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 memtester(8)                    memtester 4                    memtester(8)
 Maintenance Commands                                   Maintenance Commands

                               September 2020



 NAME
      memtester - stress test to find memory subsystem faults.

 SYNOPSIS
      memtester [ -p PHYSADDR [ -d DEVICE]] <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 available (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 a device
           specified by the -d option (below, or /dev/mem by default).  This
           is mostly of use to hardware developers, for testing memory-



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 memtester(8)                    memtester 4                    memtester(8)
 Maintenance Commands                                   Maintenance Commands

                               September 2020



           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.

 ENVIRONMENT
      If the environment variable MEMTESTER_TEST_MASK is set, memtester
      treats the value as a bitmask of which tests (other than the stuck
      address test) to run.  The value can be specified in decimal, in octal
      (with a leading 0), or in hexadecimal (with a leading 0x).  The
      specific bit values corresponding to particular tests may change from
      release to release; consult the list of tests in the source for the
      appropriate index values for the version of memtester you are running.
      Note that skipping some tests will reduce the time it takes for
      memtester to run, but also reduce memtester's effectiveness.

 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>.



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 memtester(8)                    memtester 4                    memtester(8)
 Maintenance Commands                                   Maintenance Commands

                               September 2020



 COPYRIGHT
      Copyright c 2001-2020 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.















































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