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6. Labels

In linux, hard drives are referred to as devices, and devices are pseudo files in /dev. For example, the first partition of the second lowest numbered SCSI drive is /dev/sdb1. If the drive referred to as /dev/sda is removed from the chain, then the latter partition is automatically renamed /dev/sda1 at reboot.

6.1. Volume Labels

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.

There are three tools to make volume labels: mke2fs, tune2fs and e2label.

6.1.1. Simple Invocation

e2label /dev/hdb1 pubsw

tune2fs -L pubsw /dev/hdb1

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.

mke2fs pubsw /dev/hdb1

mke2fs -L pubsw /dev/hdb1

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.

6.1.2. How to Use

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.


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

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 /k-space. The partition labeled "HOME" is always mounted on /home, 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"

6.2. Device Labels

devlabel is a script which creates symbolic links to devices. For example,

devlabel -d /dev/hdb1 -s /dev/home

will create a link from /dev/hdb1 to /dev/home. Crucially, it stores a unique identifier for the hardware that was on /dev/hdb1 and stores that identifier along with the link name that you specified in /etc/sysconfig/devlabel. If the hardware is later moved to /dev/hdc1, its unique identifier will be queried (using /usr/bin/partition_uuid), matched to its entry in /etc/sysconfig/devlabel, and again linked to /dev/home.