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.
umask — set and get the file mode creation mask
mode_t umask(mode_t cmask);
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 mkfifoat()
- mknod(), mknodat()
Bit positions that are set in cmask are cleared in the mode
of the created file.
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
No errors are defined.
The following sections are informative.
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
creat(), exec, mkdir(),
mkfifo(), mknod(), mq_open(),
The Base Definitions volume of POSIX.1‐2017,
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 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 .
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