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.TH FSTRIM 8 "May 2019" "util-linux" "System Administration"
.SH NAME
fstrim \- discard unused blocks on a mounted filesystem
.SH SYNOPSIS
.B fstrim
.RB [ \-Aa ]
.RB [ \-o
.IR offset ]
.RB [ \-l
.IR length ]
.RB [ \-m
.IR minimum-size ]
.RB [ \-v ]
.I mountpoint
.SH DESCRIPTION
.B 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.
.PP
By default,
.B 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.
.PP
The
.I mountpoint
argument is the pathname of the directory where the filesystem
is mounted.
.PP
Running
.B fstrim
frequently, or even using
.BR "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.
.SH OPTIONS
The \fIoffset\fR, \fIlength\fR, and \fIminimum-size\fR 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.
.IP "\fB\-A, \-\-fstab\fP"
Trim all mounted filesystems mentioned in \fI/etc/fstab\fR 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 \fB\-\-offset\fR, \fB\-\-length\fR and
\fB-\-minimum\fR, 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.
.IP "\fB\-a, \-\-all\fP"
Trim all mounted filesystems on devices that support the discard operation.
The other supplied options, like \fB\-\-offset\fR, \fB\-\-length\fR and
\fB-\-minimum\fR, 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.
.IP "\fB\-n, \-\-dry\-run\fP"
This option does everything apart from actually call FITRIM ioctl.
.IP "\fB\-o, \-\-offset\fP \fIoffset\fP"
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.
.IP "\fB\-l, \-\-length\fP \fIlength\fP"
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,
.B fstrim
will stop at the filesystem size boundary. The default value extends to
the end of the filesystem.
.IP "\fB\-I, \-\-listed\-in\fP \fIlist\fP"
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
\fIlist\fP stops after first non-empty file. For example: \fB--listed-in /etc/fstab:/proc/self/mountinfo\fR.
.IP "\fB\-m, \-\-minimum\fP \fIminimum-size\fP"
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.
.IP "\fB\-v, \-\-verbose\fP"
Verbose execution. With this option
.B 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
.I FITRIM
ioctl called repeated will keep sending the same sectors for discard repeatedly.
.sp
.B 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
.B \-\-length
option).
.TP
.B \-\-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 scripts to hide warnings
that are result of known problems,
such as NTFS driver
reporting
.I Bad file descriptor
when device is mounted read-only, or lack of file system support for ioctl
FITRIM call.
.TP
.BR \-V , " \-\-version"
Display version information and exit.
.TP
.BR \-h , " \-\-help"
Display help text and exit.
.SH EXIT STATUS
.IP 0
success
.IP 1
failure
.IP 32
all failed
.IP 64
some filesystem discards have succeeded, some failed
.PP
The command
.B fstrim \-\-all
returns 0 (all succeeded), 32 (all failed) or 64 (some failed, some succeeded).
.SH AUTHORS
.nf
Lukas Czerner <lczerner@redhat.com>
Karel Zak <kzak@redhat.com>
.fi
.SH SEE ALSO
.BR blkdiscard (8),
.BR mount (8)
.SH AVAILABILITY
The fstrim command is part of the util-linux package and is available from
https://www.kernel.org/pub/linux/utils/util-linux/.
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