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+<html>
+ <body>
+ <h1>Hooks for specific system management</h1>
+ <p>Libvirt includes synchronous hooks, starting from version 0.8.0, as a
+ way to tie in specific tailored system actions at a specific time.
+ If these scripts are present on the host where the hypervisor
+ is running, then they are called when the libvirt daemon is doingi
+ some significant action.</p>
+ <p>The scripts are expected to execute quickly, return a zero exit
+ status if all conditions are set for the daemon to continue the
+ action (non zero will be considered a failure which may
+ be ignored but in general will stop the ongoing operation).
+ The script also should not call back into libvirt as the daemon
+ is waiting for the script exit and deadlock is likely to occur.</p>
+ <p>The scripts are stored in the directory <code>/etc/libvirt/hooks/</code>
+ when using a standard installation path
+ (<code>$SYSCONF_DIR/libvirt/hooks/</code> in general).</p>
+ <p>Each script is given the following command line arguments:</p>
+ <ul>
+ <li> the first argument is the name of the object involved in the
+ operation, or '-' if there is none.
+ <li> the second argument is the name of the operation.
+ <li> the third argument is a suboperation indication like 'start' or
+ 'end', or '-' if there is none.
+ <li> the last argument is an extra argument string or '-' if there
+ is none.
+ </ul>
+ <p>There are currently scripts for 3 domains of operation:
+ <ul>
+ <li><p><code>/etc/libvirt/hooks/daemon</code> script if
+ present is called at 3 points in time:</p>
+ <p>at daemon startup, typically started with the following
+ arguments:</p>
+ <pre>/etc/libvirt/hooks/daemon - start - start</pre>
+ <p>at daemon shutdown when it is about to exit, with the following
+ arguments:</p>
+ <pre>/etc/libvirt/hooks/daemon - shutdown - shutdown</pre>
+ <p>When the daemon is asked to reload its driver state when
+ receiving the SIGHUP signal, arguments are:</p>
+ <pre>/etc/libvirt/hooks/daemon - reload begin SIGHUP</pre>
+ </li>
+ <li><p><code>/etc/libvirt/hooks/qemu</code> script and <br/>
+ <code>/etc/libvirt/hooks/lxc</code> associate hooks for domain
+ operation on the respective QEmu/KVM and LXC drivers.</p>
+ <p> The domain related hooks also receive the full XML description
+ for the concerned domain on their stdin, which allows them to get
+ all the information from the domain, including UUID or storage
+ if that is needed for the script operation.</p>
+ <p> Currently only domain startup and domain end operations
+ involve the hook, the first one just before the domain gets
+ created.
+ For example if starting a QEmu domain named <code>test</code>
+ the following script will get called:</p>
+ <pre>/etc/libvirt/hooks/qemu test start begin -</pre>
+ <p> note that a non-zero return value from the script will abort the
+ domain startup operation, and if an error string is passed on
+ stderr by the hook script, it will be provided back to the user
+ at the libvirt API level.</p>
+ <p> For domain shutdown, the script will be called just after the
+ domain has finished execution, and the script will get:</p>
+ <pre>/etc/libvirt/hooks/qemu test stopped end -</pre>
+ <p> It is expected that other operations will be associated to hooks
+ but at the time of 0.8.0 only those 2 are associated to the
+ domains life cycle</p>
+ </li>
+ </ul>
+ <p></p>
+ </body>
+</html>
projects / thirdparty / libvirt.git / commitdiff
