UMASK(3P) POSIX Programmer's Manual UMASK(3P)

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

#include <sys/stat.h>
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 following functions:

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 those bits.

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 POSIX.1‐2017.


creat(), exec, mkdir(), mkfifo(), mknod(), mq_open(), open(), sem_open()

The Base Definitions volume of POSIX.1‐2017, <sys_stat.h>, <sys_types.h>

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 .

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2017 IEEE/The Open Group