Add LABEL/UUID information
Sven Vermeulen
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e089867ad8
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a13277d290
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@ -1,3 +1,6 @@
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** (2011-02-12) Sven Vermeulen <sven.vermeulen@siphos.be>
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- Add information on file system UUIDs and LABELs
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** (2010-11-02) Sven Vermeulen <sven.vermeulen@siphos.be>
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- Switch from slocate to mlocate
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- Add information on Portage error where a dependency cannot
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@ -497,7 +497,8 @@ brw-r----- 1 root disk 8, 8 Sep 30 18:11 /dev/sda8</programlisting>
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<orderedlist>
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<listitem>
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<para>The device to mount</para>
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<para>The device to mount (also supports labels - we'll discuss
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that later)</para>
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</listitem>
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<listitem>
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@ -505,6 +505,104 @@ is corrupt, and you might try running e2fsck with an alternate superblock:
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<programlisting>~# <command>e2fsck -y /dev/hda4</command></programlisting>
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</section>
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</section>
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<section>
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<title>Using File System Labels or IDs</title>
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<para>Most, if not all file systems allow you to give them an
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appropriate label. Such labels can then later be used to identify a file
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system without having to mount it (and look at it). Linux even supports
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the use of these labels for the various mount and file system
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operations. The use of labels (or UUIDs, as we will see later) also
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allows one to use configurations (such as in the
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<filename>fstab</filename> file) which do not need to be modified when
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your system gets changed (for instance, new partitions created, new
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disks added, reshuffling of disks and more).</para>
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<section>
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<title>Labels versus UUIDs</title>
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<para>There are two identifiers commonly used when dealing with file
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systems: LABEL and UUID.</para>
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<itemizedlist>
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<listitem>
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<para>a <emphasis>LABEL</emphasis><indexterm>
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<primary>LABEL</primary>
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</indexterm> is a user-provided name for a file system. An
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example could be "ROOT", "HOME" or "DATA".</para>
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</listitem>
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<listitem>
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<para>a <emphasis>UUID</emphasis><indexterm>
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<primary>UUID</primary>
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</indexterm> (Universally Unique Identifier) is a
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system-generated identifier for a file system. Examples are
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"bae98338-ec29-4beb-aacf-107e44599b2e" and
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"31f8eb0d-612b-4805-835e-0e6d8b8c5591"</para>
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</listitem>
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</itemizedlist>
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<para>As you can imagine, a given label is much more user friendly
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than a UUID. So, how do you set a label for a file system? Well, this
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heavily depends on the file system you use. For ext2, ext3 or ext4
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file systems, you can use the <command>e2label</command><indexterm>
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<primary>e2label</primary>
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</indexterm> command:</para>
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<programlisting>~# <command>e2label /dev/sda2 ROOT</command></programlisting>
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<para>For an XFS file system, the command would be given with
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<command>xfs_admin</command>:</para>
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<programlisting>~# <command>xfs_admin -L ROOT /dev/sda2</command></programlisting>
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<para>You can even set labels for swap file systems (<command>mkswap
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-L <labelname> <device></command>), FAT file systems
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(<command>mlabel -i <device> ::<labelname></command>) and
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JFS file systems (<command>jfs_tune -L <labelname>
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<device></command>).</para>
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<para>The easiest method to read the label and UUID of a file system
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is to use the <command>blkid</command><indexterm>
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<primary>blkid</primary>
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</indexterm> command:</para>
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<programlisting>~# <command>blkid /dev/sda3</command>
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/dev/sda3: UUID="2bc32022-27a8-47d5-8d33-83c86e23618c" LABEL="ROOT" TYPE="ext4"</programlisting>
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</section>
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<section>
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<title>Using Labels/UUIDs in fstab</title>
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<para>If you have set a label for your file system(s) (or use UUIDs)
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you can use this information in the <filename>/etc/fstab</filename>
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file. Just substitute the value in the first column (where the device
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is located) with the correct LABEL= or UUID= setting:</para>
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<programlisting>/dev/sda2 / ext4 defaults,noatime 0 0</programlisting>
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<para>could then become one of the following:</para>
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<programlisting>LABEL="ROOT" / ext4 defaults,noatime 0 0</programlisting>
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<para>or</para>
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<programlisting>UUID="bc32022-27a8-47d5-8d33-83c86e23618c" / ext4 defaults,noatime 0 0</programlisting>
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</section>
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<section>
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<title>(Not) Using Labels/UUIDs as Kernel Options</title>
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<para>Some people hope to use the same information as kernel option
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(for instance, to change the <parameter>root=/dev/sda2</parameter>
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kernel parameter to <parameter>root=LABEL=ROOT</parameter>). This is
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possible, but only if you use an initramfs (so use this for the
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<parameter>real_root=</parameter> parameter). The Linux kernel itself
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does not support calling devices through their UUID or LABEL
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information.</para>
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</section>
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</section>
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</section>
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<section>
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@ -68,13 +68,16 @@
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<para>Once your environment is set up, you'll need to setup your disks by
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partitioning them and then putting a file system on them. Partitioning and
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file system management has been discussed <link
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linkend="hdpartitions">beforehand</link>:</para>
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linkend="hdpartitions">beforehand</link>. If you want, assign labels to
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the file systems to make it easier to create your
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<filename>fstab</filename> file later:</para>
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<programlisting># <command>fdisk /dev/sda</command>
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<emphasis>(Partition the disk)</emphasis>
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# <command>mkfs.ext2 /dev/sda1</command>
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# <command>mkfs.ext3 /dev/sda2</command>
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# <command>mkfs.ext3 /dev/sda3</command></programlisting>
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# <command>mkfs.ext2 -L BOOT /dev/sda1</command>
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# <command>mkfs.ext3 -L ROOT /dev/sda2</command>
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# <command>mkfs.ext3 -L HOME /dev/sda3</command>
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# <command>mkswap -L SWAP /dev/sda4</command></programlisting>
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<para>Once that your partitions are created and a file system is put on
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it, it is time to really start the Gentoo Linux installation.</para>
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@ -380,7 +383,9 @@ de_DE@euro ISO-8859-15
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<para>To start with the file system information, you need to edit the
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<filename>/etc/fstab</filename> file. The structure of this file has
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been discussed before so this shouldn't be an issue (see <link
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linkend="mountsection">The mount command</link>).</para>
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linkend="mountsection">The mount command</link>). If you want to use
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labels instead of device locations, use the
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<parameter>LABEL="..."</parameter> syntax in the first column.</para>
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<programlisting>/dev/sda1 /boot ext2 noauto,noatime 0 0
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/dev/sda2 / ext3 defaults,noatime 0 0
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