启动
时间：2006-06-15 来源：zhuyong486
0 N0.1936 huan ~ ]$ cat /etc/init.d/README
Configuration of System V init under Debian GNU/Linux
Most Unix versions have a file here that describes how the scripts
in this directory work, and how the links in the /etc/rc?.d/ directories
influence system startup/shutdown.
For Debian, this information is contained in the policy manual, chapter
"System run levels and init.d scripts". The Debian Policy Manual is
available at:
http://www.debian.org/doc/debian-policy/#contents
The Debian Policy Manual is also available in the Debian package
"debian-policy". When this package is installed, the policy manual can be
found in directory /usr/share/doc/debian-policy. If you have a browser
installed you can probably read it at
file://localhost/usr/share/doc/debian-policy/
Some more detailed information can also be found in the files in the
/usr/share/doc/sysv-rc directory.
Debian Policy dictates that /etc/init.d/*.sh scripts must work properly
when sourced. The following additional rules apply:
* /etc/init.d/*.sh scripts may not rely for their correct functioning
on their being sourced rather than executed. That is, they must work
properly when executed too. They must include "#!/bin/sh" at the top.
* /etc/init.d/*.sh scripts must conform to the rules for sh scripts as
spelled out in the Debian policy section entitled "Scripts" (§10.4).
[0 N0.1937 huan ~ ]$ zcat /usr/share/doc/sysv-rc/README.runlevels.gz
Order of scripts run in /etc/rc?.d
==================================
0. Overview.
All scripts executed by the init system are located in /etc/init.d.
The directories /etc/rc?.d (? = S, 0 .. 6) contain relative links to
those scripts. These links are named S<2-digit-number>
or K<2-digit-number>.
If a scripts has the ".sh" suffix it is a bourne shell script and
MAY be handled in an optimized manner. The behaviour of executing the
script in an optimized way will not differ in any way from it being
forked and executed in the regular way.
The following runlevels are defined:
N System bootup (NONE).
S Single user mode (not to be switched to directly)
0 halt
1 single user mode
2 .. 5 multi user mode
6 reboot
1. Boot.
When the systems boots, the /etc/init.d/rcS script is executed. It
in turn executes all the S* scripts in /etc/rcS.d in alphabetical
(and thus numerical) order. The first argument passed to the
executed scripts is "start". The runlevel at this point is "N" (none).
Only things that need to be run once to get the system in a consistent
state are to be run. The rcS.d directory is NOT meant to replace rc.local.
One should not start daemons in this runlevel unless absolutely
necessary. Eg, NFS might need the portmapper, so it is OK to start it
early in the bootprocess. But this is not the time to start the
squid proxy server.
2. Going multiuser.
After the rcS.d scripts have been executed, init switches to the
default runlevel as specified in /etc/inittab, usually "2".
Init then executes the /etc/init.d/rc script which takes care of
starting the services in /etc/rc2.d.
Because the previous runlevel is "N" (none) the /etc/rc2.d/KXXxxxx
scripts will NOT be executed - there is nothing to stop yet,
the system is busy coming up.
If for example there is a service that wants to run in runlevel 4
and ONLY in that level, it will place a KXXxxxx script in
/etc/rc{2,3,5}.d to stop the service when switching out of runlevel 4.
We do not need to run that script at this point.
The /etc.rc2.d/SXXxxxx scripts will be executed in alphabetical
order, with the first argument set to "start".
3. Switching runlevels.
When one switches from (for example) runlevel 2 to runlevel 3,
/etc/init.d/rc will first execute in alphabetical order all K
scripts for runlevel 3 (/etc/rc3.d/KXXxxxx) with as first argument
"stop" and then all S scripts for runlevel 3 (/etc/rc3.d/SXXxxxx)
with as first argument "start".
As an optimization, a check is made for each "service" to see if
it was already running in the previous runlevel. If it was, and there
is no K (stop) script present for it in the new runlevel, there is
no need to start it a second time so that will not be done.
On the other hand, if there was a K script present, it is assumed the
service was stopped on purpose first and so needs to be restarted.
We MIGHT make the same optimization for stop scripts as well-
if no S script was present in the previous runlevel, we can assume
that service was not running and we don't need to stop it either.
In that case we can remove the "coming from level N" special case
mentioned above in 2). But right now that has not been implemented.
4. Single user mode.
Switching to single user mode is done by switching to runlevel 1.
That will cause all services to be stopped (assuming they all have
a K script in /etc/rc1.d). The runlevel 1 scripts will then switch
to runlevel "S" which has no scripts - all it does is spawn
a shell directly on /dev/console for maintenance.
5. Halt/reboot
Going to runlevel 0 or 6 will cause the system to be halted or rebooted,
respectively. For example, if we go to runlevel 6 (reboot) first
all /etc/rc6.d/KXXxxxx scripts will be executed alphabetically with
"stop" as the first argument.
Then the /etc/rc6.d/SXXxxxx scripts will be executed alphabetically
with "stop" as the first argument as well. The reason is that there
is nothing to start anymore at this point - all scripts that are
run are meant to bring the system down.
In the future, the /etc/rc6.d/SXXxxxx scripts MIGHT be moved to
/etc/rc6.d/K1XXxxxx for clarity.
