fstrim [-a] [-o offset] [-l length] [-m minimum-size] [-v] mountpoint
fstrim is used on a mounted filesystem to discard (or "trim") blocks which are not in use by the filesystem. This is useful for solid-state drives (SSDs) and thinly-provisioned storage.
By default, fstrim will discard all unused blocks in the filesystem. Options may be used to modify this behavior based on range or size, as explained below.
The mountpoint argument is the pathname of the directory where the filesystem is mounted.
Running fstrim frequently, or even using mount -o discard, might negatively affect the lifetime of poor-quality SSD devices. For most desktop and server systems a sufficient trimming frequency is once a week. Note that not all devices support a queued trim, so each trim command incurs a performance penalty on whatever else might be trying to use the disk at the time.
The offset, length, and minimum-size arguments may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB") or the suffixes KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB.
fstrim will report the same potential discard bytes each time, but only sectors which had been written to between the discards would actually be discarded by the storage device. Further, the kernel block layer reserves the right to adjust the discard ranges to fit raid stripe geometry, non-trim capable devices in a LVM setup, etc. These reductions would not be reflected in fstrim_range.len (the --length option).
The command fstrim --all returns 0 (all succeeded), 32 (all failed) or 64 (some failed, some succeeded).
Lukas Czerner <email@example.com> Karel Zak <firstname.lastname@example.org>
The fstrim command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.