BADBLOCKS(8) System Manager's Manual BADBLOCKS(8)
badblocks - search a device for bad blocks
badblocks [ -svwnfBX ] [ -b block_size ] [ -c blocks_at_once ] [ -d
read_delay_factor ] [ -e max_bad_blocks ] [ -i input_file ] [ -o out-
put_file ] [ -p num_passes ] [ -t test_pattern ] device [ last_block ]
[ first_block ]
badblocks is used to search for bad blocks on a device (usually a disk
partition). device is the special file corresponding to the device
(e.g /dev/hdc1). last_block is the last block to be checked; if it is
not specified, the last block on the device is used as a default.
first_block is an optional parameter specifying the starting block num-
ber for the test, which allows the testing to start in the middle of
the disk. If it is not specified the first block on the disk is used
as a default.
Important note: If the output of badblocks is going to be fed to the
e2fsck or mke2fs programs, it is important that the block size is prop-
erly specified, since the block numbers which are generated are very
dependent on the block size in use by the filesystem. For this reason,
it is strongly recommended that users not run badblocks directly, but
rather use the -c option of the e2fsck and mke2fs programs.
Specify the size of blocks in bytes. The default is 1024.
-c number of blocks
is the number of blocks which are tested at a time. The default
-d read delay factor
This parameter, if passed and non-zero, will cause bad blocks to
sleep between reads if there were no errors encountered in the
read operation; the delay will be calculated as a percentage of
the time it took for the read operation to be performed. In
other words, a value of 100 will cause each read to be delayed
by the amount the previous read took, and a value of 200 by
twice the amount.
-e max bad block count
Specify a maximum number of bad blocks before aborting the test.
The default is 0, meaning the test will continue until the end
of the test range is reached.
-f Normally, badblocks will refuse to do a read/write or a non-
destructive test on a device which is mounted, since either can
cause the system to potentially crash and/or damage the filesys-
tem even if it is mounted read-only. This can be overridden
using the -f flag, but should almost never be used --- if you
think you're smarter than the badblocks program, you almost cer-
tainly aren't. The only time when this option might be safe to
use is if the /etc/mtab file is incorrect, and the device really
Read a list of already existing known bad blocks. Badblocks
will skip testing these blocks since they are known to be bad.
If input_file is specified as "-", the list will be read from
the standard input. Blocks listed in this list will be omitted
from the list of new bad blocks produced on the standard output
or in the output file. The -b option of dumpe2fs(8) can be used
to retrieve the list of blocks currently marked bad on an exist-
ing filesystem, in a format suitable for use with this option.
-n Use non-destructive read-write mode. By default only a non-
destructive read-only test is done. This option must not be
combined with the -w option, as they are mutually exclusive.
Write the list of bad blocks to the specified file. Without
this option, badblocks displays the list on its standard output.
The format of this file is suitable for use by the -l option in
e2fsck(8) or mke2fs(8).
Repeat scanning the disk until there are no new blocks discov-
ered in num_passes consecutive scans of the disk. Default is 0,
meaning badblocks will exit after the first pass.
-s Show the progress of the scan by writing out rough percentage
completion of the current badblocks pass over the disk. Note
that badblocks may do multiple test passes over the disk, in
particular if the -p or -w option is requested by the user.
Specify a test pattern to be read (and written) to disk blocks.
The test_pattern may either be a numeric value between 0 and
ULONG_MAX-1 inclusive, or the word "random", which specifies
that the block should be filled with a random bit pattern. For
read/write (-w) and non-destructive (-n) modes, one or more test
patterns may be specified by specifying the -t option for each
test pattern desired. For read-only mode only a single pattern
may be specified and it may not be "random". Read-only testing
with a pattern assumes that the specified pattern has previously
been written to the disk - if not, large numbers of blocks will
fail verification. If multiple patterns are specified then all
blocks will be tested with one pattern before proceeding to the
-v Verbose mode. Will write the number of read errors, write
errors and data- corruptions to stderr.
-w Use write-mode test. With this option, badblocks scans for bad
blocks by writing some patterns (0xaa, 0x55, 0xff, 0x00) on
every block of the device, reading every block and comparing the
contents. This option may not be combined with the -n option,
as they are mutually exclusive.
-B Use buffered I/O and do not use Direct I/O, even if it is avail-
-X Internal flag only to be used by e2fsck(8) and mke2fs(8). It
bypasses the exclusive mode in-use device safety check.
Never use the -w option on a device containing an existing file system.
This option erases data! If you want to do write-mode testing on an
existing file system, use the -n option instead. It is slower, but it
will preserve your data.
The -e option will cause badblocks to output a possibly incomplete list
of bad blocks. Therefore it is recommended to use it only when one
wants to know if there are any bad blocks at all on the device, and not
when the list of bad blocks is wanted.
badblocks was written by Remy Card <Remy.Card@linux.org>. Current
maintainer is Theodore Ts'o <email@example.com>. Non-destructive
read/write test implemented by David Beattie <firstname.lastname@example.org>.
badblocks is part of the e2fsprogs package and is available from
E2fsprogs version 1.44.1 March 2018 BADBLOCKS(8)
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