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

           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.

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 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

           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

REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       The blockdev command is part of the util-linux package which can
       be downloaded from Linux Kernel Archive
       <>. 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
       2023-12-22. (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-14.) 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 2.39.594-1e0ad      2023-07-19                    BLOCKDEV(8)

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