https://halfgeek.org/wiki/index.php?action=history&feed=atom&title=DdDd - Revision history2026-05-28T12:11:28ZRevision history for this page on the wikiMediaWiki 1.34.0https://halfgeek.org/wiki/index.php?title=Dd&diff=2292&oldid=prevPsmay: /* Print status messages */2017-05-03T17:56:53Z<p><span dir="auto"><span class="autocomment">Print status messages</span></span></p>
<p><b>New page</b></p><div>{{unix}}{{lowercase|title=dd}}<br />
'''dd''' (doesn't stand for anything that matters) is a powerful and dangerous unix program that performs raw block copies of data. In particular, it is often used for copying hard disk data raw partition-to-partition, partition-to-file, and/or file-to-partition.<br />
<br />
==Synopsis==<br />
<br />
Often the invocation is as simple as<br />
<br />
dd if=''<input file = stdin>'' of=''<output file = stdout>'' bs=''<block size = 512>'' count=''<block count = until end of input>''<br />
<br />
That is, from the beginning of ''if'' copy ''count'' blocks of ''bs'' bytes to the file ''of''.<br />
<br />
===Block sizes===<br />
<br />
bs can use human suffixes. Use e.g. kB, MB, GB for decimal meanings (1000^n), but use e.g. K, M, G or KiB, MiB, GiB for the binary equivalents (1024^n).<br />
<br />
bs can be replaced by ibs and obs to set in and out block sizes separately.<br />
<br />
===Writing to files in-place===<br />
<br />
See conv=notrunc, seek=, skip=.<br />
<br />
===Hard disk recovery===<br />
<br />
When recovering a failing drive, among the recommendations are:<br />
<br />
* Use a small block size, such as 512 bytes<br />
* Use the conv option noerror, which causes the program to continue even if a read fails<br />
* Use the conv option sync, which causes short (erroneously read) blocks to be padded out so that any good output still aligns correctly<br />
<br />
In other words:<br />
<br />
dd bs=512 if=/dev/''<some device>'' of=output.img conv=noerror,sync<br />
<br />
==Print status messages==<br />
<br />
By default, dd keeps quiet about its progress. In most versions, there is a way to send it a signal to request a progress report.<br />
<br />
In Linux, this signal is the USR1 signal. The following command will cause all running dd processes to echo status every second:<br />
<br />
while killall -USR1 dd; do sleep 1; done<br />
<br />
killall can be replaced with the equivalent kill command and pid to signal only one process.<br />
<br />
===dcfldd===<br />
<br />
The program '''dcfldd''' is a fork of dd that has special security- and display-related options. The USR1 signal is not necessary to produce a readout; by default, a status is printed to stderr every 256 blocks. Set <code>statusinterval=<''number of blocks''></code> to change the interval.</div>Psmay