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This is the BSDA Study Guide Book written via a
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Determine which filesystems are currently mounted and which will be mounted at system boot
Concept
Be able to determine:
* which filesystems are currently mounted, and
* which will be mounted at boot time.
Introduction
The UNIX paradigm "everything is a file" means that almost any device can be mounted to almost any location on the filesystem hierarchy.
At boot time, init(8) mounts devices as shown in the file /etc/fstab, which may be edited by the superuser to add or remove additional boot-time mounts or change their parameters. To see all devices currently mounted on the filesystem, call mount(8) with no arguments.
Examples
A typical 'fstab'. Note that the "noauto" option for the entry /dev/acd0 means that init will not attempt to mount the cdrom during bootup, but the CD can be mounted with mount /cdrom by a user with the appropriate privileges.
$ 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
Here is the output of mount(8) for the same system:
$mount
/dev/ad0s1a on / (ufs, local, soft-updates)
devfs on /dev (devfs, local)
/dev/ad0s1e on /usr (ufs, NFS exported, local, soft-updates)
/dev/ad0s1d on /var (ufs, local, soft-updates)
devfs on /var/named/dev (devfs, local)
Mount here gives a couple of details not visible in the system fstab --- one is the existence of devfs(5), the "device file system", which occurs twice here because this system runs named(8) in a "sandbox" (chrooted) environment. The other is the fact that /usr is exported as a Network File System. In this case, you might wish to call showmount(8) to see if anyone is connected to your exported file system before you umount(8) it or call shutdown(8). (Network mounts are introduced in section Configure data to be available through NFS.)
The 'df' tool can also show mounted filesystems:
$ df -m
Filesystem 1M-blocks Used Avail Capacity Mounted on
/dev/wd0a 1008 23 934 2% /
/dev/wd0f 4032 10 3820 0% /var
/dev/wd0e 15121 1541 12823 10% /usr
/dev/wd0g 10081 500 9076 5% /home
kernfs 0 0 0 100% /kern
The -t switch for df can be used to specify or exclude some filesystems.
To exclude, prefix the filesystem name with "no", such as "noffs" or "noprocfs".
For example, on DragonFly- and NetBSD:
$ df -t nfs
Filesystem 1K-blocks Used Avail Capacity Mounted on
office:/pub 20644846 858522 18134738 5% /pub
$ df -t noffs
Filesystem 512-blocks Used Avail Capacity Mounted on
kernfs 2 2 0 100% /kern
More details on df are covered in Determine disk capacity and which files are consuming the most disk space.
Practice Exercises
Compare the output of mount on your system(s) with the output shown above. If the machine isn't "mission-critical", try removing the "noauto" option above and rebooting the system with the optical drive empty. What do you predict will happen? What actually happens? (Note that you might want to have a backup copy of /etc/fstab stored somewhere in the root of your filesystem if you try this.) What is a quick "one-liner" to get everything "back to normal" if mount shows only the following (when you expect 3 or 4 filesystems)?
# mount
/dev/ad0s1a on / (ufs, local, read-only)
More information
mount(1), df(1), fstab(5)
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