# man > badblocks(8) [_BADBLOCKS_(8)](https://www.chedong.com/phpMan.php/man/BADBLOCKS/8/markdown) System Manager's Manual [_BADBLOCKS_(8)](https://www.chedong.com/phpMan.php/man/BADBLOCKS/8/markdown) ## 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 ## OPTIONS ### -b _ Specify the size of blocks in bytes. The default is 1024. ### -c _ is the number of blocks which are tested at a time. The default is 64. ### -d _ 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 _ 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 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 _ 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)](https://www.chedong.com/phpMan.php/man/dumpe2fs/8/markdown) 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 is done. This option must not be combined with the **-w **option, as they are mutually exclusive. ### -o _ 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)](https://www.chedong.com/phpMan.php/man/e2fsck/8/markdown) or [**mke2fs**(8)](https://www.chedong.com/phpMan.php/man/mke2fs/8/markdown). ### -p _ 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 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 _ 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 tions to stderr. ### -w 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 ### -X 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 <>. Current maintainer is Theodore Ts'o <>. Non-destructive read/write test implemented by David Beattie <>. ## AVAILABILITY **badblocks **is part of the e2fsprogs package and is available from ‐ forge.net. ## SEE ALSO [**e2fsck**(8)](https://www.chedong.com/phpMan.php/man/e2fsck/8/markdown), [**mke2fs**(8)](https://www.chedong.com/phpMan.php/man/mke2fs/8/markdown) E2fsprogs version 1.47.0 February 2023 [_BADBLOCKS_(8)](https://www.chedong.com/phpMan.php/man/BADBLOCKS/8/markdown)