Linux

Grub Notes

To re-install grub manually (mostly for raid systems, if you want more than one drive to be bootable)

grub
grub> device (hd0) /dev/sda
grub> root (hd0,0)
grub> setup (hd0)

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded
Done.

grub> quit

Repeat above for each drive. Note the (hd0,0) refers to the boot partion.

mdadm

Example: To replace a drive

Fail the drive you want to replace in the array, i.e.

mdadm --manage /dev/mdx --fail /dev/hdxy

shutdown the system, replace the drive.

If the drive is not already blank, you may need to remove any previous raid usage:

boot from cd, rescue mode.

For most commands to work you need an /etc/mdadm.conf.

This can be setup using "mdadm -E --scan >/etc/mdadm.conf"

To get the /etc/mdadm.conf file from the drives in the system.

madam --zero-superblock /dev/hdxy for each partionion.

remove the partitions, recreate from an existing drive

sfdisk -d /dev/hdx | sfdiisk /dev/hdy

start the array used by the root filesystem

madam -A /dev/md1 --force --run

add the new drive/partion to the root md device

madam --manage /dev/md1 --add /dev/hdxy

wait for rebuild

do the same for the /boot patron

finally any data partions you have, these can be done either from a rescue setup or after a reboot.

Growing encrypted disks

This example show a domU client, since the disk is allocated in the Dom0 using lvm, you need to grow that first!

[root@skype ~]# mkdir /data
[root@skype ~]# mount /dev/mapper/data /data
[root@skype ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda              2064208   1499312    460040  77% /
tmpfs                    98396         0     98396   0% /dev/shm
/dev/mapper/data      77403712    184220  73287612   1% /data

fdisk -l (to find the correct partion layout/names etc)

Disk /dev/xvdb: 268 MB, 268435456 bytes
255 heads, 63 sectors/track, 32 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdb1               1          32      257008+  82  Linux swap / Solaris

Disk /dev/xvdc: 107.3 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdc1               1        9790    78638143+  83  Linux

Use fdisk to remove and re add a partition to grow the disk into

[root@skype ~]# fdisk /dev/xvdc

The number of cylinders for this disk is set to 13054.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/xvdc: 107.3 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdc1               1        9790    78638143+  83  Linux

Delete and re add partition

Command (m for help): d
Selected partition 1

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-13054, default 1): 
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-13054, default 13054): 
Using default value 13054

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

Re Open the Luks Device

[root@skype ~]# cryptsetup luksOpen /dev/xvdc1 data
Enter LUKS passphrase for /dev/xvdc1: 
padlock: VIA PadLock not detected.
key slot 0 unlocked.
Command successful.

Make sure crypto is aware of the new size

[root@skype ~]# cryptsetup resize data

Then resize it

[root@skype ~]# fsck.ext3 -f /dev/mapper/data 
e2fsck 1.39 (29-May-2006)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/data: 30743/9830400 files (0.1% non-contiguous), 546498/19659406 blocks

[root@skype ~]# resize2fs /dev/mapper/data 
resize2fs 1.39 (29-May-2006)
Resizing the filesystem on /dev/mapper/data to 26213926 (4k) blocks.
The filesystem on /dev/mapper/data is now 26213926 blocks long.

And re-mount it ready for use

[root@skype ~]# mount /dev/mapper/data /data

[root@skype ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda              2064208   1499392    459960  77% /
tmpfs                    98396         0     98396   0% /dev/shm
/dev/mapper/data     103210424    960112  97007532   1% /data