Fabrice,

> So: which files must be writable?

For sure:

1) the log file, named firebird.log
2) the security file, named security.fbk
3) the lock file.

This one I will need assistance too. I don't have 1.5 on a *nux machine yet.
Firebird 1 will need isc_lockXX.YourHostName. I notice some more files open
for the guardian, and some other If you use the guardian, there will be
additional files for it in Linux.

I hope this helps,

Artur