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truncate(2)
NAME
  truncate, ftruncate - Changes file length

SYNOPSIS
  #include <unistd.h>

  int truncate(
	  const char *path,
	  off_t length);

  int ftruncate(
	  int filedes,
	  off_t length);

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  ftruncate(), truncate():  XSH4.2

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  path	    Specifies the name of a file that is opened, truncated, and then
	    closed.  The path parameter must point to a pathname which names
	    a regular file for which the calling process has write
	    permission.	 If the path parameter refers to a symbolic link, the
	    length of the file pointed to by the symbolic link is truncated.

  filedes   Specifies the descriptor of a file that must be open for writing.

  length    Specifies the new length of the file in bytes.

DESCRIPTION
  The truncate() and ftruncate() functions change the length of a file to the
  size in bytes specified by the length parameter.  If the new length is less
  than the previous length, the truncate() and ftruncate() functions remove
  all data beyond length bytes from the specified file.	 All file data
  between the new end-of-file and the previous end-of-file is discarded.  If
  the new length is greater than the previous length, one byte of zero (0x00)
  is written at the offset of the new length.  The space in between the
  previous end-of-file and the new end-of-file is left as a hole; that is, no
  blocks are allocated to the space in between the previous last block and
  the new last block.

  Full blocks are returned to the file system so that they can be used again,
  and the file size is changed to the value of the length parameter.

  The truncate() and ftruncate() functions have no effect on FIFO special
  files or directories.	 These functions do not modify the seek pointer of
  the file.


  Upon successful completion, the truncate() and ftruncate() functions mark
  the st_ctime and st_mtime fields of the file for update.  If the file is a
  regular file, the  ftruncate() and truncate() functions clear the S_ISUID
  and S_ISGID attributes of the file.

  If the file has enforced file locking enabled and there are file locks on
  the file, the truncate() or ftruncate() function fails.

RETURN VALUES
  Upon successful completion, a value of 0 (zero) is returned. If the
  truncate() or ftruncate() function fails, it returns a value of -1, and
  errno is set to indicate the error.

ERRORS
  The ftruncate() and truncate() functions set errno to the specified values
  for the following conditions:

  [EAGAIN]  [Tru64 UNIX]  The write operation failed due to an enforced write
	    lock on the file.

	    [Tru64 UNIX]  The file has enforced mode file locking enabled and
	    there are file locks on the file.

  [EFBIG]   The length parameter was greater than the maximum file size.

  [EINTR]   A signal was caught during execution.

  [EINVAL]  The length parameter was less than 0 (zero).

	    [Tru64 UNIX]  The file is not a regular file.

  [EIO]	    An I/O error occurred while reading from or writing to a file
	    system.

  [ESTALE]  [Tru64 UNIX]  The process' root or current directory is located
	    in a virtual file system that has been unmounted.

  In addition, the ftruncate() function sets errno to the specified values
  for the following conditions:

  [EACCES]  [Tru64 UNIX]  Write access permission to the file was denied.

  [EBADF]   The filedes parameter is not a valid file descriptor open for
	    writing.

  [EINVAL]  The fildes parameter references a file that was opened without
	    write permission.

  [EROFS]   [Tru64 UNIX]  The file resides on a read-only file system.

  In addition, the truncate() function fails if errors occur that apply to
  any service requiring pathname resolution, or if one of the following are
  true:

  [EACCES]  A component of the path prefix denies search permission, or write
	    permission is denied on the file.

  [EISDIR]  The named file is a directory.

  [ELOOP]   Too many symbolic links were encountered in resolving path.

  [ENAMETOOLONG]
	    The size of the pathname exceeds PATH_MAX or a pathname component
	    is longer than NAME_MAX.

  [ENOENT]  A component of the specified pathname does not exist, or the path
	    parameter points to an empty string.

  [ENOTDIR] A component of the path prefix is not a directory.

  [EROFS]   The file resides on a read-only file system.

RELATED INFORMATION
  Functions: chmod(2), fcntl(2), open(2)

  Standards: standards(5)

Index for Section 2

Alphabetical listing for T

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