[fhs-discuss] static sharable files

Tollef Fog Heen tfheen at err.no
Mon May 9 00:33:48 PDT 2011


]] Bruce Dubbs 

| Currently the FHS has a discussion in Chapter 2 about sharable and 
| unsharable files that are static or dynamic.
| 
| The example shows /usr as a prototypical static, shared directory.  The 
| implication is that /usr can be mounted from a remote host.
| 
| The problem is that /usr has become a place that is necessary before a 
| network mount is available.  For instance, if an administrator finds it 
| necessary to use lspci, or lsusb before the networked /usr is mounted, 
| the pci.ids and usb.ids files are not available.

I think
http://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
is relevant in this context.

| Where then, should a program store auxiliary data files that may be 
| needed before any networking is configured?  Candidates from the current 
| top level programs include /bin, /boot, /dev, /lib, /root, and /sbin. 
| None of these seems appropriate.
| 
| Perhaps a subdirectory hierarchy in /lib, say /lib/data/<package>/ may 
| be appropriate, but that goes against the current definition of /lib 
| that says: 'Essential shared libraries and kernel modules'.
| 
| Another option is yet another top level directory, but that is unappealing.

Another option is to deprecate or disallow /usr not being on the root
file system.

Separate /usr made sense back when drives were small and disk space was
expensive, but in the vast majority of cases today, having /usr on the
root file system is no real burden.  Not having it on the root file
system means more brittle setups and trying to share /usr between
installations can easily lead to maintenance headaches.

Separate /usr makes sense is in the embedded case where you are
seriously space-restricted and you might want have your OS on fast flash
and the apps and user data on cheaper, but slower flash.  In those
cases, I'd suggest putting apps in /opt rather than the more common
/usr.

Regards,
-- 
Tollef Fog Heen
UNIX is user friendly, it's just picky about who its friends are


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