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 Truncate
  57 causes the file named by
  58 .Fa path
  59 or referenced by
  60 .Fa fildes
  61 to be truncated or extended to
  62 .Fa length
  63 bytes in size.  If the file previously
  64 was larger than this size, the extra data
  65 is lost. If the file was smaller than this size, it will be extended as
  66 if by writing bytes with the value zero.
  67 With
  68 .Fn ftruncate ,
  69 the file must be open for writing.
  70 .Sh RETURN VALUES
  71 A value of 0 is returned if the call succeeds.  If the call
  72 fails a -1 is returned, and the global variable
  73 .Va errno
  74 specifies the error.
  75 .Sh ERRORS
  76 .Pp
  77 The
  78 .Fn ftruncate
  79 system call will fail if:
  80 .Bl -tag -width Er
  81 .\" ===========
  82 .It Bq Er EBADF
  83 .Fa fildes
  84 is not a valid descriptor open for writing.
  85 .\" ===========
  86 .It Bq Er EFBIG
  87 The file is a regular file and
  88 .Fa length
  89 is greater than the offset maximum established
  90 in the open file description associated with
  91 .Fa fildes .
  92 .\" ===========
  93 .It Bq Er EINVAL
  94 .Fa fildes
  95 references a socket, not a file.
  96 .\" ===========
  97 .It Bq Er EINVAL
  98 .Fa fildes
  99 is not open for writing.
 100 .\" ===========
 101 .It Bq Er EROFS
 102 The named file resides on a read-only file system.
 103 .El
 104 .Pp
 105 The
 106 .Fn truncate
 107 system call will fail if:
 108 .Bl -tag -width Er
 109 .\" ===========
 110 .It Bq Er EACCES
 111 Search permission is denied for a component of the path prefix.
 112 .\" ===========
 113 .It Bq Er EACCES
 114 The named file is not writable by the user.
 115 .\" ===========
 116 .It Bq Er EFAULT
 117 .Fa Path
 118 points outside the process's allocated address space.
 119 .\" ===========
 120 .It Bq Er EISDIR
 121 The named file is a directory.
 122 .\" ===========
 123 .It Bq Er ELOOP
 124 Too many symbolic links are encountered in translating the pathname.
 125 This is taken to be indicative of a looping symbolic link.
 126 .\" ===========
 127 .It Bq Er ENAMETOOLONG
 128 A component of a pathname exceeds
 129 .Dv {NAME_MAX}
 130 characters, or an entire path name exceeds
 131 .Dv {PATH_MAX}
 132 characters.
 133 .\" ===========
 134 .It Bq Er ENOENT
 135 The named file does not exist.
 136 .\" ===========
 137 .It Bq Er ENOTDIR
 138 A component of the path prefix is not a directory.
 139 .\" ===========
 140 .It Bq Er EROFS
 141 The named file resides on a read-only file system.
 142 .\" ===========
 143 .It Bq Er ETXTBSY
 144 The file is a pure procedure (shared text) file that is being executed.
 145 .El
 146 .Pp
 147 The
 148 .Fn ftruncate
 149 and
 150 .Fn truncate
 151 system calls will fail if:
 152 .Bl -tag -width Er
 153 .\" ===========
 154 .It Bq Er EFBIG
 155 The length argument was greater than the maximum file size.
 156 .\" ===========
 157 .It Bq Er EINTR
 158 A signal is caught during execution.
 159 .\" ===========
 160 .It Bq Er EINVAL
 161 The
 162 .Fa length
 163 argument is less than 0.
 164 .\" ===========
 165 .It Bq Er EIO
 166 An I/O error occurred while reading from or writing to a file system.
 167 .El
 168 .Sh SEE ALSO
 169 .Xr open 2
 170 .Sh BUGS
 171 These calls should be generalized to allow ranges
 172 of bytes in a file to be discarded.
 173 .Pp
 174 Use of
 175 .Fn truncate
 176 to extend a file is not portable.
 177 .Sh HISTORY
 178 The
 179 .Fn truncate
 180 and
 181 .Fn ftruncate
 182 function calls appeared in
 183 .Bx 4.2 .