1FSTRIM(8) System Administration FSTRIM(8)
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6 fstrim - discard unused blocks on a mounted filesystem
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9 fstrim [-Aa] [-o offset] [-l length] [-m minimum-size] [-v] mountpoint
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13 fstrim is used on a mounted filesystem to discard (or "trim") blocks
14 which are not in use by the filesystem. This is useful for solid-state
15 drives (SSDs) and thinly-provisioned storage.
16 By default, fstrim will discard all unused blocks in the filesystem.
18 Options may be used to modify this behavior based on range or size, as
19 explained below.
20 The mountpoint argument is the pathname of the directory where the
22 filesystem is mounted.
23 Running fstrim frequently, or even using mount -o discard, might nega‐
25 tively affect the lifetime of poor-quality SSD devices. For most desk‐
26 top and server systems a sufficient trimming frequency is once a week.
27 Note that not all devices support a queued trim, so each trim command
28 incurs a performance penalty on whatever else might be trying to use
29 the disk at the time.
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33 The offset, length, and minimum-size arguments may be followed by the
34 multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on for
35 GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has
36 the same meaning as "KiB") or the suffixes KB (=1000), MB (=1000*1000),
37 and so on for GB, TB, PB, EB, ZB and YB.
38 -A, --fstab
41 Trim all mounted filesystems mentioned in /etc/fstab on devices
42 that support the discard operation. The root filesystem is
43 determined from kernel command line if missing in the file. The
44 other supplied options, like --offset, --length and --minimum,
45 are applied to all these devices. Errors from filesystems that
46 do not support the discard operation, read-only devices and
47 read-only filesystems are silently ignored.
48 -a, --all
50 Trim all mounted filesystems on devices that support the discard
51 operation. The other supplied options, like --offset, --length
52 and --minimum, are applied to all these devices. Errors from
53 filesystems that do not support the discard operation, read-only
54 devices and read-only filesystems are silently ignored.
55 -n, --dry-run
57 This option does everything apart from actually call FITRIM
58 ioctl.
59 -o, --offset offset
61 Byte offset in the filesystem from which to begin searching for
62 free blocks to discard. The default value is zero, starting at
63 the beginning of the filesystem.
64 -l, --length length
66 The number of bytes (after the starting point) to search for
67 free blocks to discard. If the specified value extends past the
68 end of the filesystem, fstrim will stop at the filesystem size
69 boundary. The default value extends to the end of the filesys‐
70 tem.
71 -m, --minimum minimum-size
73 Minimum contiguous free range to discard, in bytes. (This value
74 is internally rounded up to a multiple of the filesystem block
75 size.) Free ranges smaller than this will be ignored and fstrim
76 will adjust the minimum if it's smaller than the device's mini‐
77 mum, and report that (fstrim_range.minlen) back to userspace.
78 By increasing this value, the fstrim operation will complete
79 more quickly for filesystems with badly fragmented freespace,
80 although not all blocks will be discarded. The default value is
81 zero, discarding every free block.
82 -v, --verbose
84 Verbose execution. With this option fstrim will output the num‐
85 ber of bytes passed from the filesystem down the block stack to
86 the device for potential discard. This number is a maximum dis‐
87 card amount from the storage device's perspective, because
88 FITRIM ioctl called repeated will keep sending the same sectors
89 for discard repeatedly.
90 fstrim will report the same potential discard bytes each time,
92 but only sectors which had been written to between the discards
93 would actually be discarded by the storage device. Further, the
94 kernel block layer reserves the right to adjust the discard
95 ranges to fit raid stripe geometry, non-trim capable devices in
96 a LVM setup, etc. These reductions would not be reflected in
97 fstrim_range.len (the --length option).
98 --quiet
100 Suppress error messages. This option is meant to be used in
101 systemd service file or in cron scripts to hide warnings that
102 are result of known problems, such as NTFS driver reporting Bad
103 file descriptor when device is mounted read-only, or lack of
104 file system support for ioctl FITRIM call.
105 -V, --version
107 Display version information and exit.
108 -h, --help
110 Display help text and exit.
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114 0 success
115 1 failure
117 32 all failed
119 64 some filesystem discards have succeeded, some failed
121 The command fstrim --all returns 0 (all succeeded), 32 (all failed) or
123 64 (some failed, some succeeded).
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127 Lukas Czerner <lczerner@redhat.com>
128 Karel Zak <kzak@redhat.com>
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131 blkdiscard(8), mount(8)
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134 The fstrim command is part of the util-linux package and is available
135 from https://www.kernel.org/pub/linux/utils/util-linux/.
136util-linux May 2019 FSTRIM(8)