dd is a traditional utility for binary data copies

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35
votes
4answers
17k views

Is there a way to determine the optimal value for the bs parameter to dd?

On occasion I've seen comments online along the lines of "make sure you set 'bs=' because the default value will take too long," and my own extremely-unscientific experiences of, "well that seemed to ...
36
votes
3answers
5k views

When is dd suitable for copying data? (or, when are read() and write() partial)

Short version: In what circumstances is dd safe to use for copying data, safe meaning that there is no risk of corruption due to a partial read or write? Long version — preamble: dd is often used to ...
61
votes
7answers
11k views

dd vs cat — is dd still relevant these days?

I recently realized we can use cat as much as dd, and it's actually faster than dd I know that dd was useful in dealing with tapes where block size actually mattered in correctness, not just ...
19
votes
4answers
5k views

Why does dd from /dev/random give different file sizes?

I am running the following command on an ubuntu system: dd if=/dev/random of=rand bs=1K count=2 However, every time I run it, I end up with a file of a different size. Why is this? How can I ...
11
votes
3answers
1k views

saving data from a failing drive

An external 3½" HDD seems to be in danger of failing — it's making ticking sounds when idle. I've acquired a replacement drive, and want to know the best strategy to get the data off of the dubious ...
69
votes
10answers
45k views

How do I know if dd is still working?

I've not used dd all that much, but so far it's not failed me yet. Right now, I've had a dd going for over 12 hours - I'm writing an image back to the disk it came from - and I'm getting a little ...
19
votes
4answers
8k views

Clone whole partition or hard drive to a sparse file

I like to clone a whole partition or a whole hard drive onto a larger external disk but like to create a sparse file. I often use dd for cloning, but it doesn't support sparse files. As a workaround I ...
7
votes
2answers
2k views

Create random data with dd and get “partial read warning”. Is the data after the warning now really random?

I create a 1TB file with random data with dd if=/dev/urandom of=file bs=1M count=1000000. Now I check with kill -SIGUSR1 <PID> the progress and get the following: 691581+0 Datensätze ein ...
32
votes
7answers
22k views

Best way to remove bytes from the start of a file?

Today I had to remove the first 1131 bytes from an 800MB mixed text / binary file, a filtered subversion dump I'm hacking for a new repository. What's the best way to do this? To start with I tried ...
10
votes
1answer
16k views

How do I mount an `img` created with /bin/dd of a hard drive?

I used dd to backup a 80GB drive dd if=/dev/sdb of=~/sdb.img Now I need to access some files on that drive, but I don't want to copy the ".img" back over the drive. mount ~/sdb.img /mnt/sdb ...
21
votes
4answers
8k views

What does dd stand for?

I know very well what the command does, but man dd, info dd tell me: 'Convert and copy a file', as does GNU Coreutils. Google says its an abbreviation of everything between medicine and bad webchat ...
4
votes
2answers
437 views

How to parallelize dd?

I'm currently having trouble with dd invoked with a sparse file as input (if) and a file as output (of) with conv=sparse. dd seems to be using one core of the CPU (Intel(R) Core(TM) i7-3632QM CPU @ ...
3
votes
1answer
204 views

Why is dd so slow with a bs of 100M [closed]

I just tried to overwrite a fast ssd using dd. Using the ubuntu boot image I typed in: dd if=/dev/zero of=/dev/sda bs=100M error writing '/dev/sda': No space left on device blah blah 256 GB copied, ...
3
votes
2answers
3k views

Check integrity of a dd backup

I just made a backup of an entire hard drive (50GB) over ssh via: dd if=/dev/hda | buffer -s 64k -S 10m | ssh myuser@myhost "cat > ~/image.img" What's now the best way to check the integrity of ...
10
votes
5answers
681 views

Is it safe to take the drive image of the current working drive?

I have to backup my hard disk. I want to use dd and put the image on an external hdd. Can I do this using dd from the OS that resides on the hdd itself or do I have to boot from another device, for ...
7
votes
4answers
8k views

'seek' argument in command dd

Can some explain me what is happening in the following lines? dd if=/dev/urandom bs=4096 seek=7 count=2 of=file_with_holes especially seek part is not clear Man pages says : seek=BLOCKS ...
5
votes
2answers
5k views

Unpack files and directories from an image created by dd?

I created an image of an NTFS partition using dd. I wonder if I can unload/unpack the files and directories in the image to any partition whose size is larger than the image size, so that I can ...
4
votes
6answers
2k views

How to write repeated free-form strings to a file, as fast as 'dd'?

dd can write repeating \0 bytes to a file very fast, but it can't write repeating arbitary strings. Is there a bash-shell method to write repeating arbitary strings equally as fast as 'dd' (including ...
1
vote
2answers
6k views

How do I resize a disk image device?

I'm trying to reduce the size of a backup drive image. Original disk had these partitions: Model: ST916082 1A (scsi) Disk /dev/sde: 160GB Sector size (logical/physical): 512B/512B Partition Table: ...
1
vote
2answers
4k views

How to write a file at various offsets to a filesystem partition with dd command

Requirement I want to write a file at various offsets into the partition Partition /dev/part2 is mounted at /mypart I tried the command below: dd if=/dev/urandom of=/mypart/aaa bs=1024 seek=0 ...
13
votes
3answers
2k views

Read the middle of a large file

I have a 1 TB file. I would like to read from byte 12345678901 to byte 19876543212 and put that on standard output on a machine with 100 MB RAM. I can easily write a perl script that does this. ...
10
votes
2answers
7k views

Use `dd` to cut file end part

There is probably simple trick to do this, but I can't figure from man page. How do I cut last 1MB from file with undetermined size for example, by using dd?
6
votes
3answers
1k views

Linux/GParted can see partition table but dd bs=512 count=1 can't

I have an MBR formatted sd card and when connect to a Linux machine (xubuntu 12.04) it can mount a partition and parse the file system (as can GParted). However, when I try to read the MBR from the ...
4
votes
3answers
667 views

from a sparse file to a block device over the network

If I have a sparse file representing a block device, then how can I efficiently restore the file over a network? Ideally, I'd use rsync -S host:file /dev/sdb, but rsync won't write to block devices. ...
3
votes
3answers
230 views

How to inspect the contents of /dev/sdt?

I have what I hope is not a huge problem, but could end up being a very large problem. For some context, I mistakenly ran this command on my 27'' iMac: sudo dd if=ubuntu-rescue.img of=/dev/sdt ...
2
votes
2answers
2k views

How to use DD to clone a partition off a disk image?

I have a disk image, it's a "whole" disk image, e.g., contains multiple partitions, and I want to clone just one of them (not the first one..) onto a partition on an external drive with multiple ...
2
votes
3answers
2k views

How to clone linux installation onto an external harddisk?

I see a lot of dd related questions, but could not find answers to the following. If question/answers already exist, please point to them, then flag to close, delete or merge. Can a working linux ...