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10 .TH TRUNCATE 3C "Apr 5, 2002"
11 .SH NAME
12 truncate, ftruncate \- set a file to a specified length
13 .SH SYNOPSIS
14 .LP
15 .nf
16 #include <unistd.h>
18 \fBint\fR \fBtruncate\fR(\fBconst char *\fR\fIpath\fR, \fBoff_t\fR \fIlength\fR);
19 .fi
21 .LP
22 .nf
23 \fBint\fR \fBftruncate\fR(\fBint\fR \fIfildes\fR, \fBoff_t\fR \fIlength\fR);
24 .fi
26 .SH DESCRIPTION
27 .sp
28 .LP
29 The \fBtruncate()\fR function causes the regular file named by \fIpath\fR to
30 have a size equal to \fIlength\fR bytes.
31 .sp
32 .LP
33 If the file previously was larger than \fIlength\fR, the extra data is
34 discarded. If the file was previously shorter than length, its size is
35 increased, and the extended area appears as if it were zero-filled.
36 .sp
37 .LP
38 The application must ensure that the process has write permission for the file.
39 .sp
40 .LP
41 This function does not modify the file offset for any open file descriptions
42 associated with the file.
43 .sp
44 .LP
45 The \fBftruncate()\fR function causes the regular file referenced by
46 \fIfildes\fR to be truncated to \fIlength\fR. If the size of the file
47 previously exceeded \fIlength\fR, the extra data is no longer available to
48 reads on the file. If the file previously was smaller than this size,
49 \fBftruncate()\fR increases the size of the file with the extended area
50 appearing as if it were zero-filled. The value of the seek pointer is not
51 modified by a call to \fBftruncate()\fR.
52 .sp
53 .LP
54 The \fBftruncate()\fR function works only with regular files and shared memory.
55 If \fIfildes\fR refers to a shared memory object, \fBftruncate()\fR sets the
56 size of the shared memory object to \fIlength\fR. If \fIfildes\fR refers to a
57 directory or is not a valid file descriptor open for writing, \fBftruncate()\fR
58 fails.
59 .sp
60 .LP
61 If the effect of \fBftruncate()\fR is to decrease the size of a shared memory
62 object or memory mapped file and whole pages beyond the new end were previously
63 mapped, then the whole pages beyond the new end shall be discarded.
64 .sp
65 .LP
66 If the effect of \fBftruncate()\fR is to increase the size of a shared memory
67 object, it is unspecified if the contents of any mapped pages between the old
68 end-of-file and the new are flushed to the underlying object.
69 .sp
70 .LP
71 These functions do not modify the file offset for any open file descriptions
72 associated with the file. On successful completion, if the file size is
73 changed, these functions will mark for update the \fBst_ctime\fR and
74 \fBst_mtime\fR fields of the file, and if the file is a regular file, the
75 \fBS_ISUID\fR and \fBS_ISGID\fR bits of the file mode are left unchanged.
76 .sp
77 .LP
78 If the request would cause the file size to exceed the soft file size limit for
79 the process, the request will fail and a \fBSIGXFSZ\fR signal will be generated
80 for the process.
81 .SH RETURN VALUES
82 .sp
83 .LP
84 Upon successful completion, \fBftruncate()\fR and \fBtruncate()\fR return
85 \fB0\fR. Otherwise, \fB\(mi1\fR is returned and \fBerrno\fR is set to indicate
86 the error.
87 .SH ERRORS
88 .sp
89 .LP
90 The \fBftruncate()\fR and \fBtruncate()\fR functions will fail if:
91 .sp
92 .ne 2
93 .na
94 \fB\fBEINTR\fR\fR
95 .ad
96 .RS 19n
97 A signal was caught during execution.
98 .RE
100 .sp
101 .ne 2
102 .na
103 \fB\fBEINVAL\fR\fR
104 .ad
105 .RS 19n
106 The \fIlength\fR argument was less than 0.
107 .RE
109 .sp
110 .ne 2
111 .na
112 \fB\fBEFBIG\fR or \fBEINVAL\fR\fR
113 .ad
114 .RS 19n
115 The \fIlength\fR argument was greater than the maximum file size.
116 .RE
118 .sp
119 .ne 2
120 .na
121 \fB\fBEIO\fR\fR
122 .ad
123 .RS 19n
124 An I/O error occurred while reading from or writing to a file system.
125 .RE
127 .sp
128 .ne 2
129 .na
130 \fB\fBEROFS\fR\fR
131 .ad
132 .RS 19n
133 The named file resides on a read-only file system.
134 .RE
136 .sp
137 .LP
138 The \fBtruncate()\fR function will fail if:
139 .sp
140 .ne 2
141 .na
142 \fB\fBEACCES\fR\fR
143 .ad
144 .RS 16n
145 A component of the path prefix denies search permission, or write permission is
146 denied on the file.
