Reordering the Debian boot sequence for correctness and speed

Autodetecting and configuring hardware during installation and at runtime

Summary

SysV init in Debian - Booting

Note, this is the stuff going on after the initrd part is done. The very early boot is done before hard drive partitions is mounted.

1. /sbin/init start, which look at /etc/inittab and decides what to do.
2. The scripts in /etc/rcS.d/ is executed in sequence by /etc/init.d/rc, with start as the argument.
3. Depending on the runlevel, the scripts for the given runlevel is executed (normally the ones in /etc/rc2.d/) are executed in sequence, first the stop scripts with stop as their argument, next the start scripts with start as their argument. The rc*.d/ directories contain symlinks the files in to /etc/init.d/.
4. The ordering is important.
5. The single-user runlevel will present a login prompt after rcS.d/ was executed. Runlevel 1 is not the single user runlevel, but it behaves as a better single user.

SysV init in Debian - Switching runlevels

• Call telinit X where X is the new runlevel, one of S, 0, 1, 2, 3, 4, 5, 6.
• init runs in sequence all stop scripts in /etc/rcX.d/ that also has a start symlink in the previous runlevel /etc/rcY.d/, with stop as their argument.
• init then run in sequence all start scripts in /etc/rcX.d/, with start as their argument.

Note that switching to runlevel S will not run the scripts in /etc/rcS.d/. To get a similar effect after boot, switch to runlevel 1. It will (should) kill all services and prepare the machine for maintenance.

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.

about ordering

Script ordering is vital for this to work. And how are the scripts ordered? update-rc.d numbers.

LSB headers for insserv

• "Provides" header, list the Facility/service provided by the script. Do not list virtual facilities (like $time)
• Runlevel entries (Default-Start and Default-Stop headers), list what runlevels to activate for this script
• Dependency entries (Required-Start, Required-Stop, Should-Start, Should-Stop, X-Start-Before, X-Stop-After), list the facilities/services needed by this script. It will start after its start dependencies and stop before its stop dependencies. The X-* entreis are reverse dependencies. Required-* are hard dependencies (will install even if they are missing), while Should-* and X-* are soft dependencies (only taken into account if scripts providing them are present).

What to list as dependencies I

If your package used the default update-rc.d settings before, this is the header for you:

### BEGIN INIT INFO
# Provides:          scriptname
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
### END INIT INFO

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

Status of dependency based boot

Release goal for Debian Lenny.

Packages with LSB header: 654 of 866 (76%)
Unsolved BTS reports: XXX
Packages without BTS reports: ~150

Need better documentation

Need debian policy updates

- status in debian - need better doc - fix insserv bugs

Thank you very much

Questions?

http://www.hungry.com/~pere/mypapers/200802-bootsequence/200802-bootsequence.html