mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-12-23 14:15:28 +00:00
190 lines
9.1 KiB
XML
190 lines
9.1 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|
<body>
|
|
<h1 >Logging in the library and the daemon</h1>
|
|
<p>Libvirt includes logging facilities starting from version 0.6.0,
|
|
this complements the <a href="errors.html">error handling</a>
|
|
mechanism and APIs to allow tracing through the execution of the
|
|
library as well as in the libvirtd daemon.</p>
|
|
<ul>
|
|
<li>
|
|
<a href="#log_library">Logging in the library</a>
|
|
</li>
|
|
<li>
|
|
<a href="#log_config">Configuring logging in the library</a>
|
|
</li>
|
|
<li>
|
|
<a href="#log_daemon">Logging in the daemon</a>
|
|
</li>
|
|
<li>
|
|
<a href="#log_syntax">Syntax for filters and output values</a>
|
|
</li>
|
|
<li>
|
|
<a href="#log_examples">Examples</a>
|
|
</li>
|
|
</ul>
|
|
<h3>
|
|
<a name="log_library">Logging in the library</a>
|
|
</h3>
|
|
<p>The logging functionalities in libvirt are based on 3 key concepts,
|
|
similar to the one present in other generic logging facilities like
|
|
log4j:</p>
|
|
<ul>
|
|
<li><b>log messages</b>: they are information generated at runtime by
|
|
the libvirt code. Each message includes a priority level (DEBUG = 1,
|
|
INFO = 2, WARNING = 3, ERROR = 4), a category, function name and
|
|
line number, indicating where it originated from, and finally
|
|
a formatted message. In addition the library adds a timestamp
|
|
at the beginning of the message</li>
|
|
<li><b>log filters</b>: a set of patterns and priorities to accept
|
|
or reject a log message. If the message category matches a filter,
|
|
the message priority is compared to the filter priority, if lower
|
|
the message is discarded, if higher the message is output. If
|
|
no filter matches, then a general priority level is applied to
|
|
all remaining messages. This allows, for example, capturing all
|
|
debug messages for the QEmu driver, but otherwise only allowing
|
|
errors to show up from other parts.</li>
|
|
<li><b>log outputs</b>: once a message has gone through filtering a set of
|
|
output defines where to send the message, they can also filter
|
|
based on the priority, for example it may be useful to output
|
|
all messages to a debugging file but only allow errors to be
|
|
logged through syslog.</li>
|
|
</ul>
|
|
<p>Note that the logging module saves all logs to a <b>debug buffer</b>
|
|
filled in a round-robin fashion as to keep a full log of the
|
|
recent logs including all debug. The debug buffer can be resized
|
|
or deactivated in the daemon using the log_buffer_size variable,
|
|
default is 64 kB. This can be used when debugging the library
|
|
(see the virLogBuffer variable content).</p>
|
|
|
|
<h3>
|
|
<a name="log_config">Configuring logging in the library</a>
|
|
</h3>
|
|
<p>The library configuration of logging is through 3 environment variables
|
|
allowing to control the logging behaviour:</p>
|
|
<ul>
|
|
<li>LIBVIRT_DEBUG: it can take the four following values:
|
|
<ul>
|
|
<li>1 or "debug": asking the library to log every message emitted,
|
|
though the filters can be used to avoid filling up the output</li>
|
|
<li>2 or "info": log all non-debugging information</li>
|
|
<li>3 or "warn": log warnings and errors, that's the default value</li>
|
|
<li>4 or "error": log only error messages</li>
|
|
</ul></li>
|
|
<li>LIBVIRT_LOG_FILTERS: defines logging filters</li>
|
|
<li>LIBVIRT_LOG_OUTPUTS: defines logging outputs</li>
|
|
</ul>
|
|
<p>Note that, for example, setting LIBVIRT_DEBUG= is the same as unset. If
|
|
you specify an invalid value, it will be ignored with a warning. If you
|
|
have an error in a filter or output string, some of the settings may be
|
|
applied up to the point at which libvirt encountered the error.</p>
|
|
<h3>
|
|
<a name="log_daemon">Logging in the daemon</a>
|
|
</h3>
|
|
<p>Similarly the daemon logging behaviour can be tuned using 3 config
|
|
variables, stored in the configuration file:</p>
|
|
<ul>
|
|
<li>log_level: accepts the following values:
|
|
<ul>
|
|
<li>4: only errors</li>
|
|
<li>3: warnings and errors</li>
|
|
<li>2: information, warnings and errors</li>
|
|
<li>1: debug and everything</li>
|
|
</ul></li>
|
|
<li>log_filters: defines logging filters</li>
|
|
<li>log_outputs: defines logging outputs</li>
|
|
</ul>
|
|
<p>When starting the libvirt daemon, any logging environment variable
|
|
settings will override settings in the config file. Command line options
|
|
take precedence over all. If no outputs are defined for libvirtd, it
|
|
defaults to logging to /var/log/libvirt/libvirtd.log (before 0.9.0
|
|
it was using syslog) when it is running as a daemon, or to
|
|
stderr when it is running in the foreground.</p>
|
|
<p>Libvirtd does not reload its logging configuration when issued a SIGHUP.
