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umask(1)
NAME
umask - Displays or sets the file mode creation mask
SYNOPSIS
umask [-S] [mask]
Note
The C shell has a built-in version of the umask command. If you are
using the C shell, and want to guarantee that you are using the
command described here, you must specify the full path /usr/bin/umask.
See the csh(1) reference page for a description of the built-in
command.
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
umask: XCU5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
-S Produce symbolic output.
Output is produced in a format that is recognized on a subsequent
invocation of umask as a mask operand to restore the previous file mode
creation mask.
If the -S option is not used, output is displayed as an octal integer, but
is still usable as input on a subsequent invocation of the umask command.
OPERANDS
mask
A string specifying the new file mode creation mask. This string may
may be an octal value or a symbolic_mode value.
For a symbolic_mode value, the new value of the file mode creation mask
is 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 characters + and - are interpreted
relative to the current file mode creation mask; + causes the bits for
the indicated permissions to be cleared in the mask; - causes the bits
for the indicated permissions to be set in the mask.
The file mode creation mask is set to the resulting numeric value.
In the obsolescent octal integer form of mode, the specified bits are
set in the file mode creation mask.
DESCRIPTION
The umask command sets the file mode creation mask of the current shell
execution environment to the value specified by the mask operand. This
mask affects the initial value of the file permission bits of subsequently
created files.
If the mask operand is not specified, the umask command writes the value of
the invoking process's file mode creation mask to standard output.
If the -S option is specified, the output is in the following format:
"u=%s,g=%s,o=%s\n", <owner permissions>,
<group permissions>, <other permissions>"
The three values are combinations of letters from the set {r, w, x}; the
presence of a letter indicates that the corresponding bit is clear in the
file mode creation mask.
NOTES
1. Any mask operand such as -r, -w, -x, or anything beginning with a
hyphen, must be preceded by -- to keep it from being interpreted as a
option.
2. Since umask affects the current shell execution environment, it is
provided as a shell regular built-in.
3. 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 operand specifies those permissions that are
left alone.
4. Although the references to octal modes are obsolescent in the ISO/IEC
9945-2:1993 standard, they are maintained for portable applications
until further notice.
RESTRICTIONS
If umask is called in a subshell or separate utility execution environment,
it does not affect the file mode creation mask of the caller's environment.
A separate execution environment could be one of the following:
(umask 002)
nohup umask ...
find . -exec umask ... \;
EXIT STATUS
The following exit values are returned:
0 The file mode creation mask was successfully changed, or no mask
operand was supplied.
>0 An error occurred.
EXAMPLES
1. To set the file mode creation mask so that subsequently created files
have their write by all others bit cleared, enter either of the
following commands:
umask a=rx,ug+w
umask 002
2. If the file mode creation mask was set with either of the above
commands, the umask command can be used to write out the current value
of the mask. To write the value in octal format, enter:
umask
This provides the output:
0002
To write the value in symbolic format, enter:
umask -S
This provides the output:
u=rwx,g=rwx,o=rx
3. The following sequence of commands is an example of how to save the
current file mode creation mask and later restore the value using the
umask command and octal integer formats.
a. Examine the current value of the mask:
umask
The current mask is reported as:
022
b. Save the current value, and verify the saved value:
SAVEMASK =`umask`
echo $SAVEMASK
The saved value is reported as:
022
c. Change the current mask:
umask 444
d. Verify the change:
umask
e. The new mask is reported:
0444
f. Restore the previous mask:
umask $SAVEMASK
g. Verify the restored value:
umask
The value is now restored:
022
4. The following sequence of commands is an example of how to save the
current file mode creation mask and later restore the value using the
umask command and symbolic_mode formats.
a. Examine the current value of the mask:
umask -S
The current mask is reported as:
u=rwx,g=rx,o=rx
b. Save the current value, and verify the saved value:
SAVEMASK=`umask -S`
echo $SAVEMASK
The saved value is reported as:
u=rwx,g=rx,o=rx
c. Change the current mask:
umask a=
d. Verify the change:
umask -S
e. The new mask is reported:
u=,g=,o=
f. Restore the previous mask:
umask $SAVEMASK
g. Verify the restored value:
umask -S
The value is now restored:
u=rwx,g=rx,o=rx
5. To set the file mode creation mask so that subsequently created files
have all their write bits cleared, enter:
umask -- -w
ENVIRONMENT VARIABLES
The following environment variables affect the execution of umask:
LANG
Provides a default value for the internationalization variables that
are unset or null. If LANG is unset or null, the corresponding value
from the default locale is used. If any of the internationalization
variables contain an invalid setting, the utility behaves as if none of
the variables had been defined.
LC_ALL
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
LC_CTYPE
Determines the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multibyte characters in arguments).
LC_MESSAGES
Determines the locale for the format and contents of diagnostic
messages written to standard error.
NLSPATH
Determines the location of message catalogues for the processing of
LC_MESSAGES.
SEE ALSO
Commands: chmod(1)
Functions: chmod(2), umask(2)
Standards: standards(5)
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