ASGAUR

If you don't want to take any chances with your data, it is recommended that you backup hard disk partition table. Last Friday I was discussing some issues with one of our customer and he pointed out me dd command.

Backup MBR with dd command

dd the old good command which now backup partition tables even writes CDs . Backing up partition is nothing but actually backing up MBR (master boot record). The command is as follows for backing up MBR stored on /dev/sdX or /dev/hdX :

#dd if=/dev/sdX of=/tmp/sda-mbr.bin bs=512 count=1

Replace X with actual device name such as /dev/sda.

Now to restore partition table to disk, all you need to do is use dd command:

#dd if=sda-mbr.bin of=/dev/sdX bs=1 count=64 \
skip=446 seek=446

dd command works with Solaris, HP-UX and all other UNIX like operating systems. Read man page of dd for more info.

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man dd

NAME
dd - convert and copy a file

SYNOPSIS
dd [OPERAND]...
dd OPTION

DESCRIPTION
Copy a file, converting and formatting according to the operands.

bs=BYTES
force ibs=BYTES and obs=BYTES

cbs=BYTES
convert BYTES bytes at a time

conv=CONVS
convert the file as per the comma separated symbol list

count=BLOCKS
copy only BLOCKS input blocks

ibs=BYTES
read BYTES bytes at a time

if=FILE
read from FILE instead of stdin

iflag=FLAGS
read as per the comma separated symbol list

obs=BYTES
write BYTES bytes at a time

of=FILE
write to FILE instead of stdout

oflag=FLAGS
write as per the comma separated symbol list

seek=BLOCKS
skip BLOCKS obs-sized blocks at start of output

skip=BLOCKS
skip BLOCKS ibs-sized blocks at start of input

status=noxfer
suppress transfer statistics

BLOCKS and BYTES may be followed by the following multiplicative suffixes: xM M, c 1, w 2, b 512, kB 1000, K 1024, MB 1000*1000, M
1024*1024, GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y.

Each CONV symbol may be:

ascii from EBCDIC to ASCII

ebcdic from ASCII to EBCDIC

ibm from ASCII to alternate EBCDIC

block pad newline-terminated records with spaces to cbs-size

unblock
replace trailing spaces in cbs-size records with newline

lcase change upper case to lower case

nocreat
do not create the output file

excl fail if the output file already exists

notrunc
do not truncate the output file

ucase change lower case to upper case

swab swap every pair of input bytes

noerror
continue after read errors

sync pad every input block with NULs to ibs-size; when used

with block or unblock, pad with spaces rather than NULs

fdatasync physically write output file data before finishing fsync likewise, but also write metadata

Each FLAG symbol may be:

append append mode (makes sense only for output)

direct use direct I/O for data

dsync use synchronized I/O for data

sync likewise, but also for metadata

nonblock
use non-blocking I/O

nofollow
do not follow symlinks

noctty do not assign controlling terminal from file

Sending a USR1 signal to a running âddâ process makes it print I/O statistics to standard error and then resume copying.

$ dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid; sleep 1; kill $pid

18335302+0 records in 18335302+0 records out 9387674624 bytes (9.4 G copied, 34.6279 seconds, 271 MB/s

Options are:

--help display this help and exit
--version
output version information and exit

AUTHOR
Written by Paul Rubin, David MacKenzie, and Stuart Kemp.

REPORTING BUGS
Report bugs to . COPYRIGHT Copyright © 2006 Free Software Foundation, Inc. This is free software. You may redistribute copies of it under the terms of the GNU General Public License . There is NO WARRANTY, to the extent permitted by law. SEE ALSO The full documentation for dd is maintained as a Texinfo manual. If the info and dd programs are properly installed at your site, the command info dd should give you access to the complete manual. dd (coreutils) 5.97 November 2006 DD(1)