The proper startup
and shutdown of services required for a system to function and fulfill its purpose
is central to its management. While Unix init scripts (also known as System V or SysV
scripts, due to their origin in Unix System V) have a long history and are in one form or
another, common to all Unix and Linux systems, the way in which they are managed,
sequenced, enabled, disabled, and the preferred script format often differs somewhat
between distributions. The primary areas to be aware of for Debian startup and shutdown
scripts include the purpose of run levels, dependency-based
sequencing, and
utilities available for administering the boot sequence.
See also:
Debian run levels
In Debian, as in
nearly all Unix/Linux operating systems, run levels from 0 through 6 are available,
defined as follows:
• 0: System Halt
• 1: Single User
(maintenance)
• 2 to 5: Multi-User
Modes
•
6: System Reboot
Note that run levels
2 through 5 are identical in Debian. This is unlike some other
distributions, such
as RedHat, Fedora, SuSE, or OpenSuSE, which give specific
purposes to some of
these run levels. For example, run level 2 in these distributions
is often defined as
one without network support, 3 with networking, 4 with file
sharing, and 5
includes a display manager which isn't active in the other run levels.
In most Debian
systems, there is no difference between the multiuser run levels, and
all of the init
scripts default to active in levels 2 through 5. This doesn't mean you
can't define your own
purposes for different run levels. However, if you do choose
to do this, do not
manually edit the various links to init scripts in the run level
directories. The update-rc.d
command should be used instead. The reason for this
is that Debian now defaults
to dependency based boot sequencing.
