umask

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



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.

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
           0002

       (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(1P)