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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)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-01-09                          UMASK(2)

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