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💾 BLOCKDEV(8) System Administration BLOCKDEV(8)

📜 NAME

blockdev - call block device ioctls from the command line

🚀 Quick Reference

Use Case	Command	Description
Get device size in bytes	blockdev --getsize64 /dev/sda	📏 Print device size in bytes
Check read-only status	blockdev --getro /dev/sda	🔒 Returns 1 if read-only, 0 otherwise
Set read-only	blockdev --setro /dev/sda	🔒 Set device to read-only (remount may be needed)
Get readahead value	blockdev --getra /dev/sda	📖 Print readahead in 512-byte sectors
Flush buffers	blockdev --flushbufs /dev/sda	🧹 Write all cached data to disk
Reread partition table	blockdev --rereadpt /dev/sda	🔄 Force kernel to reload partition layout

⚙️ SYNOPSIS

blockdev [-q] [-v] command [command...] device [device...]

blockdev --report [device...]

blockdev -h|-V

📖 DESCRIPTION

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

⚙️ OPTIONS

• -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. ℹ️

📂 COMMANDS

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. ♻️
• --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

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

🐛 REPORTING BUGS

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

📦 AVAILABILITY

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/>.

util-linux 2.37.2 2021-06-02 BLOCKDEV(8)

📜 NAME 🚀 Quick Reference ⚙️ SYNOPSIS 📖 DESCRIPTION ⚙️ OPTIONS 📂 COMMANDS 👤 AUTHORS 🐛 REPORTING BUGS 📦 AVAILABILITY