[Voyage-linux] when remountro fails

[tictacbum]

Hello,
I have a voyage 0.8 installation, sometimes when I try to remountro it
fails showing "/ is busy", specially if I had it mounted rw for a
while (for example to apt-get upgrade)
when I get this I try to stop all services running, until I don't know
what more to stop, ps aux is almost empty, and I can't recognize any
process to stop with lsof
I tryed to stop sshd and login from terminal too, finally what I do is
a reboot...
how can I find which process keeps / busy?

regards,
Lluís