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BADBLOCKS(8) System Manager's Manual BADBLOCKS(8)

NAME
badblocks - search a device for bad blocks

SYNOPSIS
badblocks [ -svwnfBX ] [ -b block_size ] [ -c blocks_at_once ] [ -d read_delay_factor ] [ -e
max_bad_blocks ] [ -i input_file ] [ -o output_file ] [ -p num_passes ] [ -t test_pattern ]
device [ last_block ] [ first_block ]

DESCRIPTION
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 number 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 pro‐
grams, it is important that the block size is properly specified, since the block numbers
which are generated are very dependent on the block size in use by the file system. 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.

OPTIONS
-b block_size
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 is 64.

-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 calcu‐
lated 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 pre‐
vious 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 de‐
vice which is mounted, since either can cause the system to potentially crash and/or
damage the file system 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 certainly 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 isn't
mounted.

-i input_file
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 existing file system, 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.

-o output_file
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).

-p num_passes
Repeat scanning the disk until there are no new blocks discovered in num_passes con‐
secutive 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 cur‐
rent 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.

-t test_pattern
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 spec‐
ified 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
next pattern.

-v Verbose mode. Will write the number of read errors, write errors and data- corrup‐
tions 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 available.

-X Internal flag only to be used by e2fsck(8) and mke2fs(8). It bypasses the exclusive
mode in-use device safety check.

WARNING
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 in‐
stead. It is slower, but it will preserve your data.

The -e option will cause badblocks to output a possibly incomplete list of bad blocks. There‐
fore 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.

AUTHOR
badblocks was written by Remy Card <Remy.Card AT linux.org>. Current maintainer is Theodore
Ts'o <tytso AT alum.edu>. Non-destructive read/write test implemented by David Beattie
<dbeattie AT softhome.net>.

AVAILABILITY
badblocks is part of the e2fsprogs package and is available from http://e2fsprogs.source‐
forge.net.