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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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UMASK(1P) POSIX Programmer's Manual UMASK(1P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
umask — get or set the file mode creation mask
umask [-S] [mask]
The umask utility shall set the file mode creation mask of the
current shell execution environment (see Section 2.12, Shell
Execution Environment) to the value specified by the mask
operand. This mask shall affect the initial value of the file
permission bits of subsequently created files. If umask is called
in a subshell or separate utility execution environment, such as
one of the following:
(umask 002)
nohup umask ...
find . -exec umask ... \;
it shall not affect the file mode creation mask of the caller's
environment.
If the mask operand is not specified, the umask utility shall
write to standard output the value of the file mode creation mask
of the invoking process.
The umask utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
-S Produce symbolic output.
The default output style is unspecified, but shall be recognized
on a subsequent invocation of umask on the same system as a mask
operand to restore the previous file mode creation mask.
The following operand shall be supported:
mask A string specifying the new file mode creation mask.
The string is treated in the same way as the mode
operand described in the EXTENDED DESCRIPTION section
for chmod.
For a symbolic_mode value, the new value of the file
mode creation mask shall be the logical complement of
the file permission bits portion of the file mode
specified by the symbolic_mode string.
In a symbolic_mode value, the permissions op characters
'+' and '-' shall be interpreted relative to the
current file mode creation mask; '+' shall cause the
bits for the indicated permissions to be cleared in the
mask; '-' shall cause the bits for the indicated
permissions to be set in the mask.
The interpretation of mode values that specify file
mode bits other than the file permission bits is
unspecified.
In the octal integer form of mode, the specified bits
are set in the file mode creation mask.
The file mode creation mask shall be set to the
resulting numeric value.
The default output of a prior invocation of umask on
the same system with no operand also shall be
recognized as a mask operand.
Not used.
None.
The following environment variables shall affect the execution of
umask:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of
sequences of bytes of text data as characters (for
example, single-byte as opposed to multi-byte
characters in arguments).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
When the mask operand is not specified, the umask utility shall
write a message to standard output that can later be used as a
umask mask operand.
If -S is specified, the message shall be in the following format:
"u=%s,g=%s,o=%s\n", <owner permissions>, <group permissions>,
<other permissions>
where the three values shall be combinations of letters from the
set {r, w, x}; the presence of a letter shall indicate that the
corresponding bit is clear in the file mode creation mask.
If a mask operand is specified, there shall be no output written
to standard output.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 The file mode creation mask was successfully changed, or no
mask operand was supplied.
>0 An error occurred.
Default.
The following sections are informative.
Since umask affects the current shell execution environment, it
is generally provided as a shell regular built-in.
In contrast to the negative permission logic provided by the file
mode creation mask and the octal number form of the mask
argument, the symbolic form of the mask argument specifies those
permissions that are left alone.
Either of the commands:
umask a=rx,ug+w
umask 002
sets the mode mask so that subsequently created files have their
S_IWOTH bit cleared.
After setting the mode mask with either of the above commands,
the umask command can be used to write out the current value of
the mode mask:
$ umask
0002
(The output format is unspecified, but historical implementations
use the octal integer mode format.)
$ umask -S
u=rwx,g=rwx,o=rx
Either of these outputs can be used as the mask operand to a
subsequent invocation of the umask utility.
Assuming the mode mask is set as above, the command:
umask g-w
sets the mode mask so that subsequently created files have their
S_IWGRP and S_IWOTH bits cleared.
The command:
umask -- -w
sets the mode mask so that subsequently created files have all
their write bits cleared. Note that mask operands -r, -w, -x or
anything beginning with a <hyphen-minus>, must be preceded by
"--" to keep it from being interpreted as an option.
Since umask affects the current shell execution environment, it
is generally provided as a shell regular built-in. If it is
called in a subshell or separate utility execution environment,
such as one of the following:
(umask 002)
nohup umask ...
find . -exec umask ... \;
it does not affect the file mode creation mask of the environment
of the caller.
The description of the historical utility was modified to allow
it to use the symbolic modes of chmod. The -s option used in
early proposals was changed to -S because -s could be confused
with a symbolic_mode form of mask referring to the S_ISUID and
S_ISGID bits.
The default output style is unspecified to permit implementors to
provide migration to the new symbolic style at the time most
appropriate to their users. A -o flag to force octal mode output
was omitted because the octal mode may not be sufficient to
specify all of the information that may be present in the file
mode creation mask when more secure file access permission checks
are implemented.
It has been suggested that trusted systems developers might
appreciate ameliorating the requirement that the mode mask
``affects'' the file access permissions, since it seems access
control lists might replace the mode mask to some degree. The
wording has been changed to say that it affects the file
permission bits, and it leaves the details of the behavior of how
they affect the file access permissions to the description in the
System Interfaces volume of POSIX.1‐2017.
None.
Chapter 2, Shell Command Language, chmod(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, umask(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 UMASK(1P)
Pages that refer to this page: c99(1p), chmod(1p), fort77(1p), mkdir(1p), mkfifo(1p), sh(1p), uudecode(1p)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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