blockdev(8) — Linux manual page


BLOCKDEV(8)                 System Administration                BLOCKDEV(8)

NAME         top

       blockdev - call block device ioctls from the command line

SYNOPSIS         top

       blockdev [-q] [-v] command [command...] device [device...]
       blockdev --report [device...]
       blockdev -h|-V

DESCRIPTION         top

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

OPTIONS         top

       -q     Be quiet.

       -v     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.

COMMANDS         top

       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

              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

              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.

AUTHORS         top

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

AVAILABILITY         top

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

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found at 
       ⟨⟩.  If you have a
       bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2020-09-18.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-09-15.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

util-linux                       August 2010                     BLOCKDEV(8)

Pages that refer to this page: fdisk(8)mount(8)sfdisk(8)systemd-udevd(8)systemd-udevd-control.socket(8)systemd-udevd-kernel.socket(8)systemd-udevd.service(8)