Mounting and Sharing ZFS File Systems

This section describes how mount points and shared file systems are managed in ZFS.

• Managing ZFS Mount Points

• Mounting ZFS File Systems

• Using Temporary Mount Properties

• Unmounting ZFS File Systems

• Sharing and Unsharing ZFS File Systems

Managing ZFS Mount Points

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.

ZFS file systems are automatically mounted at boot time 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 The 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.

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 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.

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 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

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/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.

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
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

By default, ZFS does not allow mounting on top of a nonempty directory. To force a mount on top of a nonempty directory, you must use the -O option. For example:

# 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.

You can use the NFSv4 mirror mount features to help you better manage NFS-mounted ZFS home directories. For a description of mirror mounts, see ZFS and File System Mirror Mounts.

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 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).

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 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).

Sharing and Unsharing ZFS File Systems

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.

Controlling Share Semantics

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

The sharenfs property is inherited, and file systems are automatically shared on creation if their inherited property is not off. For example:

# 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.

Unsharing ZFS File Systems

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

This command unshares the tank/home/tabriz file system. To unshare all ZFS file systems on the system, you need to use the -a option.

# zfs unshare -a

Sharing ZFS File Systems

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

Legacy Share Behavior

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.

Sharing ZFS Files in an Oracle Solaris SMB Environment

The sharesmb property is provided to share ZFS files by using the Oracle Solaris SMB software product. When this property is set on a ZFS file system, these shares are visible to SMB client systems. For more information about using the Oracle Solaris SMB software product, see the System Administration Guide: Windows Interoperability.

For a detailed description of the sharesmb property, see The sharesmb Property.

Example 6-1 Example—Sharing ZFS File Systems (sharesmb)

In this example, a ZFS file system sandbox/fs1 is created and shared with the sharesmb property. If necessary, enable the SMB services.

# svcadm enable -r smb/server
svcadm: svc:/milestone/network depends on svc:/network/physical, which has multiple instances.
# svcs | grep smb
online         10:47:15 svc:/network/smb/server:default

# zpool create sandbox mirror c0t2d0 c0t4d0
# zfs create sandbox/fs1
# zfs set sharesmb=on sandbox/fs1

The sharesmb property is set for sandbox/fs1 and its descendents.

Verify that the file system was shared. For example:

# sharemgr show -vp
default nfs=()
zfs nfs=()
    zfs/sandbox/fs1 smb=()
          sandbox_fs1=/sandbox/fs1

A default SMB resource name, sandbox_fs1, is assigned automatically.

In this example, another file system is created, sandbox/fs2, and shared with a resource name, myshare.

# zfs create sandbox/fs2
# zfs set sharesmb=name=myshare sandbox/fs2
# sharemgr show -vp
default nfs=()
zfs nfs=()
    zfs/sandbox/fs1 smb=()
          sandbox_fs1=/sandbox/fs1
    zfs/sandbox/fs2 smb=()
          myshare=/sandbox/fs2

The sandbox/fs2/fs2_sub1 file system is created and is automatically shared. The inherited resource name is myshare_fs2_sub1.

# zfs create sandbox/fs2/fs2_sub1
# sharemgr show -vp
default nfs=()
zfs nfs=()
    zfs/sandbox/fs1 smb=()
          sandbox_fs1=/sandbox/fs1
    zfs/sandbox/fs2 smb=()
          myshare=/sandbox/fs2
          myshare_fs2_sub1=/sandbox/fs2/fs2_sub1

Disable SMB sharing for sandbox/fs2 and its descendents.

# zfs set sharesmb=off sandbox/fs2
# sharemgr show -vp
default nfs=()
zfs nfs=()
    zfs/sandbox/fs1 smb=()
          sandbox_fs1=/sandbox/fs1

In this example, the sharesmb property is set on the pool's top-level file system. The descendent file systems are automatically shared.

# zpool create sandbox mirror c0t2d0 c0t4d0
# zfs set sharesmb=on sandbox
# zfs create sandbox/fs1
# zfs create sandbox/fs2

The top-level file system has a resource name of sandbox, but the descendents have their dataset name appended to the resource name.

# sharemgr show -vp
default nfs=()
zfs nfs=()
    zfs/sandbox smb=()
          sandbox=/sandbox
          sandbox_fs1=/sandbox/fs1       smb=()
          sandbox_fs2=/sandbox/fs2       smb=()