blockdev - Man Page

• Print a report for all devices: sudo blockdev --report
• Print a report for a specific device: sudo blockdev --report /dev/sdXY
• Get the size of a device in 512-byte sectors: sudo blockdev --getsz /dev/sdXY
• Set read-only: sudo blockdev --setro /dev/sdXY
• Set read-write: sudo blockdev --setrw /dev/sdXY
• Flush buffers: sudo blockdev --flushbufs /dev/sdXY
• Get the physical block size: sudo blockdev --getpbsz /dev/sdXY
• Set the read-ahead value to 128 sectors: sudo blockdev --setra 128 /dev/sdXY

tldr.sh

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 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.

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

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

The blockdev command is part of the util-linux package which can be downloaded from Linux Kernel Archive.

fdisk(8), guestfish(1), guestfs(3), mount(8), scsi_ch_swp(8), sfdisk(8), systemd-udevd.service(8).