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 GB) 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
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)