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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 |
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.1‐2008, 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.1‐2008, 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>, 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.1‐2008.
None.
Chapter 2, Shell Command Language, chmod(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2008, umask(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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 2013 UMASK(1P)
Pages that refer to this page: c99(1p), chmod(1p), fort77(1p), mkdir(1p), mkfifo(1p), sh(1p), uudecode(1p)