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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 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  environ-
       ment, 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 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 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
              IEEE Std 1003.1-2001, 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 implementation-defined to permit implemen-
       tors 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 descrip-
       tion 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 original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                            UMASK(1P)