PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       umask — get or set the file mode creation mask

SYNOPSIS         top

       umask [−S] [mask]

DESCRIPTION         top

       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         top

       The umask utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, 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         top

       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         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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.1‐2008, 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         top

       Default.

STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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         top

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

RATIONALE         top

       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.1‐2008.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Chapter 2, Shell Command Language, chmod(1p)

       The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, umask(3p)

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                           UMASK(1P)

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