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August 2010


Miscellaneous system utilities for Linux


blockdev - call block device ioctls from the command line


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


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


-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 Print version and exit.


It is possible to give multiple devices and multiple commands.
--flushbufs Flush buffers.
--getalignoff Get alignment offset.
--getbsz Print blocksize in bytes. This size does not describe device topology. It’s size used internally by kernel and it maybe modified (for example) by filesystem driver on mount.
--getdiscardzeroes Get discard zeroes support status.
--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 like --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 filesystem already mounted in read-write mode will not be affected. The change applies after remount.
--setrw 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
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