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 (con-
       sult 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 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 invoking process'
       file mode creation mask.

OPTIONS
       The  umask  utility  shall  conform  to the Base Definitions volume of IEEE Std 1003.1-2001, 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  per-
       mission 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  IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
              ization 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 stan-
              dard 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, 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 implementation-defined 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
       IEEE Std 1003.1-2001.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Shell Command Language, chmod, the System Interfaces volume of IEEE Std 1003.1-2001, umask()

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     UMASK(1P)