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34 .\" @(#)truncate.2 6.9 (Berkeley) 3/10/91
36 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
37 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
38 .\" Modified 1998-12-21 by Andries Brouwer <aeb@cwi.nl>
39 .\" Modified 2002-01-07 by Michael Kerrisk <mtk.manpages@gmail.com>
40 .\" Modified 2002-04-06 by Andries Brouwer <aeb@cwi.nl>
41 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
43 .TH TRUNCATE 2 2015-05-07 "Linux" "Linux Programmer's Manual"
45 truncate, ftruncate \- truncate a file to a specified length
47 .B #include <unistd.h>
49 .B #include <sys/types.h>
51 .BI "int truncate(const char *" path ", off_t " length );
53 .BI "int ftruncate(int " fd ", off_t " length );
56 Feature Test Macro Requirements for glibc (see
57 .BR feature_test_macros (7)):
64 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
65 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
67 || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
72 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
73 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
75 || /* Since glibc 2.3.5: */ _POSIX_C_SOURCE\ >=\ 200112L
84 functions cause the regular file named by
88 to be truncated to a size of precisely
92 If the file previously was larger than this size, the extra data is lost.
93 If the file previously was shorter, it is extended, and
94 the extended part reads as null bytes (\(aq\\0\(aq).
96 The file offset is not changed.
98 If the size changed, then the st_ctime and st_mtime fields
99 (respectively, time of last status change and
100 time of last modification; see
102 for the file are updated,
103 and the set-user-ID and set-group-ID mode bits may be cleared.
107 the file must be open for writing; with
109 the file must be writable.
111 On success, zero is returned.
112 On error, \-1 is returned, and
114 is set appropriately.
120 Search permission is denied for a component of the path prefix,
121 or the named file is not writable by the user.
123 .BR path_resolution (7).)
128 points outside the process's allocated address space.
133 is larger than the maximum file size. (XSI)
136 While blocked waiting to complete,
137 the call was interrupted by a signal handler; see
145 is negative or larger than the maximum file size.
148 An I/O error occurred updating the inode.
151 The named file is a directory.
154 Too many symbolic links were encountered in translating the pathname.
157 A component of a pathname exceeded 255 characters,
158 or an entire pathname exceeded 1023 characters.
161 The named file does not exist.
164 A component of the path prefix is not a directory.
167 .\" This happens for at least MSDOS and VFAT filesystems
169 The underlying filesystem does not support extending
170 a file beyond its current size.
173 The operation was prevented by a file seal; see
177 The named file resides on a read-only filesystem.
180 The file is a pure procedure (shared text) file that is being executed.
184 the same errors apply, but instead of things that can be wrong with
186 we now have things that can be wrong with the file descriptor,
191 is not a valid descriptor.
193 .BR EBADF " or " EINVAL
195 is not open for writing.
199 does not reference a regular file.
201 .BR EINVAL " or " EBADF
204 is not open for writing.
205 POSIX permits, and portable applications should handle,
206 either error for this case.
210 4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
212 .\" .BR ftruncate ().
213 .\" POSIX.1-2001 also has
215 .\" as an XSI extension.
217 .\" SVr4 documents additional
219 .\" error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK. SVr4 documents for
221 .\" an additional EAGAIN error condition.
223 The details in DESCRIPTION are for XSI-compliant systems.
224 For non-XSI-compliant systems, the POSIX standard allows
229 exceeds the file length
232 is not specified at all in such an environment):
233 either returning an error, or extending the file.
234 Like most UNIX implementations, Linux follows the XSI requirement
235 when dealing with native filesystems.
236 However, some nonnative filesystems do not permit
240 to be used to extend a file beyond its current length:
241 a notable example on Linux is VFAT.
242 .\" At the very least: OSF/1, Solaris 7, and FreeBSD conform, mtk, Jan 2002
248 system calls were not designed to handle large file offsets.
249 Consequently, Linux 2.4 added
253 system calls that handle large files.
254 However, these details can be ignored by applications using glibc, whose
255 wrapper functions transparently employ the more recent system calls
256 where they are available.
258 On some 32-bit architectures,
259 the calling signature for these system calls differ,
260 for the reasons described in
263 A header file bug in glibc 2.12 meant that the minimum value of
264 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=12037
266 required to expose the declaration of
268 was 200809L instead of 200112L.
269 This has been fixed in later glibc versions.
273 .BR path_resolution (7)