memtester <root

memtester(8)                                            Maintenance Commands                                           memtester(8)

NAME
       memtester - stress test to find memory subsystem faults.

SYNOPSIS
       memtester [-p PHYSADDR [-d DEVICE]]  [ITERATIONS]

DESCRIPTION
       memtester  is an effective userspace tester for stress-testing the memory subsystem.  It is very effective at finding inter‐
       mittent 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 lim‐
       ited 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 mem‐
       ory 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 run‐
       ning, this can lead to excessive swapping and slowing the system down to the point that it is difficult to use.  If the sys‐
       tem  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 dur‐
              ing 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 skip‐
       ping 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 .

COPYRIGHT
       Copyright © 2001-2012 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                                                  June 2012                                                 memtester(8)

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