May 15, 2009

Show progress when using "dd"

dd is a generic command-line tool for copying files from 1 location to another. It is often used to copy entire disk images.

Like many Linux command line tools, it operates silently unless something unexpected happens. Its lack of visual progress feedback is a nice feature for scripting. However, it can leave you wondering about its progress if you are interactively dd-copying a large disk.

To illustrate, you run the following (valid, but perhaps not very useful) dd copy:

$ dd if=/dev/random of=/dev/null bs=1K count=100

It will run for a few minutes as it copies (and immediately discards) 100 blocks of randomly generated data, each of size 1 KB.

To get a progress report while dd is running, you need to open another virtual terminal, and then send a special USR1 signal to the dd process.

First, find out the process id of the dd process by running the following in the new virtual terminal.

$ pgrep -l '^dd$'
8789 dd

To send the USR1 signal to the dd prcoess:

$ kill -USR1 8789

Note that as soon as the USR1 signal is detected, dd will print out the current statistics to its STDERR.

$ dd if=/dev/random of=/dev/null bs=1K count=100

0+14 records in
0+14 records out
204 bytes (204 B) copied, 24.92 seconds, 0.0 kB/s

After reporting the status, dd will resume copying. You can repeat the above kill command any time you want to see the interim statistics. Alternatively, you can use the watch command to execute kill at a set interval.

$ watch -n 10 kill -USR1 8789

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Or you can use "pv" command from "pv" package.
pv - is a terminal-based tool for monitoring the progress of data through a pipeline.

Try for example:

pv -ptre FILE | dd of=FILE bs=1M

Gives a nice output with a progressbar, good for writing cf cards from images.

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Or just use dcfldd - (DoD Computer Forensics Lab) dd replacement with hashing.

Click Here!