badblocks - search a device for bad blocks
SYNOPSIS badblocks [ -svwnf ] [ -b block-size ] [ -c blocks_at_once ] [ -i input_file ] [ -o output_file ] [ -p num_passes ] device [ last-block ] [ start-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. start-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 is very dependent on the block size in use. 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.
-b block-size Specify the size of blocks in bytes. -c number of blocks is the number of blocks which are tested at a time. The default is 16. Increasing this number will increase the efficiency of badblocks but also will increase its memory usage. Badblocks needs memory proportional to the number of blocks tested at once, in read-only mode, proportional to twice that number in read-write mode, and proportional to three times that number in non-destructive read-write mode. If you set the number-of-blocks parameter to too high a value, badblocks will exit almost immediately with an out-of-memory error “while allocating buffers”. If you set it too low, however, for a non-destructive-write-mode test, then it’s possble for questionable blocks on an unreliable hard drive to be hidden by the effects of the hard disk track buffer. -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 overriden 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. -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 pass. -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. -s Show the progress of the scan by writing out the block numbers as they are checked. -v Verbose mode. -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.
Never use the -w option on an 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.
SEE ALSO e2fsck(8), mke2fs(8)