READMeよめばいいじゃん

If you want a "preferred" master to always be the master (even if another
host is already the master), add the preempt switch (--preempt or -P) and
assign a shorter interval via the advertisement base (--advbase or -b) an
skew (--advskew or -k).  This will cause the preferred node to ignore a
master who is advertising a longer interval and promote itself to master.
The old master will quickly hear the preferred node advertising a shorter
interval and immediately demote itself.


--shutdown (-z) will run the downscript at exit, unless ucarp is already in
the backup state.