blockdev — call block device ioctls from the command line


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

blockdev −−report [ device... ]


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



Print version and exit.


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.


It is possible to give multiple devices and multiple commands.


Flush buffers.


Get alignment offset.


Print blocksize in bytes.


Get discard zeroes support status.


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 sectorsize 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 like --setra on 2.6 kernels).

−−setra sectors

Set readahead (in 512-byte sectors).


Set read-only.


Set read-write.


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


The blockdev command is part of the util-linux package and is available from

  Copyright 1998 Andries E. Brouwer (
Copyright 2007 Karel Zak <>

May be distributed under the GNU General Public License