Remounting filesystems after enabling ACL's for NFS filesystems

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I currently have a RHEL 5.4 server running as an NFS server. It exports 3 filesystems with the default option in /etc/fstab like this:

/dev/vg-LU99/LU99     /lu99      ext3    defaults        0 0
/dev/vg-U99/U99       /u99       ext3    defaults        0 0
/dev/vg-SYSADMIN/SYSADMIN   /sysadmin   ext3  defaults   0 0

I need to enable ACL's by changing "defaults" to "acl" and then remount.

I need to refresh these mounts on both the nfs server and about 50 clients without a reboot. If I understand correctly, I can run:

> mount -o remount /<mountpoint>

And this will allow the ACL support to the client. But I must also remount the filesystem on the client. I believe I can use the same command on the client for this.

However, these are production systems and downtime/reboots are not possible. I'm concerned about how filehandles and read/write operations are affected during and after the remount.  In particular, are they disrupted, cached. I'm hoping I can simply issue the command above without losing any read/write's. Can anyone help provide a little explaination or point me to the appropriate documentation?


According to the nfs(5) man page:


acl / noacl    Selects whether to use the NFSACL sideband  protocol  on
                      this  mount  point.   The  NFSACL sideband protocol is a
                      proprietary protocol implemented in Solaris that manages
                      Access  Control  Lists. NFSACL was never made a standard
                      part of the NFS protocol specification.


Since you're on RHEL, you should have no support for the NFSACL sideband protocol, so using the 'acl' option on your fstab should be of no use.


Regarding the /etc/exports file, the exports(5) man page mentions that:


The default is to export with  ACL  support  (i.e. by default, no_acl is off)


So, no need to change anything in /etc/exports.


What you should do is:

  1. Server: Enable ACLs on NFS's back-end filesystem.
  2. Server: Restart the nfsd or nfs-server service.
  3. Clients: Unmount then mount the NFS export(s).


By doing this, you ensure that both your NFS server and all your NFS clients are aware of the presence of ACLs on NFS's back-end filesystem.