linux man page for umask

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

NAME
       umask - set and get the file mode creation mask

SYNOPSIS
       #include <sys/stat.h>

       mode_t umask(mode_t cmask);

DESCRIPTION
       The  umask() function shall set the process' file mode creation mask to cmask and return the previous value of the mask. Only the file per-
       mission bits of cmask (see <sys/stat.h>) are used; the meaning of the other bits is implementation-defined.

       The process' file mode creation mask is used during open(), creat(), mkdir(), and mkfifo() to turn off permission bits in the mode argument
       supplied. Bit positions that are set in cmask are cleared in the mode of the created file.

RETURN VALUE
       The  file  permission  bits  in	the value returned by umask() shall be the previous value of the file mode creation mask. The state of any
       other bits in that value is unspecified, except that a subsequent call to umask() with the returned value as cmask shall leave the state of
       the mask the same as its state before the first call, including any unspecified use of those bits.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       Unsigned argument and return types for umask() were proposed.  The return type and the argument were both changed to mode_t.

       Historical  implementations  have  made use of additional bits in cmask for their implementation-defined purposes. The addition of the text
       that the meaning of other bits of the field  is	implementation-defined	permits  these	implementations  to  conform  to  this	volume	of
       IEEE Std 1003.1-2001.

FUTURE DIRECTIONS
       None.

SEE ALSO
       creat() , mkdir() , mkfifo() , open() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/stat.h>, <sys/types.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								  UMASK(P)