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    2      What is Anacron ?
    3      -----------------
    5    Anacron is a periodic command scheduler.  It executes commands at
    6 intervals specified in days.  Unlike cron, it does not assume that the
    7 system is running continuously.  It can therefore be used to control
    8 the execution of daily, weekly and monthly jobs (or anything with a
    9 period of n days), on systems that don't run 24 hours a day.  When
   10 installed and configured properly, Anacron will make sure that the
   11 commands are run at the specified intervals as closely as
   12 machine-uptime permits.
   14    Every time Anacron is run, it reads a configuration file that
   15 specifies the jobs Anacron controls, and their periods in days.  If a
   16 job wasn't executed in the last n days, where n is the period of that
   17 job, Anacron executes it.  Anacron then records the date in a special
   18 timestamp file that it keeps for each job, so it can know when to run
   19 it again.  When all the executed commands terminate, Anacron exits.
   21    It is recommended to run Anacron from the system boot-scripts.
   22 This way the jobs "whose time has come" will be run shortly after the
   23 machine boots.  A delay can be specified for each job so that the
   24 machine isn't overloaded at boot time.
   26    In addition to running Anacron from the boot-scripts, it is also
   27 recommended to schedule it as a daily cron-job (usually at an early
   28 morning hour), so that if the machine is kept running for a night,
   29 jobs for the next day will still be executed.
   32      Why this may be useful ?
   33      ------------------------
   35    Most Unix-like systems have daily, weekly and monthly scripts that
   36 take care of various "housekeeping chores" such as log-rotation,
   37 updating the "locate" and "man" databases, etc.  Daily scripts are
   38 usually scheduled as cron-jobs to execute around 1-7 AM.  Weekly
   39 scripts are scheduled to run on Sundays.  On machines that are turned
   40 off for the night or for the weekend, these scripts rarely get run.
   42    Anacron solves this problem.  These jobs can simply be scheduled as
   43 Anacron-jobs with periods of 1, 7 and 30 days.
   46      What Anacron is not ?
   47      ---------------------
   49    Anacron is not an attempt to make cron redundant.  It cannot
   50 currently be used to schedule commands at intervals smaller than days.
   51 It also does not guarantee that the commands will be executed at any
   52 specific day or hour.
   54    It isn't a full-time daemon.  It has to be executed from boot
   55 scripts, from cron-jobs, or explicitly.
   58    For more details, see the anacron(8) manpage.
   61      Requirements
   62      ------------
   64  - A Linux system. (maybe other *NIX systems)
   65  - A functioning syslog daemon.
   66  - A functioning /usr/lib/sendmail command.  (all MTAs should have
   67    that).
   70      Compilation and Installation
   71      ----------------------------
   73  - Untar the source package.
   75  - Check the Makefile.  Edit as required.
   77  - Check the top of "global.h".  You may want to change the syslog
   78    facility and priorities, and the path to your MTA's sendmail
   79    compatible command (/usr/lib/sendmail).
   81  - cd to the directory.
   83  - Type "make".
   84    You can safely ignore warnings of the form: "*.d: No such file or
   85    directory"
   87  - Become root.  Type "make install".
   90      Setup
   91      -----
   93 1. Locate your system's daily, weekly and monthly cron-jobs.
   94    See your cron documentation for more details.
   96 2. Decide which of these jobs should be controlled by Anacron.
   97    Remember that Anacron does not guarantee execution at any specific
   98    day of the month, day of the week, or time of day.  Jobs for which
   99    the timing is critical should probably not be controlled by
  100    Anacron.
  102 3. Comment these jobs out of their crontab files.  (You may have to
  103    use the "crontab" command for this.  See the cron documentation.)
  105 4. Put them in /etc/anacrontab.  Note that the format is not the same
  106    as the crontab entries.  See the anacrontab(5) manpage.  Here's an
  107    example from a typical Debian system:
  109 -----Cut
  110 # /etc/anacrontab example
  111 SHELL=/bin/sh
  112 PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
  113 # format: period delay job-identifier command
  114 1       5       cron.daily      run-parts /etc/cron.daily
  115 7       10      cron.weekly     run-parts /etc/cron.weekly
  116 30      15      cron.monthly    run-parts /etc/cron.monthly
  117 -----Cut
  119 5. Put the command "anacron -s" somewhere in your boot-scripts.
  120    Make sure that syslogd is started before this command.
  122 6. Schedule the command "anacron -s" as a daily cron-job (preferably
  123    at some early morning hour).  This will make sure that jobs are run
  124    when the systems is left running for a night.
  126 That's it.
  128 It is a good idea to check what your daily, weekly and monthly scripts
  129 actually do, and disable any parts that may be irrelevant for your
  130 system.
  133      Credits
  134      -------
  136 Anacron was originally conceived and implemented by Christian Schwarz
  137 <schwarz@monet.m.isar.de>.
  139 The current implementation is a complete rewrite by Itai Tzur
  140 <itzur@actcom.co.il>.
  142 Current code base maintained by Sean 'Shaleh' Perry <shaleh@(debian.org|valinux.com)>.