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fstrim - Man Page

discard unused blocks on a mounted filesystem

Examples (TL;DR)


fstrim [-Aav] [-o offset] [-l length] [-m minimum-size] [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 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.


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).


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

Print version and exit.

Exit Status






all failed


some filesystem discards have succeeded, some failed

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


Lukas Czerner, Karel Zak

See Also

blkdiscard(8), mount(8)

Reporting Bugs

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


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

Referenced By

blkdiscard(8), btrfs(5), dmeventd(8), public-inbox-tuning(7), public-inbox-v2-format(5), virt-v2v(1).

2024-04-24 util-linux 2.40.2 System Administration