UMASK(1)                   POSIX Programmer's Manual                  UMASK(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       umask -- get or set the file mode creation mask

SYNOPSIS
       umask [[-S]] [[mask]]

DESCRIPTION
       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.

OPTIONS
       The umask utility shall conform to the Base Definitions volume of
       POSIX.1-2017, 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.

OPERANDS
       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.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       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.1-2017, 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.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       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.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       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.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       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.

EXAMPLES
       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
           00000022

       (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-minus>, must be preceded by ""----"" to keep it
       from being interpreted as an option.

RATIONALE
       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.1-2017.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Chapter _2, Shell Command Language, chmod

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1-2017, umask()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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                  2017                             UMASK(1)
