mypapers/200802-bootsequence/200802-bootsequence.html

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  10
  11 <a href="200706-bootseq/200706-bootseq.html">forrige foredrag</a>
  12
  13 <h1>Reordering the Debian boot sequence for correctness and speed</h1>
  14
  15 <p>Autodetecting and configuring hardware during installation and at
  16    runtime</p>
  17
  18 <div class="presenter">Petter Reinholdtsen
  19   <br>pere@hungry.com
  20   <br>FOSDEM 2008, 2008-02-26</div>
  21
  22 <h2>Summary</h2>
  23
  24 <!--
  25
  26  - how do sysvinit boot work
  27    - runlevels
  28    - inittab
  29    - rc*.d/
  30  - ordering issue
  31  - how does it work in debian
  32  - effect on the boot
  33  - insserv
  34  - speed change?
  35  - concurrency
  36
  37  - how to write lsb headers
  38    - provides
  39    - deps
  40    - runlevel list
  41
  42  - status in debian
  43    - need better doc
  44    - fix insserv bugs
  45
  46  - what is needed to convert
  47    - add LSB header to packages and get the change into testing
  48    - update policy
  49    - more users to test headers and detect errors
  50    - install and activate insserv by default
  51
  52 -->
  53
  54 <h2>SysV init in Debian - Booting</h2>
  55
  56 <p>Note, this is the stuff going on after the initrd part is done.
  57 The very early boot is done before hard drive partitions is mounted.</p>
  58
  59 <ol>
  60
  61 <li>/sbin/init start, which look at /etc/inittab and decides what to
  62   do.</li>
  63
  64 <li>The scripts in /etc/rcS.d/ is executed in sequence by
  65   /etc/init.d/rc, with <tt>start</tt> as the argument.</li>
  66
  67 <li>Depending on the runlevel, the scripts for the given runlevel is
  68   executed (normally the ones in /etc/rc2.d/) are executed in
  69   sequence, first the stop scripts with <tt>stop</tt> as their
  70   argument, next the start scripts with <tt>start</tt> as their
  71   argument.  The rc*.d/ directories contain symlinks the files in to
  72   /etc/init.d/.</li>
  73
  74 <li>The ordering is important.</li>
  75
  76 <li>The single-user runlevel will present a login prompt after rcS.d/
  77   was executed.  Runlevel 1 is not the single user runlevel, but it
  78   behaves as a better single user.</li>
  79
  80 </ol>
  81
  82 <h2>SysV init in Debian - Switching runlevels</h2>
  83
  84 <ul>
  85
  86 <li>Call <tt>telinit X</tt> where X is the new runlevel, one of S, 0,
  87   1, 2, 3, 4, 5, 6.</li>
  88
  89 <li>init runs in sequence all stop scripts in /etc/rcX.d/ that also
  90    has a start symlink in the previous runlevel /etc/rcY.d/, with
  91    <tt>stop</tt> as their argument.</li>
  92
  93 <li>init then run in sequence all start scripts in /etc/rcX.d/, with
  94   <tt>start</tt> as their argument.</li>
  95
  96 </ul>
  97
  98 <p>Note that switching to runlevel S will not run the scripts in
  99 /etc/rcS.d/.  To get a similar effect after boot, switch to runlevel
 100 1.  It will (should) kill all services and prepare the machine for
 101 maintenance.</p>
 102
 103 <h2>SysV init in Debian - Shutting down</h2>
 104
 105 <p>This is equivalent to switching to runlevel 0 (halt) or 6 (reboot),
 106   with a minor exception.  All scripts (both start and stop) are
 107   executed with the <tt>stop</tt> argument.
 108
 109 <h2> about ordering </h2>
 110
 111 <p>Script ordering is vital for this to work.  And how are the scripts
 112 ordered?
 113
 114  update-rc.d numbers.
 115
 116
 117
 118
 119 <h2>LSB headers for insserv</h2>
 120
 121 <ul>
 122   <li>"Provides" header, list the Facility/service provided by the
 123     script.  Do not list virtual facilities (like $time)</li>
 124
 125   <li>Runlevel entries (Default-Start and Default-Stop headers), list
 126     what runlevels to activate for this script
 127
 128   <li>Dependency entries (Required-Start, Required-Stop, Should-Start,
 129     Should-Stop, X-Start-Before, X-Stop-After), list the
 130     facilities/services needed by this script.  It will start after
 131     its start dependencies and stop before its stop dependencies.  The
 132     X-* entreis are reverse dependencies.  Required-* are hard
 133     dependencies (will install even if they are missing), while
 134     Should-* and X-* are soft dependencies (only taken into account if
 135     scripts providing them are present).</li>
 136
 137 </ul>
 138
 139 <h2>What to list as dependencies I</h2>
 140
 141 <p>If your package used the default update-rc.d settings before, this
 142 is the header for you:</p>
 143 <pre>
 144 ### BEGIN INIT INFO
 145 # Provides:          scriptname
 146 # Required-Start:    $remote_fs $syslog
 147 # Required-Stop:     $remote_fs $syslog
 148 # Default-Start:     2 3 4 5
 149 # Default-Stop:      0 1 6
 150 ### END INIT INFO
 151 </pre>
 152
 153 <p>$remote_fs is needed by all scripts using files in /usr/.  $syslog
 154 is needed only by scripts starting services logging to syslog.</p>
 155
 156
 157 <h2>Status of dependency based boot</h2>
 158
 159 <img alt="LSB header progress graph" src="lsb-header-progress.png" width="50%" align="right">
 160
 161 <p>Release goal for Debian Lenny.
 162
 163 <p>Packages with LSB header: 654 of 866 (76%)
 164 <br>Unsolved BTS reports: XXX
 165 <br>Packages without BTS reports: ~150
 166
 167 <p>Need better documentation
 168
 169 <p>Need debian policy updates
 170
 171 <p>
 172
 173  - status in debian
 174    - need better doc
 175    - fix insserv bugs
 176
 177
 178
 179     <h2>Thank you very much</h2>
 180
 181     <h3>Questions?</h3>
 182
 183     <p><a href="http://www.hungry.com/~pere/mypapers/200802-bootsequence/200802-bootsequence.html">http://www.hungry.com/~pere/mypapers/200802-bootsequence/200802-bootsequence.html</a></p>
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