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.TH UMASK "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

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.

.SH NAME

umask

\(em get or set the file mode creation mask

.SH SYNOPSIS

.LP

.nf

umask \fB[\fR\(miS\fB] [\fImask\fB]\fR

.fi

.SH DESCRIPTION

The

.IR umask

utility shall set the file mode creation mask of the current shell

execution environment (see

.IR "Section 2.12" ", " "Shell Execution Environment")

to the value specified by the

.IR mask

operand. This mask shall affect the initial value of the file

permission bits of subsequently created files. If

.IR umask

is called in a subshell or separate utility execution environment, such

as one of the following:

.sp

.RS 4

.nf

\fB

(umask 002)

nohup umask ...

find . \(miexec umask ... \e;

.fi \fR

.P

.RE

.P

it shall not affect the file mode creation mask of the caller's

environment.

.P

If the

.IR mask

operand is not specified, the

.IR umask

utility shall write to standard output the value of the

file mode creation mask of the invoking process.

.SH OPTIONS

The

.IR umask

utility shall conform to the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 12.2" ", " "Utility Syntax Guidelines".

.P

The following option shall be supported:

.IP "\fB\(miS\fP" 10

Produce symbolic output.

.P

The default output style is unspecified, but shall be recognized on a

subsequent invocation of

.IR umask

on the same system as a

.IR mask

operand to restore the previous file mode creation mask.

.SH OPERANDS

The following operand shall be supported:

.IP "\fImask\fR" 10

A string specifying the new file mode creation mask. The string is

treated in the same way as the

.IR mode

operand described in the EXTENDED DESCRIPTION section for

.IR chmod .

.RS 10 

.P

For a

.IR 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

.IR symbolic_mode

string.

.P

In a

.IR symbolic_mode

value, the permissions

.IR op

characters

.BR '\(pl' 

and

.BR '\(mi' 

shall be interpreted relative to the current file mode creation mask;

.BR '\(pl' 

shall cause the bits for the indicated permissions to be cleared in the

mask;

.BR '\(mi' 

shall cause the bits for the indicated permissions to be set in the

mask.

.P

The interpretation of

.IR mode

values that specify file mode bits other than the file permission bits

is unspecified.

.P

In the octal integer form of

.IR mode ,

the specified bits are set in the file mode creation mask.

.P

The file mode creation mask shall be set to the resulting numeric

value.

.P

The default output of a prior invocation of

.IR umask

on the same system with no operand also shall be recognized as a

.IR mask

operand.

.RE

.SH STDIN

Not used.

.SH "INPUT FILES"

None.

.SH "ENVIRONMENT VARIABLES"

The following environment variables shall affect the execution of

.IR umask :

.IP "\fILANG\fP" 10

Provide a default value for the internationalization variables that are

unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 8.2" ", " "Internationalization Variables"

for the precedence of internationalization variables used to determine

the values of locale categories.)

.IP "\fILC_ALL\fP" 10

If set to a non-empty string value, override the values of all the

other internationalization variables.

.IP "\fILC_CTYPE\fP" 10

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).

.IP "\fILC_MESSAGES\fP" 10

.br

Determine the locale that should be used to affect the format and

contents of diagnostic messages written to standard error.

.IP "\fINLSPATH\fP" 10

Determine the location of message catalogs for the processing of

.IR LC_MESSAGES .

.SH "ASYNCHRONOUS EVENTS"

Default.

.SH STDOUT

When the

.IR mask

operand is not specified, the

.IR umask

utility shall write a message to standard output that can later be used

as a

.IR umask

.IR mask

operand.

.P

If

.BR \(miS

is specified, the message shall be in the following format:

.sp

.RS 4

.nf

\fB

"u=%s,g=%s,o=%s\en", <\fIowner permissions\fR>, <\fIgroup permissions\fR>,

    <\fIother permissions\fR>

.fi \fR

.P

.RE

.P

where the three values shall be combinations of letters from the set

{\c

.IR r ,

.IR w ,

.IR x };

the presence of a letter shall indicate that the corresponding bit is

clear in the file mode creation mask.

.P

If a

.IR mask

operand is specified, there shall be no output written to standard

output.

.SH STDERR

The standard error shall be used only for diagnostic messages.

.SH "OUTPUT FILES"

None.

.SH "EXTENDED DESCRIPTION"

None.

.SH "EXIT STATUS"

The following exit values shall be returned:

.IP "\00" 6

The file mode creation mask was successfully changed, or no

.IR mask

operand was supplied.

.IP >0 6

An error occurred.

.SH "CONSEQUENCES OF ERRORS"

Default.

.LP

.IR "The following sections are informative."

.SH "APPLICATION USAGE"

Since

.IR umask

affects the current shell execution environment, it is generally

provided as a shell regular built-in.

.P

In contrast to the negative permission logic provided by the file mode

creation mask and the octal number form of the

.IR mask

argument, the symbolic form of the

.IR mask

argument specifies those permissions that are left alone.

.SH EXAMPLES

Either of the commands:

.sp

.RS 4

.nf

\fB

umask a=rx,ug+w

.P

umask 002

.fi \fR

.P

.RE

.P

sets the mode mask so that subsequently created files have their

S_IWOTH bit cleared.

.P

After setting the mode mask with either of the above commands, the

.IR umask

command can be used to write out the current value of the mode mask:

.sp

.RS 4

.nf

\fB

\fB$ \fRumask

\fB0002\fR

.fi \fR

.P

.RE

.P

(The output format is unspecified, but historical implementations use

the octal integer mode format.)

.sp

.RS 4

.nf

\fB

\fB$ \fRumask \(miS

\fBu=rwx,g=rwx,o=rx\fR

.fi \fR

.P

.RE

.P

Either of these outputs can be used as the mask operand to a subsequent

invocation of the

.IR umask

utility.

.P

Assuming the mode mask is set as above, the command:

.sp

.RS 4

.nf

\fB

umask g\(miw

.fi \fR

.P

.RE

.P

sets the mode mask so that subsequently created files have their

S_IWGRP and S_IWOTH bits cleared.

.P

The command:

.sp

.RS 4

.nf

\fB

umask \(mi\|\(mi \(miw

.fi \fR

.P

.RE

.P

sets the mode mask so that subsequently created files have all their

write bits cleared. Note that

.IR mask

operands

.BR \(mir ,

.BR \(miw ,

.BR \(mix

or anything beginning with a

<hyphen>,

must be preceded by

.BR \(dq\(mi\|\(mi\(dq 

to keep it from being interpreted as an option.

.SH RATIONALE

Since

.IR 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:

.sp

.RS 4

.nf

\fB

(umask 002)

nohup umask ...

find . \(miexec umask ... \e;

.fi \fR

.P

.RE

.P

it does not affect the file mode creation mask of the environment of

the caller.

.P

The description of the historical utility was modified to allow it to

use the symbolic modes of

.IR chmod .

The

.BR \(mis

option used in early proposals was changed to

.BR \(miS

because

.BR \(mis

could be confused with a

.IR symbolic_mode

form of mask referring to the S_ISUID and S_ISGID bits.

.P

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

.BR \(mio

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.

.P

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\(hy2008.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "Chapter 2" ", " "Shell Command Language",

.IR "\fIchmod\fR\^"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables",

.IR "Section 12.2" ", " "Utility Syntax Guidelines"

.P

The System Interfaces volume of POSIX.1\(hy2008,

.IR "\fIumask\fR\^(\|)"

.SH COPYRIGHT

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 .