fence_node (8)

fence_node [OPTIONS] nodename

This utility runs a fence agent against nodename. The agent and args are taken from the running cluster configuration based on cluster.conf(5).

fence_node is a wrapper around the libfence functions: fence_node() and unfence_node(). These libfence functions use libccs to read the node fencing configuration, which means that corosync (with cman and ccs) must be running to use fence_node(8).

The fenced(8) daemon is the main user of libfence:fence_node(), and the configuration details for that function are given in the fenced(8) man page.

Fencing vs. Unfencing

The main use for unfencing is with storage/SAN (non-power) agents.

When using power-based fencing agents, the fencing action itself is supposed to turn a node back on after first turning the power off (this happens automatically with a "reboot" action, and needs to be configured explicitly as "off" + "on" otherwise.)

When using storage-based fencing agents, the fencing action is not allowed to re-enable a node after disabling it. Re-enabling a fenced node is only safe once the node has been rebooted. A natural way to re-enable a fenced node's access to storage, is for that node to re-enable the access itself during its startup process. The cman init script calls fence_node -U (nodename defaults to local nodename when unfencing). Unfencing a node without an <unfence> configuration (see below) is a no-op.

The basic differences between fencing and unfencing:

Fencing

1.

libfence: fence_node(), command line: fence_node nodename

2.

Turns off or disables a node.

3.

Agents run with the default action of "off", "disable" or "reboot".

4.

Performed by a cluster node against another node that fails (by the fenced daemon).

Unfencing

1.

libfence: unfence_node(), command line: fence_node -U nodename

2.

Turns on or enables a node.

3.

Agents run with the explicit action of "on" or "enable".

4.

Performed by a cluster node "against" itself during startup (by the cman init script).

-U

Unfence the node, default local node name.

-v

Show fence agent results, -vv to also show agent args.

-h

Print a help message describing available options, then exit.

-V

Print program version information, then exit.

The Unfencing/unfence_node() configuration is very similar to the Fencing/fence_node() configuration shown in fenced(8). Unfencing is only performed for a node with an <unfence> section:

<clusternode name="node1" nodeid="1">
        <fence>
        </fence>
        <unfence>
        </unfence>
</clusternode>

The <unfence> section does not contain <method> sections like the <fence> section does. It contains <device> references directly, which mirror the corresponding device sections for <fence>, with the notable addition of the explicit action of "on" or "enable". The same <fencedevice> is referenced by both fence and unfence <device> lines, and the same per-node args should be repeated.

<clusternode name="node1" nodeid="1">
        <fence>
        <method name="1">
        <device name="myswitch" foo="x"/>
        </method>
        </fence>

        <unfence>
        <device name="myswitch" foo="x" action="on"/>
        </unfence>
</clusternode>

fenced(8)