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.