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Full Discussion: Shared memory in linux
Operating Systems Linux Red Hat Shared memory in linux Post 302404518 by jim mcnamara on Tuesday 16th of March 2010 05:50:55 PM
Old 03-16-2010
Shared memory is physical memory that is used by two or more different processes at the same time.

Ex: shared libraries. This is code that gets loaded into memory, and all processes running on the system see it an use it at the same time.
 

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memx(8) 						      System Manager's Manual							   memx(8)

Name
       memx - memory exerciser

Syntax
       /usr/field/memx [ -h ] [ -s ] [ -ofile ] [ -ti ] [ -mj ] [ -pk ]

Description
       The memory exerciser spawns processes to exercise memory by writing and reading three patterns: 1's and 0's, 0's and 1's, and a random pat-
       tern.

       You specify the number of processes to spawn and the size of memory to be tested by each process. The first  process  is  a  shared  memory
       exerciser, the remaining are standard memory exercisers. The exerciser will run until the process receives a or a kill -15 pid.

       A  logfile  is  made in for you to examine and then remove. If there are errors in the logfile, check the file, where the driver and kernel
       error messages are saved.

Options
       The options are:

       -h	 Print the help message for the command.

       -s	 Disable shared memory testing.

       -ofile	 Save diagnostic output in file.

       -ti	 Run time in minutes (i).  The default is to run until the process receives a or a kill -15 pid.

       -mj	 The memory size in bytes (j) to be tested by each spawned process.  Must be greater than 4095.  The default is (total-memory)/20.

       -pk	 The number of processes to spawn (k).	The default is 20.  The maximum is also 20.

Restrictions
       The exerciser is restricted by the size of swap space available.  The size of the swap space and the size of internal memory available will
       determine  how  many processes can run on the system.  For example, If there were 16Mbytes of swap space and 16Mbytes of memory, all of the
       swap space would be used if all 20 spawned memory exercisers were running.  In that event, no new processes would be able to run.  On  sys-
       tems  with  large amounts of memory and small swap space, you must restrict the number of memory exercisers and/or the size of memory being
       tested.

       If there is a need to run a system exerciser over an NFS link or on a diskless system there are some  restrictions.   For  exercisers  that
       need  to  write into a file system, such as the target file system must be writable by root.  Also the directory, in which any of the exer-
       cisers are executed, must be writable by root because temporary files are written into the current directory.   These  latter  restrictions
       are sometimes difficult to overcome because often NFS file systems are mounted in a way that prevents root from writing into them.  Some of
       the restrictions may be overcome by copying the exerciser to another directory and then executing it.

Examples
       The following example tests all of memory by running 20 spawned processes until a or kill -15 pid is received.
       % /usr/field/memx
       The following example runs 10 spawned processes, memory size 500,000 bytes, for 180 minutes in the background.
       % /usr/field/memx -t180 -m500000 -p10 &

See Also
       Guide to System Exercisers

																	   memx(8)
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