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1 | .\" Copyright (c) 1983, 1991 The Regents of the University of California. |
2 | .\" All rights reserved. | |
3 | .\" | |
a9cd9cb7 | 4 | .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB) |
fea681da MK |
5 | .\" Redistribution and use in source and binary forms, with or without |
6 | .\" modification, are permitted provided that the following conditions | |
7 | .\" are met: | |
8 | .\" 1. Redistributions of source code must retain the above copyright | |
9 | .\" notice, this list of conditions and the following disclaimer. | |
10 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
11 | .\" notice, this list of conditions and the following disclaimer in the | |
12 | .\" documentation and/or other materials provided with the distribution. | |
13 | .\" 3. All advertising materials mentioning features or use of this software | |
14 | .\" must display the following acknowledgement: | |
15 | .\" This product includes software developed by the University of | |
16 | .\" California, Berkeley and its contributors. | |
17 | .\" 4. Neither the name of the University nor the names of its contributors | |
18 | .\" may be used to endorse or promote products derived from this software | |
19 | .\" without specific prior written permission. | |
20 | .\" | |
21 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
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23 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
24 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
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31 | .\" SUCH DAMAGE. | |
8c9302dc | 32 | .\" %%%LICENSE_END |
fea681da MK |
33 | .\" |
34 | .\" @(#)truncate.2 6.9 (Berkeley) 3/10/91 | |
35 | .\" | |
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> | |
c11b1abf | 39 | .\" Modified 2002-01-07 by Michael Kerrisk <mtk.manpages@gmail.com> |
fea681da | 40 | .\" Modified 2002-04-06 by Andries Brouwer <aeb@cwi.nl> |
c11b1abf | 41 | .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com> |
fea681da | 42 | .\" |
4b8c67d9 | 43 | .TH TRUNCATE 2 2017-09-15 "Linux" "Linux Programmer's Manual" |
fea681da MK |
44 | .SH NAME |
45 | truncate, ftruncate \- truncate a file to a specified length | |
46 | .SH SYNOPSIS | |
47 | .B #include <unistd.h> | |
48 | .br | |
49 | .B #include <sys/types.h> | |
68e4db0a | 50 | .PP |
fea681da MK |
51 | .BI "int truncate(const char *" path ", off_t " length ); |
52 | .br | |
53 | .BI "int ftruncate(int " fd ", off_t " length ); | |
68e4db0a | 54 | .PP |
cc4615cc MK |
55 | .in -4n |
56 | Feature Test Macro Requirements for glibc (see | |
57 | .BR feature_test_macros (7)): | |
58 | .in | |
59 | .ad l | |
68e4db0a | 60 | .PP |
3ca7341f | 61 | .BR truncate (): |
729166ed | 62 | .RS 4 |
f8619b6a | 63 | _XOPEN_SOURCE\ >=\ 500 |
cf7fa0a1 | 64 | .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
3ba63d80 | 65 | .br |
cf7fa0a1 | 66 | || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L |
f8619b6a | 67 | || /* Glibc versions <= 2.19: */ _BSD_SOURCE |
729166ed | 68 | .RE |
68e4db0a | 69 | .PP |
3ca7341f | 70 | .BR ftruncate (): |
729166ed | 71 | .RS 4 |
f8619b6a | 72 | _XOPEN_SOURCE\ >=\ 500 |
cf7fa0a1 | 73 | .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
cf7fa0a1 | 74 | || /* Since glibc 2.3.5: */ _POSIX_C_SOURCE\ >=\ 200112L |
f8619b6a | 75 | || /* Glibc versions <= 2.19: */ _BSD_SOURCE |
729166ed | 76 | .RE |
cc4615cc | 77 | .ad b |
fea681da MK |
78 | .SH DESCRIPTION |
79 | The | |
310b7919 | 80 | .BR truncate () |
fea681da | 81 | and |
310b7919 | 82 | .BR ftruncate () |
fea681da MK |
83 | functions cause the regular file named by |
84 | .I path | |
85 | or referenced by | |
86 | .I fd | |
87 | to be truncated to a size of precisely | |
