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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)

COLOPHON

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