This is the web page of a project that originally was Linux-related, but has collected much information about the "traditional" Unix filesystem layout:
http://www.pathname.com/fhs/In short:
/etc is for configuration files
/usr is for things that are not essential for system boot and single user mode (= almost everything). In a diskless NFS environment, it should be possible to share a single copy of /usr directory tree to multiple client hosts, assuming that all the hosts are using the same hardware architecture. The /usr hierarchy might be mounted read-only in a diskless NFS environment, so any well-behaved user-level applications should not assume they can write to /usr.
NOTE: /usr/local is the traditional place for sysadmin's own local customizations.
/var is for "variable data" that is usually host-specific.
/opt is for "add-on software packages", although HP-UX comes with quite a lot of stuff in /opt as standard, probably for historical reasons. In HP-UX, anything installed in /opt/
should put its configuration to /etc/opt/ and any data files it generates should go in /var/opt/ respectively.
In my opinion, when the system is in normal use, there should be no significant growth of disk space use in neither /usr nor /opt. Only software updates and new installations should cause additional disk space consumption in these filesystems. Unfortunately, not all software packages are quite that well-behaved.
MK
MK
