ultrix man page for ftruncate

truncate(2)							System Calls Manual						       truncate(2)

Name
       truncate, ftruncate - truncate a file to a specified length

Syntax
       truncate(path, length)
       char *path;
       int length;

       ftruncate(fd, length)
       int fd, length;

Description
       The  system  call  causes the file named by path or referenced by fd to be truncated to, at most, length bytes in size.	If the file previ-
       ously was larger than this size, the extra data is lost.  With the file must be open for writing.

Return Values
       A value of zero (0) is returned if the call succeeds.  If the call fails, a -1 is returned, and the global  variable  errno  specifies  the
       error.

Restrictions
       Partial blocks discarded as the result of truncation are not zero-filled. This can result in holes in files that do not read as zero.

Diagnostics
       The system call succeeds unless:

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

       [ENOENT]       The named file does not exist.

       [EACCES]       Search permission is denied for a component of the path prefix.

       [EISDIR]       The named file is a directory.

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

       [ETXTBSY]      The file is a pure procedure (shared text) file that is being executed.

       [EFAULT]       The path points outside the process's allocated address space.

       [ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.

       [ELOOP]	      Too many symbolic links were encountered in translating the pathname.

       [EIO]	      An I/O error occurred updating the inode.

       The system call succeeds unless:

       [EBADF]	      The fd is not a valid descriptor.

       [EINVAL]       The fd references a socket, not a file.

       [ETIMEDOUT]    A  connect  request  or remote file operation failed, because the connected party did not properly respond after a period of
		      time that is dependent on the communications protocol.

See Also
       open(2)

																       truncate(2)