memtester(8)						       Maintenance Commands						      memtester(8)

NAME

       memtester - stress test to find memory subsystem faults.

SYNOPSIS

       memtester [-p PHYSADDR] <MEMORY> [ITERATIONS]

DESCRIPTION

       memtester  is an effective userspace tester for stress-testing the memory subsystem.  It is very effective at finding intermittent and non-
       deterministic faults.  Note that problems in other hardware areas (overheating CPU, out-of-specification  power	supply,  etc.)	can  cause
       intermittent  memory  faults,  so  it  is  still up to you to determine where the fault lies through normal hardware diagnostic procedures;
       memtester just helps you determine whether a problem exists.

       memtester will malloc(3) the amount of memory specified, if possible.  If this fails, it will decrease the amount of memory requested until
       it  succeeds.   It  will  then  attempt	to  mlock(3) this memory; if it cannot do so, testing will be slower and much less effective.  Run
       memtester as root so that it can mlock the memory it tests.

       Note that the maximum amount of memory that memtester can test will be less than the total amount of memory installed in  the  system;  the
       operating  system, libraries, and other system limits take some of the available memory.  memtester is also limited to the amount of memory
       available to a single process; for example, on 32-bit machines with more than 4GB of memory, memtester is still limited to less than 4GB.

       Note that it is up to you to know how much memory you can safely allocate for testing.  If you attempt to  allocate  more  memory  than	is
       available,  memtester  should figure that out, reduce the amount slightly, and try again.  However, this can lead to memtester successfully
       allocating and mlocking essentially all free memory on the system -- if other programs are running, this can lead to excessive swapping and
       slowing	the  system down to the point that it is difficult to use.  If the system allows allocation of more memory than is actually avail-
       able (overcommit), it may lead to a deadlock, where the system halts.  If the system has an  out-of-memory  process  killer  (like  Linux),
       memtester or another process may be killed by the OOM killer.

       So choose wisely.

OPTIONS

       -p PHYSADDR
	      tells  memtester	to  test a specific region of memory starting at physical address PHYSADDR (given in hex), by mmap(2)ing /dev/mem.
	      This is mostly of use to hardware developers, for testing memory-mapped I/O devices and similar.	Note that the memory  region  will
	      be  overwritten  during  testing,  so  it is not safe to specify memory which is allocated for the system or for other applications;
	      doing so will cause them to crash.  If you absolutely must test a particular region of actual physical memory, arrange to have  that
	      memory allocated by your test software, and hold it in this allocated state, then run memtester on it with this option.

       MEMORY the  amount  of  memory to allocate and test, in megabytes by default.  You can include a suffix of B, K, M, or G to indicate bytes,
	      kilobytes, megabytes, or gigabytes respectively.

       ITERATIONS
	      (optional) number of loops to iterate through.  Default is infinite.

NOTE

       memtester must be run with root privileges to mlock(3) its pages.  Testing memory without locking the pages in place  is  mostly  pointless
       and slow.

EXIT CODE

       memtester's exit code is 0 when everything works properly.  Otherwise, it is the logical OR of the following values:

       x01    error allocating or locking memory, or invocation error

       x02    error during stuck address test

       x04    error during one of the other tests

AUTHOR

       Written by Charles Cazabon.

REPORTING BUGS

       Report bugs to <charlesc-memtester-bugs@pyropus.ca>.

COPYRIGHT

       Copyright (C) 2009 Charles Cazabon
       This  is  free  software; see the file COPYING for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
       PARTICULAR PURPOSE.

memtester 4							     July 2009							      memtester(8)