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<div class="section" id="the-expire-backups-command">
<h1>The <strong class="program">expire_backups</strong> command<a class="headerlink" href="#the-expire-backups-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="synopsis">
<h2>Synopsis<a class="headerlink" href="#synopsis" title="Permalink to this headline">¶</a></h2>
<div class="highlight-commandline"><div class="highlight"><pre><span class="l">expire_backups </span><span class="ge">[options]</span><span class="l"> </span><span class="nv"><age></span><span class="l"> </span><span class="ge">[<age> ...]</span><span class="l"></span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>The <strong class="command">expire_backups</strong> command intelligently remove old backups that are no
longer needed.</p>
<p>To define what backups you want to keep for how long, you define a
number of <em>age ranges</em>. <strong class="program">expire_backups</strong> ensures that you
will have at least one backup in each age range at all times. It will
keep exactly as many backups as are required for that and delete any
backups that become redundant.</p>
<p>Age ranges are specified by giving a list of range boundaries in terms
of backup cycles. Every time you create a new backup, the existing
backups age by one cycle.</p>
<p>Example: when <strong class="program">expire_backups</strong> is called with the age range
definition <tt class="docutils literal"><span class="pre">1</span> <span class="pre">3</span> <span class="pre">7</span> <span class="pre">14</span> <span class="pre">31</span></tt>, it will guarantee that you always have the
following backups available:</p>
<ol class="arabic simple">
<li>A backup that is 0 to 1 cycles old (i.e, the most recent backup)</li>
<li>A backup that is 1 to 3 cycles old</li>
<li>A backup that is 3 to 7 cycles old</li>
<li>A backup that is 7 to 14 cycles old</li>
<li>A backup that is 14 to 31 cycles old</li>
</ol>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If you do backups in fixed intervals, then one cycle will be
equivalent to the backup interval. The advantage of specifying the
age ranges in terms of backup cycles rather than days or weeks is
that it allows you to gracefully handle irregular backup intervals.
Imagine that for some reason you do not turn on your computer for
one month. Now all your backups are at least a month old, and if you
had specified the above backup strategy in terms of absolute ages,
they would all be deleted! Specifying age ranges in terms of backup
cycles avoids these sort of problems.</p>
</div>
<p><strong class="program">expire_backups</strong> usage is simple. It requires backups to have
names of the forms <tt class="docutils literal"><span class="pre">year-month-day_hour:minute:seconds</span></tt>
(<tt class="docutils literal"><span class="pre">YYYY-MM-DD_HH:mm:ss</span></tt>) and works on all backups in the current
directory. So for the above backup strategy, the correct invocation
would be:</p>
<div class="highlight-commandline"><div class="highlight"><pre><span class="l">expire_backups.py 1 3 7 14 31</span>
</pre></div>
</div>
<p>When storing your backups on an S3QL file system, you probably want to
specify the <tt class="docutils literal"><span class="pre">--use-s3qlrm</span></tt> option as well. This tells
<strong class="program">expire_backups</strong> to use the <a class="reference internal" href="../special.html#s3qlrm"><em>s3qlrm</em></a> command to
delete directories.</p>
<p><strong class="program">expire_backups</strong> uses a “state file” to keep track which
backups are how many cycles old (since this cannot be inferred from
the dates contained in the directory names). The standard name for
this state file is <tt class="file docutils literal"><span class="pre">.expire_backups.dat</span></tt>. If this file gets
damaged or deleted, <strong class="program">expire_backups</strong> no longer knows the ages
of the backups and refuses to work. In this case you can use the
<tt class="cmdopt docutils literal"><span class="pre">--reconstruct-state</span></tt> option to try to reconstruct the state
from the backup dates. However, the accuracy of this reconstruction
depends strongly on how rigorous you have been with making backups (it
is only completely correct if the time between subsequent backups has
always been exactly the same), so it’s generally a good idea not to
tamper with the state file.</p>
</div>
<div class="section" id="options">
<h2>Options<a class="headerlink" href="#options" title="Permalink to this headline">¶</a></h2>
<p>The <strong class="command">expire_backups</strong> command accepts the following options:</p>
<blockquote>
<div><table class="docutils option-list" frame="void" rules="none">
<col class="option" />
<col class="description" />
<tbody valign="top">
<tr><td class="option-group">
<kbd><span class="option">--quiet</span></kbd></td>
<td>be really quiet</td></tr>
<tr><td class="option-group">
<kbd><span class="option">--debug</span></kbd></td>
<td>activate debugging output</td></tr>
<tr><td class="option-group">
<kbd><span class="option">--version</span></kbd></td>
<td>just print program version and exit</td></tr>
<tr><td class="option-group">
<kbd><span class="option">--state <var><file></var></span></kbd></td>
<td>File to save state information in (default:
”.expire_backups.dat”)</td></tr>
<tr><td class="option-group">
<kbd><span class="option">-n</span></kbd></td>
<td>Dry run. Just show which backups would be deleted.</td></tr>
<tr><td class="option-group" colspan="2">
<kbd><span class="option">--reconstruct-state</span></kbd></td>
</tr>
<tr><td> </td><td>Try to reconstruct a missing state file from backup
dates.</td></tr>
<tr><td class="option-group">
<kbd><span class="option">--use-s3qlrm</span></kbd></td>
<td>Use <tt class="docutils literal"><span class="pre">s3qlrm</span></tt> command to delete backups.</td></tr>
</tbody>
</table>
</div></blockquote>
</div>
<div class="section" id="exit-status">
<h2>Exit Status<a class="headerlink" href="#exit-status" title="Permalink to this headline">¶</a></h2>
<p><strong class="command">expire_backups</strong> returns exit code 0 if the operation succeeded and 1 if some
error occured.</p>
</div>
<div class="section" id="see-also">
<h2>See Also<a class="headerlink" href="#see-also" title="Permalink to this headline">¶</a></h2>
<p><strong class="command">expire_backups</strong> is shipped as part of S3QL, <a class="reference external" href="http://code.google.com/p/s3ql/">http://code.google.com/p/s3ql/</a>.</p>
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