|
|
If you want to reload the configuration, you must do a <code>service
|
|
libvirtd restart</code> or manually stop and restart the daemon
|
|
yourself.</p>
|
|
<p>Starting from 0.9.0, the daemon can save all the content of the debug
|
|
buffer to the defined error channels (or /var/log/libvirt/libvirtd.log
|
|
by default) in case of crash, this can also be activated explicitly
|
|
for debugging purposes by sending the daemon a USR2 signal:</p>
|
|
<pre>killall -USR2 libvirtd</pre>
|
|
<h3>
|
|
<a name="log_syntax">Syntax for filters and output values</a>
|
|
</h3>
|
|
<p>The syntax for filters and outputs is the same for both types of
|
|
variables.</p>
|
|
<p>The format for a filter is one of:</p>
|
|
<pre>
|
|
x:name (log message only)
|
|
x:+name (log message + stack trace)</pre>
|
|
<p>where <code>name</code> is a string which is matched against source
|
|
file name, e.g., <code>remote</code>, <code>qemu</code>, or
|
|
<code>util/json</code>, the optional <code>+</code> prefix tells libvirt
|
|
to log stack trace for each message matching <code>name</code>, and
|
|
<code>x</code> is the minimal level where matching messages should
|
|
be logged:</p>
|
|
<ul>
|
|
<li>1: DEBUG</li>
|
|
<li>2: INFO</li>
|
|
<li>3: WARNING</li>
|
|
<li>4: ERROR</li>
|
|
</ul>
|
|
<p>Multiple filters can be defined in a single string, they just need to be
|
|
separated by spaces, e.g: <code>"3:remote 4:event"</code> to only get
|
|
warning or errors from the remote layer and only errors from the event
|
|
layer.</p>
|
|
<p>If you specify a log priority in a filter that is below the default log
|
|
priority level, messages that match that filter will still be logged,
|
|
while others will not. In order to see those messages, you must also have
|
|
an output defined that includes the priority level of your filter.</p>
|
|
<p>The format for an output can be one of those 3 forms:</p>
|
|
<ul>
|
|
<li><code>x:stderr</code> output goes to stderr</li>
|
|
<li><code>x:syslog:name</code> use syslog for the output and use the
|
|
given <code>name</code> as the ident</li>
|
|
<li><code>x:file:file_path</code> output to a file, with the given
|
|
filepath</li>
|
|
</ul>
|
|
<p>In all cases the x prefix is the minimal level, acting as a filter:</p>
|
|
<ul>
|
|
<li>1: DEBUG</li>
|
|
<li>2: INFO</li>
|
|
<li>3: WARNING</li>
|
|
<li>4: ERROR</li>
|
|
</ul>
|
|
<p>Multiple output can be defined, they just need to be separated by
|
|
spaces, e.g.: <code>"3:syslog:libvirtd 1:file:/tmp/libvirt.log"</code>
|
|
will log all warnings and errors to syslog under the libvirtd ident
|
|
but also log all debug and information included in the
|
|
file <code>/tmp/libvirt.log</code></p>
|
|
<h3>
|
|
<a name="log_examples">Examples</a>
|
|
</h3>
|
|
<p>For example setting up the following:</p>
|
|
<pre>export LIBVIRT_DEBUG=1
|
|
export LIBVIRT_LOG_OUTPUTS="1:file:virsh.log"</pre>
|
|
<p>and then running virsh will accumulate the logs in the
|
|
<code>virsh.log</code> file in a way similar to:</p>
|
|
<pre>14:29:04.771: debug : virInitialize:278 : register drivers
|
|
14:29:04.771: debug : virRegisterDriver:618 : registering Test as driver 0</pre>
|
|
<p>the messages are timestamped, there is also the level recorded,
|
|
if debug the name of the function is also printed and then the formatted
|
|
message. This should be sufficient to at least get a precise idea of
|
|
what is happening and where things are going wrong, allowing to then
|
|
put the correct breakpoints when running under a debugger.</p>
|
|
<p>To activate full debug of the libvirt entry points, utility
|
|
functions and the QEmu/KVM driver, set:</p>
|
|
<pre>log_filters="1:libvirt 1:util 1:qemu"
|
|
log_outputs="1:file:/var/log/libvirt/libvirtd.log"</pre>
|
|
<p>in libvirtd.conf and restart the daemon will allow to
|
|
gather a copious amount of debugging traces for the operations done
|
|
in those areas.</p>
|
|
<p>On the other hand to deactivate the logbuffer in the daemon
|
|
for stable high load servers, set</p>
|
|
<pre>log_buffer_size=0</pre>
|
|
<p>in the libvirtd.conf.</p>
|
|
</body>
|
|
</html>
|