mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-12-26 15:45:28 +00:00
2a004db6c7
* docs/logging.html[.in] qemud/libvirtd.conf qemud/qemud.c src/logging.[ch]: cleanup the logging code and docs to remove all references to log level 0, cleanup hardcoded values and add a default VIR_LOG_DEFAULT value, patch by Amy Griffis daniel
110 lines
5.3 KiB
XML
110 lines
5.3 KiB
XML
<?xml version="1.0"?>
|
|
<html>
|
|
<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 though the execution of the
|
|
library as well as in the libvirtd daemon.</p>
|
|
<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>log messages: they are information generated at runtime by
|
|
the libvirt code, it 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 begining of the message</li>
|
|
<li>log filters: it's a set of patter and priorities allowing to acept
|
|
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 to capture for example all
|
|
debug messages for the QEmu driver, but otherwise only allow
|
|
errors to show up from other parts</li>
|
|
<li>log outputs: once a message has gone though 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 though syslog.</li>
|
|
</ul>
|
|
<p>The library configuration of logging is though 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 informations</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: allow to define logging filters</li>
|
|
<li>LIBVIRT_LOG_OUTPUTS: allow to define logging outputs</li>
|
|
</ul>
|
|
<p>Similary the daemon logging behaviour can be tuned using 3 config
|
|
variables, stored in the configuration file:
|
|
<ul>
|
|
<li>log_level: accepts the following values:
|
|
<ul>
|
|
<li>4: only errors</li>
|
|
<li>3: warnings and errors</li>
|
|
<li>2: informations, warnings and errors</li>
|
|
<li>1: debug and everything</li>
|
|
</ul></li>
|
|
<li>log_filters: allow to define logging filters</li>
|
|
<li>log_outputs: allow to define logging outputs</li>
|
|
</ul>
|
|
<p>In both case the syntax for filters and outputs is similar.</p>
|
|
<p>The format for a filter is:</p>
|
|
<pre>x:name</pre>
|
|
<p>where <code>name</code> is a match string e.g. <code>remote</code> or
|
|
<code>qemu</code> and the x 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 filter 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>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 everything debugging and informations included in the
|
|
file <code>/tmp/libvirt.log</code></p>
|
|
<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>
|
|
</body>
|
|
</html>
|