UPDATE-RC.D(8)							      sysv-rc							    UPDATE-RC.D(8)

NAME

       update-rc.d - install and remove System-V style init script links

SYNOPSIS

       update-rc.d [-n] [-f] name remove

       update-rc.d [-n] name defaults [NN | SS KK]

       update-rc.d [-n] name start|stop NN runlevel [runlevel]...  .  start|stop NN runlevel [runlevel]...  . ...

       update-rc.d [-n] name disable|enable [ S|2|3|4|5 ]

DESCRIPTION

       update-rc.d updates the System V style init script links /etc/rcrunlevel.d/NNname whose target is the script /etc/init.d/name.  These links
       are run by init when it changes runlevels; they are generally used to start and stop system services such as daemons.  runlevel is  one	of
       the  runlevels  supported  by init, namely, 0123456789S, and NN is the two-digit sequence number that determines where in the sequence init
       will run the scripts.

       This manpage documents only the usage and behaviour of update-rc.d.  For a discussion of the System V style init script arrangements please
       see init(8) and the Debian Policy Manual.

INSTALLING INIT SCRIPT LINKS

       update-rc.d  has two modes of operation for installing scripts into the boot sequence.  A legacy mode where command line arguments are used
       to decide the sequence and runlevel configuration, and the default mode where dependency and runlevel information in the init.d script  LSB
       comment header is used instead.	Such header is required to be present in init.d scripts.  See the insserv(8) manual page for details about
       the LSB header format.  The boot sequencing method is decided during installation or upgrades.  During upgrades, if there are no  loops	in
       the  dependencies  declared  by LSB headers of all installed init.d scripts and no obsolete init.d scripts, the boot system is converted to
       dependency based boot sequencing.  The conversion to dependency based boot sequencing is one-way.  The machines using the legacy mode  will
       have a file /etc/init.d/.legacy-bootordering .

       Packages installing init.d scripts should make sure both methods work, for compatiblity with systems where the migration have not been done
       yet.

       For legacy mode, the following section documents the old behaviour.

       When run with either the defaults, start, or stop options, update-rc.d makes links /etc/rcrunlevel.d/[SK]NNname that point  to  the  script
       /etc/init.d/name.

       If  any	files  /etc/rcrunlevel.d/[SK]??name already exist then update-rc.d does nothing.  The program was written this way so that it will
       never change an existing configuration, which may have been customized by the system administrator.  The program will only install links if
       none are present, i.e., if it appears that the service has never been installed before.

       A  common  system  administration  error is to delete the links with the thought that this will "disable" the service, i.e., that this will
       prevent the service from being started.	However, if all links have been deleted then the next time the package is upgraded, the  package's
       postinst  script  will  run update-rc.d again and this will reinstall links at their factory default locations.	The correct way to disable
       services is to configure the service as stopped in all runlevels in which it is started by default.  In the System V init system this means
       renaming the service's symbolic links from S to K.

       If  defaults  is used then update-rc.d will make links to start the service in runlevels 2345 and to stop the service in runlevels 016.	By
       default all the links will have sequence number 20, but this should be overridden if there  are	dependencies.  For  example  if  daemon  B
       depends on A, then A must be started before B and B must be killed before A. You accomplish this by supplying two NN arguments. In general,
       core daemons should start early and be killed late, whilst applications can start late and be killed early. See EXAMPLES below.

       The first NN argument supplies the start sequence number and the second NN argument supplies the kill sequence number.	Kill  scripts  are
       called  first,  passing	a stop argument. Then start scripts are called passing a start argument. In either case, calls happen in ascending
       sequence number order.

       Supplying a single NN argument will use the same number for both start and kill links. This is supported for backward compatibility but	is
       discouraged,  as  it  may  lead	to  inconsistent  settings.  As a rule of thumb, if you increase the start sequence number you should also
       decrease the stop sequence number, and vice-versa.

       As a rule of thumb, the sequence number of the stop link should be 100 minus the sequence number of the start link; this causes services to
       be  stopped  in the opposite order to that in which they are started.  Obviously, therefore, the default stop sequence number should be 80.
       Defaulting to 20, as update-rc.d does, is an old bug that cannot be fixed because of the risk of breaking things.

