memtester(8) memtester 4 memtester(8)
Maintenance Commands Maintenance Commands
June 2012
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-
- 1 - Formatted: October 25, 2025
memtester(8) memtester 4 memtester(8)
Maintenance Commands Maintenance Commands
June 2012
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>.
- 2 - Formatted: October 25, 2025
memtester(8) memtester 4 memtester(8)
Maintenance Commands Maintenance Commands
June 2012
COPYRIGHT
Copyright c 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.
- 3 - Formatted: October 25, 2025
