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 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         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

       -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 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

       -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

       -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

       -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
       filesystems) project.  Information about the project can be found
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E2fsprogs version 1.47.0      February 2023                 BADBLOCKS(8)

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