man2/truncate.2

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  32 .\"     @(#)truncate.2  6.9 (Berkeley) 3/10/91
  33 .\"
  34 .\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
  35 .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
  36 .\" Modified 1998-12-21 by Andries Brouwer <aeb@cwi.nl>
  37 .\" Modified 2002-01-07 by Michael Kerrisk <mtk-manpages@gmx.net>
  38 .\" Modified 2002-04-06 by Andries Brouwer <aeb@cwi.nl>
  39 .\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
  40 .\"
  41 .TH TRUNCATE 2 2004-06-23 "Linux 2.6.7" "Linux Programmer's Manual"
  42 .SH NAME
  43 truncate, ftruncate \- truncate a file to a specified length
  44 .SH SYNOPSIS
  45 .B #include <unistd.h>
  46 .br
  47 .B #include <sys/types.h>
  48 .sp
  49 .BI "int truncate(const char *" path ", off_t " length );
  50 .br
  51 .BI "int ftruncate(int " fd ", off_t " length );
  52 .SH DESCRIPTION
  53 The
  54 .BR truncate ()
  55 and
  56 .BR ftruncate ()
  57 functions cause the regular file named by
  58 .I path
  59 or referenced by
  60 .I fd
  61 to be truncated to a size of precisely
  62 .I length
  63 bytes.
  64 .LP
  65 If the file previously was larger than this size, the extra data is lost.
  66 If the file previously was shorter, it is extended, and
  67 the extended part reads as null bytes ('\\0').
  68 .LP
  69 The file offset is not changed.
  70 .LP
  71 If the size changed, then the st_ctime and st_mtime fields
  72 (respectively, time of last status change and
  73 time of last modification; see
  74 .BR stat (2))
  75 for the file are updated,
  76 and the set-user-ID and set-group-ID permission bits may be cleared.
  77 .LP
  78 With
  79 .BR ftruncate (),
  80 the file must be open for writing; with
  81 .BR truncate (),
  82 the file must be writable.
  83 .SH "RETURN VALUE"
  84 On success, zero is returned.
  85 On error, \-1 is returned, and
  86 .I errno
  87 is set appropriately.
  88 .SH ERRORS
  89 For
  90 .BR truncate ():
  91 .TP
  92 .B EACCES
  93 Search permission is denied for a component of the path prefix,
  94 or the named file is not writable by the user.
  95 (See also
  96 .BR path_resolution (2).)
  97 .TP
  98 .B EFAULT
  99 .I Path
 100 points outside the process's allocated address space.
 101 .TP
 102 .B EFBIG
 103 The argument
 104 .I length
 105 is larger than the maximum file size. (XSI)
 106 .TP
 107 .B EINTR
 108 A signal was caught during execution.
 109 .TP
 110 .B EINVAL
 111 The argument
 112 .I length
 113 is negative or larger than the maximum file size.
 114 .TP
 115 .B EIO
 116 An I/O error occurred updating the inode.
 117 .TP
 118 .B EISDIR
 119 The named file is a directory.
 120 .TP
 121 .B ELOOP
 122 Too many symbolic links were encountered in translating the pathname.
 123 .TP
 124 .B ENAMETOOLONG
 125 A component of a pathname exceeded 255 characters,
 126 or an entire pathname exceeded 1023 characters.
 127 .TP
 128 .B ENOENT
 129 The named file does not exist.
 130 .TP
 131 .B ENOTDIR
 132 A component of the path prefix is not a directory.
 133 .TP
 134 .B EPERM
 135 .\" This happens for at leas MSDOS and VFAT fil systems
 136 .\" on kernel 2.6.13
 137 The underlying file system does not support extending
 138 a file beyond its current size.
 139 .TP
 140 .B EROFS
 141 The named file resides on a read-only file system.
 142 .TP
 143 .B ETXTBSY
 144 The file is a pure procedure (shared text) file that is being executed.
 145 .PP
 146 For
 147 .BR ftruncate ()
 148 the same errors apply, but instead of things that can be wrong with
 149 .IR path ,
 150 we now have things that can be wrong with
 151 .IR fd :
 152 .TP
 153 .B EBADF
 154 The
 155 .I fd
 156 is not a valid descriptor.
 157 .TP
 158 .BR EBADF " or " EINVAL
 159 The
 160 .I fd
 161 is not open for writing.
 162 .TP
 163 .B EINVAL
 164 The
 165 .I fd
 166 does not reference a regular file.
 167 .SH "CONFORMING TO"
 168 4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
 169 .\" POSIX.1-1996 has
 170 .\" .BR ftruncate ().
 171 .\" POSIX.1-2001 also has
 172 .\" .BR truncate (),
 173 .\" as an XSI extension.
 174 .\" .LP
 175 .\" SVr4 documents additional
 176 .\" .BR truncate ()
 177 .\" error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK.  SVr4 documents for
 178 .\" .BR ftruncate ()
 179 .\" an additional EAGAIN error condition.
 180 .SH NOTES
 181 The above description is for XSI-compliant systems.
 182 For non-XSI-compliant systems, the POSIX standard allows
 183 two behaviours for
 184 .BR ftruncate ()
 185 when
 186 .I length
 187 exceeds the file length
 188 (note that
 189 .BR truncate ()
 190 is not specified at all in such an environment):
 191 either returning an error, or extending the file.
 192 Like most Unix implementations, Linux follows the XSI requirement
 193 when dealing with native file systems.
 194 However, some non-native file systems do not permit
 195 .BR truncate ()
 196 and
 197 .BR ftruncate ()
 198 to be used to extend a file beyond its current length:
 199 a notable example on Linux is VFAT.
 200 .\" At the very least: OSF/1, Solaris 7, and FreeBSD conform, mtk, Jan 2002
 201 .SH "SEE ALSO"
 202 .BR open (2),
 203 .BR path_resolution (2),
 204 .BR stat (2)