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Copyediting filesystems
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@ -302,6 +302,11 @@ command allows the user to do this manually. Typically, only the superuser
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can perform mounts. The root filesystem, mounted on ``/``, is unique and
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can perform mounts. The root filesystem, mounted on ``/``, is unique and
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it is mounted at boot. See :doc:`boot_process_101`.
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it is mounted at boot. See :doc:`boot_process_101`.
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In the following example, the filesystem of ``/dev/sdb1`` will be mounted to
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the folder ``/mnt``. That means anything inside ``/dev/sdb1`` will become
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accessible under ``/mnt/...``. (Don't worry about the options ``-t`` and
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``-o`` just yet; those will be described in more detail below).
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.. code-block:: console
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.. code-block:: console
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root@opsschool # mount -t ext4 -o noatime /dev/sdb1 /mnt
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root@opsschool # mount -t ext4 -o noatime /dev/sdb1 /mnt
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@ -318,21 +323,25 @@ above:
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The filesystem type refers to the format of the data structure that is used as
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The filesystem type refers to the format of the data structure that is used as
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the filesystem on disk. Files (generally) do not care what kind of filesystem
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the filesystem on disk. Files (generally) do not care what kind of filesystem
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they are on, it is only in initial filesystem creation, automatic
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they are on. You have to concern yourself with the filesystem type only in
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mounting, and performance tuning that you have to concern yourself with the
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the initial filesystem creation, automatic mounting, and performance tuning.
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filesystem type. Example filesystem types are ``ext2, ext3, ext4, FAT, NTFS
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HFS, JFS, XFS, ZFS, BtrFS``. On Linux hosts, ext4 is a good default. For
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maximum compatibility with Windows and Macintosh, use FAT.
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http://en.wikipedia.org/wiki/Comparison_of_file_systems
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Example filesystem types are ``ext2``, ``ext3``, ``ext4``, ``FAT``, ``NTFS``,
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``HFS``, ``JFS``, ``XFS``, ``ZFS``, ``Btrfs``. On Linux hosts, ``ext4`` is a
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good default. For maximum compatibility with Windows and Macintosh, use ``FAT``.
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See the following Wikipedia page for a more thorough `comparison of file systems.
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<http://en.wikipedia.org/wiki/Comparison_of_file_systems>`_
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Automatic mounting using ``fstab``
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----------------------------------
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The fstab, or file system table, is the file that configures automatic mounting
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The fstab, or file system table, is the file that configures automatic mounting
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at boot. It tabulates block devices, mount points, type and options for each
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at boot. It tabulates block devices, mount points, type and options for each
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mount. The dump and pass fields control booting behavior. Dumping is the act
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mount. The dump and pass fields control booting behavior. Dumping is the act
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of creating a backup of the filesystem (often to tape), and is not in common use.
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of creating a backup of the filesystem (often to tape), and is not in common use.
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Pass is much more important. When the pass value is nonzero, the filesystem is
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Pass is much more important. When the pass value is nonzero, the filesystem is
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analyzed early in the boot process by fsck, the file system checker, for errors.
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analyzed early in the boot process by ``fsck``, the file system checker, for errors.
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The number, fs_passno, indicates priority. The root filesystem should always be
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The number, ``fs_passno``, indicates priority. The root filesystem should always be
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1, other filesystems should be 2 or more. A zero value causes checks to be
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1, other filesystems should be 2 or more. A zero value causes checks to be
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skipped, an option often used to accelerate the boot process. In ``/etc/fstab``,
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skipped, an option often used to accelerate the boot process. In ``/etc/fstab``,
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there are a number of ways to specify the block device containing the filesystem
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there are a number of ways to specify the block device containing the filesystem
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@ -351,11 +360,21 @@ based systems to specify a filesystem.
