Some thoughts on NFS

December 23, 2013

In the last weeks I was working (from time to time 😉 ) on a new setup of my NAS at home. During this I learn some stuff I didn’t know about NFS which I want to share here. I assume that you got the basis NFS stuff working or know how it works and want some addition tips and ticks

1. How to query a NFS server for the exported directories and the settings? Easy, use showmount -e <servername>. Here an example:
   $ showmount -e 10.x.x.x
Export list for 10.x.x.x:
/data/home                   10.x.x.0/255.255.255.0
2. Use fsid – why?
   1. NFS needs to be able to identify each filesystem that it exports.  Normally it will use a UUID for the filesystem (if the filesystem has such a thing) or the device number of the device holding the filesystem (if  the  filesystem is stored on the device). If you want to an export different file system (e.g. replacement HDD) the fsid changes and you’re clients have to remount (as they have a stale NFS mount). Read more on this topic here.
   2. Some file systems don’t have a UUID, e.g. encfs does not … use a separate fsid for each export!
3. You can export multiple file system with one mount request by the client, if you use nohide. Normally, if a server exports two file systems one of which is mounted on the other, then the client will have to mount both file systems explicitly to  get access to them.  If it just mounts the parent, it will see an empty directory at the place where the other file system is mounted.  That file system is “hidden” – if you don’t want that use nohide, like in this example:
   /data/media     10.x.x.0/255.255.255.0(fsid=1,rw,async,no_subtree_check)
/data/media/movies     10.x.x.0/255.255.255.0(fsid=2,rw,async,no_subtree_check,nohide)
4. If you changed /etc/exports you don’t need to restart your NFS daemon. If the init script provides a reload thats good – if not use exportfs -rav.

So far  that are my new learned tips and tricks … I think there was one more but I can’t remember it now. Will add it later if I remember.

 

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