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



NAME
       umask - set file mode creation mask

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

       mode_t umask(mode_t mask);

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

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

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

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2008-01-09                                   UMASK(2)