147 .RE
149 .sp
150 .ne 2
151 .na
152 \fB\fBEFAULT\fR\fR
153 .ad
154 .RS 16n
155 The \fIpath\fR argument points outside the process' allocated address space.
156 .RE
158 .sp
159 .ne 2
160 .na
161 \fB\fBEINVAL\fR\fR
162 .ad
163 .RS 16n
164 The \fIpath\fR argument is not an ordinary file.
165 .RE
167 .sp
168 .ne 2
169 .na
170 \fB\fBEISDIR\fR\fR
171 .ad
172 .RS 16n
173 The named file is a directory.
174 .RE
176 .sp
177 .ne 2
178 .na
179 \fB\fBELOOP\fR\fR
180 .ad
181 .RS 16n
182 Too many symbolic links were encountered in resolving \fIpath\fR.
183 .RE
185 .sp
186 .ne 2
187 .na
188 \fB\fBEMFILE\fR\fR
189 .ad
190 .RS 16n
191 The maximum number of file descriptors available to the process has been
192 reached.
193 .RE
195 .sp
196 .ne 2
197 .na
198 \fB\fBENAMETOOLONG\fR\fR
199 .ad
200 .RS 16n
201 The length of the specified pathname exceeds {\fBPATH_MAX\fR} bytes, or the
202 length of a component of the pathname exceeds {\fBNAME_MAX\fR} bytes.
203 .RE
205 .sp
206 .ne 2
207 .na
208 \fB\fBENOENT\fR\fR
209 .ad
210 .RS 16n
211 A component of \fIpath\fR does not name an existing file or \fIpath\fR is an
212 empty string.
213 .RE
215 .sp
216 .ne 2
217 .na
218 \fB\fBENFILE\fR\fR
219 .ad
220 .RS 16n
221 Additional space could not be allocated for the system file table.
222 .RE
224 .sp
225 .ne 2
226 .na
227 \fB\fBENOTDIR\fR\fR
228 .ad
229 .RS 16n
230 A component of the path prefix of \fIpath\fR is not a directory.
231 .RE
233 .sp
234 .ne 2
235 .na
236 \fB\fBENOLINK\fR\fR
237 .ad
238 .RS 16n
239 The \fIpath\fR argument points to a remote machine and the link to that machine
240 is no longer active.
241 .RE
243 .sp
244 .LP
245 The \fBftruncate()\fR function will fail if:
246 .sp
247 .ne 2
248 .na
249 \fB\fBEAGAIN\fR\fR
250 .ad
251 .RS 19n
252 The file exists, mandatory file/record locking is set, and there are
253 outstanding record locks on the file (see \fBchmod\fR(2)).
254 .RE
256 .sp
257 .ne 2
258 .na
259 \fB\fBEBADF\fR or \fBEINVAL\fR\fR
260 .ad
261 .RS 19n
262 The \fIfildes\fR argument is not a file descriptor open for writing.
263 .RE
265 .sp
266 .ne 2
267 .na
268 \fB\fBEFBIG\fR\fR
269 .ad
270 .RS 19n
271 The file is a regular file and \fIlength\fR is greater than the offset maximum
272 established in the open file description associated with \fIfildes\fR.
273 .RE
275 .sp
276 .ne 2
277 .na
278 \fB\fBEINVAL\fR\fR
279 .ad
280 .RS 19n
281 The \fIfildes\fR argument references a file that was opened without write
282 permission.
283 .RE
285 .sp
286 .ne 2
287 .na
288 \fB\fBEINVAL\fR\fR
289 .ad
290 .RS 19n
291 The \fIfildes\fR argument does not correspond to an ordinary file.
292 .RE
294 .sp
295 .ne 2
296 .na
297 \fB\fBENOLINK\fR\fR
298 .ad
299 .RS 19n
300 The \fIfildes\fR argument points to a remote machine and the link to that
301 machine is no longer active.
302 .RE
304 .sp
305 .LP
306 The \fBtruncate()\fR function may fail if:
307 .sp
308 .ne 2
309 .na
310 \fB\fBENAMETOOLONG\fR\fR
311 .ad
312 .RS 16n
313 Pathname resolution of a symbolic link produced an intermediate result whose
314 length exceeds {\fBPATH_MAX\fR}.
315 .RE
317 .SH USAGE
318 .sp
319 .LP
320 The \fBtruncate()\fR and \fBftruncate()\fR functions have transitional
321 interfaces for 64-bit file offsets. See \fBlf64\fR(5).
322 .SH ATTRIBUTES
323 .sp
324 .LP
325 See \fBattributes\fR(5) for descriptions of the following attributes:
326 .sp
328 .sp
329 .TS
330 box;
331 c | c
332 l | l .
333 ATTRIBUTE TYPE ATTRIBUTE VALUE
334 _
335 Interface Stability Standard
336 _
337 MT-Level MT-Safe
338 .TE
340 .SH SEE ALSO
341 .sp
342 .LP
343 \fBchmod\fR(2), \fBfcntl\fR(2), \fBopen\fR(2), \fBattributes\fR(5),
344 \fBlf64\fR(5), \fBstandards\fR(5)