1TRUNCATE(2) Linux Programmer's Manual TRUNCATE(2)
2
6 truncate, ftruncate - truncate a file to a specified length
7
9 #include <unistd.h>
10 #include <sys/types.h>
11 int truncate(const char *path, off_t length);
13 int ftruncate(int fd, off_t length);
14 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16 truncate():
18 _XOPEN_SOURCE >= 500
19 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
20 || /* Glibc versions <= 2.19: */ _BSD_SOURCE
21 ftruncate():
23 _XOPEN_SOURCE >= 500
24 || /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
25 || /* Glibc versions <= 2.19: */ _BSD_SOURCE
26
28 The truncate() and ftruncate() functions cause the regular file named
29 by path or referenced by fd to be truncated to a size of precisely
30 length bytes.
31 If the file previously was larger than this size, the extra data is
33 lost. If the file previously was shorter, it is extended, and the
34 extended part reads as null bytes ('\0').
35 The file offset is not changed.
37 If the size changed, then the st_ctime and st_mtime fields (respec‐
39 tively, time of last status change and time of last modification; see
40 inode(7)) for the file are updated, and the set-user-ID and set-group-
41 ID mode bits may be cleared.
42 With ftruncate(), the file must be open for writing; with truncate(),
44 the file must be writable.
45
47 On success, zero is returned. On error, -1 is returned, and errno is
48 set appropriately.
49
51 For truncate():
52 EACCES Search permission is denied for a component of the path prefix,
54 or the named file is not writable by the user. (See also
55 path_resolution(7).)
56 EFAULT The argument path points outside the process's allocated address
58 space.
59 EFBIG The argument length is larger than the maximum file size. (XSI)
61 EINTR While blocked waiting to complete, the call was interrupted by a
63 signal handler; see fcntl(2) and signal(7).
64 EINVAL The argument length is negative or larger than the maximum file
66 size.
67 EIO An I/O error occurred updating the inode.
69 EISDIR The named file is a directory.
71 ELOOP Too many symbolic links were encountered in translating the
73 pathname.
74 ENAMETOOLONG
76 A component of a pathname exceeded 255 characters, or an entire
77 pathname exceeded 1023 characters.
78 ENOENT The named file does not exist.
80 ENOTDIR
82 A component of the path prefix is not a directory.
83 EPERM The underlying filesystem does not support extending a file
85 beyond its current size.
86 EPERM The operation was prevented by a file seal; see fcntl(2).
88 EROFS The named file resides on a read-only filesystem.
90 ETXTBSY
92 The file is an executable file that is being executed.
93 For ftruncate() the same errors apply, but instead of things that can
95 be wrong with path, we now have things that can be wrong with the file
96 descriptor, fd:
97 EBADF fd is not a valid file descriptor.
99 EBADF or EINVAL
101 fd is not open for writing.
102 EINVAL fd does not reference a regular file or a POSIX shared memory
104 object.
105 EINVAL or EBADF
107 The file descriptor fd is not open for writing. POSIX permits,
108 and portable applications should handle, either error for this
109 case. (Linux produces EINVAL.)
110
112 POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in
113 4.2BSD).
114
116 ftruncate() can also be used to set the size of a POSIX shared memory
117 object; see shm_open(7).
118 The details in DESCRIPTION are for XSI-compliant systems. For non-XSI-
120 compliant systems, the POSIX standard allows two behaviors for ftrun‐
121 cate() when length exceeds the file length (note that truncate() is not
122 specified at all in such an environment): either returning an error, or
123 extending the file. Like most UNIX implementations, Linux follows the
124 XSI requirement when dealing with native filesystems. However, some
125 nonnative filesystems do not permit truncate() and ftruncate() to be
126 used to extend a file beyond its current length: a notable example on
127 Linux is VFAT.
128 The original Linux truncate() and ftruncate() system calls were not
130 designed to handle large file offsets. Consequently, Linux 2.4 added
131 truncate64() and ftruncate64() system calls that handle large files.
132 However, these details can be ignored by applications using glibc,
133 whose wrapper functions transparently employ the more recent system
134 calls where they are available.
135 On some 32-bit architectures, the calling signature for these system
137 calls differ, for the reasons described in syscall(2).
138
140 A header file bug in glibc 2.12 meant that the minimum value of
141 _POSIX_C_SOURCE required to expose the declaration of ftruncate() was
142 200809L instead of 200112L. This has been fixed in later glibc ver‐
143 sions.
144
146 truncate(1), open(2), stat(2), path_resolution(7)
147
149 This page is part of release 4.15 of the Linux man-pages project. A
150 description of the project, information about reporting bugs, and the
151 latest version of this page, can be found at
152 https://www.kernel.org/doc/man-pages/.
153Linux 2017-09-15 TRUNCATE(2)