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 mount.

              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
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  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.service(8)