Sbd

You want to use the sbd command. The description is

sbd <options> <command> <cmdarguments>

ok what does this mean

# sbd -d /dev/sdb list
0       vm1     clear
1       vm2     reset   vm1

Still this does not work:

sbd -d /dev/sdb message reset vm1

despite:

message <node> (test|reset|off|clear|exit)
                Writes the specified message to node's slot.