bsd/man/man2/truncate.2

   1 .\"     $NetBSD: truncate.2,v 1.7 1995/02/27 12:39:00 cgd Exp $
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  34 .\"     @(#)truncate.2  8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt TRUNCATE 2
  38 .Os BSD 4.2
  39 .Sh NAME
  40 .Nm ftruncate ,
  41 .Nm truncate
  42 .Nd truncate or extend a file to a specified length
  43 .Sh SYNOPSIS
  44 .Fd #include <unistd.h>
  45 .Ft int
  46 .Fo ftruncate
  47 .Fa "int fildes"
  48 .Fa "off_t length"
  49 .Fc
  50 .Ft int
  51 .Fo truncate
  52 .Fa "const char *path"
  53 .Fa "off_t length"
  54 .Fc
  55 .Sh DESCRIPTION
  56 .Fn ftruncate
  57 and
  58 .Fn truncate
  59 cause the file named by
  60 .Fa path ,
  61 or referenced by
  62 .Fa fildes ,
  63 to be truncated (or extended) to
  64 .Fa length
  65 bytes in size. If the file size exceeds
  66 .Fa length ,
  67 any extra data is discarded. If the file size is smaller than
  68 .Fa length ,
  69 the file is extended and filled with zeros to the indicated length.
  70 The
  71 .Fn ftruncate
  72 form requires the file to be open for writing.
  73 .Pp
  74 Note:
  75 .Fn ftruncate
  76 and
  77 .Fn truncate
  78 do not modify the current file offset for any open file descriptions associated with the file.
  79 .Sh RETURN VALUES
  80 A value of 0 is returned if the call succeeds.  If the call
  81 fails a -1 is returned, and the global variable
  82 .Va errno
  83 specifies the error.
  84 .Sh ERRORS
  85 .Pp
  86 The
  87 .Fn ftruncate
  88 system call will fail if:
  89 .Bl -tag -width Er
  90 .\" ===========
  91 .It Bq Er EBADF
  92 .Fa fildes
  93 is not a valid descriptor open for writing.
  94 .\" ===========
  95 .It Bq Er EFBIG
  96 The file is a regular file and
  97 .Fa length
  98 is greater than the offset maximum established
  99 in the open file description associated with
 100 .Fa fildes .
 101 .\" ===========
 102 .It Bq Er EINVAL
 103 .Fa fildes
 104 references a socket, not a file.
 105 .\" ===========
 106 .It Bq Er EINVAL
 107 .Fa fildes
 108 is not open for writing.
 109 .\" ===========
 110 .It Bq Er EROFS
 111 The named file resides on a read-only file system.
 112 .El
 113 .Pp
 114 The
 115 .Fn truncate
 116 system call will fail if:
 117 .Bl -tag -width Er
 118 .\" ===========
 119 .It Bq Er EACCES
 120 Search permission is denied for a component of the path prefix.
 121 .\" ===========
 122 .It Bq Er EACCES
 123 The named file is not writable by the user.
 124 .\" ===========
 125 .It Bq Er EFAULT
 126 .Fa Path
 127 points outside the process's allocated address space.
 128 .\" ===========
 129 .It Bq Er EISDIR
 130 The named file is a directory.
 131 .\" ===========
 132 .It Bq Er ELOOP
 133 Too many symbolic links are encountered in translating the pathname.
 134 This is taken to be indicative of a looping symbolic link.
 135 .\" ===========
 136 .It Bq Er ENAMETOOLONG
 137 A component of a pathname exceeds
 138 .Dv {NAME_MAX}
 139 characters, or an entire path name exceeds
 140 .Dv {PATH_MAX}
 141 characters.
 142 .\" ===========
 143 .It Bq Er ENOENT
 144 The named file does not exist.
 145 .\" ===========
 146 .It Bq Er ENOTDIR
 147 A component of the path prefix is not a directory.
 148 .\" ===========
 149 .It Bq Er EROFS
 150 The named file resides on a read-only file system.
 151 .\" ===========
 152 .It Bq Er ETXTBSY
 153 The file is a pure procedure (shared text) file that is being executed.
 154 .El
 155 .Pp
 156 The
 157 .Fn ftruncate
 158 and
 159 .Fn truncate
 160 system calls will fail if:
 161 .Bl -tag -width Er
 162 .\" ===========
 163 .It Bq Er EFBIG
 164 The length argument was greater than the maximum file size.
 165 .\" ===========
 166 .It Bq Er EINTR
 167 A signal is caught during execution.
 168 .\" ===========
 169 .It Bq Er EINVAL
 170 The
 171 .Fa length
 172 argument is less than 0.
 173 .\" ===========
 174 .It Bq Er EIO
 175 An I/O error occurred while reading from or writing to a file system.
 176 .El
 177 .Sh SEE ALSO
 178 .Xr open 2
 179 .Sh BUGS
 180 These calls should be generalized to allow ranges
 181 of bytes in a file to be discarded.
 182 .Pp
 183 Use of
 184 .Fn truncate
 185 to extend a file is not portable.
 186 .Sh HISTORY
 187 The
 188 .Fn truncate
 189 and
 190 .Fn ftruncate
 191 function calls appeared in
 192 .Bx 4.2 .