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-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>.

COPYRIGHT

       Copyright © 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.

memtester 4                                      September 2020                                     memtester(8)