/etc/auto.master

The /etc/auto.master file is a configuration file for the autofs service on Unix-like systems. autofs is a service used to automatically mount filesystems when they are accessed and to unmount them when they are no longer needed. This can be useful for managing network shares and other filesystems without manually mounting them.

Structure and Purpose of /etc/auto.master

The /etc/auto.master file defines the mount points and their associated maps (or configuration files) for autofs. It specifies where to look for additional map files that define the details of the filesystems to be mounted.

File Format

The /etc/auto.master file consists of a list of lines where each line represents a mount point and the map file associated with it. The basic syntax is:

<mount_point> <map_file> [options]

• <mount_point>: The directory where the filesystem or share will be mounted.

• <map_file>: The path to the map file or configuration file that contains the details of what should be mounted at <mount_point>.

• [options]: Optional parameters to control the behavior of autofs for that mount point.

Example /etc/auto.master Entries

Basic Example

/mnt/auto /etc/auto.misc

In this example:

• /mnt/auto is the mount point where filesystems will be mounted.

• /etc/auto.misc is the map file that contains the details for the filesystems to be mounted under /mnt/auto.

Example with Options

/home /etc/auto.home --timeout=60 --ghost

In this example:

• /home is the mount point.

• /etc/auto.home is the map file.

• --timeout=60 specifies that filesystems should be unmounted after 60 seconds of inactivity.

• --ghost ensures that empty directories are created for the mount points even if the filesystem is not currently mounted.

Related Map Files

The map files specified in /etc/auto.master define what should be mounted at each mount point. For example, the /etc/auto.misc file might contain entries like:

# /etc/auto.misc
share -fstype=nfs,rw,soft server:/path/to/share

In this map file:

• share is the directory under /mnt/auto where the NFS share will be mounted.

• -fstype=nfs,rw,soft specifies the filesystem type (NFS), read-write mode, and soft mount options.

• server:/path/to/share is the network path to the NFS share.

Key Points

• Dynamic Mounting: autofs dynamically mounts filesystems when accessed and unmounts them after a period of inactivity.

• Flexibility: Allows for easy configuration of multiple mount points and filesystems.

• Map Files: Define specific details for each mount point, such as filesystem type and mount options.

Summary

The /etc/auto.master file is a critical component in configuring the autofs service. It provides a centralized location for defining mount points and their associated map files. Proper configuration ensures efficient and dynamic management of filesystems and network shares, reducing the need for manual mounting and unmounting.