Manual: fstrim

FSTRIM(8) System Administration FSTRIM(8)

NAME
fstrim - discard unused blocks on a mounted filesystem

SYNOPSIS
fstrim [-v] [-o offset] [-l length] [-m minimum-size] -A|-a|mountpoint

DESCRIPTION
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 and is
required when -A, -a, --fstab, or --all are unspecified.

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.

OPTIONS
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.

-A, --fstab
Trim all mounted filesystems mentioned in /etc/fstab on devices that support the discard
operation. The root filesystem is determined from kernel command line if missing in the file. The
other supplied options, like --offset, --length and --minimum, are applied to all these devices.
Errors from filesystems that do not support the discard operation, read-only devices, autofs and
read-only filesystems are silently ignored. Filesystems with "X-fstrim.notrim" mount option are
skipped.

-a, --all
Trim all mounted filesystems on devices that support the discard operation. The other supplied
options, like --offset, --length and --minimum, are applied to all these devices. Errors from
filesystems that do not support the discard operation, read-only devices and read-only
filesystems are silently ignored.

-n, --dry-run
This option does everything apart from actually call FITRIM ioctl.

-o, --offset offset
Byte offset in the filesystem from which to begin searching for free blocks to discard. The
default value is zero, starting at the beginning of the filesystem.

-l, --length length
The number of bytes (after the starting point) to search for free blocks to discard. If the
specified value extends past the end of the filesystem, fstrim will stop at the filesystem size
boundary. The default value extends to the end of the filesystem.

-I, --listed-in list
Specifies a colon-separated list of files in fstab or kernel mountinfo format. All missing or
empty files are silently ignored. The evaluation of the list stops after first non-empty file.
For example:

--listed-in /etc/fstab:/proc/self/mountinfo.

Filesystems with "X-fstrim.notrim" mount option in fstab are skipped.

-m, --minimum minimum-size
Minimum contiguous free range to discard, in bytes. (This value is internally rounded up to a
multiple of the filesystem block size.) Free ranges smaller than this will be ignored and fstrim
will adjust the minimum if it’s smaller than the device’s minimum, and report that
(fstrim_range.minlen) back to userspace. By increasing this value, the fstrim operation will
complete more quickly for filesystems with badly fragmented freespace, although not all blocks
will be discarded. The default value is zero, discarding every free block.

-t, --types list
Specifies allowed or forbidden filesystem types when used with --all or --fstab. The list is a
comma-separated list of the filesystem names. The list follows how mount -t evaluates type
patterns. Only specified filesystem types are allowed. All specified types are forbidden if the
list is prefixed by "no" or each filesystem prefixed by "no" is forbidden. If the option is not
used, then all filesystems (except "autofs") are allowed.

-v, --verbose
Verbose execution. With this option fstrim will output the number of bytes passed from the
filesystem down the block stack to the device for potential discard. This number is a maximum
discard amount from the storage device’s perspective, because FITRIM ioctl called repeated will
keep sending the same sectors for discard repeatedly.

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).

--quiet-unsupported
Suppress error messages if trim operation (ioctl) is unsupported. This option is meant to be used
in systemd service file or in cron(8) scripts to hide warnings that are result of known problems,
such as NTFS driver reporting Bad file descriptor when device is mounted read-only, or lack of
file system support for ioctl FITRIM call. This option also cleans exit status when unsupported
filesystem specified on fstrim command line.

-h, --help
Display help text and exit.

-V, --version
Display version and exit.

EXIT STATUS
0
success

1
failure

32
all failed

64
some filesystem discards have succeeded, some failed

The command fstrim --all returns 0 (all succeeded), 32 (all failed) or 64 (some failed, some
succeeded).

AUTHORS
Lukas Czerner , Karel Zak

Manual: fstrim

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