linux man page for truncate

TRUNCATE(P)						     POSIX Programmer's Manual						       TRUNCATE(P)

NAME
       truncate - truncate a file to a specified length

SYNOPSIS
       #include <unistd.h>

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

DESCRIPTION
       The truncate() function shall cause the regular file named by path to have a size which shall be equal to length bytes.

       If  the	file  previously  was larger than length, the extra data is discarded. If the file was previously shorter than length, its size is
       increased, and the extended area appears as if it were zero-filled.

       The application shall ensure that the process has write permission for the file.

       If the request would cause the file size to exceed the soft file size limit for the process, the request shall fail and the  implementation
       shall generate the SIGXFSZ signal for the process.

       This  function shall not modify the file offset for any open file descriptions associated with the file. Upon successful completion, if the
       file size is changed, this function shall mark for update the st_ctime and st_mtime fields of the file, and the S_ISUID and S_ISGID bits of
       the file mode may be cleared.

RETURN VALUE
       Upon successful completion, truncate() shall return 0. Otherwise, -1 shall be returned, and errno set to indicate the error.

ERRORS
       The truncate() function shall fail if:

       EINTR  A signal was caught during execution.

       EINVAL The length argument was less than 0.

       EFBIG or EINVAL
	      The length argument was greater than the maximum file size.

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

       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  A loop exists in symbolic links encountered during resolution of the path argument.

       ENAMETOOLONG
	      The length of the path argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.

       ENOENT A component of path does not name an existing file or path is an empty string.

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

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

       The truncate() function may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       ENAMETOOLONG
	      Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       open() , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
       and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							       TRUNCATE(P)