umask — set file mode creation mask
#include <sys/types.h> #include <sys/stat.h>
mode_t
umask( |
mode_t mask); |
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).
Alternatively, if the parent directory has a default ACL
(see acl(5)), the umask is ignored,
the default ACL is inherited, the permission bits are set
based on the inherited ACL, and permission bits absent in the
mode argument are
turned off. For example, the following default ACL is
equivalent to a umask of 022:
u::rwx,g::r-x,o::r-x
Combining the effect of this default ACL with a mode argument of 0666
(rw-rw-rw-), the resulting file permissions would be 0644
(rw-r--r--).
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−−).
A child process created via fork(2) inherits its parent's umask. The umask is left unchanged by execve(2).
Since Linux 4.7, the umask of any process can be viewed
via the umask field
of /proc/[pid]/status.
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)).
This page is part of release 4.07 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
https://www.kernel.org/doc/man−pages/.
|
Copyright (c) 2006, 2008, Michael Kerrisk <mtk.manpagesgmail.com> (A few fragments remain from an earlier (1992) version written in 1992 by Drew Eckhardt <drewcs.colorado.edu>.) %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END Modified by Michael Haardt <michaelmoria.de> Modified Sat Jul 24 12:51:53 1993 by Rik Faith <faithcs.unc.edu> Modified Tue Oct 22 22:39:04 1996 by Eric S. Raymond <esrthyrsus.com> Modified Thu May 1 06:05:54 UTC 1997 by Nicolás Lichtmaier <nickdebian.com> with Lars Wirzenius <liwiki.fi> suggestion 2006-05-13, mtk, substantial rewrite of description of 'mask' 2008-01-09, mtk, a few rewrites and additions. |