88 | .I length | |
89 | bytes. | |
dd3568a1 | 90 | .PP |
c13182ef | 91 | If the file previously was larger than this size, the extra data is lost. |
fea681da | 92 | If the file previously was shorter, it is extended, and |
f81fb444 | 93 | the extended part reads as null bytes (\(aq\\0\(aq). |
dd3568a1 | 94 | .PP |
1e568304 | 95 | The file offset is not changed. |
dd3568a1 | 96 | .PP |
c13182ef | 97 | If the size changed, then the st_ctime and st_mtime fields |
310b7919 MK |
98 | (respectively, time of last status change and |
99 | time of last modification; see | |
e6fc1596 | 100 | .BR inode (7)) |
c13182ef | 101 | for the file are updated, |
ed948c28 | 102 | and the set-user-ID and set-group-ID mode bits may be cleared. |
dd3568a1 | 103 | .PP |
fea681da | 104 | With |
310b7919 | 105 | .BR ftruncate (), |
fea681da | 106 | the file must be open for writing; with |
310b7919 | 107 | .BR truncate (), |
fea681da | 108 | the file must be writable. |
47297adb | 109 | .SH RETURN VALUE |
c13182ef MK |
110 | On success, zero is returned. |
111 | On error, \-1 is returned, and | |
fea681da MK |
112 | .I errno |
113 | is set appropriately. | |
114 | .SH ERRORS | |
115 | For | |
e511ffb6 | 116 | .BR truncate (): |
fea681da MK |
117 | .TP |
118 | .B EACCES | |
119 | Search permission is denied for a component of the path prefix, | |
120 | or the named file is not writable by the user. | |
121 | (See also | |
ad7cc990 | 122 | .BR path_resolution (7).) |
fea681da MK |
123 | .TP |
124 | .B EFAULT | |
2d1b2fbc MK |
125 | The argument |
126 | .I path | |
fea681da MK |
127 | points outside the process's allocated address space. |
128 | .TP | |
129 | .B EFBIG | |
130 | The argument | |
131 | .I length | |
132 | is larger than the maximum file size. (XSI) | |
133 | .TP | |
134 | .B EINTR | |
374ce867 SL |
135 | While blocked waiting to complete, |
136 | the call was interrupted by a signal handler; see | |
137 | .BR fcntl (2) | |
138 | and | |
139 | .BR signal (7). | |
fea681da MK |
140 | .TP |
141 | .B EINVAL | |
142 | The argument | |
143 | .I length | |
144 | is negative or larger than the maximum file size. | |
145 | .TP | |
146 | .B EIO | |
147 | An I/O error occurred updating the inode. | |
148 | .TP | |
149 | .B EISDIR | |
150 | The named file is a directory. | |
151 | .TP | |
152 | .B ELOOP | |
153 | Too many symbolic links were encountered in translating the pathname. | |
154 | .TP | |
155 | .B ENAMETOOLONG | |
156 | A component of a pathname exceeded 255 characters, | |
2d7195b8 | 157 | or an entire pathname exceeded 1023 characters. |
fea681da MK |
158 | .TP |
159 | .B ENOENT | |
160 | The named file does not exist. | |
161 | .TP | |
162 | .B ENOTDIR | |
163 | A component of the path prefix is not a directory. | |
164 | .TP | |
5b548b31 | 165 | .B EPERM |
9ee4a2b6 | 166 | .\" This happens for at least MSDOS and VFAT filesystems |
5b548b31 | 167 | .\" on kernel 2.6.13 |
9ee4a2b6 | 168 | The underlying filesystem does not support extending |
5b548b31 MK |
169 | a file beyond its current size. |
170 | .TP | |
fbab10e5 MK |
171 | .B EPERM |
172 | The operation was prevented by a file seal; see | |
173 | .BR fcntl (2). | |
174 | .TP | |
fea681da | 175 | .B EROFS |
9ee4a2b6 | 176 | The named file resides on a read-only filesystem. |
fea681da MK |
177 | .TP |
178 | .B ETXTBSY | |
3aa74315 | 179 | The file is an executable file that is being executed. |
fea681da MK |
180 | .PP |
181 | For | |
310b7919 | 182 | .BR ftruncate () |
fea681da MK |
183 | the same errors apply, but instead of things that can be wrong with |
184 | .IR path , | |
3ade1aa9 | 185 | we now have things that can be wrong with the file descriptor, |
fea681da MK |
186 | .IR fd : |
187 | .TP | |
188 | .B EBADF | |
fea681da | 189 | .I fd |
