Partition Table Backup
Many of us are doing backups of all kinds of data: from regular files, databases, to full partitions or hard drives. What I have noticed that very few peoples even think about the partition table. Given the importance of the partition table I would suggest to have a backup of it, in case you will have a corrupted partition table, if you made a change by mistake or even if that gets deleted somehow (by mistake or intentionally). You still have the data on the disk but without recreating the correct partition table it will not be very easy to get the data back. Anyway this is very easy to do, so it is better to have it on hand, than regret that you have not done this when needed.
We can get a quick look on all the existing partitions on all the available hard drives with fdisk using the -l switch without any other parameter:
fdisk -l Disk /dev/sda: 74.3 GB, 74355769344 bytes 255 heads, 63 sectors/track, 9039 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sda1 1 16 128488+ 83 Linux /dev/sda2 17 259 1951897+ 82 Linux swap / Solaris /dev/sda3 260 2083 14651280 83 Linux /dev/sda4 2084 9039 55874070 83 Linux Disk /dev/sdb: 73.4 GB, 73407820800 bytes 255 heads, 63 sectors/track, 8924 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 1 8924 71681998+ 83 Linux
If we add to the command line the particular device that corresponds to a hard disk, like /dev/sdb we get the same result only for that device:
fdisk -l /dev/sdb
Disk /dev/sdb: 73.4 GB, 73407820800 bytes 255 heads, 63 sectors/track, 8924 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sdb1 1 8924 71681998+ 83 Linux
Of course someone might use only this information to recreate the partition table by manually creating the same partitions with the same start/end blocks (in case you want to do that you just have to save the above output in a file so you have that information on hand when needed), but there is a simpler way using sfdisk:
sfdisk -d /dev/sda # partition table of /dev/sda unit: sectors /dev/sda1 : start= 63, size= 256977, Id=83 /dev/sda2 : start= 257040, size= 3903795, Id=82 /dev/sda3 : start= 4160835, size= 29302560, Id=83 /dev/sda4 : start= 33463395, size=111748140, Id=83
Using sfdisk with the -d option we can get a dump of the current partition table in a regular file, and if needed we can restore it from that file:
sfdisk -d /dev/sda > sda_table
and to restore the partition table:
sfdisk /dev/sda < sda_table
Regardless on the method used, having a backup of the partition table might be handy. ;)
One more tip: another usage of sfdisk with -d is to create an identical partition table from another hard disk. In this example we are partitioning sdb with the exact same partitions as sda:
sfdisk -d /dev/sda | sfdisk /dev/sdb
of course this can be handy when the hard drives are identical, in raid1 setups, etc.
Cleaning a MBR
dd if=/dev/zero of=/dev/sdb bs=512 count=1
LILO ERROR codes
- L : It means the first stage of boot loader is loaded in the main memory and initialized, but it can not load second stage of the boot loader. It generally indicates a hard drive geometry mismatch or media failure problem.
- LI : The first stage of boot loader has loaded second state of the boot loader, but it is unable to execute it. It can occur when you move /boot/boot.b without running map installer.
- LIL :It states that second stage of boot loader is started, but descriptor table can not be loaded from map file. It is generally caused due to media failure.
- LIL- : It denotes descriptor table corruption.