2004-11-03 13:51:07 +00:00
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\" and Copyright (c) 2006, Michael Kerrisk (mtk-manpages@gmx.net)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified by Michael Haardt <michael@moria.de>
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.\" Modified Sat Jul 24 12:51:53 1993 by Rik Faith <faith@cs.unc.edu>
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.\" Modified Tue Oct 22 22:39:04 1996 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified Thu May 1 06:05:54 UTC 1997 by Nicol<6F>s Lichtmaier
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.\" <nick@debian.com> with Lars Wirzenius <liw@iki.fi> suggestion
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.\" 2006-05-13, mtk, substantial rewrite of description of 'mask'
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.TH UMASK 2 2006-05-13 "Linux" "Linux Programmer's Manual"
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.SH NAME
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umask \- set file mode creation mask
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.SH SYNOPSIS
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.B #include <sys/types.h>
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.br
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.B #include <sys/stat.h>
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.sp
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.BI "mode_t umask(mode_t " mask );
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.SH DESCRIPTION
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.BR umask ()
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sets the calling process's file mode creation mask (umask) to
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.I mask
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& 0777.
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The umask is used by
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.BR open (2),
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.BR mkdir (2),
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and other system calls that create files
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.\" e.g., mkfifo(), creat(), mknod(), sem_open(), mq_open(), shm_open()
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.\" but NOT the System V IPC *get() calls
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to modify the permissions placed on newly created files or directories.
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Specifically, permissions in the umask are turned off from
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the \fImode\fR argument to
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.BR open (2)
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and
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.BR mkdir (2).
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The constants that should be used to specify
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.I mask
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are described under
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.BR stat (2).
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The typical default value for the process umask is
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S_IWGRP\ |\ S_IWOTH
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(octal 022).
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In the usual case where the
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.I mode
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argument to
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.BR open (2)
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is specified as:
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.nf
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S_IRUSR | S_IWUSR | S_IRGRP | S_IWRGRP | S_IROTH | S_IWOTH
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.fi
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(octal 0666) when creating a new file, the permissions on the
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resulting file will be:
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.nf
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S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
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.fi
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(because 0666 & ~022 = 0644; i.e., rw-r--r--).
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.SH "RETURN VALUE"
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This system call always succeeds and the previous value of the mask
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is returned.
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.SH "CONFORMING TO"
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SVr4, SVID, POSIX, X/OPEN, 4.3BSD
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.SH "SEE ALSO"
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.BR chmod (2),
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.BR mkdir (2),
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.BR open (2),
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.BR stat (2)
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