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<table class="head">
<tr>
<td class="head-ltitle">CRASH(8)</td>
<td class="head-vol">System Manager's Manual</td>
<td class="head-rtitle">CRASH(8)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">crash</code> — <span class="Nd">FreeBSD
system failures</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">This section explains a bit about system crashes and (very
briefly) how to analyze crash dumps.</p>
<p class="Pp">When the system crashes voluntarily it prints a message of the
form</p>
<dl class="Bl-diag Bd-indent">
<dt>panic: why i gave up the ghost</dt>
<dd></dd>
</dl>
<p class="Pp">on the console, and if dumps have been enabled (see
<a class="Xr">dumpon(8)</a>), takes a dump on a mass storage peripheral, and
then invokes an automatic reboot procedure as described in
<a class="Xr">reboot(8)</a>. Unless some unexpected inconsistency is
encountered in the state of the file systems due to hardware or software
failure, the system will then resume multi-user operations.</p>
<p class="Pp">The system has a large number of internal consistency checks; if
one of these fails, then it will panic with a very short message indicating
which one failed. In many instances, this will be the name of the routine
which detected the error, or a two-word description of the inconsistency. A
full understanding of most panic messages requires perusal of the source
code for the system.</p>
<p class="Pp">The most common cause of system failures is hardware failure,
which can reflect itself in different ways. Here are the messages which are
most likely, with some hints as to causes. Left unstated in all cases is the
possibility that hardware or software error produced the message in some
unexpected way.</p>
<p class="Pp"></p>
<dl class="Bl-diag Bl-compact">
<dt>Mounting from <device> failed with error <err></dt>
<dd>The system was unable to mount the configured root filesystem. Either the
root filesystem has been corrupted, or the system is attempting to use the
wrong device as root filesystem.
<p class="Pp" id="mountroot_">This is not a panic message; rather it is
followed by an interactive
<a class="permalink" href="#mountroot_"><b class="Sy">mountroot></b></a>
prompt where the operator can list detected devices and filesystems, and
select an alternative root filesystem to mount. Alternatively, the
system can be booted from recovery media to repair the situation. The
system install media provides a live environment which is suitable for
this task.</p>
<p class="Pp"></p>
</dd>
<dt>init: not found</dt>
<dd>This is not a panic message, as reboots are likely to be futile. Late in
the bootstrap procedure, the system was unable to locate and execute the
initialization process, <a class="Xr">init(8)</a>. The root file system is
incorrect or has been corrupted, or the mode or type of
<span class="Pa">/sbin/init</span> forbids execution or is totally
missing.
<p class="Pp"></p>
</dd>
<dt>ffs_realloccg: bad optim</dt>
<dd></dd>
<dt>ffs_valloc: dup alloc</dt>
<dd></dd>
<dt>ffs_alloccgblk: cyl groups corrupted</dt>
<dd></dd>
<dt>ffs_alloccg: map corrupted</dt>
<dd></dd>
<dt>blkfree: freeing free block</dt>
<dd></dd>
<dt>blkfree: freeing free frag</dt>
<dd></dd>
<dt>ifree: freeing free inode</dt>
<dd>These panic messages are among those that may be produced when file system
inconsistencies are detected. The problem generally results from a failure
to repair damaged file systems after a crash, hardware failures, or other
condition that should not normally occur. A file system check will
normally correct the problem.
<p class="Pp"></p>
</dd>
<dt>init died (signal #, exit #)</dt>
<dd>The system initialization process has exited with the specified signal
number and exit code. This is bad news, as no new users will then be able
to log in. Rebooting is the only fix, so the system just does it right
away.</dd>
</dl>
<p class="Pp">That completes the list of panic types you are likely to see.</p>
<p class="Pp">If the system has been configured to take crash dumps (see
<a class="Xr">dumpon(8)</a>), then when it crashes it will write (or at
least attempt to write) an image of memory into the back end of the dump
device, usually the same as the primary swap area. After the system is
rebooted, the program <a class="Xr">savecore(8)</a> runs and preserves a
copy of this core image and the current system in a specified directory for
later perusal. See <a class="Xr">savecore(8)</a> for details.</p>
<p class="Pp">To analyze a dump you should begin by running
<a class="Xr">kgdb(1)</a> (<span class="Pa">ports/devel/gdb</span>) on the
system load image and core dump. If the core image is the result of a panic,
the panic message is printed. For more details consult the chapter on kernel
debugging in the <i class="RsB">FreeBSD Developers' Handbook</i>
(<span class="Pa">https://www.freebsd.org/doc/en/books/developers-handbook/</span>).</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">kgdb(1)</a>
(<span class="Pa">ports/devel/gdb</span>), <a class="Xr">dumpon(8)</a>,
<a class="Xr">reboot(8)</a>, <a class="Xr">savecore(8)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">crash</code> manual page first appeared in
<span class="Ux">FreeBSD 2.2</span>.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">July 25, 2025</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
