| BLKDISCARD(8) | System Manager's Manual | BLKDISCARD(8) | 
blkdiscard —
| blkdiscard | [ -h] [-llength] [-pchunksize] [-n]
      [-ofirstbyte]
      [-R] [-s]
      [-V] [-v]
      [-z] file | 
| fdiscard | [ -ffirstbyte]
      [-h] [-llength] [-mchunksize] [-n]
      [-R] [-s]
      [-V] [-v]
      [-z] file | 
blkdiscard program can be used to discard portions
  of storage, and works on either device files directly or upon files inside of
  a mounted file-system. It provides access to the
  fdiscard(2) system call, and
  relies upon the backing device to have support in both the
  blkdiscard driver and in the hardware itself.
The fdiscard interface defaults to the
    “no-run” mode and requires the -R
    option to perform any actions.
-f
    firstbyte-h-l
    length-m
    chunksize-n-o
    firstbyte-f flag.-p
    chunksize-m flag.-R-s-V-v-z# blkdiscard -n -v filename # blkdiscard -n -v /dev/rwd0b
To discard all the blocks on a swap device:
# blkdiscard -v /dev/rwd0b
To discard all but the first 256MiB of a device, using 128MiB increments:
# blkdiscard -v -f 256m -m 128m /dev/rwd0c
To zero out the contents of a file or device:
# blkdiscard -v -z filename # blkdiscard -v -z /dev/device
blkdiscard command first appeared linux-util. This
  implementation was originally called fdiscard-stuff and has been converted to
  be blkdiscard(8) compatible
  and appeared in NetBSD 10.0.
blkdiscard command was written by
  Matthew R. Green ⟨mrg@eterna23.net⟩.
-s option is not
  yet implemented.
| January 13, 2024 | NetBSD 10.0 |