d9cb0d7d | 190 | is not a valid file descriptor. |
fea681da MK |
191 | .TP |
192 | .BR EBADF " or " EINVAL | |
fea681da MK |
193 | .I fd |
194 | is not open for writing. | |
195 | .TP | |
196 | .B EINVAL | |
fea681da | 197 | .I fd |
dc951c84 | 198 | does not reference a regular file or a POSIX shared memory object. |
29218e62 MK |
199 | .TP |
200 | .BR EINVAL " or " EBADF | |
8cc4d071 | 201 | The file descriptor |
29218e62 MK |
202 | .I fd |
203 | is not open for writing. | |
204 | POSIX permits, and portable applications should handle, | |
205 | either error for this case. | |
206 | (Linux produces | |
207 | .BR EINVAL .) | |
47297adb | 208 | .SH CONFORMING TO |
84d596e8 MK |
209 | POSIX.1-2001, POSIX.1-2008, |
210 | 4.4BSD, SVr4 (these calls first appeared in 4.2BSD). | |
97c1eac8 MK |
211 | .\" POSIX.1-1996 has |
212 | .\" .BR ftruncate (). | |
213 | .\" POSIX.1-2001 also has | |
214 | .\" .BR truncate (), | |
215 | .\" as an XSI extension. | |
216 | .\" .LP | |
217 | .\" SVr4 documents additional | |
218 | .\" .BR truncate () | |
219 | .\" error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK. SVr4 documents for | |
220 | .\" .BR ftruncate () | |
221 | .\" an additional EAGAIN error condition. | |
fea681da | 222 | .SH NOTES |
dc951c84 MK |
223 | .BR ftruncate () |
224 | can also be used to set the size of a POSIX shared memory object; see | |
225 | .BR shm_open (7). | |
efeece04 | 226 | .PP |
c0697399 | 227 | The details in DESCRIPTION are for XSI-compliant systems. |
fea681da | 228 | For non-XSI-compliant systems, the POSIX standard allows |
d9bfdb9c | 229 | two behaviors for |
310b7919 | 230 | .BR ftruncate () |
fea681da MK |
231 | when |
232 | .I length | |
233 | exceeds the file length | |
234 | (note that | |
310b7919 | 235 | .BR truncate () |
fea681da MK |
236 | is not specified at all in such an environment): |
237 | either returning an error, or extending the file. | |
008f1ecc | 238 | Like most UNIX implementations, Linux follows the XSI requirement |
9ee4a2b6 MK |
239 | when dealing with native filesystems. |
240 | However, some nonnative filesystems do not permit | |
5b548b31 | 241 | .BR truncate () |
c13182ef | 242 | and |
5b548b31 MK |
243 | .BR ftruncate () |
244 | to be used to extend a file beyond its current length: | |
245 | a notable example on Linux is VFAT. | |
fea681da | 246 | .\" At the very least: OSF/1, Solaris 7, and FreeBSD conform, mtk, Jan 2002 |
efeece04 | 247 | .PP |
0290f437 MK |
248 | The original Linux |
249 | .BR truncate () | |
250 | and | |
251 | .BR ftruncate () | |
252 | system calls were not designed to handle large file offsets. | |
253 | Consequently, Linux 2.4 added | |
254 | .BR truncate64 () | |
255 | and | |
256 | .BR ftruncate64 () | |
257 | system calls that handle large files. | |
258 | However, these details can be ignored by applications using glibc, whose | |
dd7f1928 | 259 | wrapper functions transparently employ the more recent system calls |
0290f437 | 260 | where they are available. |
efeece04 | 261 | .PP |
63ec43ae MK |
262 | On some 32-bit architectures, |
263 | the calling signature for these system calls differ, | |
264 | for the reasons described in | |
265 | .BR syscall (2). | |
9dcef0c0 MK |
266 | .SH BUGS |
267 | A header file bug in glibc 2.12 meant that the minimum value of | |
268 | .\" http://sourceware.org/bugzilla/show_bug.cgi?id=12037 | |
269 | .BR _POSIX_C_SOURCE | |
270 | required to expose the declaration of | |
271 | .BR ftruncate () | |
272 | was 200809L instead of 200112L. | |
273 | This has been fixed in later glibc versions. | |
47297adb | 274 | .SH SEE ALSO |
ef2c6228 | 275 | .BR truncate (1), |
fea681da | 276 | .BR open (2), |
ad7cc990 MK |
277 | .BR stat (2), |
278 | .BR path_resolution (7) |