1 .\" Copyright (c) 2006, Michael Kerrisk <mtk.manpages@gmail.com>
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .TH POSIX_FALLOCATE 3 2021-03-22 "GNU" "Linux Programmer's Manual"
27 posix_fallocate \- allocate file space
32 .BI "int posix_fallocate(int " fd ", off_t " offset ", off_t " len );
37 Feature Test Macro Requirements for glibc (see
38 .BR feature_test_macros (7)):
41 .BR posix_fallocate ():
43 _POSIX_C_SOURCE >= 200112L
47 .BR posix_fallocate ()
48 ensures that disk space is allocated for the file referred to by the
51 for the bytes in the range starting at
56 After a successful call to
57 .BR posix_fallocate (),
58 subsequent writes to bytes in the specified range are
59 guaranteed not to fail because of lack of disk space.
61 If the size of the file is less than
63 then the file is increased to this size;
64 otherwise the file size is left unchanged.
66 .BR posix_fallocate ()
67 returns zero on success, or an error number on failure.
75 is not a valid file descriptor, or is not opened for writing.
79 exceeds the maximum file size.
82 A signal was caught during execution.
88 was less than or equal to 0, or the underlying filesystem does not
89 support the operation.
93 does not refer to a regular file.
96 There is not enough space left on the device containing the file
101 The filesystem containing the file referred to by
103 does not support this operation.
104 This error code can be returned by C libraries that don't perform the
105 emulation shown in NOTES, such as musl libc.
111 .BR posix_fallocate ()
112 is available since glibc 2.1.94.
114 For an explanation of the terms used in this section, see
122 Interface Attribute Value
124 .BR posix_fallocate ()
126 MT-Safe (but see NOTES)
135 POSIX.1-2008 says that an implementation
144 POSIX.1-2001 says that an implementation
158 In the glibc implementation,
159 .BR posix_fallocate ()
160 is implemented using the
162 system call, which is MT-safe.
163 If the underlying filesystem does not support
165 then the operation is emulated with the following caveats:
167 The emulation is inefficient.
169 There is a race condition where concurrent writes from another thread or
170 process could be overwritten with null bytes.
172 There is a race condition where concurrent file size increases by
173 another thread or process could result in a file whose size is smaller
178 has been opened with the
182 flags, the function fails with the error
185 In general, the emulation is not MT-safe.
186 On Linux, applications may use
188 if they cannot tolerate the emulation caveats.
190 only recommended if the application plans to terminate the operation if
192 is returned, otherwise the application itself will need to implement a
193 fallback with all the same problems as the emulation provided by glibc.
198 .BR posix_fadvise (2)