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

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 cre-
       ated 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 invoca-
       tion of umask on the same system as a mask operand to restore the previous file mode  cre-
       ation 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 logi-
       cal complement of the file permission bits portion of the file mode specified by the  sym-
       bolic_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  indi-
       cated  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  permis-
       sion 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, Inter-
	      nationalization 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  interna-
	      tionalization 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  argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic 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  stan-
       dard 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 pres-
       ence of a letter shall indicate that the corresponding bit is clear in the file mode  cre-
       ation 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 sup-
	      plied.

       >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  speci-
       fies 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  envi-
       ronment, 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, Copyright (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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					 UMASK(P)
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