old-www/HOWTO/Partition/labels.html

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><A
NAME="labels"
></A
>6. Labels</H1
><P
>&#13; In linux, hard drives are referred to as devices, and devices are
pseudo files in <TT
CLASS="filename"
>/dev</TT
>. For
example, the first partition of the second lowest numbered SCSI
drive is <TT
CLASS="filename"
>/dev/sdb1</TT
>. If the drive referred to as
<TT
CLASS="filename"
>/dev/sda</TT
> is removed from the chain, then the
latter partition is automatically renamed
<TT
CLASS="filename"
>/dev/sda1</TT
> at reboot.
</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="volumelabels"
></A
>6.1. Volume Labels</H2
><P
>&#13; Volume labels make it possible for partitions to retain a consistent
name regardless of where they are connected, and regardless of
whatever else is connected. Labels are not mandatory for a linux
volume. Each can be a maximum of 16 characters long.
</P
><P
>&#13; There are three tools to make volume labels: mke2fs, tune2fs and e2label.
</P
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="labelinvocation"
></A
>6.1.1. Simple Invocation</H3
><P
>&#13; <B
CLASS="command"
>e2label</B
> <TT
CLASS="filename"
>/dev/hdb1</TT
> <TT
CLASS="filename"
>pubsw</TT
>
</P
><P
>&#13; <B
CLASS="command"
>tune2fs</B
> -L <TT
CLASS="filename"
>pubsw</TT
> <TT
CLASS="filename"
>/dev/hdb1</TT
>
</P
><P
>&#13; Either of thse two commands will label the first partition of the
second drive "pubsw". That label stays with that particular
partition, even if the drive is moved to another controller or even
another computer.
</P
><P
>&#13; <B
CLASS="command"
>mke2fs</B
> <TT
CLASS="filename"
>pubsw</TT
>
<TT
CLASS="filename"
>/dev/hdb1</TT
>
</P
><P
>&#13; <B
CLASS="command"
>mke2fs</B
> -L <TT
CLASS="filename"
>pubsw</TT
>
<TT
CLASS="filename"
>/dev/hdb1</TT
>
</P
><P
>&#13; will do the same thing as the first two commands - after they make
the file system. This means that either of these last two commands
will delete any existing data in the partition.
</P
></DIV
><DIV
CLASS="sect3"
><H3
CLASS="sect3"
><A
NAME="howtousevolumelabels"
></A
>6.1.2. How to Use</H3
><P
>&#13; Here is a sample fstab. This is a text file located in /etc, which
is usually set up during the installation of the operating system.
it describes where each partition wil be mounted, and how it will be
mounted. It can be modified by you, either through a utility or
manually, when you add/remove devices.
</P
><P
>&#13;<TABLE
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><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>&#13;LABEL=/ / ext3 defaults 1 1
LABEL=/boot /boot ext2 defaults 1 2
none /dev/pts devpts gid=5,mode=620 0 0
none /dev/shm tmpfs defaults 0 0
LABEL=HOME /home ext3 defaults 1 2
none /proc proc defaults 0 0
none /sys sysfs defaults 0 0
LABEL=/usr /usr ext3 defaults 1 2
/dev/hdc1 /k-space ext3 defaults 1 2
/dev/hda6 swap swap defaults 0 0
/dev/hdd /media/cdrecorder auto pamconsole,ro,exec,noauto,managed 0 0
/dev/fd0 /media/floppy auto pamconsole,exec,noauto,managed 0 0
</PRE
></FONT
></TD
></TR
></TABLE
>
</P
><P
>&#13; The leftmost column lists devices and the second column lists mount
points. This example contains a mixture of devices and labels. The
master drive of the second controller is always mounted on <TT
CLASS="filename"
>/k-space</TT
>.
The partition labeled "HOME" is always mounted on <TT
CLASS="filename"
>/home</TT
>, regardless
of which drive it is on or which partition number it has. Notice
that it is permissible to use mount points as labels, such as "/usr"
</P
></DIV
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="devicelabels"
></A
>6.2. Device Labels</H2
><P
>&#13; <B
CLASS="command"
>devlabel</B
> is a script which creates symbolic links to devices. For
example,
</P
><P
>&#13; <B
CLASS="command"
>devlabel</B
> -d <TT
CLASS="filename"
>/dev/hdb1</TT
>
-s <TT
CLASS="filename"
>/dev/home</TT
>
</P
><P
>&#13; will create a link from <TT
CLASS="filename"
>/dev/hdb1</TT
> to <TT
CLASS="filename"
>/dev/home</TT
>. Crucially, it stores a
unique identifier for the hardware that was on <TT
CLASS="filename"
>/dev/hdb1</TT
> and stores that identifier along with
the link name that you specified in /etc/sysconfig/devlabel. If the
hardware is later moved to <TT
CLASS="filename"
>/dev/hdc1</TT
>,
its unique identifier will be queried (using
/usr/bin/partition_uuid), matched to its entry in
/etc/sysconfig/devlabel, and again linked to <TT
CLASS="filename"
>/dev/home</TT
>.
</P
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