1FALLOCATE(1) User Commands FALLOCATE(1)
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6 fallocate - preallocate or deallocate space to a file
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9 fallocate [-c|-p|-z] [-o offset] -l length [-n] filename
10 fallocate -d [-o offset] [-l length] filename
12 fallocate -x [-o offset] -l length filename
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16 fallocate is used to manipulate the allocated disk space for a file,
17 either to deallocate or preallocate it. For filesystems which support
18 the fallocate system call, preallocation is done quickly by allocating
19 blocks and marking them as uninitialized, requiring no IO to the data
20 blocks. This is much faster than creating a file by filling it with
21 zeroes.
22 The exit status returned by fallocate is 0 on success and 1 on failure.
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26 The length and offset arguments may be followed by the multiplicative
27 suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB,
28 EiB, ZiB, and YiB (the "iB" is optional, e.g., "K" has the same meaning
29 as "KiB") or the suffixes KB (=1000), MB (=1000*1000), and so on for
30 GB, TB, PB, EB, ZB, and YB.
31 The options --collapse-range, --dig-holes, --punch-hole, and
33 --zero-range are mutually exclusive.
34 -c, --collapse-range
36 Removes a byte range from a file, without leaving a hole. The byte
37 range to be collapsed starts at offset and continues for length
38 bytes. At the completion of the operation, the contents of the file
39 starting at the location offset+length will be appended at the
40 location offset, and the file will be length bytes smaller. The
41 option --keep-size may not be specified for the collapse-range
42 operation.
43 Available since Linux 3.15 for ext4 (only for extent-based files)
45 and XFS.
46 A filesystem may place limitations on the granularity of the
48 operation, in order to ensure efficient implementation. Typically,
49 offset and len must be a multiple of the filesystem logical block
50 size, which varies according to the filesystem type and
51 configuration. If a filesystem has such a requirement, the
52 operation will fail with the error EINVAL if this requirement is
53 violated.
54 -d, --dig-holes
56 Detect and dig holes. This makes the file sparse in-place, without
57 using extra disk space. The minimum size of the hole depends on
58 filesystem I/O block size (usually 4096 bytes). Also, when using
59 this option, --keep-size is implied. If no range is specified by
60 --offset and --length, then the entire file is analyzed for holes.
61 You can think of this option as doing a "cp --sparse" and then
63 renaming the destination file to the original, without the need for
64 extra disk space.
65 See --punch-hole for a list of supported filesystems.
67 -i, --insert-range
69 Insert a hole of length bytes from offset, shifting existing data.
70 -l, --length length
72 Specifies the length of the range, in bytes.
73 -n, --keep-size
75 Do not modify the apparent length of the file. This may effectively
76 allocate blocks past EOF, which can be removed with a truncate.
77 -o, --offset offset
79 Specifies the beginning offset of the range, in bytes.
80 -p, --punch-hole
82 Deallocates space (i.e., creates a hole) in the byte range starting
83 at offset and continuing for length bytes. Within the specified
84 range, partial filesystem blocks are zeroed, and whole filesystem
85 blocks are removed from the file. After a successful call,
86 subsequent reads from this range will return zeroes. This option
87 may not be specified at the same time as the --zero-range option.
88 Also, when using this option, --keep-size is implied.
89 Supported for XFS (since Linux 2.6.38), ext4 (since Linux 3.0),
91 Btrfs (since Linux 3.7), tmpfs (since Linux 3.5) and gfs2 (since
92 Linux 4.16).
93 -v, --verbose
95 Enable verbose mode.
96 -x, --posix
98 Enable POSIX operation mode. In that mode allocation operation
99 always completes, but it may take longer time when fast allocation
100 is not supported by the underlying filesystem.
101 -z, --zero-range
103 Zeroes space in the byte range starting at offset and continuing
104 for length bytes. Within the specified range, blocks are
105 preallocated for the regions that span the holes in the file. After
106 a successful call, subsequent reads from this range will return
107 zeroes.
108 Zeroing is done within the filesystem preferably by converting the
110 range into unwritten extents. This approach means that the
111 specified range will not be physically zeroed out on the device
112 (except for partial blocks at the either end of the range), and I/O
113 is (otherwise) required only to update metadata.
114 Option --keep-size can be specified to prevent file length
116 modification.
117 Available since Linux 3.14 for ext4 (only for extent-based files)
119 and XFS.
120 -V, --version
122 Display version information and exit.
123 -h, --help
125 Display help text and exit.
126
128 Eric Sandeen <sandeen@redhat.com>, Karel Zak <kzak@redhat.com>
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131 truncate(1), fallocate(2), posix_fallocate(3)
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134 For bug reports, use the issue tracker at
135 https://github.com/karelzak/util-linux/issues.
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138 The fallocate command is part of the util-linux package which can be
139 downloaded from Linux Kernel Archive
140 <https://www.kernel.org/pub/linux/utils/util-linux/>.
141util-linux 2.37.2 2021-06-02 FALLOCATE(1)