       Instead of defaults one can give one or more sets of arguments specifying particular runlevels in which to start or stop the service.  Each
       of  these  sets of arguments starts with the keyword start or stop and a sequence number NN, followed by one or more runlevel numbers.  The
       set is terminated by a solitary full stop character.  When explicit specification, rather than defaults, is used there will usually be  one
       start  and  one stop set.  If different sequence codes are required in different runlevels then several start sets or several stop sets may
       be specified.  If this is done and the same runlevel is named in multiple sets then only the last one counts.  Therefore it is not possible
       to create multiple start or multiple stop links for a service in a single runlevel directory.

       The script /etc/init.d/name must exist before update-rc.d is run to create the links.

REMOVING SCRIPTS

       When  invoked  with  the  remove option, update-rc.d removes any links in the /etc/rcrunlevel.d directories to the script /etc/init.d/name.
       The script must have been deleted already.  If the script is still present then update-rc.d aborts with an error message.

       update-rc.d is usually called from a package's post-removal script when that script  is	given  the  purge  argument.   Any  files  in  the
       /etc/rcrunlevel.d directories that are not symbolic links to the script /etc/init.d/name will be left untouched.

DISABLING INIT SCRIPT START LINKS

       When  run  with the disable [ S|2|3|4|5 ] options, update-rc.d modifies existing runlevel links for the script /etc/init.d/name by renaming
       start links to stop links with a sequence number equal to the difference of 100 minus the original sequence number.

       When run with the enable [ S|2|3|4|5 ] options, update-rc.d modifies existing runlevel links for the script  /etc/init.d/name  by  renaming
       stop  links  to start links with a sequence number equal to the positive difference of current sequence number minus 100, thus returning to
       the original sequence number that the script had been installed with before disabling it.

       Both of these options only operate on start runlevel links of S, 2, 3, 4 or 5. If no start runlevel  is	specified  after  the  disable	or
       enable keywords, the script will attempt to modify links in all start runlevels.

OPTIONS

       -n     Don't do anything, just show what we would do.

       -f     Force removal of symlinks even if /etc/init.d/name still exists.

EXAMPLES

       Insert links using the defaults:
	  update-rc.d foobar defaults
       The equivalent dependency header would have start and stop
       dependencies on $remote_fs and $syslog, and start in
       runlevels 2-5 and stop in runlevels 0, 1 and 6.
       Equivalent command using explicit argument sets:
	  update-rc.d foobar start 20 2 3 4 5 . stop 20 0 1 6 .
       More typical command using explicit argument sets:
	  update-rc.d foobar start 30 2 3 4 5 . stop 70 0 1 6 .
       Insert links at default runlevels when B requires A
	  update-rc.d script_for_A defaults 80 20
	  update-rc.d script_for_B defaults 90 10
       Insert a link to a service that (presumably) will not be needed by any other daemon
	  update-rc.d top_level_app defaults 98 02
       Insert links for a script that requires services that start/stop at sequence number 20
	  update-rc.d script_depends_on_svc20 defaults 21 19
       Remove all links for a script (assuming foobar has been deleted already):
	  update-rc.d foobar remove
       Example of disabling a service:
	  update-rc.d -f foobar remove
	  update-rc.d foobar stop 20 2 3 4 5 .
       Example of a command for installing a system initialization-and-shutdown script:
	  update-rc.d foobar start 45 S . stop 31 0 6 .
       Example of a command for disabling a system initialization-and-shutdown script:
	  update-rc.d -f foobar remove
	  update-rc.d foobar stop 45 S .

BUGS

       See http://bugs.debian.org/sysv-rc.

FILES

       /etc/init.d/
	      The directory containing the actual init scripts.

       /etc/rc?.d/
	      The directories containing the links used by init and managed by update-rc.d.

       /etc/init.d/skeleton
	      Model for use by writers of init.d scripts.

       /var/lib/sysv-rc/legacy-bootsequence
	      Flag indicating the machine is using legacy mode for boot script ordering.

SEE ALSO

       Debian Policy Manual,
       /etc/init.d/skeleton,
       insserv(8), sysv-rc-conf(8), bum(8), init(8).

Debian Project							 14 November 2005						    UPDATE-RC.D(8)