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trying to understand rationale of unix stream i/o concept

 
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Old 07-11-2009
trying to understand rationale of unix stream i/o concept
I am an entry level programmer with no formal training in computer science. I am trying to enhance my conceptual knowledge about operating systems in general.

I have been using the C programming language on Linux systems for some time and have used the traditional unix stream I/O APIs. The introductory material in books and on the web, typically introduce the unix stream I/O model as "basic unix I/O model is a stream of bytes which can be accessed sequentially or randomly". I understand this part, but I am unable to visualize how else would one access the data. Were the I/O models different before the I/O stream model came in to existence? Are there models in current computing paradigm which are different from the stream I/O. I will appreciate if some can help me visualize both the stream I/O model vs other models (if they exist or existed). Pros-Cons will be a great addition too.

In addition, I came across the following statement on the web (I/O System)

"The basic model of the UNIX I/O system is a sequence of bytes that can be accessed either randomly or sequentially. There are no access methods and no control blocks in a typical UNIX user process."

I do not understand the last statement - what are access methods and control blocks in the context of I/O?

Thanks
Kay
 
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LEARN ABOUT OSX

mcxquery

mcxquery(1)						    BSD General Commands Manual 					       mcxquery(1)

NAME

     mcxquery -- Managed Client (MCX) compositor query tool

SYNOPSIS

     mcxquery [options] [-user recordName] [-group recordName] [-computer spec]

	      options:

	      -o path			 Writes output to a file at the specified path.

	      -format space | tab | xml  Specifies the format of the output.

	      -computerOnly		 Ignore values for -user and -group.

	      -useCache 		 Return the cached computer settings in the local node if they are available.

	      -raw			 Dumps Directory Service data for records contributing to managed preferences.

	      -forApple 		 Convenience for specifying options when sending bug reports to Apple. Currently enables "-raw" and "-for-
					 mat xml". See usage example below.

DESCRIPTION

     mcxquery is a utility to determine the effective managed preferences for a user logging in to a workgroup from a specific computer.

     -user	Specify the short name of the user record to read managed preferences from. If this parameter is omitted, or a value of "=" speci-
		fied, the short name of the currently logged in console user will be used.

     -group	Specify the short name of the group record to read managed preferences from. A value of "=" may be specified to mean the name of
		the workgroup (if any) chosen for the current login session.

     -computer	Specify the computer record to read managed preferences from. The computer can be specified using either an Ethernet MAC address
		(e.g. "11:22:33:44:55:66"), a Hardware UUID (e.g. "00112233-4455-6677-8899-AABBCCDDEEFF") or the short name of the computer record
		itself (e.g. "lab1_12"). If this parameter is omitted, or a value of "=" specified, the record for the current computer will be
		used.

EXAMPLES

     mcxquery -user jane -group science -computer lab1_12
	      Displays the managed preferences that would be in effect if user "jane" logged in using workgroup "science" from the computer speci-
	      fied in the "lab1_12" computer record.

     mcxquery -user jane -group science -computer 11:22:33:44:55:66
	      Displays the managed preferences that would be in effect if user "jane" logged in using workgroup "science" from a computer with an
	      Ethernet MAC address of 11:22:33:44:55:66.

     mcxquery -user = -group = -computer guest
	      Displays the managed preferences that would be in effect if the current user logged in using the current workgroup into a computer
	      not specified by any computer record (i.e. a "guest" computer).

     mcxquery -user jane -group math
	      Displays the managed preferences that would be in effect if the user "jane" logged into the "math" workgroup on the current com-
	      puter.

     mcxquery -o /tmp/report.txt -format xml -user jane
	      Writes the managed preferences that would be in effect if user "jane" logged into the current computer without a workgroup.  The
	      report is written in XML format to /tmp/report.txt.

     mcxquery -computerOnly -computer lab1_12
	      Displays the managed preferences for the computer specified in the "lab1_12" computer record only. Useful for determining managed
	      settings when computer is at login window.

     mcxquery -computerOnly -computer 00112233-4455-6677-8899-AABBCCDDEEFF
	      Displays the managed preferences for the computer with the Hardware UUID "00112233-4455-6677-8899-AABBCCDDEEFF". Supported on Mac OS
	      X 10.6 and later.

     mcxquery -forApple -o results.plist
	      Creates a plist, suitable for submitting along with bug reports to Apple, containing the managed preferences for the current user on
	      the current computer. Also includes relevant records from Directory Services. Supported on Mac OS X 10.7 and later.

SEE ALSO

     dscl(1)

MacOSX								 November 30, 2010							    MacOSX