gno/usr.man/man2/umask.2

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.\"     @(#)umask.2	8.1 (Berkeley) 6/4/93
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.\" .TH UMASK 2 GNO "System Calls" "14 December 1996"
.TH UMASK 2 "14 December 1996" GNO "System Calls"
.SH NAME
.BR umask
\- set file creation mode mask
.SH SYNOPSIS
.nf
#include <sys/stat.h>

mode_t umask (mode_t \fInumask\fR);
.SH DESCRIPTION
The
.BR umask 
routine sets the process's file mode creation mask to
.I numask
and returns the previous value of the mask.  The 9 low-order
access permission
bits of
.I numask
are used by system calls, including
.BR open (2),
.BR mkdir (2),
and
.BR mkfifo (2),
to turn off corresponding bits
requested in file mode.
(See
.BR chmod (2)).
This clearing allows each user to restrict the default access
to his files.
.LP
The default mask value is S_IWGRP|S_IWOTH (022, write access for the
owner only).
Child processes inherit the mask of the calling process.
.LP
Because the GNO kernel does not currently implement a mask, the mask
value is maintained into child processes through the environment
variable
.BR UMASK ,
which is assumed to be a string representing an octal mask value.  For
shells such as
.BR gsh (1)
which don't support a umask builtin command, the user's default mask may
be controlled by setting the 
.BR UMASK
environment variable.
.SH RETURN VALUES
The previous value of the file mode mask is returned by the call.
.SH ERRORS
The
.BR umask 
function will never return an error condition, however it is possible
that the 
.BR setenv (3)
call used in the GNO implementation may fail.  To detect this condition,
the user must set
.BR errno
to zero prior to calling
.BR umask ,
and check it's value afterward.  Under most circumstances this possible
error condition may be ignored; the only side effect of 
.BR setenv
failing in this case will be that the value of 
.I numask
will not be maintained after an 
.BR execve (2).
.SH SEE ALSO
.BR chmod (2),
.BR mknod (2),
.BR open (2)
.SH STANDARDS
The
.BR umask 
function call is expected to conform to IEEE Std 1003.1-1988 (POSIX).