Convert and copy a file

See also ddrescue (gddrescue in the Debian repository)
The difference between dd and ddrescue:

• dd stops the transfer on a read error and displays the error
• ddrescue notes the error, leaves a blank spot in the output file, and continues transferring what data it can

See the dd man page for more options

Read from partition sdp1 and save in some_file.dd

dd if=/dev/sdp1 bs=512 of=/home/user/some_file.dd

Copy a chunck of data from a harddisk to a file

dd if=/dev/sdp of=/mnt/mountedPartition/file.dd ibs=4096 obs=512 skip=10000 count=20000 status=progress
dd if=/dev/sdp of=/mnt/sdq/file.dd ibs=512 obs=1024 seek=20000 count=1000000 status=progress

Read device sdp. Delete all 0x00's. Save the output to file nonull.txt

dd if=/dev/sdp ibs=512 obs=4096 | tr -d '\000' > nonull.txt

Read 2000 blocks of 512 bytes, skip blocks only containing NULL's and show them in hexdump

dd status=progress if=/dev/sdp1 bs=512 conv=sparse count=2000 | hexdump | less

Wipe the MBR (Master Boot Record)

dd if=/dev/zero of=/dev/sdp bs=446 count=1 

Save the contents of a SDcard to an image file
To check the contents of the image see Mount an img file

dd if=/dev/sdx of=/home/user/SDcard.img bs=4096

Put the contents of an image file on a SDcard

dd if=/home/user/SDcard.img of=/dev/sdd bs=4096

Copy all but the last 352 blocks because they contain bad blocks. dd does not have an option to skip bad blocks. A diskette has 2880 blocks of 512 bytes

dd if=/dev/sdc of=diskette.dd bs=512 count=2528 status=progress

Create a file filled with zero's

dd bs=1000000 count=1 if=/dev/zero of=hello.txt
dd if=/dev/zero of=~/testfile4.txt bs=20000000 count=1 status=progress

Fill the free space of a partition, hard disk, with zero's:

1. Boot the computer with a live CD like gParted
2. CTRL-ALT-F2
3. cd /mnt
4. mkdir filltemp
5. CTRL-ALT-F3
   1. lsblk (to see which partitions are on the computer)
6. CTRL-ALT-F2
   1. mount /dev/sdX filltemp (replace X with the partitionletter at hand)
   2. df (to see how big, in blocks, the frees space of the partitions is) → SEEdf value of the partition in 1k (1024 bytes) blocks
   3. dd if=/dev/zero of=/mnt/sdX/zerofill.txt bs=1024 count=SEEdf status=progress
   4. umount filltemp
   5. repeat from point 6.a for an other partition. Check with CTRL-ALT-F3 which one if needed

dd: /dev/sdp: cannot skip: Invalid argument

Solution

• Check the bs and ibs values in relation to the skip and count values. bs * skip = bytes to skip

ddrescue is a data recovery tool (gddrescue in the Debian repository)
GNU ddrescue manual

ddrescue -n /dev/sda /home/user/ddrescue.img /home/user/ddrescue.mapfile
ddrescue -f -r3 /dev/sda /dev/sdb /home/user/ddrescue.mapfile

Example output:

GNU ddrescue 1.27
Press Ctrl-C to interrupt
     ipos:  524222 kB, non-trimmed:        0 B,  current rate:  67567 kB/s
     opos:  524222 kB, non-scraped:        0 B,  average rate:  58246 kB/s
non-tried:  159517 MB,  bad-sector:        0 B,    error rate:       0 B/s
  rescued:  524222 kB,   bad areas:        0,        run time:          9s
pct rescued:    0.32%, read errors:        0,  remaining time:         45m
                              time since last successful read:          0s
Copying non-tried blocks... Pass 1 (forwards)

ddrescue: Can't open input file: Permission denied

You need to be root or use sudo

Loop devices
The fallocate command

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