The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### 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 permission 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 to turn off permission bits in the mode argument supplied during calls to the following functions:

> - open(), creat(), mkdir(), and mkfifo()

> - [XSI] mknod()

> - [MSG] mq_open()

> - [SEM] sem_open()

> 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(), mknod(), mq_open(), open(), sem_open(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/stat.h>, <sys/types.h>

#### CHANGE HISTORY

> First released in Issue 1. Derived from Issue 1 of the SVID.

#### Issue 6

> In the SYNOPSIS, the optional include of the <sys/types.h> header is removed.

> The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

> - The requirement to include <sys/types.h> has been removed. Although <sys/types.h> was required for conforming implementations of previous POSIX specifications, it was not required for UNIX applications.

> IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/143 is applied, adding the mknod(), mq_open(), and sem_open() functions to the DESCRIPTION and SEE ALSO sections.

End of informative text.

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