Thanks to all who anserwerd. My UPSs are not APC compliant, so I'm stuck
with this linux binary (for which I don't have sources, of course :().
Howerver I found in Simon Gerraty's scripts an interesting part: the stty
command to setup the serial line. I added it to my startup script, along
with a few 'echo' to send some breaks and random characters on the
serial line (this seems necessary, maybe to get the UPS auto-detect the
serial line speed ?) and now the daemon starts reliably !
it's still looks like an ugly hack, however :)

--
Manuel Bouyer, LIP6, Universite Paris VI.           Manuel.Bouyer@lip6.fr
--