Originální popis anglicky:
umask - get or set the file mode creation mask
Návod, kniha: POSIX Programmer's Manual
umask [-S][mask]
The
umask utility shall set the file mode creation mask of the current
shell execution environment (see
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 invoking process' file mode creation
mask.
The
umask utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, 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
IEEE Std 1003.1-2001, 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:
(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:
sets the mode mask so that subsequently created files have their S_IWGRP and
S_IWOTH bits cleared.
The command:
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 implementation-defined 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 IEEE Std 1003.1-2001.
None.
Shell Command Language ,
chmod , the System Interfaces volume of
IEEE Std 1003.1-2001,
umask()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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
.
