badblocks(8) — Linux manual page


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

NAME         top

       badblocks - search a device for bad blocks

SYNOPSIS         top

       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         top

       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 programs, 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 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

OPTIONS         top

       -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 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
              filesystem 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 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.

       -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 consecutive scans of the disk.
              Default is 0, meaning badblocks will exit after the first

       -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.

       -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 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 next pattern.

       -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

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

WARNING         top

       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.

AUTHOR         top

       badblocks was written by Remy Card <>.  Current
       maintainer is Theodore Ts'o <>.  Non-destructive
       read/write test implemented by David Beattie <>.

AVAILABILITY         top

       badblocks is part of the e2fsprogs package and is available from

SEE ALSO         top

       e2fsck(8), mke2fs(8)

COLOPHON         top

       This page is part of the e2fsprogs (utilities for ext2/3/4
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E2fsprogs version 1.46-WIP       March 2020                     BADBLOCKS(8)

Pages that refer to this page: e2fsck(8)mke2fs(8)mkfs(8)