X-Git-Url: https://pere.pagekite.me/gitweb/homepage.git/blobdiff_plain/864756f2f60f29cf2ea397e7445746eb5a582cda..45f7f5e186d8a1bcc88fe9f9794d3aa3333c83ab:/mypapers/200802-bootsequence/200802-bootsequence.html diff --git a/mypapers/200802-bootsequence/200802-bootsequence.html b/mypapers/200802-bootsequence/200802-bootsequence.html index 21e9e045bf..bdd8957556 100644 --- a/mypapers/200802-bootsequence/200802-bootsequence.html +++ b/mypapers/200802-bootsequence/200802-bootsequence.html @@ -6,6 +6,11 @@ + @@ -55,7 +60,11 @@ This talk is about how all of this can be done with Debian. - how does it work in debian - effect on the boot - insserv + - how to verify the boot sequence + - check script + - dependency graph using dotty - how to test it + - overriding included headers - speed change? - concurrency @@ -104,6 +113,9 @@ The very early boot is done before hard drive partitions is mounted.

Note that because the Linux kernel is becoming more and more event +based, the boot sequence is no longer sequencial.

SysV init in Debian - Switching runlevels

SysV init in Debian - Shutting down

This is equivalent to switching to runlevel 0 (halt) or 6 (reboot), - with a minor exception. All scripts (both start and stop) are - executed with the stop argument. +

This is roughtly equivalent to switching to runlevel 0 (halt) or 6 +(reboot).

Minor exception: all scripts (both start and stop) are executed + with the stop argument, ignoring their start and stop + setting and confusing script writers.

Only stop scripts for services started in the previous runlevel is + executed.

The ordering problem

Checking the current boot sequence

Static checking of current headers: +/usr/share/insserv/check-initd-order [-o] [-k] - report mismatch +in current ordering. + +

Graph of the dependencies: +/usr/share/insserv/check-initd-order -g - for reviewing dependencies + +

Enabling dependency based boot sequencing I

Use the insserv package in unstable and testing +
Low priority debconf question. +
Only enabled after verfiying that it is safe to enable +
Converts all start symlinks in rc0.d/ and rc6.d with stop symlinks. +
Replaces update-rc.d with wrapper calling insserv +
All of rc*.d/ is reordered +

Enabling dependency based boot sequencing II

+# aptitude install insserv
+# dpkg-reconfigure insserv
+info: Checking if it is safe to convert to dependency based boot.
+info: Backing up existing boot scripts in \
+  /var/lib/insserv/bootscripts-20080223T0742.tar.gz
+info: Reordering boot system, log to \
+  /var/lib/insserv/run-20080223T0742.log
+info: Recording new boot sequence in \
+  /var/lib/insserv/bootscripts-20080223T0742-after.list
+info: Use '/usr/sbin/update-bootsystem-insserv \
+  restore' to restore the old boot sequence.
+Adding `diversion of /usr/sbin/update-rc.d to \
+  /usr/sbin/update-rc.d.distrib by insserv'
+success: Boot system successfully converted
+# /var/lib/insserv/insserv-seq-changes \
+  /var/lib/insserv/bootscripts-20080223T0742.tar.gz
+#
+

With dependency based boot sequencing

update-rc.d refuse to Insert scripts which create a loop.

update-rc.d require scripts to be inserted in dependency order.

Incorrect dependencies give the wrong boot and shutdown order.

It is possible to enable concurrent booting, running boot scripts + in parallel (CONCURRENCY=startpar in /etc/default/rcS)

Disabling dependency based boot sequencing

Run dpkg-reconfigure insserv and disable it. + +

It is always possible to disable just after it was enabled, before +any new packages are installed.

To disable it, a backup of the old boot sequence is restored if no +changes has been done to the boot sequence since it was enabled. + +

If restoring is not possible, All postinst scripts for packages +with init.d scripts will be executed again to get them to call +update-rc.d and add the boot scripts again.

LSB headers for insserv

$remote_fs is needed by all scripts using files in /usr/. $syslog is needed only by scripts starting services logging to syslog.

What to list as dependencies II

In the common case, the start and stop dependencies are identical. - -

Prefer virtual dependencies over specific dependencies - -XXX More -

Virtual facilities

Linux Software Base version 3.2 define these virtual facilities: @@ -273,6 +349,23 @@ facility, then that daemon has been started.

All of these represent points in time during boot and shutdown. +

What to list as dependencies II

Normally, the start and stop dependencies are the same. + +

Prefer virtual dependencies over specific dependencies. + +

When using specific dependencies, use the string listed in the + provides header of the scripts you depend on. + +

Scripts started in rcS.d/ need extra care. + +

Depend on $remote_fs unless started in rcS.d/. Make sure /usr/ is +available during start and that it is stopped before sendsigs kill all +processes during shutdown.

Status of dependency based boot

Release goal for Debian Lenny.

Packages with LSB header (in Sid): 654 of 866 (76%) -
Unsolved BTS reports: XXX +
Unsolved BTS reports: 85
Packages without BTS reports: ~150
Last package projected fixed 2008-07-19 with the current rate

Need better documentation -

Need debian policy updates +

Should update Debian policy to reflect this new feature. -

Fix insserv bugs +

Two insserv bugs to fix. +

Avoid adding unwanted stop symlinks. +
Do not fail on "fake" loops. (minor) +

SysV init in Debian - Switching runlevels

SysV init in Debian - Shutting down

The ordering problem

Checking the current boot sequence

Enabling dependency based boot sequencing I

Enabling dependency based boot sequencing II

With dependency based boot sequencing

Disabling dependency based boot sequencing

LSB headers for insserv

What to list as dependencies II

Virtual facilities

What to list as dependencies II

Status of dependency based boot

Tracking status

References

Thank you very much