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<a name="Invoking-ddrescue"></a>
<div class="header">
<p>
Next: <a href="Logfile-structure.html#Logfile-structure" accesskey="n" rel="next">Logfile structure</a>, Previous: <a href="Algorithm.html#Algorithm" accesskey="p" rel="prev">Algorithm</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="Concept-index.html#Concept-index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Invoking-ddrescue-1"></a>
<h2 class="chapter">5 Invoking ddrescue</h2>
<a name="index-invoking-ddrescue"></a>
<a name="index-options"></a>
<a name="index-usage"></a>
<a name="index-version"></a>
<p>The format for running ddrescue is:
</p>
<div class="example">
<pre class="example">ddrescue [<var>options</var>] <var>infile</var> <var>outfile</var> [<var>logfile</var>]
</pre></div>
<p>ddrescue supports the following options:
</p>
<dl compact="compact">
<dt>‘<samp>-h</samp>’</dt>
<dt>‘<samp>--help</samp>’</dt>
<dd><p>Print an informative help message describing the options and exit.
</p>
</dd>
<dt>‘<samp>-V</samp>’</dt>
<dt>‘<samp>--version</samp>’</dt>
<dd><p>Print the version number of ddrescue on the standard output and exit.
</p>
</dd>
<dt>‘<samp>-a <var>bytes</var></samp>’</dt>
<dt>‘<samp>--min-read-rate=<var>bytes</var></samp>’</dt>
<dd><p>Minimum read rate of good non-tried areas, in bytes per second. If the
read rate falls below this value, ddrescue will skip ahead a variable
amount depending on rate and error histories. The skipped blocks are
tried in additional passes (before trimming) where the minimum read rate
is divided by ten before each pass, until there are no more non-tried
blocks left.
</p>
<p>If <var>bytes</var> is 0 (auto), the minimum read rate is recalculated for
each block as <span class="nolinebreak">(average_rate</span> / 10)<!-- /@w -->. Values above device capabilities
are ignored.
</p>
</dd>
<dt>‘<samp>-A</samp>’</dt>
<dt>‘<samp>--try-again</samp>’</dt>
<dd><p>Mark all non-trimmed and non-scraped blocks inside the rescue domain as
non-tried before beginning the rescue. Try this if the drive stops
responding and ddrescue immediately starts scraping failed blocks when
restarted. If ‘<samp>--retrim</samp>’ is also specified, mark all failed blocks
inside the rescue domain as non-tried.
</p>
</dd>
<dt>‘<samp>-b <var>bytes</var></samp>’</dt>
<dt>‘<samp>--sector-size=<var>bytes</var></samp>’</dt>
<dd><p>Sector (hardware block) size of input device in bytes (usually 512 for
hard discs and 3.5" floppies, 1024 for 5.25" floppies, and 2048 for
cdroms). Defaults to 512.
</p>
</dd>
<dt>‘<samp>-B</samp>’</dt>
<dt>‘<samp>--binary-prefixes</samp>’</dt>
<dd><p>Show units with binary prefixes (powers of 1024).<br>
SI prefixes (powers of 1000) are used by default. (See table below).
</p>
</dd>
<dt>‘<samp>-c <var>sectors</var></samp>’</dt>
<dt>‘<samp>--cluster-size=<var>sectors</var></samp>’</dt>
<dd><p>Number of sectors to copy at a time. Defaults to 64 KiB / <span class="nolinebreak">sector_size</span><!-- /@w -->.
Try smaller values for slow drives. The number of sectors per track (18
or 9) is a good value for floppies.
</p>
</dd>
<dt>‘<samp>-C</samp>’</dt>
<dt>‘<samp>--complete-only</samp>’</dt>
<dd><p>Limit rescue domain to the blocks listed in the <var>logfile</var>. Do not
read new data beyond <var>logfile</var> limits. This is useful when reading
from devices of undefined size (like raw devices), when the drive
returns an incorrect size, or when reading from a partial copy. It can
only be used after a first rescue attempt, possibly limited with the
‘<samp>--size</samp>’ option, has produced a complete <var>logfile</var>.
