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 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>) shall be used; ^[XSI]  the S_ISVTX bit shall be ignored, and  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()

• ^[XSI] mknod(), mknodat()

• ^[MSG] mq_open()

• sem_open()

Permission 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. ^[XSI]  The S_ISVTX bit in the returned value shall be clear.  The state of any other bits in the returned 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.

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 POSIX.1-2024.

FUTURE DIRECTIONS

None.

SEE ALSO

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

XBD <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.

Issue 8

Austin Group Defect 1522 is applied, adding requirements relating to the S_ISVTX bit.