From df5e69705f66e4fc6bcd939846bc4fb2de90a614 Mon Sep 17 00:00:00 2001 From: Bernhard Voelker Date: Wed, 26 Feb 2014 07:55:04 +0100 Subject: [PATCH] doc: add dd example for failing disks * doc/coreutils.texi (dd invocation): Add an example for how to call dd to save data from a failing disk. Mention GNU 'ddrescue' as one of the more specialized tools in such a case. --- doc/coreutils.texi | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/doc/coreutils.texi b/doc/coreutils.texi index 95453c7460..12ff311626 100644 --- a/doc/coreutils.texi +++ b/doc/coreutils.texi @@ -8928,6 +8928,25 @@ tape=/dev/rmt/0 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk @end example +@cindex ddrescue +@cindex disks, failing +For failing disks, other tools come with a great variety of extra +functionality to ease the saving of as much data as possible before the +disk finally dies, e.g. +@uref{http://www.gnu.org/software/ddrescue/, GNU @command{ddrescue}}. +However, in some cases such a tool is not available or the administrator +feels more comfortable with the handling of @command{dd}. +As a simple rescue method, call @command{dd} as shown in the following +example: the options @samp{conv=noerror,sync} are used to continue +after read errors and to pad out bad reads with NULs, while +@samp{iflag=fullblock} caters for short reads (which traditionally never +occur on disk based devices): + +@example +# Rescue data from an (unmounted!) partition of a failing disk. +dd conv=noerror,sync iflag=fullblock /mnt/rescue.img +@end example + Sending an @samp{INFO} signal to a running @command{dd} process makes it print I/O statistics to standard error and then resume copying. In the example below, -- 2.47.2