</p>
</dd>
<dt>‘<samp>-d</samp>’</dt>
<dt>‘<samp>--direct</samp>’</dt>
<dd><p>Use direct disc access to read from <var>infile</var>, bypassing the kernel
cache. (Open the file with the O_DIRECT flag). Use it only on devices or
partitions, not on regular files. Sector size must be correctly set for
this to work. Not all systems support this.
</p>
<p>If your system does not support direct disc access, ddrescue will warn
you. If the sector size is not correctly set, all reads will result in
errors, and no data will be rescued.
</p>
</dd>
<dt>‘<samp>-D</samp>’</dt>
<dt>‘<samp>--synchronous</samp>’</dt>
<dd><p>Use synchronous writes for <var>outfile</var>. (Issue a fsync call after
every write). May be useful when forcing the drive to remap its bad
sectors.
</p>
</dd>
<dt>‘<samp>-e [+]<var>n</var></samp>’</dt>
<dt>‘<samp>--max-errors=[+]<var>n</var></samp>’</dt>
<dd><p>Maximum number of error areas allowed before giving up. Defaults to
infinity. If <var>n</var> is preceded by ‘<samp>+</samp>’ the number refers to new
error areas found in this run, not counting those already annotated in
the <var>logfile</var>.
</p>
</dd>
<dt>‘<samp>-E <var>bytes</var></samp>’</dt>
<dt>‘<samp>--max-error-rate=<var>bytes</var></samp>’</dt>
<dd><p>Maximum rate of errors allowed before giving up, in bytes per second.
Defaults to infinity. The rate being measured is that of actually failed
reads, so the rescue may finish because of this rate being exceeded even
if the total error size (errsize) does not change because the areas
being tried are already marked as errors.
</p>
</dd>
<dt>‘<samp>-f</samp>’</dt>
<dt>‘<samp>--force</samp>’</dt>
<dd><p>Force overwrite of <var>outfile</var>. Needed when <var>outfile</var> is not a
regular file, but a device or partition. This option is just a safeguard
to prevent the inadvertent destruction of partitions, and is ignored for
regular files.
</p>
</dd>
<dt>‘<samp>-F <var>types</var></samp>’</dt>
<dt>‘<samp>--fill-mode=<var>types</var></samp>’</dt>
<dd><p>Fill the blocks in <var>outfile</var> specified as any of <var>types</var> in
<var>logfile</var>, with data read from <var>infile</var>. <var>types</var> contains
one or more of the status characters defined in the chapter Logfile
structure (see <a href="Logfile-structure.html#Logfile-structure">Logfile structure</a>). See the chapter Fill mode
(see <a href="Fill-mode.html#Fill-mode">Fill mode</a>) for a complete description of the fill mode.
</p>
</dd>
<dt>‘<samp>-G</samp>’</dt>
<dt>‘<samp>--generate-mode</samp>’</dt>
<dd><p>Generate an approximate <var>logfile</var> from the <var>infile</var> and
<var>outfile</var> of the original rescue run. Note that you must keep the
original offset between ‘<samp>--input-position</samp>’ and
‘<samp>--output-position</samp>’ of the original rescue run. See the chapter
Generate mode (see <a href="Generate-mode.html#Generate-mode">Generate mode</a>) for a complete description of the
generate mode.
</p>
</dd>
<dt>‘<samp>-H <var>file</var></samp>’</dt>
<dt>‘<samp>--test-mode=<var>file</var></samp>’</dt>
<dd><p>Builds a map of good/bad blocks using the logfile <var>file</var> and uses it
to simulate read errors in <var>infile</var>. The blocks marked as finished
in <var>file</var> will be read normally. All other block types will be
considered read errors without even trying to read them from
<var>infile</var>. This mode is an aid in improving the algorithm of ddrescue
and is also useful to verify that ddrescue produces accurate results in
presence of read errors.
