Tribblix: manual page: umask.1

UMASK(1) User Commands UMASK(1)

NAME

umask - get or set the file mode creation mask

SYNOPSIS

/usr/bin/umask [-S] [mask]

sh
umask [ooo]

csh
umask [ooo]

ksh
umask [-S] [mask]

ksh93
umask [-S] [mask]

DESCRIPTION

The umask utility 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 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 does not affect the file mode creation mask of the caller's
environment. For this reason, the /usr/bin/umask utility cannot be
used to change the umask in an ongoing session. Its usefulness is
limited to checking the caller's umask. To change the umask of an
ongoing session you must use one of the shell builtins.

If the mask operand is not specified, the umask utility writes the
value of the invoking process's file mode creation mask to standard
output.

sh
The user file-creation mode mask is set to ooo. The three octal
digits refer to read/write/execute permissions for owner, group, and
other, respectively (see chmod(1), chmod(2), and umask(2)). The value
of each specified digit is subtracted from the corresponding
``digit'' specified by the system for the creation of a file (see
creat(2)). For example, umask 022 removes write permission for group
and other. Files (and directories) normally created with mode 777
become mode 755. Files (and directories) created with mode 666 become
mode 644).

o If ooo is omitted, the current value of the mask is
printed.

o umask is recognized and executed by the shell.

o umask can be included in the user's .profile (see
profile(5)) and invoked at login to automatically set the
user's permissions on files or directories created.

csh
See the description above for the Bourne shell (sh)umask built-in.

ksh
The user file-creation mask is set to mask. mask can either be an
octal number or a symbolic value as described in chmod(1). If a
symbolic value is given, the new umask value is the complement of the
result of applying mask to the complement of the previous umask
value. If mask is omitted, the current value of the mask is printed.

ksh93
umask sets the file creation mask of the current shell execution
environment to the value specified by the mask operand. This mask
affects the file permission bits of subsequently created files. mask
can either be an octal number or a symbolic value as described in
chmod(1). If a symbolic value is specified, the new file creation
mask is the complement of the result of applying mask to the
complement of the current file creation mask. If mask is not
specified, umask writes the value of the file creation mask for the
current process to standard output.

OPTIONS

ksh
The following option is supported for /usr/bin/umask and umask in
ksh:

-S
Produces symbolic output.

The default output style is unspecified, but will be recognized on a
subsequent invocation of umask on the same system as a mask operand
to restore the previous file mode creation mask.

ksh93
The following option is supported in ksh93:

-S
Causes the file creation mask to be written or treated as a
symbolic value rather than an octal number.

OPERANDS

The following operand is 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 chmod(1) manual page.

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 permissions op 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 of 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.

The file mode creation mask is set to the resulting numeric
value.

The default output of a prior invocation of umask on the same
system with no operand will also be recognized as a mask
operand. The use of an operand obtained in this way is not
obsolescent, even if it is an octal number.

OUTPUT

When the mask operand is not specified, the umask utility will write
a message to standard output that can later be used as a umask mask
operand.

If -S is specified, the message will be in the following format:

"u=%s,g=%s,o=%s\n", owner permissions, group permissions, \
other permissions

where the three values will be combinations of letters from the set
{r, w, x}. The presence of a letter will indicate that the
corresponding bit is clear in the file mode creation mask.

If a mask operand is specified, there will be no output written to
standard output.

EXAMPLES

Example 1: Using the umask Command

The examples in this section refer to the /usr/bin/umask utility and
the ksh umask builtin.

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 the current value of the mode
mask:

example$ umask
0002

The output format is unspecified, but historical implementations use
the obsolescent octal integer mode format.

example$ 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. Notice 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.

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment
variables that affect the execution of umask: LANG, LC_ALL,
LC_COLLATELC_CTYPE, LC_MESSAGES, and NLSPATH.

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.

ATTRIBUTES