Configuring the NFS automounter

How automount works

``Configuring the Network File System (NFS)'', explains how to mount remote filesystems on an NFS client using the conventional NFS mounting approach whose major characteristics are:

Automatic mounting at boot time.
Manual mounting if mounting is required after boot time.

automount provides an alternative approach that mounts filesystems automatically, but not until they are needed.

Filesystem mounting: conventional vs. automount

Conventional method automount method

Mounts occur automatically and transparently at boot time or manually thereafter. Mounts occur automatically and transparently when a user tries to access any files or directories under the designated mount point of the remote filesystem to be mounted.

Mounts must be removed manually, or during system reboot. Mounts are removed automatically when the contents of the mounted filesystem have not been used for a specified period of time.

To manually access mounts, users must use the mount and umount commands. (In both conventional and automount methods, all user mounts must be preconfigured by the system administrator). Users have transparent mount access; the mounts are automatically triggered when the user uses a command like cd to access files or directories that are actually on a remote filesystem. (In both conventional and automount methods, all user mounts must be preconfigured by the system administrator).

New links can be added at any time by the system administrator. New links cannot be manually added and made active without rebooting automount.

Only one NFS server may be designated as the source of a filesystem, so mounts fail if that server is unavailable. One or more NFS servers may be designated as the source of a filesystem. This redundancy means that if one server is unavailable, the mount may be obtained from another.

Service is primarily provided by the mount(ADM) and umount commands. Service primarily provided by the automount(NADM) command.

Files used are /etc/default/filesys for configuring automatic mounts at boot time; /etc/mnttab for a listing of all the currently mounted filesystems. Files used are a variety of maps for configuring automatic mounts; /etc/mnttab for a listing of all the currently mounted filesystems. (see ``The mount table'' for more information).

Conventional method	automount method
Mounts occur automatically and transparently at boot time or manually thereafter.	Mounts occur automatically and transparently when a user tries to access any files or directories under the designated mount point of the remote filesystem to be mounted.
Mounts must be removed manually, or during system reboot.	Mounts are removed automatically when the contents of the mounted filesystem have not been used for a specified period of time.
To manually access mounts, users must use the mount and umount commands. (In both conventional and automount methods, all user mounts must be preconfigured by the system administrator).	Users have transparent mount access; the mounts are automatically triggered when the user uses a command like cd to access files or directories that are actually on a remote filesystem. (In both conventional and automount methods, all user mounts must be preconfigured by the system administrator).
New links can be added at any time by the system administrator.	New links cannot be manually added and made active without rebooting automount.
Only one NFS server may be designated as the source of a filesystem, so mounts fail if that server is unavailable.	One or more NFS servers may be designated as the source of a filesystem. This redundancy means that if one server is unavailable, the mount may be obtained from another.
Service is primarily provided by the mount(ADM) and umount commands.	Service primarily provided by the automount(NADM) command.
Files used are /etc/default/filesys for configuring automatic mounts at boot time; /etc/mnttab for a listing of all the currently mounted filesystems.	Files used are a variety of maps for configuring automatic mounts; /etc/mnttab for a listing of all the currently mounted filesystems. (see ``The mount table'' for more information).

NOTE: The differences between these two approaches apply only to the client side of NFS mounting. With both approaches, the server must be configured to export the filesystems the client wants to mount and be configured to let that client mount those filesystems.

In summary, the benefits of automount are:

Booting time is significantly reduced because no mounting is done at boot time.
Network access and efficiency are improved by reducing the number of permanently active mount points.
Failed mount requests can be reduced by designating alternate servers as the source of a filesystem.

The one possible drawback to automount is:

Adding new mounts manually requires rebooting, unlike the conventional method.

Therefore, if you know you will regularly need to add new mounts, you may want to consider the relative benefits and drawbacks of both systems for your needs.