What file and directory permissions to set for database files on Linux?

It's wise to keep your databases in a directory with following permissions (770 in chmod terminology):

drwxrwx--- 2 firebird firebird 1136 2007-05-31 18:21 databases/

If it's a development machine and you wish to be able to manipulate files directly, add yourself to the 'firebird' group. Please note that you usually need to completely log off before the group membership changes are applied to your account on Linux.

As for the database files, use the following privilege (660 in chmod terminology):

-rw-rw---- 1 firebird firebird 6123520 2007-05-14 14:49 database.fdb

This ensures that only the firebird user (typically the one that runs the Firebird server) and members of firebird group (admins on the machine) will be able to access databases directly.

Note that you must give write access for database files, even if users will only run SELECTs. It because each transaction number needs to be recorded in database file.