This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The umask() function shall set the file mode creation mask of the
process to cmask and return the previous value of the mask. Only the
file permission bits of cmask (see <sys/stat.h>) are used; the
meaning of the other bits is implementation-defined.
The file mode creation mask of the process is used to turn off
permission bits in the mode argument supplied during calls to the
* open(), openat(), creat(), mkdir(), mkdirat(), mkfifo(), and
* mknod(), mknodat()
Bit positions that are set in cmask are cleared in the mode of the
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.
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
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 UMASK(3P)