</p>
</dd>
<dt>‘<samp>-i <var>bytes</var></samp>’</dt>
<dt>‘<samp>--input-position=<var>bytes</var></samp>’</dt>
<dd><p>Starting position of the rescue domain in <var>infile</var>, in bytes.
Defaults to 0. This is not the point from which ddrescue starts copying.
(For example, if you pass the ‘<samp>--reverse</samp>’ option to ddrescue, it
starts copying from the end of the rescue domain). In fill mode it
refers to a position in the <var>infile</var> of the original rescue run. See
the chapter Fill mode (see <a href="Fill-mode.html#Fill-mode">Fill mode</a>) for details.
</p>
</dd>
<dt>‘<samp>-I</samp>’</dt>
<dt>‘<samp>--verify-input-size</samp>’</dt>
<dd><p>Compare the size of <var>infile</var> with the size calculated from the list
of blocks contained in the <var>logfile</var>, and exit with status 1 if they
differ. This is not enabled by default because the size of some devices
can’t be known in advance and because the size derived from the
<var>logfile</var> may be incomplete, for example after doing a partial
rescue.
</p>
</dd>
<dt>‘<samp>-K [<var>initial</var>][,<var>max</var>]</samp>’</dt>
<dt>‘<samp>--skip-size=[<var>initial</var>][,<var>max</var>]</samp>’</dt>
<dd><p>Set limits to skip size during the copying phase. At least one of
<var>initial</var> or <var>max</var> must be specified. <var>initial</var> is the size
to skip on the first read error or slow read, in bytes. <var>max</var> is the
maximum size to skip. The values given will be rounded to the next
multiple of sector size. The skip size will be doubled for each read
error or slow read until it reaches <var>max</var> or, if <var>max</var> is
omitted, 1% of the size of <var>infile</var> or 1 GiB (whichever is smaller),
and will be reset to <var>initial</var> when good data is found. Valid values
range from 64 KiB to 1 GiB. <var>initial</var> defaults to 64 KiB. An
<var>initial</var> value of 0 disables skipping entirely.
</p>
<p>If ddrescue is having difficulties skipping away from a large area with
scattered errors, or if the device has large error areas at regular
intervals, you can increase the initial skip size with this option.
Inversely, if ddrescue is skipping too much, leaving large non-tried
areas behind each error (which will be read later in the usually slower
backwards direction), you can reduce the maximum skip size, or disable
skipping.
</p>
<p>‘<samp>--skip-size</samp>’ is independent from ‘<samp>--cluster-size</samp>’. The size
to skip is calculated from the end of the block that just failed.
</p>
</dd>
<dt>‘<samp>-L</samp>’</dt>
<dt>‘<samp>--loose-domain</samp>’</dt>
<dd><p>Accept an incomplete synthetic (user fabricated) domain logfile or
test-mode logfile and fill the gaps in the list of data blocks with
non-tried blocks. The blocks in the logfile must be strictly ascending
and non-overlapping, but they do not need to be contiguous. This option
allows making quick edits to a logfile without all the size calculations
involved in making all data blocks contiguous again.
</p>
</dd>
<dt>‘<samp>-m <var>file</var></samp>’</dt>
<dt>‘<samp>--domain-logfile=<var>file</var></samp>’</dt>
<dd><p>Restrict the rescue domain to the blocks marked as finished in the
logfile <var>file</var>. This is useful for merging partially recovered
images of backups, or if the destination drive fails during the rescue.
</p>
</dd>
<dt>‘<samp>-M</samp>’</dt>
<dt>‘<samp>--retrim</samp>’</dt>
<dd><p>Mark all failed blocks inside the rescue domain as non-trimmed before
beginning the rescue. The effect is similar to ‘<samp>--retry-passes=1</samp>’,
but the bad sectors are tried in a different order, making perhaps
possible to rescue some of them.
</p>
</dd>
<dt>‘<samp>-n</samp>’</dt>
<dt>‘<samp>--no-scrape</samp>’</dt>
<dd><p>Skip the scraping phase. Avoids spending a lot of time trying to rescue
the most difficult parts of the file.
