badblocks
Scan a storage device for bad sectors
TLDR
Search a disk for bad blocks by using a non-destructive read-only test
Search an unmounted disk for bad blocks with a [n]on-destructive read-write test
Search an unmounted disk for bad blocks with a destructive [w]rite test
Use the destructive [w]rite test and [s]how [v]erbose progress
In destructive mode, [o]utput found blocks to a file
Use the destructive mode with improved speed using 4K [b]lock size and 64K block [c]ount
SYNOPSIS
badblocks [-sSvwz] [-b blocksize] [-c count] [-i input] [-o output] [-t patterns] [-B] device [first-block [last-block]]
PARAMETERS
-b blocksize
Specify block size in bytes (default 1024)
-c count
Number of blocks to read per pass (default 64)
-i input
File containing known bad blocks to skip
-o output
Write bad block list to file instead of stdout
-s
Show progress report with estimated completion time
-t patterns
Specify test patterns (hex bytes, e.g., 'a0' or multiple '0xaa:0x55')
-v
Verbose mode, print more details
-w
Destructive read-write test mode (erases data!)
-z
Zero-fill blocks after writing patterns (destructive)
-B
Validate last-block arg against device size
-S
Use device size from filesystem superblock
-V
Print version information
DESCRIPTION
badblocks is a Linux utility from the e2fsprogs package used to test hard disks and other block devices for bad sectors or blocks. It performs read-only scans by default, reporting unreadable blocks, or destructive read-write-verify tests with the -w option, which writes test patterns, reads them back, and verifies integrity—but erases all data in the process.
In non-destructive mode, it sequentially reads blocks, marking bad ones in output. Progress can be shown with -s, and verbose details with -v. Output lists bad block numbers, suitable for input to tools like e2fsck -l badblocks.list to mark them bad on filesystems.
Specify block size with -b, test range with first/last block args, or patterns like 0xaa with -t. It's essential for disk diagnostics before formatting or when suspecting media failure, but requires unmounted devices. Tests can take hours or days on large drives.
CAVEATS
Destructive modes (-w, -z) permanently erase data; use only on empty, unmounted devices. Tests are extremely time-intensive on large drives. Not suitable for SSDs (use smartctl instead). May falsely report bad blocks on slow/removable media.
OUTPUT USAGE
Bad block list can pipe to e2fsck -l - or save as file for mke2fs -B to exclude during formatting.
Example: badblocks -v /dev/sda > badblocks.list
TEST PATTERNS
Default: sequential byte increments. Custom: -t 0xaa:0x55:0xff cycles through patterns. Use hex values for thorough testing.
HISTORY
Developed in 1992 by Remy Card for ext2 filesystem tools; maintained by Theodore Ts'o in e2fsprogs since 1994. Evolved for ext3/4 support, with options added for better progress reporting and patterns over decades.
