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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 2021-03-22 "Linux" "Linux Programmer's Manual"
45 truncate, ftruncate \- truncate a file to a specified length
48 .B #include <unistd.h>
49 .B #include <sys/types.h>
51 .BI "int truncate(const char *" path ", off_t " length );
52 .BI "int ftruncate(int " fd ", off_t " length );
56 Feature Test Macro Requirements for glibc (see
57 .BR feature_test_macros (7)):
63 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
64 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
65 || /* Glibc <= 2.19: */ _BSD_SOURCE
71 .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
72 || /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
73 || /* Glibc <= 2.19: */ _BSD_SOURCE
80 functions cause the regular file named by
84 to be truncated to a size of precisely
88 If the file previously was larger than this size, the extra data is lost.
89 If the file previously was shorter, it is extended, and
90 the extended part reads as null bytes (\(aq\e0\(aq).
92 The file offset is not changed.
94 If the size changed, then the st_ctime and st_mtime fields
95 (respectively, time of last status change and
96 time of last modification; see
98 for the file are updated,
99 and the set-user-ID and set-group-ID mode bits may be cleared.
103 the file must be open for writing; with
105 the file must be writable.
107 On success, zero is returned.
108 On error, \-1 is returned, and
110 is set to indicate the error.
116 Search permission is denied for a component of the path prefix,
117 or the named file is not writable by the user.
119 .BR path_resolution (7).)
124 points outside the process's allocated address space.
129 is larger than the maximum file size. (XSI)
132 While blocked waiting to complete,
133 the call was interrupted by a signal handler; see
141 is negative or larger than the maximum file size.
144 An I/O error occurred updating the inode.
147 The named file is a directory.
150 Too many symbolic links were encountered in translating the pathname.
153 A component of a pathname exceeded 255 characters,
154 or an entire pathname exceeded 1023 characters.
157 The named file does not exist.
160 A component of the path prefix is not a directory.
163 .\" This happens for at least MSDOS and VFAT filesystems
165 The underlying filesystem does not support extending
166 a file beyond its current size.
169 The operation was prevented by a file seal; see
173 The named file resides on a read-only filesystem.
176 The file is an executable file that is being executed.
180 the same errors apply, but instead of things that can be wrong with
182 we now have things that can be wrong with the file descriptor,
187 is not a valid file descriptor.
189 .BR EBADF " or " EINVAL
191 is not open for writing.
195 does not reference a regular file or a POSIX shared memory object.
197 .BR EINVAL " or " EBADF
200 is not open for writing.
201 POSIX permits, and portable applications should handle,
202 either error for this case.
206 POSIX.1-2001, POSIX.1-2008,
207 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).
209 .\" .BR ftruncate ().
210 .\" POSIX.1-2001 also has
212 .\" as an XSI extension.
214 .\" SVr4 documents additional
216 .\" error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK. SVr4 documents for
218 .\" an additional EAGAIN error condition.
221 can also be used to set the size of a POSIX shared memory object; see
224 The details in DESCRIPTION are for XSI-compliant systems.
225 For non-XSI-compliant systems, the POSIX standard allows
230 exceeds the file length
233 is not specified at all in such an environment):
234 either returning an error, or extending the file.
235 Like most UNIX implementations, Linux follows the XSI requirement
236 when dealing with native filesystems.
237 However, some nonnative filesystems do not permit
241 to be used to extend a file beyond its current length:
242 a notable example on Linux is VFAT.
243 .\" At the very least: OSF/1, Solaris 7, and FreeBSD conform, mtk, Jan 2002
249 system calls were not designed to handle large file offsets.
250 Consequently, Linux 2.4 added
254 system calls that handle large files.
255 However, these details can be ignored by applications using glibc, whose
256 wrapper functions transparently employ the more recent system calls
257 where they are available.
259 On some 32-bit architectures,
260 the calling signature for these system calls differ,
261 for the reasons described in
264 A header file bug in glibc 2.12 meant that the minimum value of
265 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=12037
267 required to expose the declaration of
269 was 200809L instead of 200112L.
270 This has been fixed in later glibc versions.
275 .BR path_resolution (7)