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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.
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nibalizer committed Mar 15, 2013
1 parent 539b7f8 commit 51e19d627bea5d8d886f199186903b03457c5220
Showing with 86 additions and 1 deletion.
  1. +86 −1 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.
Filesystem options

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