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Commits on Mar 18, 2013
@nibalizer nibalizer Introduce mounting, fstab, autofs
Introduces the mount command and some of its options. Takes apart
an /etc/fstab file. Briefly introduces autofs and an
/etc/auto.master file. Autofs has a bit too many prerequisites to
be meaningfully covered here, but it is at least introduced with
an example, and discusses the chain of events during an automount.
Commits on Mar 22, 2013
@miketheman miketheman Merge pull request #122 from nibalizer/mount_fstab_autofs
Introduce mounting, fstab, autofs
Showing with 86 additions and 1 deletion.
  1. +86 −1 filesystems_101.rst
87 filesystems_101.rst
@@ -144,7 +144,92 @@ man mkfs
Mounting a filesystem
-.. todo:: explain different kinds of mounts, autofs, /etc/fstab
+Mounting a filesystem is the act of placing the root of one filesystem on
+a directory, or mount point, of a currently mounted filesystem. The mount
+command allows the user to do this manually. Typically, only the superuser
+can perform mounts. The root filesystem, mounted on ``/``, is unique and
+it is mounted at boot. See :doc:`boot_process_101`.
+.. code-block:: console
+ -root@opsschool # mount -t ext4 -o noatime /dev/sdb1 /mnt
+It is common to specify which filesystem type is present on ``/dev/sdb1`` and
+which mounting options you would like to use, but if that information is not
+specified then the Linux ``mount`` command is pretty good at picking sane
+defaults. Most administrators would have typed the following instead of the
+.. code-block:: console
+ -root@opsschool # mount /dev/sdb1 /mnt
+The root filesystem, mounted on ``/``, is unique and its mounting
+The type of the filesystem refers to the format of the data structure that is
+the filesystem on disk. Files (generally) do not care what kind of filesystem
+they are on, it is only in initial filesystem creation, automatic
+mounting, and performance tuning that you have to concern yourself with the
+filesystem type. Example filesystem types are ``ext2, ext3, ext4, FAT, NTFS
+HFS, JFS, XFS, ZFS, BtrFS``. On Linux hosts, ext4 is a good default. For
+maximum compatibility with Windows and Macintosh, use FAT.
+The fstab, or file system table, is the file that configures automatic mounting
+at boot. It tabulates block devices, mount points, type and options for each
+mount. The dump and pass fields control booting behavior. Dumping is the act
+of creating a backup of the filesystem (often to tape), and is not in common use.
+Pass is much more important. When the pass value is nonzero, the filesystem is
+analyzed early in the boot process by fsck, the file system checker, for errors.
+The number, fs_passno, indicated priority. The root filesystem should always be
+1, other filesystems should be 2 or more. A zero value causes skips to be
+checked, an option often used to accelerate the boot process. In ``/etc/fstab``,
+there are a number of ways to specify the block device containing the filesystem
+. ``UUID``, or universally unique identifier, is one common way in modern Linux
+based systems to specify a filesystem.
+.. code-block:: console
+ -root@opsschool # cat /etc/fstab
+ # <file system> <mount point> <type> <options> <dump> <pass>
+ /dev/sda5 / ext4 errors=remount-ro 0 1
+ /dev/sda6 none swap sw 0 0
+ /dev/sda1 /boot/efi auto auto 0 0
+This ``/etc/fstab`` file mounts ``/dev/sda5`` on ``/`` using the ext4 filesystem
+. If it encounters a filesystem corruption it will use the ``fsck`` utility
+early in the boot process to try to clear the problem. If the physical disk
+reports errors in writing while the filesystem is mounted, the os will remount
+``/`` readonly. The ``/dev/sda6`` partition will be used as swap. The
+``/dev/sda1`` partition will be mounted on ``/boot/efi`` using autodetection, the
+partition will not be scanned for filesystem errors.
+.. code-block:: console
+ -root@opsschool # cat /etc/auto.master
+ /home -rw,hard,intr,nosuid,nobrowse bigserver:/exports/home/&
+ /stash ldap:ou=auto_stash,ou=Autofs,dc=example,dc=com -rw,hard,intr,nobrowse
+The ``auto.master`` file controls the ``autofs`` service. It is another way to
+tabulate filesystems for mounting. It is different from the ``/etc/fstab``
+because the filesystems listed in ``auto.master`` are not mounted at boot. The
+automounter allows the system to mount filesystems on demand, then clean up those
+filesystems when they are no longer being used. In this case, the system mounts
+home directories for each user from a remote NFS server. The filesystem remains
+unmounted until the user logs in, and is unmounted a short time after the user
+logs out. The automounter is triggered by an attempt to cd into ``/home/<key``,
+it will then attempt to find an nfs share on ``/exports/home/<key>`` and mount it
+on ``/home/key``, then allow the ``cd`` command to return successfully. The
+``/home`` example above is using the ``&`` expansion syntax, the second line is
+using the LDAP syntax to look up a key under ``/stash/<key>`` in LDAP. LDAP will
+be covered later in the curriculum. The ``auto.master`` file is known as
+``auto_master`` on FreeBSD, Solaris, and Mac OS X.
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