tail head cat sleep
QR code linking to this page

Manual Pages  — UMASK


umask – set file creation mode mask



Standard C Library (libc, -lc)


#include <sys/stat.h>

umask(mode_t numask);


The umask() routine sets the process's file mode creation mask to numask and returns the previous value of the mask. The 9 low-order access permission bits of numask are used by system calls, including open(2), mkdir(2), and mkfifo(2), to turn off corresponding bits requested in file mode. (See chmod(2)). This clearing allows each user to restrict the default access to his files.

The default mask value is S_IWGRP|S_IWOTH (022, write access for the owner only). Child processes inherit the mask of the calling process.


The previous value of the file mode mask is returned by the call.


The umask() system call is always successful.


chmod(2), mkfifo(2), mknod(2), open(2)


The umask() system call is expected to conform to IEEE Std 1003.1-90 ("POSIX.1").


The umask() function appeared in AT&T v7 .

UMASK (2) June 4, 1993

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

"I liken starting one's computing career with Unix, say as an undergraduate, to being born in East Africa. It is intolerably hot, your body is covered with lice and flies, you are malnourished and you suffer from numerous curable diseases. But, as far as young East Africans can tell, this is simply the natural condition and they live within it. By the time they find out differently, it is too late. They already think that the writing of shell scripts is a natural act."
— Ken Pier, Xerox PARC