Chris Tyler - Fedora Linux

If the Initialize Entity button is deactivated (grayed-out and unclickable), look in the right pane for the reason that the partition is "Not initializable." The most common reason given is Foreign boot partition , which means that the partition is marked as bootable in the drive's partition table. To correct this, use fdisk on the disk containing the partition; for example, run fdisk on the disk /dev/sdb to edit the settings for the partition /dev/sdb1 :

# fdisk /dev/sdb

fdisk accepts single-letter commands. Enter pto print the partition table:

Command (m for help): p

Disk /dev/sdb: 8 MB, 8192000 bytes

4 heads, 16 sectors/track, 250 cylinders

Units = cylinders of 64 * 512 = 32768 bytes

Device Boot Start End Blocks Id System

/dev/sdb1 * 1 250 7987+ 1 FAT12

There is only one partition on this particular disk, and it is bootable (note the * in the Boot column). Use the a (activate) command to toggle the boot flag:

Command (m for help): a

Partition number (1-4):

1

Then use w to write the partition table to disk and exit:

Command (m for help): w

The partition table has been altered!

Calling ioctl( ) to re-read partition table.

Syncing disks.

You can now rerun the graphical LVM administration tool and initialize the partition for use with LVM. This gives you a new physical volume that you can work with.

The next step is to add the new physical volume to the volume group. You'll see the newly initialized partition under Unallocated Volumes in the left pane. Click on it, and then click on the button labeled "Add Volume to existing Volume Group." A menu of volume groups will appear; select the one to add it to, and then click Add.

Once you've added a PV, you can use the extra space to create new logical volumes or grow an existing volume.

To take a physical volume (partition) out of a volume group, select the PV in the left pane, and then click "Remove Volume from Volume Group." You will be prompted for confirmation (including any move of data to another device), and the PV will be removed (as long as the free space in the VG exceeds the size of the PV; otherwise, removing the PV would destroy data).

Logical volumes are almost always used to contain filesystems (the other common use is to hold swapspace). In essence, an LV serves as a container for a filesystem. This has several ramifications:

 The LV must be created before the filesystem can be created.

 The filesystem must be removed before the LV is destroyed.

 When growing an LV and filesystem, the LV must be grown first.

 When shrinking an LV and filesystem, the filesystem must be reduced first.

Fedora's LVM2 system provides the lvm command for administration. Typing lvmby itself starts a specialized shell:

# lvm

lvm>

At the lvm> prompt, you can enter any of the subcommands shown in Table 6-1.

Table 6-1. LVM subcommands

You can also enter any of these subcommands as the first argument on the lvm command line:

# lvm lvs

LV VG Attr LSize Origin Snap% Move Log Copy%

home main -wi-ao 1.00G

multimedia main -wi-ao 512.00M

root main -wi-ao 9.77G

swap main -wi-ao 1.00G

Symbolic links have been set up from /usr/sbin/ > to /usr/sbin/lvm , so you can just type the name of the subcommand at the regular bash shell prompt:

# ls -l /usr/sbin/lvs

lrwxrwxrwx 1 root root 3 Mar 20 14:49 /usr/sbin/lvs -> lvm

# lvs

LV VG Attr LSize Origin Snap% Move Log Copy%

home main -wi-ao 1.00G

multimedia main -wi-ao 512.00M

root main -wi-ao 9.77G

swap main -wi-ao 1.00G

The symbolic links are not available when you are in rescue mode (see Lab 10.6, "Using Rescue Mode on an Installation Disc"), so it's important to remember that you can also use these subcommands as arguments to the lvm command (for example, when in rescue mode, type lvm lvdisplay instead of lvdisplay).

Logical volumes can be accessed using any of three different device nodes:

 In the /dev/mapper directory, the entry named by the pattern vg - lv . For example, if the volume group main had a logical volume named home , it could be accessed using the name /dev/mapper/main-home .

 There is a separate directory in /dev for each volume group, and an entry for each logical volume within that directory. Our sample volume could be accessed as /dev/main/home . These names are slightly shorter to type than the ones in /dev/mapper , and are actually symbolic links to the longer names.

 Using /dev/dm- , where is a number sequentially assigned when volume groups are initially scanned at boot time (or when the LV is created, if it was created after the last boot). If a volume is the second one found during the vgscan , it can be accessed as /dev/dm-1 (the first one found is numbered 0 ). These names are a bit harder to use, since the VG and LV are not identified; to find the corresponding entry in /dev/mapper , compare the minor device numbers. You cannot use these names in rescue mode.

In addition to these device node names, some LVM commands allow the volume group and logical volume names to be written as vg / lv for example, main/multimedia refers to the LV multimedia within the VG main .