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Mount or unmount local filesystems


Be familiar with all aspects of mounting and unmounting local filesystems including:

  • how to mount/umount a specified filesystem
  • how to mount all filesystems
  • configuring filesystems to be mounted at boot
  • passing options to mount(8), and
  • resolving mount errors.


A traditional BSD system has several hard disk partitions; modern computers also have optical drives, perhaps an older "floppy" drive, and other special devices, such as USB or firewire storage devices, flash disks, cameras that are really mass storage devices, etc. In order for these devices to be read from or written to, they must be "mounted" to some portion of the filesystem "tree". Critical local filesystems are mounted automatically at boot time. Some removable devices can be configured to mount when attached. Sometimes you don't wish to mount a filesystem at boot time: these filesystems can be mounted manually.

/etc/fstab and rc

The rc process mounts all filesystems listed in /etc/fstab, unless they are marked "noauto". A traditional fstab might look like this:

cat /etc/fstab
# Device                Mountpoint      FStype  Options         Dump    Pass#
/dev/ad0s1b             none            swap    sw              0       0
/dev/ad0s1a             /               ufs     rw              1       1
/dev/ad0s1e             /usr            ufs     rw              2       2
/dev/ad0s1d             /var            ufs     rw              2       2
/dev/acd0               /cdrom          cd9660 ro,noauto        0       0

At the very least, the root filesystem (second line above) must be mounted.

Using mount(8) and umount(8) manually

mount and umount (note: that doesn't say "unmount") vary in the amount and types of arguments they expect. Generally, umount is a little simpler. When given no type parameter, mount expects a device to be of type UFS or UFS2. A good number of examples appear below; see the manual pages for comprehensive instruction on these system calls. Note that when using umount, the device must not be "busy" (example, you can't umount /mnt when you [or anyone else] is working in that directory....)


Show all mounted filesystems

# mount

Mount partition e on the first slice of the primary master IDE hard disk at /usr:

# mount /dev/ad0s1e /usr

Same thing, SCSI disk

# mount /dev/da0s1e /usr

*Unmount /usr

# umount /usr

Mount all filesystems listed in /etc/fstab:

# mount -a

Note that filesystems marked "noauto" in /etc/fstab would not be mounted by the above command.

Mount optical media in the CD-ROM drive as listed in /etc/fstab:

# mount /cdrom

Mount a floppy disk to /mnt:

# mount -t msdos /dev/fd0 /mnt

*Prepare the floppy to be removed:

#**umount /mnt**

Mount a FAT32 formatted USB "key" on /mnt:

# mount_msdosfs /dev/da0s1 /mnt

Note that USB devices are assigned SCSI device names; if usbd(8) is running, the system log file /var/log/messages should show the name of the device within a few seconds after the device is inserted. Also, note that mount -t msdos and mount_msdosfs actually accomplish the same operation.

Practice Exercises

  1. Practice mounting and un-mounting non-critical filesystems.
  2. What do you think would happen if you attempted to umount /?

More information

mount(8), umount(8), fstab(5)

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