mount point ZFS file

Automatic Mount Points

• When you change the mountpoint property from legacy or none to a specific path, ZFS automatically mounts the file system.
• If ZFS is managing a file system but it is currently unmounted, and the mountpoint property is changed, the file system remains unmounted.

Any file system whose mountpoint property is not legacy is managed by ZFS. In the following example, a file system is created whose mount point is automatically managed by ZFS:

# zfs create pool/filesystem
# zfs get mountpoint pool/filesystem
NAME             PROPERTY      VALUE                      SOURCE
pool/filesystem  mountpoint    /pool/filesystem           default
# zfs get mounted pool/filesystem
NAME             PROPERTY      VALUE                      SOURCE
pool/filesystem  mounted       yes                        -

You can also explicitly set the mountpoint property as shown in the following example:

# zfs set mountpoint=/mnt pool/filesystem
# zfs get mountpoint pool/filesystem
NAME             PROPERTY      VALUE                      SOURCE
pool/filesystem  mountpoint    /mnt                       local
# zfs get mounted pool/filesystem
NAME             PROPERTY      VALUE                      SOURCE
pool/filesystem  mounted       yes                        -

When the mountpoint property is changed, the file system is automatically unmounted from the old mount point and remounted to the new mount point. Mount-point directories are created as needed. If ZFS is unable to unmount a file system due to it being active, an error is reported, and a forced manual unmount is necessary.

Legacy Mount Points

You can manage ZFS file systems with legacy tools by setting the mountpoint property to legacy. Legacy file systems must be managed through the mount and umount commands and the /etc/vfstab file. ZFS does not automatically mount legacy file systems at boot time, and the ZFS mount and umount commands do not operate on file systems of this type. The following examples show how to set up and manage a ZFS file system in legacy mode:

# zfs set mountpoint=legacy tank/home/eric
# mount -F zfs tank/home/eschrock /mnt

To automatically mount a legacy file system at boot time, you must add an entry to the /etc/vfstab file. The following example shows what the entry in the /etc/vfstab file might look like:

#device         device        mount           FS      fsck    mount   mount
#to mount       to fsck       point           type    pass    at boot options
#

tank/home/eric  -        /mnt           zfs        -        yes        -    

The device to fsck and fsck pass entries are set to - because the fsck command is not applicable to ZFS file systems. For more information about ZFS data integrity, see Transactional Semantics.

Mounting ZFS File Systems

ZFS automatically mounts file systems when file systems are created or when the system boots. Use of the zfs mount command is necessary only when you need to change mount options, or explicitly mount or unmount file systems.
The zfs mount command with no arguments shows all currently mounted file systems that are managed by ZFS. Legacy managed mount points are not displayed. For example:

# zfs mount | grep tank/home
zfs mount | grep tank/home
tank/home                       /tank/home
tank/home/jeff                  /tank/home/jeff

You can use the -a option to mount all ZFS managed file systems. Legacy managed file systems are not mounted. For example:

# zfs mount -a

By default, ZFS does not allow mounting on top of a nonempty directory. For example:

# zfs mount tank/home/lori
cannot mount 'tank/home/lori': filesystem already mounted

Legacy mount points must be managed through legacy tools. An attempt to use ZFS tools results in an error. For example:

# zfs mount tank/home/bill
cannot mount 'tank/home/bill': legacy mountpoint
use mount(1M) to mount this filesystem
# mount -F zfs tank/home/billm

When a file system is mounted, it uses a set of mount options based on the property values associated with the file system. The correlation between properties and mount options is as follows:
Table 6-4 ZFS Mount-Related Properties and Mount Options

Property Mount Option atime atime/noatime devices devices/nodevices exec exec/noexec nbmand nbmand/nonbmand readonly ro/rw setuid setuid/nosetuid xattr xattr/noaxttr

The mount option nosuid is an alias for nodevices,nosetuid.
You can use the NFSv4 mirror mount features to help you better manage NFS-mounted ZFS home directories.
When file systems are created on the NFS server, the NFS client can automatically discover these newly created file systems within their existing mount of a parent file system.
For example, if the server neo already shares the tank file system and client zee has it mounted, /tank/baz is automatically visible on the client after it is created on the server.

zee# mount neo:/tank /mnt
zee# ls /mnt
baa    bar

neo# zfs create tank/baz

zee% ls /mnt
baa    bar    baz
zee% ls /mnt/baz
file1    file2 

Using Temporary Mount Properties

If any of the mount options described in the preceding section are set explicitly by using the-o option with the zfs mount command, the associated property value is temporarily overridden. These property values are reported as temporary by the zfs get command and revert back to their original values when the file system is unmounted. If a property value is changed while the file system is mounted, the change takes effect immediately, overriding any temporary setting.
In the following example, the read-only mount option is temporarily set on the tank/home/neil file system. The file system is assumed to be unmounted.

# zfs mount -o ro users/home/neil

To temporarily change a property value on a file system that is currently mounted, you must use the special remount option. In the following example, the atime property is temporarily changed to off for a file system that is currently mounted:

# zfs mount -o remount,noatime users/home/neil
NAME             PROPERTY  VALUE  SOURCE
users/home/neil  atime     off    temporary
# zfs get atime users/home/perrin

For more information about the zfs mount command, see zfs(1M).

Unmounting ZFS File Systems

You can unmount ZFS file systems by using the zfs unmount subcommand. The unmount command can take either the mount point or the file system name as an argument.
In the following example, a file system is unmounted by its file system name:

# zfs unmount users/home/mark

In the following example, the file system is unmounted by its mount point:

# zfs unmount /users/home/mark

The unmount command fails if the file system is busy. To forcibly unmount a file system, you can use the -f option. Be cautious when forcibly unmounting a file system if its contents are actively being used. Unpredictable application behavior can result.

# zfs unmount tank/home/eric
cannot unmount '/tank/home/eric': Device busy
# zfs unmount -f tank/home/eric

To provide for backward compatibility, the legacy umount command can be used to unmount ZFS file systems. For example:

# umount /tank/home/bob

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Technique 4. Lazy Unmount

To fix umount target is busy error, a methodical way is the Lazy unmount. It unmounts the mount point from the Linux filesystem. To remove all the processes attached to the device (that are not in use) slowly, you can use this solution. Since the Lazy unmount removes all references to the detached file system, it will detach the file system when there is no more process accessing the unmounted file system. So, if the last suggested method is your choice, type:

sudo umount -l /Path/to/target

In this way, all ideal processes will be automatically removed and the device will be unmounted. According to your used case, all the recent solutions can be chosen to fix umount target is busy error.

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