blockdev(8) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| OPTIONS \| COMMANDS \| AUTHORS \| REPORTING BUGS \| AVAILABILITY

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.

       --report
           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
           Display version and exit.

COMMANDS top

       It is possible to give multiple devices and multiple commands.

       --flushbufs
           Flush buffers.

       --getalignoff
           Get alignment offset.

       --getbsz
           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.

       --getdiscardzeroes
           Get discard zeroes support status.

       --getdiskseq
           Get disk sequence number.

       --getzonesz
           Get zone size in 512-byte sectors.

       --getfra
           Get filesystem readahead in 512-byte sectors.

       --getiomin
           Get minimum I/O size.

       --getioopt
           Get optimal I/O size.

       --getmaxsect
           Get max sectors per request.

       --getpbsz
           Get physical block (sector) size.

       --getra
           Print readahead (in 512-byte sectors).

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

       --getsize64
           Print device size in bytes.

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

       --getss
           Print logical sector size in bytes - usually 512.

       --getsz
           Get size in 512-byte sectors.

       --rereadpt
           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).

       --setro
           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.

       --setrw
           Set read-write.

AUTHORS top

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

REPORTING BUGS top

       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY top

       The blockdev command is part of the util-linux package which can
       be downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
       part of the util-linux (a random collection of Linux utilities)
       project. Information about the project can be found at 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
       bug report for this manual page, send it to
       [email protected]. This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2025-08-11. (At that time, the date of the most recent commit that
       was found in the repository was 2025-08-05.) 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 [email protected]

util-linux 2.42-start-521-ec46  2025-08-09                    BLOCKDEV(8)

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