Permissions can only be changed by the owner (or the superuser).
UGO permissions are suitable for most scenarios. However, IEEE POSIX workgroup was conscious that sometimes they are too limiting and defined an interface in POSIX 1003.1e DRAFT 17 intended to manage file ACLs. That proposal was left out from the standard but is implemented in several BSD (Solaris and FreeBSD 5) and GNU/Linux (as of version 2.6 of the kernel).
ACL allow to set permissions in a per-user or per-group fashion. For instance, it is not feasible in UGO permissions to have two users (bob and alice) where bob can only read, alice can read and write and no other user can access the file.
Traditionally, tools to manage file ACL entries have been setfacl and getfacl. Those are command-line tools and some people can feel uncomfortable using them.
Eiciel allows you to visually edit file ACL entries. You can add and remove users and groups who will be granted permissions through the graphical interface.
After checking you satisfy all the requirements of Eiciel.
$ tar xvfj eiciel-XXX.tar.bz2
$ cd eiciel-XXX
# make install
Don't forget to restart Nautilus. The following command will quit it, but GNOME will restart it again.
$ nautilus -q
For Eiciel 0.7 and later configure needs to know where Nautilus extensions must be installed. It will try to detect it automatically. If the directory is incorrectly guessed you can override it with --with-nautilus-extensions-dir=directory.
For Eiciel 0.6 or former configure needs to know where Bonobo servers must be installed. It will try to detect it automatically. If the directory is incorrectly guessed you can override it with --with-bonobo-dir=directory.