it crashes, it will be restarted. Normally, /etc/runit/2 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 /etc/runit/3. The systems tasks to shutdown and halt or reboot are done here.

These are working examples for Debian sarge: /etc/runit/1, /etc/runit/2, /etc/runit/3.

The program runit-init is intended to replace /sbin/init. sysvinit's command shutdown will keep working. On *BSD systems use init 0 for system halt and init 6 for 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.

runit in use: I replaced sysvinit successfully with runit on several server systems and a laptop running Debian/GNU Linux sarge, woody, and potato. Of course also the smarden.org content server is running with runit as process no 1, 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

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.

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.

See http://smarden.org/runit/ for recent informations.