BLOCKDEV(8) System Administration BLOCKDEV(8)

blockdev - call block device ioctls from the command line

blockdev [-q] [-v] command [command...] device [device...]

blockdev --report [device...]

blockdev -h|-V

The utility blockdev allows one to call block device ioctls from the command line.


Be quiet.


Be verbose.


Print a report for the specified device. It is possible to give multiple devices. If none is given, all devices which appear in /proc/partitions are shown. Note that the partition StartSec is in 512-byte sectors.

-h, --help

Display help text and exit.

-V, --version

Print version and exit.

It is possible to give multiple devices and multiple commands.


Flush buffers.


Get alignment offset.


Print the blocksize in bytes. This size does not describe device topology. It’s the size used internally by the kernel and it may be modified (for example) by filesystem driver on mount.


Get discard zeroes support status.


Get disk sequence number.


Get zone size in 512-byte sectors.


Get filesystem readahead in 512-byte sectors.


Get minimum I/O size.


Get optimal I/O size.


Get max sectors per request.


Get physical block (sector) size.


Print readahead (in 512-byte sectors).


Get read-only. Print 1 if the device is read-only, 0 otherwise.


Print device size in bytes.


Print device size (32-bit!) in sectors. Deprecated in favor of the --getsz option.


Print logical sector size in bytes - usually 512.


Get size in 512-byte sectors.


Reread partition table

--setbsz bytes

Set blocksize. Note that the block size is specific to the current file descriptor opening the block device, so the change of block size only persists for as long as blockdev has the device open, and is lost once blockdev exits.

--setfra sectors

Set filesystem readahead (same as --setra on 2.6 kernels).

--setra sectors

Set readahead (in 512-byte sectors).


Set read-only. The currently active access to the device may not be affected by the change. For example, a filesystem already mounted in read-write mode will not be affected. The change applies after remount.


Set read-write.

blockdev was written by Andries E. Brouwer and rewritten by Karel Zak.

For bug reports, use the issue tracker at

The blockdev command is part of the util-linux package which can be downloaded from Linux Kernel Archive

2024-07-04 util-linux 2.40.2