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This ``/etc/fstab`` file mounts ``/dev/sda5`` on ``/`` using the ext4 filesystem
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This ``/etc/fstab`` file mounts ``/dev/sda5`` on ``/`` using the ext4 filesystem
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. If it encounters a filesystem corruption it will use the ``fsck`` utility
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. If it encounters a filesystem corruption it will use the ``fsck`` utility
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early in the boot process to try to clear the problem. If the physical disk
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early in the boot process to try to clear the problem. If the physical disk
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reports errors in writing while the filesystem is mounted, the os will remount
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reports errors in writing while the filesystem is mounted, the OS will remount
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``/`` readonly. The ``/dev/sda6`` partition will be used as swap. The
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``/`` readonly. The ``/dev/sda6`` partition will be used as swap. The
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``/dev/sda1`` partition will be mounted on ``/boot/efi`` using autodetection, the
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``/dev/sda1`` partition will be mounted on ``/boot/efi`` using autodetection, the
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partition will not be scanned for filesystem errors.
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partition will not be scanned for filesystem errors.
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Automatic mounting using ``autofs``
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-----------------------------------
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``autofs`` is another way to tabulate filesystems for mounting. It is different from
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the ``/etc/fstab`` because the filesystems listed in ``auto.master`` are not mounted
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at boot. The automounter allows the system to mount filesystems on demand, then clean
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up those filesystems when they are no longer being used.
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The ``auto.master`` file controls the ``autofs`` service:
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.. code-block:: console
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.. code-block:: console
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root@opsschool # cat /etc/auto.master
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root@opsschool # cat /etc/auto.master
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@ -363,22 +382,17 @@ partition will not be scanned for filesystem errors.
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/home -rw,hard,intr,nosuid,nobrowse bigserver:/exports/home/&
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/home -rw,hard,intr,nosuid,nobrowse bigserver:/exports/home/&
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/stash ldap:ou=auto_stash,ou=Autofs,dc=example,dc=com -rw,hard,intr,nobrowse
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/stash ldap:ou=auto_stash,ou=Autofs,dc=example,dc=com -rw,hard,intr,nobrowse
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The ``auto.master`` file controls the ``autofs`` service. It is another way to
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In the above example, the system mounts home directories for each user from a remote NFS
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tabulate filesystems for mounting. It is different from the ``/etc/fstab``
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server. The filesystem remains unmounted until the user logs in, and is unmounted
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because the filesystems listed in ``auto.master`` are not mounted at boot. The
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a short time after the user logs out. The automounter is triggered by an attempt to
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automounter allows the system to mount filesystems on demand, then clean up those
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``cd`` into ``/home/<key>``. It will then attempt to find an NFS share on
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filesystems when they are no longer being used. In this case, the system mounts
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``/exports/home/<key>`` and mount it on ``/home/key``, then allow the ``cd`` command
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home directories for each user from a remote NFS server. The filesystem remains
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to return successfully. The ``/home`` example above is using the ``&`` expansion syntax.
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unmounted until the user logs in, and is unmounted a short time after the user
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logs out. The automounter is triggered by an attempt to cd into ``/home/<key>``,
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it will then attempt to find an nfs share on ``/exports/home/<key>`` and mount it
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on ``/home/key``, then allow the ``cd`` command to return successfully. The
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``/home`` example above is using the ``&`` expansion syntax, the second line is
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using the LDAP syntax to look up a key under ``/stash/<key>`` in LDAP. LDAP will
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be covered later in the curriculum. The ``auto.master`` file is known as
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``auto_master`` on FreeBSD, Solaris, and Mac OS X.
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The second line is using the LDAP syntax to look up a key under ``/stash/<key>`` in
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LDAP. LDAP will be covered later in the curriculum.
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The ``auto.master`` file is known as ``auto_master`` on FreeBSD, Solaris, and Mac OS X.
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Filesystem options
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Filesystem options
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==================
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==================
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@ -476,9 +490,12 @@ This is also used for security purposes.
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It is generally recommended for removable devices such as CD-ROMs, USB sticks, and network filesystems.
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It is generally recommended for removable devices such as CD-ROMs, USB sticks, and network filesystems.
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nobarrier
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---------
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nobarriers
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rbind
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rbind
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-----
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How filesystems work
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How filesystems work
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