</p>
</dd>
<dt>‘<samp>-N</samp>’</dt>
<dt>‘<samp>--no-trim</samp>’</dt>
<dd><p>Skip the trimming phase. Specially useful in the first parts of a
multi-part rescue.
</p>
</dd>
<dt>‘<samp>-o <var>bytes</var></samp>’</dt>
<dt>‘<samp>--output-position=<var>bytes</var></samp>’</dt>
<dd><p>Starting position of the image of the rescue domain in <var>outfile</var>, in
bytes. Defaults to ‘<samp>--input-position</samp>’. The bytes below <var>bytes</var>
aren’t touched if they exist and truncation is not requested. Else they
are set to 0.
</p>
</dd>
<dt>‘<samp>-O</samp>’</dt>
<dt>‘<samp>--reopen-on-error</samp>’</dt>
<dd><p>Close <var>infile</var> and then reopen it after every read error and, if
‘<samp>--min-read-rate</samp>’ is set, after every slow read encountered both
during the copying phase. Use this option if you notice a permanent drop
in transfer rate after finding read errors or slow areas. But be warned
that most probably the slowing-down is intentionally caused by the
kernel in an attempt to increase the probability of reading data from
the device.
</p>
</dd>
<dt>‘<samp>-p</samp>’</dt>
<dt>‘<samp>--preallocate</samp>’</dt>
<dd><p>Preallocate space on disc for <var>outfile</var>. Only space for regular
files can be preallocated. If preallocation succeeds, rescue will not
fail due to lack of free space on disc. If ddrescue can’t determine the
size to preallocate, you may need to specify it with some combination of
the ‘<samp>--input-position</samp>’, ‘<samp>--output-position</samp>’, ‘<samp>--size</samp>’,
and ‘<samp>--domain-logfile</samp>’ options.
</p>
</dd>
<dt>‘<samp>-P[<var>lines</var>]</samp>’</dt>
<dt>‘<samp>--data-preview[=<var>lines</var>]</samp>’</dt>
<dd><p>Show <var>lines</var> lines of the latest data read in ‘<samp><span class="nolinebreak">16-byte</span> hex + ASCII</samp>’<!-- /@w --> format. Valid values for <var>lines</var> range from 1 to 32. If
<var>lines</var> is omitted, a default value of 3 is used.
</p>
</dd>
<dt>‘<samp>-q</samp>’</dt>
<dt>‘<samp>--quiet</samp>’</dt>
<dd><p>Quiet operation. Suppress all messages.
</p>
</dd>
<dt>‘<samp>-r <var>n</var></samp>’</dt>
<dt>‘<samp>--retry-passes=<var>n</var></samp>’</dt>
<dd><p>Exit after given number of retry passes. Defaults to 0. -1 means
infinity. Every bad sector is tried only once in each pass. To retry bad
sectors detected on a previous run, you must specify a non-zero number
of retry passes.
</p>
</dd>
<dt>‘<samp>-R</samp>’</dt>
<dt>‘<samp>--reverse</samp>’</dt>
<dd><p>Reverse the direction of all passes (copying, trimming, scraping and
retrying). Every pass that is normally run forwards will now be run
backwards, and vice versa. ‘<samp>--reverse</samp>’ does not modify the size of
the blocks copied during each phase, just the order in which they are
tried.
</p>
</dd>
<dt>‘<samp>-s <var>bytes</var></samp>’</dt>
<dt>‘<samp>--size=<var>bytes</var></samp>’</dt>
<dd><p>Maximum size of the rescue domain, in bytes. It limits the amount of
input data to be copied. If ddrescue can’t determine the size of the
input device, you may need to specify it with this option. Note that
this option does not specify the size of the resulting <var>outfile</var>.
