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+ <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:
+ </p>
+ <ul><li>log_level: accepts the following values:
+ <ul><li>0: no logging at all</li><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>
+ </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>0: everything</li><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 0: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="0: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>
+ </div>
+ </div>
+ <div id="footer">
+ <p id="sponsor">
+ Sponsored by:<br /><a href="http://et.redhat.com/"><img src="et.png" alt="Project sponsored by Red Hat Emerging Technology" /></a></p>
+ </div>
+ </body>
+</html>
--- /dev/null
+<?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>0: no logging at all</li>
+ <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>0: everything</li>
+ <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 0: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="0: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>
projects / thirdparty / libvirt.git / commitdiff
