Unmount stale NFS mounts

If you have a stale NFS mount hanging on your system it can cause various programs and utilities to fail. A typical symptom is a hang when using the 'df' command.

In such cases you cant do umount /path/to/stale/nfs because it will say "the device is busy" or words to that effect

To fix this you can unmount it with the 'lazy' option;

umount -l /path/to/stale/nfs

If you don't expect that mount point to ever be available again (for example the nfs server was decommissioned) then make sure you adjust /etc/fstab accordingly.

HOWTO: Setup an NFS server and client for LDAP

In this example I am going to setup a shared home directory to hold user homes. You would typically use this if you are using a centralised LDAP server to authenticate users.

Pre-requisites:
A standard Ubuntu server with working network and pingable by name.

You have relocated your local "sudo" user out of the default /home directory.

Configure the Server.

Note:

We are going to use an NFS server to centrally locate our users home directories. Build or select one of your existing Ubuntu servers to act as the host.

My server is called nfs.tuxnetworks.com and I have made sure that it can be pinged by name by my LAN clients.

Login to your NFS server as root;

Install the server software;

~# apt-get install nfs-kernel-server

Create a folder for the user home directories;

~# mkdir -p /store/ldaphomes

To export the directory edit your exports file;

~# vi /etc/exports/

Add this line;

/store/ldaphomes          *(rw,sync,no_subtree_check,no_root_squash)

Restart the NFS server;

~# service nfs-kernel-server restart

Configure the Client.

Install the NFS client;

~# apt-get install nfs-common

We are going to mount our NFS share on /home;

Note:

If you have any home directories in /home, these will become hidden under the mounted directory. Ideally there will be no existing users in /home because you will have shifted your local admin user somewhere else.

Edit your fstab file;

~$ sudo vi /etc/fstab

Add a line like this;

nfs.tuxnetworks.com:/store/ldaphomes      /home  nfs defaults 0 0

Note:

If your /home directory was already being mounted to a block device then you should comment this entry out in your fstab file.

Mount the directory;

~$ sudo mount /home

You can check that it has worked using the df command

nfs:/exports/ldaphomes
                     961432576 153165824 759428608  17% /home

And thats it!