For example, the following command creates an <var>outfile</var> 300 bytes
long, but only writes data on the last 200 bytes:
</p>
<div class="example">
<pre class="example">ddrescue -i 100 -s 200 infile outfile logfile
</pre></div>
</dd>
<dt>‘<samp>-S</samp>’</dt>
<dt>‘<samp>--sparse</samp>’</dt>
<dd><p>Use sparse writes for <var>outfile</var>. (The blocks of zeros are not
actually allocated on disc). May save a lot of disc space in some cases.
Not all systems support this. Only regular files can be sparse.
</p>
</dd>
<dt>‘<samp>-t</samp>’</dt>
<dt>‘<samp>--truncate</samp>’</dt>
<dd><p>Truncate <var>outfile</var> to zero size before writing to it. Only works for
regular files, not for drives or partitions.
</p>
</dd>
<dt>‘<samp>-T <var>interval</var></samp>’</dt>
<dt>‘<samp>--timeout=<var>interval</var></samp>’</dt>
<dd><p>Maximum time since last successful read allowed before giving up.
Defaults to infinity. <var>interval</var> is a rational number (like 1.5 or
1/2) optionally followed by one of ‘<samp>s</samp>’, ‘<samp>m</samp>’, ‘<samp>h</samp>’ or
‘<samp>d</samp>’, meaning seconds, minutes, hours and days respectively. If no
unit is specified, it defaults to seconds.
</p>
</dd>
<dt>‘<samp>-u</samp>’</dt>
<dt>‘<samp>--unidirectional</samp>’</dt>
<dd><p>Run all passes in the same direction. Forwards by default, or backwards
if the option ‘<samp>--reverse</samp>’ is also given.
</p>
</dd>
<dt>‘<samp>-v</samp>’</dt>
<dt>‘<samp>--verbose</samp>’</dt>
<dd><p>Verbose mode. Further -v’s (up to 4) increase the verbosity level.
</p>
</dd>
<dt>‘<samp>-w</samp>’</dt>
<dt>‘<samp>--ignore-write-errors</samp>’</dt>
<dd><p>Make fill mode ignore write errors. This is useful to avoid ddrescue
exiting because of new errors developing while wiping the good sectors
of a failing drive. Fill mode normally writes to <var>outfile</var> one
cluster at a time. With this option, after the first write error is
found in an area, the rest of that area is filled sector by sector.
</p>
</dd>
<dt>‘<samp>-x <var>bytes</var></samp>’</dt>
<dt>‘<samp>--extend-outfile=<var>bytes</var></samp>’</dt>
<dd><p>Extend the size of <var>outfile</var> to make it at least <var>bytes</var> long.
If the size of <var>outfile</var> is already equal or longer than <var>bytes</var>
then this option does nothing. Use this option to guarantee a minimum
size for <var>outfile</var>. Only regular files can be extended.
</p>
</dd>
<dt>‘<samp>-X</samp>’</dt>
<dt>‘<samp>--exit-on-error</samp>’</dt>
<dd><p>Exit after the first read error is encountered during the copying phase.
This is similar but different to ‘<samp>--timeout=0</samp>’, which waits until
the screen status is refreshed (at least 1 second). If there is at least
one successful read per second, ‘<samp>--timeout=0</samp>’ does not make
ddrescue to exit.
</p>
<p>This is also similar but different to ‘<samp>--max-errors=+0</samp>’, which
exits when a new error area is found. If the read errors are adjacent to
existing error areas, no new error areas are produced (just enlarged),
and ‘<samp>--max-errors=+0</samp>’ does not make ddrescue to exit.
</p>
</dd>
<dt>‘<samp>-1 <var>file</var></samp>’</dt>
<dt>‘<samp>--log-rates=<var>file</var></samp>’</dt>
<dd><p>Log rates and error sizes every second in <var>file</var>. If <var>file</var>
already exists, it will be overwritten. Every time the screen is updated
with new details, some of those details (time, input position, current
and average rates, number of errors and error size) are written to
<var>file</var> in a format usable by plotting utilities like gnuplot. This
allows a posterior analysis of the drive to see if it has any weak zones
(areas where the transfer rate drops well below the sustained average).
