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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), 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)

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

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