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71 lines
3.8 KiB
HTML
71 lines
3.8 KiB
HTML
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<?xml version="1.0"?>
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<html>
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<body>
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<h1>Hooks for specific system management</h1>
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<p>Libvirt includes synchronous hooks, starting from version 0.8.0, as a
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way to tie in specific tailored system actions at a specific time.
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If these scripts are present on the host where the hypervisor
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is running, then they are called when the libvirt daemon is doingi
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some significant action.</p>
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<p>The scripts are expected to execute quickly, return a zero exit
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status if all conditions are set for the daemon to continue the
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action (non zero will be considered a failure which may
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be ignored but in general will stop the ongoing operation).
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The script also should not call back into libvirt as the daemon
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is waiting for the script exit and deadlock is likely to occur.</p>
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<p>The scripts are stored in the directory <code>/etc/libvirt/hooks/</code>
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when using a standard installation path
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(<code>$SYSCONF_DIR/libvirt/hooks/</code> in general).</p>
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<p>Each script is given the following command line arguments:</p>
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<ul>
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<li> the first argument is the name of the object involved in the
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operation, or '-' if there is none.
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<li> the second argument is the name of the operation.
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<li> the third argument is a suboperation indication like 'start' or
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'end', or '-' if there is none.
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<li> the last argument is an extra argument string or '-' if there
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is none.
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</ul>
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<p>There are currently scripts for 3 domains of operation:
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<ul>
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<li><p><code>/etc/libvirt/hooks/daemon</code> script if
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present is called at 3 points in time:</p>
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<p>at daemon startup, typically started with the following
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arguments:</p>
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<pre>/etc/libvirt/hooks/daemon - start - start</pre>
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<p>at daemon shutdown when it is about to exit, with the following
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arguments:</p>
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<pre>/etc/libvirt/hooks/daemon - shutdown - shutdown</pre>
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<p>When the daemon is asked to reload its driver state when
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receiving the SIGHUP signal, arguments are:</p>
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<pre>/etc/libvirt/hooks/daemon - reload begin SIGHUP</pre>
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</li>
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<li><p><code>/etc/libvirt/hooks/qemu</code> script and <br/>
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<code>/etc/libvirt/hooks/lxc</code> associate hooks for domain
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operation on the respective QEmu/KVM and LXC drivers.</p>
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<p> The domain related hooks also receive the full XML description
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for the concerned domain on their stdin, which allows them to get
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all the information from the domain, including UUID or storage
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if that is needed for the script operation.</p>
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<p> Currently only domain startup and domain end operations
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involve the hook, the first one just before the domain gets
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created.
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For example if starting a QEmu domain named <code>test</code>
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the following script will get called:</p>
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<pre>/etc/libvirt/hooks/qemu test start begin -</pre>
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<p> note that a non-zero return value from the script will abort the
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domain startup operation, and if an error string is passed on
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stderr by the hook script, it will be provided back to the user
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at the libvirt API level.</p>
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<p> For domain shutdown, the script will be called just after the
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domain has finished execution, and the script will get:</p>
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<pre>/etc/libvirt/hooks/qemu test stopped end -</pre>
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<p> It is expected that other operations will be associated to hooks
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but at the time of 0.8.0 only those 2 are associated to the
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domains life cycle</p>
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</li>
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</ul>
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<p></p>
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</body>
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</html>
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