</p>
</dd>
<dt>‘<samp>-2 <var>file</var></samp>’</dt>
<dt>‘<samp>--log-reads=<var>file</var></samp>’</dt>
<dd><p>Log all read operations in <var>file</var>. If <var>file</var> already exists, it
will be overwritten. Every read attempt and its result (position, size,
copied size and error size) is written to <var>file</var>. (The position
written is always the beginning of the block tried, even if reading
backwards). A line is also written at the beginning of each phase
(copying, trimming, scraping and retrying). Finally, a line with a time
mark is written every second (unless the read takes more time). Use this
option with caution because <var>file</var> may become very large very
quickly. Use lzip to compress <var>file</var> if you need to store or
transmit it.
</p>
</dd>
<dt>‘<samp>--ask</samp>’</dt>
<dd><p>Ask for user confirmation before starting the copy. If the first letter
of the answer is ‘<samp>y</samp>’, ddrescue starts copying. Else it exits with
status 1.<br>
If they can be obtained, ddrescue shows the model and serial number of
the input and output devices. Else it shows the size in bytes of the
corresponding file or device.
</p>
</dd>
<dt>‘<samp>--cpass=<var>n</var>[,<var>n</var>]</samp>’</dt>
<dd><p>Select what pass(es) to run during the copying phase. Valid values for
<var>n</var> range from 0 to 3. ‘<samp>--cpass=0</samp>’ skips the copying phase
entirely. To run only the given pass(es), specify also ‘<samp>--no-trim</samp>’
and ‘<samp>--no-scrape</samp>’.
</p>
</dd>
<dt>‘<samp>--pause=<var>interval</var></samp>’</dt>
<dd><p>Time to wait between passes. Defaults to 0. <var>interval</var> is formatted
as in the option ‘<samp>--timeout</samp>’ above.
</p>
</dd>
</dl>
<p>Numbers given as arguments to options (positions, sizes, rates, etc) may
be expressed as decimal, hexadecimal or octal values (using the same
syntax as integer constants in C++), and may be followed by a multiplier
and an optional ‘<samp>B</samp>’ for "byte".
</p>
<p>Table of SI and binary prefixes (unit multipliers):
</p>
<table>
<tr><td>Prefix</td><td>Value</td><td>|</td><td>Prefix</td><td>Value</td></tr>
<tr><td></td><td></td><td>|</td><td>s</td><td>sectors</td></tr>
<tr><td>k</td><td>kilobyte (10^3 = 1000)</td><td>|</td><td>Ki</td><td>kibibyte (2^10 = 1024)</td></tr>
<tr><td>M</td><td>megabyte (10^6)</td><td>|</td><td>Mi</td><td>mebibyte (2^20)</td></tr>
<tr><td>G</td><td>gigabyte (10^9)</td><td>|</td><td>Gi</td><td>gibibyte (2^30)</td></tr>
<tr><td>T</td><td>terabyte (10^12)</td><td>|</td><td>Ti</td><td>tebibyte (2^40)</td></tr>
<tr><td>P</td><td>petabyte (10^15)</td><td>|</td><td>Pi</td><td>pebibyte (2^50)</td></tr>
<tr><td>E</td><td>exabyte (10^18)</td><td>|</td><td>Ei</td><td>exbibyte (2^60)</td></tr>
<tr><td>Z</td><td>zettabyte (10^21)</td><td>|</td><td>Zi</td><td>zebibyte (2^70)</td></tr>
<tr><td>Y</td><td>yottabyte (10^24)</td><td>|</td><td>Yi</td><td>yobibyte (2^80)</td></tr>
</table>
<br>
<p>Exit status: 0 for a normal exit, 1 for environmental problems (file not
found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or
invalid input file, 3 for an internal consistency error (eg, bug) which
caused ddrescue to panic.
</p>
<p>If ddrescue is interrupted by a signal, it updates the logfile and then
terminates by raising the signal received.
</p>
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