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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 Environ‐
       ment) 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 envi‐
       ronment.

       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 invok‐
       ing process.

OPTIONS
       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
       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	 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 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 op‐
		 erand.

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	 vari‐
		 ables	that are unset or null. (See the Base Definitions vol‐
		 ume of POSIX.1‐2008, Section 8.2, Internationalization	 Vari‐
		 ables	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 oper‐
       and.

       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 correspond‐
       ing 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 gen‐
       erally 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  sym‐
       bolic  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 gen‐
       erally provided as a shell regular built-in. If it is called in a  sub‐
       shell  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  pro‐
       vide  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 descrip‐
       tion in the System Interfaces volume of POSIX.1‐2008.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Chapter 2, Shell Command Language, chmod

       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()

COPYRIGHT
       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 Electri‐
       cal 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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			     UMASK(1P)
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