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

Provided by: sysv-rc_2.88dsf-41ubuntu6.3_all

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.