runlevel - event signalling change of system runlevel
runlevel RUNLEVEL=RUNLEVEL PREVLEVEL=PREVLEVEL [ENV]...
This page describes the runlevel Upstart event, and the general implementation of run-
levels in the Upstart system. For the runlevel tool, see runlevel(8)
The runlevel event
The runlevel event signals a change of system runlevel. The new system runlevel is given
in the RUNLEVEL argument, and the previous system runlevel in the PREVLEVEL argument
(which may be empty).
Additional environment may follow these depending on the runlevel, and the tool that emit-
ted the event. The shutdown(8) tool will supply an INIT_HALT variable set to either HALT
or POWEROFF when called with -H or -P respectively.
Runlevels are a concept from UNIX(R) System V used by the init(8) daemon or other system
initialisation system to define modes of system operation.
Eight runlevels are permitted, the first seven are numbered 0-6 and the eighth is named S
or s (both are permitted).
Services and other system components are said to exist in one or more runlevels. When
switching from one runlevel to another, the services that should not exist in the new run-
level are stopped and the services that only exist in the new runlevel are started.
This is performed by the /etc/init.d/rc script executed on a change of runlevel (by jobs
run on the runlevel event in the Upstart system). This script examines symlinks in the
/etc/rc?.d directories, symlinks beginning K are services to be stopped and symlinks
beginning S are services to be started.
The authorative documentation for this process can be found in the System run levels and
init.d scripts section of the Debian Policy Manual. This may be currently found at
Runlevels 0, 1 and 6 are reserved. Runlevel 0 is used to halt the system and 6 to reboot
the system. Runlevel 1 is used to bring the system back down into single-user mode, after
which the runlevel will be S.
System V initialisation in Upstart
The compatible implementation of runlevels permits Upstart jobs to be run on the runlevel
event that perform the same functionality as the original System V init(8) daemon.
The /etc/init/rc.conf job is run on the runlevel event, thus receiving the RUNLEVEL and
PREVLEVEL environment variables. Its sole job is to execute the /etc/init.d/rc script,
passing the new runlevel as an argument.
Initial system startup is provided by the /etc/init/rc-sysinit.conf job. This is run on
the startup(7) event, and is primarily responsible for running the /etc/init.d/rc script
with the special S argument and calling telinit(8) to switch into the default runlevel
when done. This also handles the -b, emergency, -s and single kernel command-line options
as well as specifying an alternate runlevel on the kernel command-line.
Finally the /etc/init/rcS.conf job handles the special case of entering the single-user
runlevel and providing a login shell. Once that shell terminates, this restarts the rc-
sysinit job to re-enter the default runlevel.
Implementation of runlevels in Upstart
The Upstart init(8) daemon has no native concepts of runlevel, and unlike the System V
daemon, makes no attempt to keep track of the current runlevel.
Instead a compatible implementation is provided by the runlevel(8), telinit(8) and shut-
down(8) tools supplied with Upstart.
The telinit(8) and shutdown(8) tools are used by system administrators to change the run-
level, thus they both generate this runlevel event obtaining the value for the PREVLEVEL
environment variable from their own environment (the RUNLEVEL variable) or the
Additionally they update the /var/run/utmp file with the new runlevel, and append a log
entry to the /var/log/wtmp file.
The runlevel(8) tool may be used by system administrators to obtain the current runlevel,
this reads the RUNLEVEL and PREVLEVEL variables from its own environment or reads the cur-
rent and previous runlevel from /var/run/utmp.
The who(1) -r command may also be used to read the current runlevel from /var/run/utmp.
This provides full compatibility with System V.
During the boot scripts, where the /var/run/utmp file may not yet be writable, the RUN-
LEVEL and PREVLEVEL environment variables will be available so telinit(8) will still pro-
vide the correct values.
Once the boot scripts have finished, while the environment variables may no longer be
available, the /var/run/utmp file will be and the most recent telinit(8) invocation should
have successfully written to it.
Boot time records
The telinit(8) tool also takes care of writing the boot time record to both /var/run/utmp
This is written if the previous runlevel in these files does not match the previous run-
level obtained from its environment. In general this occurs when switching from runlevel
S to the default runlevel, at which point the /var/run/utmp and /var/log/wtmp files are
both writable, and the telinit(8) invocation to do the switch has RUNLEVEL=S in its envi-
A service running in the typical multi-user runlevels might use:
start on runlevel 
stop on runlevel [!2345]
runlevel(8) init(8) telinit(8) shutdown(8) who(1)
Upstart 2009-07-09 runlevel(7)