This section describes how mount points and shared file systems are managed in ZFS.
By default, a ZFS file system is automatically mounted when it is created. You can determine specific mount-point behavior for a file system as described in this section.
You can also set the default mount point for a pool's dataset at creation time by using zpool create's -m option. For more information about creating pools, see Creating a ZFS Storage Pool.
All ZFS file systems are mounted by ZFS at boot time by using the Service Management Facility's (SMF) svc://system/filesystem/local service. File systems are mounted under /path, where path is the name of the file system.
You can override the default mount point by using the zfs set command to set the mountpoint property to a specific path. ZFS automatically creates the specified mount point, if needed, and automatically mounts the associated file system when the zfs mount -a command is invoked, without requiring you to edit the /etc/vfstab file.
The mountpoint property is inherited. For example, if pool/home has the mountpoint property set to /export/stuff, then pool/home/user inherits /export/stuff/user for its mountpoint property value.
To prevent a file system from being mounted, set the mountpoint property to none. In addition, the canmount property can be used to control whether a file system can be mounted. For more information about the canmount property, see canmount Property.
File systems can also be explicitly managed through legacy mount interfaces by using zfs set to set the mountpoint property to legacy. Doing so prevents ZFS from automatically mounting and managing a file system. Legacy tools including the mount and umount commands, and the /etc/vfstab file must be used instead. For more information about legacy mounts, see Legacy 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 dataset whose mountpoint property is not legacy is managed by ZFS. In the following example, a dataset 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.
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 datasets of this type. The following examples show how to set up and manage a ZFS dataset in legacy mode:
# zfs set mountpoint=legacy tank/home/eschrock # mount -F zfs tank/home/eschrock /mnt
#device device mount FS fsck mount mount #to mount to fsck point type pass at boot options # tank/home/eschrock - /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.
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 tank /tank tank/home /tank/home tank/home/bonwick /tank/home/bonwick tank/ws /tank/ws
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
# zfs mount tank/home/lalt cannot mount '/export/home/lalt': directory is not empty use legacy mountpoint to allow this behavior, or use the -O flag # zfs mount -O tank/home/lalt
Legacy mount points must be managed through legacy tools. An attempt to use ZFS tools results in an error. For example:
# zfs mount pool/home/billm cannot mount 'pool/home/billm': 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 dataset. The correlation between properties and mount options is as follows:
Table 6-4 ZFS Mount-Related Properties and Mount Options
The mount option nosuid is an alias for nodevices,nosetuid.
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 dataset 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/perrin file system. The file system is assumed to be unmounted.
# zfs mount -o ro tank/home/perrin
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 tank/home/perrin # zfs get atime tank/home/perrin NAME PROPERTY VALUE SOURCE tank/home/perrin atime off temporary
For more information about the zfs mount command, see zfs(1M).
In the following example, a file system is unmounted by its file system name:
# zfs unmount tank/home/tabriz
In the following example, the file system is unmounted by its mount point:
# zfs unmount /export/home/tabriz
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/eschrock cannot unmount '/export/home/eschrock': Device busy # zfs unmount -f tank/home/eschrock
To provide for backward compatibility, the legacy umount command can be used to unmount ZFS file systems. For example:
# umount /export/home/bob
For more information about the zfs umount command, see zfs(1M).
ZFS can automatically share file systems by setting the sharenfs property. Using this property, you do not have to modify the /etc/dfs/dfstab file when a new file system is shared. The sharenfs property is a comma-separated list of options to pass to the share command. The value on is an alias for the default share options, which provides read/write permissions to anyone. The value off indicates that the file system is not managed by ZFS and can be shared through traditional means, such as the /etc/dfs/dfstab file. All file systems whose sharenfs property is not off are shared during boot.
By default, all file systems are unshared. To share a new file system, use zfs set syntax similar to the following:
# zfs set sharenfs=on tank/home/eschrock
# zfs set sharenfs=on tank/home # zfs create tank/home/bricker # zfs create tank/home/tabriz # zfs set sharenfs=ro tank/home/tabriz
Both tank/home/bricker and tank/home/tabriz are initially shared as writable because they inherit the sharenfs property from tank/home. After the property is set to ro (read only), tank/home/tabriz is shared as read-only regardless of the sharenfs property that is set for tank/home.
Although most file systems are automatically shared or unshared during boot, creation, and destruction, file systems sometimes need to be explicitly unshared. To do so, use the zfs unshare command. For example:
# zfs unshare tank/home/tabriz
# zfs unshare -a
Most of the time, the automatic behavior of ZFS with respect to sharing file system on boot and creation is sufficient for normal operations. If, for some reason, you unshare a file system, you can share it again by using the zfs share command. For example:
# zfs share tank/home/tabriz
You can also share all ZFS file systems on the system by using the -a option.
# zfs share -a
If the sharenfs property is set to off, then ZFS does not attempt to share or unshare the file system at any time. This value enables you to administer file system sharing through traditional means, such as the /etc/dfs/dfstab file.
Unlike the legacy mount command, the legacy share and unshare commands can still function on ZFS file systems. As a result, you can manually share a file system with options that differ from the options of the sharenfs property. This administrative model is discouraged. Choose to manage NFS shares either completely through ZFS or completely through the /etc/dfs/dfstab file. The ZFS administrative model is designed to be simpler and less work than the traditional model.