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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 dif-
       fer (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 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  invok-
       ing 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 cur-
       rent 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 unspeci-
       fied.

       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  prece-
              dence 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  exam-
              ple, 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 writ-
              ten 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 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  inter-
       preted 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  sym-
       bolic  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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)