19.4 Configuring the Automounter

The software described in this documentation is either in Extended Support or Sustaining Support. See https://www.oracle.com/us/support/library/enterprise-linux-support-policies-069172.pdf for more information.
Oracle recommends that you upgrade the software described by this documentation as soon as possible.

19.4 Configuring the Automounter

The automounter mounts file systems when they are accessed, rather than maintaining connections for those mounts at all times. When a file system becomes inactive for more than a certain period of time, the automounter unmounts it. Using automounting frees up system resources and improves system performance.

The automounter consists of two components: the autofs kernel module and the automount user-space daemon.

To configure a system to use automounting:

Install the autofs package and any other packages that are required to support remote file systems:
```
# yum install autofs
```
Edit the /etc/auto.master configuration file to define map entries. Each map entry specifies a mount point and a map file that contains definitions of the remote file systems that can be mounted, for example:
```
/-          /etc/auto.direct
/misc       /etc/auto.misc
/net        -hosts
```
Here, the /-, /misc, and /net entries are examples of a direct map, an indirect map, and a host map respectively. Direct map entries always specify /- as the mount point. Host maps always specify the keyword -hosts instead of a map file.
A direct map contains definitions of directories that are automounted at the specified absolute path. In the example, the auto.direct map file might contain an entry such as:
```
/usr/man   -fstype=nfs,ro,soft             host01:/usr/man
```
This entry mounts the file system /usr/man exported by host01 using the options ro and soft, and creates the /usr/man mount point if it does not already exist. If the mount point already exists , the mounted file system hides any existing files that it contains.
As the default file system type is NFS, the previous example can be shortened to read:
```
/usr/man   -ro,soft                        host01:/usr/man
```
An indirect map contains definitions of directories (keys) that are automounted relative to the mount point (/misc) specified in /etc/auto.master. In the example, the /etc/auto.misc map file might contain entries such as the following:
```
xyz       -ro,soft                         host01:/xyz
cd        -fstype=iso9600,ro,nosuid,nodev        :/dev/cdrom
abc       -fstype=ext3                           :/dev/hda1
fenetres  -fstype=cifs,credentials=credfile      ://fenetres/c
```
The /misc directory must already exist, but the automounter creates a mount point for the keys xyz, cd , and so on if they does not already exist, and removes them when it unmounts the file system. For example, entering a command such as ls /misc/xyz causes the automounter to the mount the /xyz directory exported by host01 as /misc/xyz.
The cd and abc entries mount local file systems: an ISO image from the CD-ROM drive on /misc/cd and an ext3 file system from /dev/hda1 on /misc/abc. The fenetres entry mounts a Samba share as /misc/fenetres.
If a host map entry exists and a command references an NFS server by name relative to the mount point (/net), the automounter mounts all directories that the server exports below a subdirectory of the mount point named for the server. For example, the command cd /net/host03 causes the automounter to mount all exports from host03 below the /net/host03 directory. By default, the automounter uses the mount options nosuid,nodev,intr options unless you override the options in the host map entry, for example:
```
/net        -hosts    -suid,dev,nointr
```
Note
The name of the NFS server must be resolvable to an IP address in DNS or in the /etc/hosts file.
For more information, including details of using maps with NIS, NIS+, and LDAP, see the hosts.master(5) manual page.
Start the autofs service, and configure the service to start following a system reboot:
```
# service autofs start
# chkconfig autofs on
```

You can configure various settings for autofs in /etc/sysconfig/autofs, such as the idle timeout value after which a file system is automatically unmounted.

If you modify /etc/auto.master or /etc/sysconfig/autofs, restart the autofs service to make it re-read these files:

# service autofs restart

For more information, see the automount(8), autofs(5), and auto.master(5) manual pages.