NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

UMASK(2)                  Linux Programmer's Manual                 UMASK(2)

NAME         top

       umask - set file mode creation mask

SYNOPSIS         top

       #include <sys/types.h>
       #include <sys/stat.h>

       mode_t umask(mode_t mask);

DESCRIPTION         top

       umask() sets the calling process's file mode creation mask (umask) to
       mask & 0777 (i.e., only the file permission bits of mask are used),
       and returns the previous value of the mask.

       The umask is used by open(2), mkdir(2), and other system calls that
       create files to modify the permissions placed on newly created files
       or directories.  Specifically, permissions in the umask are turned
       off from the mode argument to open(2) and mkdir(2).

       The constants that should be used to specify mask are described under
       stat(2).

       The typical default value for the process umask is S_IWGRP | S_IWOTH
       (octal 022).  In the usual case where the mode argument to open(2) is
       specified as:

           S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH

       (octal 0666) when creating a new file, the permissions on the
       resulting file will be:

           S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH

       (because 0666 & ~022 = 0644; i.e., rw-r--r--).

RETURN VALUE         top

       This system call always succeeds and the previous value of the mask
       is returned.

CONFORMING TO         top

       SVr4, 4.3BSD, POSIX.1-2001.

NOTES         top

       A child process created via fork(2) inherits its parent's umask.  The
       umask is left unchanged by execve(2).

       The umask setting also affects the permissions assigned to POSIX IPC
       objects (mq_open(3), sem_open(3), shm_open(3)), FIFOs (mkfifo(3)),
       and UNIX domain sockets (unix(7)) created by the process.  The umask
       does not affect the permissions assigned to System V IPC objects
       created by the process (using msgget(2), semget(2), shmget(2)).

SEE ALSO         top

       chmod(2), mkdir(2), open(2), stat(2), acl(5)

COLOPHON         top

       This page is part of release 3.70 of the Linux man-pages project.  A
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       latest version of this page, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux                            2008-01-09                         UMASK(2)