Unmounting File Systems

The unmounting of a file system removes it from the file system mount point, and deletes the entry from the /etc/mnttab file. Some file system administration tasks cannot be performed on mounted file systems. You should unmount a file system when the following occurs:

The file system is no longer needed or has been replaced by a file system that contains more current software.
You need to check and repair the file system by using the fsck command. For more information about the fsck command, see Chapter 22, Checking UFS File System Consistency (Tasks).
File systems should be unmounted before doing a complete backup. For more information about doing backups, see Chapter 25, Backing Up Files and File Systems (Tasks).

Note - File systems are automatically unmounted as part of the system shutdown procedure.

In an emergency situation, you can use the umount -f option to forcibly unmount a busy file system. This practice is not recommended under normal circumstances because the unmounting of a file system with open files could cause a loss of data. This option is only available for UFS and NFS file systems.

Prerequisites for Unmounting File Systems

The prerequisites for unmounting file systems include the following:

You must be superuser or assume an equivalent role.
A file system must be available for unmounting. You cannot unmount a file system that is busy. A file system is considered busy if a user is accessing a directory in the file system, if a program has a file open in that file system, or if the file system is being shared. You can make a file system available for unmounting by doing the following:
- Changing to a directory in a different file system.
- Logging out of the system.
- Using the fuser command to list all processes that are accessing the file system and to stop them, if necessary. For more details, see How to Stop All Processes Accessing a File System.
  Notify users if you need to unmount a file system that they are using.
- Unsharing the file system. For information about unsharing a file system, see unshare(1M).

How to Verify a File System is Unmounted

To verify that you unmounted a file system or a number of file systems, examine the output from the mount command.

$ mount | grep unmounted-file-system
$

How to Stop All Processes Accessing a File System

Become superuser or assume an equivalent role.
List all the processes that are accessing the file system so that you know which processes you are going to stop.
```
# fuser -c [ -u ] /mount-point
```
-c

Reports on files that are mount points for file systems and any files within those mounted file systems.

-u

Displays the user login name for each process ID.

/mount-point

Specifies the name of the file system for which you want to stop processes.
Stop all processes that are accessing the file system.
```
# fuser -c -k /mount-point
```
A SIGKILL is sent to each process that is using the file system.

Note - You should not stop a user's processes without first warning the user.
Verify that no processes are accessing the file system.
```
# fuser -c /mount-point
```

Example 19-9 Stopping All Processes Accessing a File System

The following example shows how to stop process 4006c that is using the /export/home file system.

# fuser -c /export/home
/export/home:     4006c
# fuser -c -k /export/home
/export/home:     4006c
# fuser -c /export/home
/export/home:

How to Unmount a File System

Use the following procedure to unmount a file system, except for the root (/), /usr, or /var file systems.

Note - The root (/), /usr, and /var file systems can be unmounted only during a shutdown. The system needs these file systems to function.

Ensure that you have met the prerequisites listed in Prerequisites for Unmounting File Systems.
Unmount the file system.
```
# umount /mount-point
```
where /mount-point is the name of the file system that you want to unmount. This can be one of the following:
- The directory name where the file system is mounted
- The device name path of the file system
- The resource for an NFS file system
- The loopback directory for an LOFS file system

Example 19-10 Unmounting a File System

The following example shows how to unmount a local home file system.

# umount /export/home

The following example shows how to unmount the file system on slice 7.

# umount /dev/dsk/c0t0d0s7

The following example shows how to forcibly unmount the /export file system.

# umount -f /export
#

The following example shows how to unmount all file systems in the /etc/vfstab file, except for the root (/), /proc, /var, and /usr file systems.

# umountall

All file systems are unmounted, except for those file systems that are busy.