[0 N0.1938 huan ~ ]$
Configuration of System V init under Debian GNU/Linux
Most Unix versions have a file here that describes how the scripts
in this directory work, and how the links in the /etc/rc?.d/ directories
influence system startup/shutdown.
For Debian, this information is contained in the policy manual, chapter
"System run levels and init.d scripts". The Debian Policy Manual is
available at:
http://www.debian.org/doc/debian-policy/#contents
The Debian Policy Manual is also available in the Debian package
"debian-policy". When this package is installed, the policy manual can be
found in directory /usr/share/doc/debian-policy. If you have a browser
installed you can probably read it at
file://localhost/usr/share/doc/debian-policy/
Some more detailed information can also be found in the files in the
/usr/share/doc/sysv-rc directory.
Debian Policy dictates that /etc/init.d/*.sh scripts must work properly
when sourced. The following additional rules apply:
* /etc/init.d/*.sh scripts may not rely for their correct functioning
on their being sourced rather than executed. That is, they must work
properly when executed too. They must include "#!/bin/sh" at the top.
* /etc/init.d/*.sh scripts must conform to the rules for sh scripts as
spelled out in the Debian policy section entitled "Scripts" (§10.4).
[0 N0.1937 huan ~ ]$ zcat /usr/share/doc/sysv-rc/README.runlevels.gz
Order of scripts run in /etc/rc?.d
==================================
0. Overview.
All scripts executed by the init system are located in /etc/init.d.
The directories /etc/rc?.d (? = S, 0 .. 6) contain relative links to
those scripts. These links are named S<2-digit-number>
or K<2-digit-number>.
If a scripts has the ".sh" suffix it is a bourne shell script and
MAY be handled in an optimized manner. The behaviour of executing the
script in an optimized way will not differ in any way from it being
forked and executed in the regular way.
The following runlevels are defined:
N System bootup (NONE).
S Single user mode (not to be switched to directly)
0 halt
1 single user mode
2 .. 5 multi user mode
6 reboot
1. Boot.
When the systems boots, the /etc/init.d/rcS script is executed. It
in turn executes all the S* scripts in /etc/rcS.d in alphabetical
(and thus numerical) order. The first argument passed to the
executed scripts is "start". The runlevel at this point is "N" (none).
Only things that need to be run once to get the system in a consistent
state are to be run. The rcS.d directory is NOT meant to replace rc.local.
One should not start daemons in this runlevel unless absolutely
necessary. Eg, NFS might need the portmapper, so it is OK to start it
early in the bootprocess. But this is not the time to start the
squid proxy server.
2. Going multiuser.
After the rcS.d scripts have been executed, init switches to the
default runlevel as specified in /etc/inittab, usually "2".
Init then executes the /etc/init.d/rc script which takes care of
starting the services in /etc/rc2.d.
Because the previous runlevel is "N" (none) the /etc/rc2.d/KXXxxxx
scripts will NOT be executed - there is nothing to stop yet,
the system is busy coming up.
If for example there is a service that wants to run in runlevel 4
and ONLY in that level, it will place a KXXxxxx script in
/etc/rc{2,3,5}.d to stop the service when switching out of runlevel 4.
We do not need to run that script at this point.
The /etc.rc2.d/SXXxxxx scripts will be executed in alphabetical
order, with the first argument set to "start".
3. Switching runlevels.
When one switches from (for example) runlevel 2 to runlevel 3,
/etc/init.d/rc will first execute in alphabetical order all K
scripts for runlevel 3 (/etc/rc3.d/KXXxxxx) with as first argument
"stop" and then all S scripts for runlevel 3 (/etc/rc3.d/SXXxxxx)
with as first argument "start".
As an optimization, a check is made for each "service" to see if
it was already running in the previous runlevel. If it was, and there
is no K (stop) script present for it in the new runlevel, there is
no need to start it a second time so that will not be done.
On the other hand, if there was a K script present, it is assumed the
service was stopped on purpose first and so needs to be restarted.
We MIGHT make the same optimization for stop scripts as well-
if no S script was present in the previous runlevel, we can assume
that service was not running and we don't need to stop it either.
In that case we can remove the "coming from level N" special case
mentioned above in 2). But right now that has not been implemented.
4. Single user mode.
Switching to single user mode is done by switching to runlevel 1.
That will cause all services to be stopped (assuming they all have
a K script in /etc/rc1.d). The runlevel 1 scripts will then switch
to runlevel "S" which has no scripts - all it does is spawn
a shell directly on /dev/console for maintenance.
5. Halt/reboot
Going to runlevel 0 or 6 will cause the system to be halted or rebooted,
respectively. For example, if we go to runlevel 6 (reboot) first
all /etc/rc6.d/KXXxxxx scripts will be executed alphabetically with
"stop" as the first argument.
Then the /etc/rc6.d/SXXxxxx scripts will be executed alphabetically
with "stop" as the first argument as well. The reason is that there
is nothing to start anymore at this point - all scripts that are
run are meant to bring the system down.
In the future, the /etc/rc6.d/SXXxxxx scripts MIGHT be moved to
/etc/rc6.d/K1XXxxxx for clarity.
[0 N0.1938 huan ~ ]$
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