memtest(1)

NAME

memtester - userspace utility to test for faulty memory

subsystem

SYNOPSIS

memtest <mem<B|K|M|G>> [runs] [-l | --log]

DESCRIPTION

memtest is a userspace program to test for a faulty memory

subsystem or faulty memory modules in Linux, or any Unix-like en

vironment.

Invoking memtest

memtest takes the first supplied argument as the amount of

memory to test. The value 'all' means to test all available mem

ory. A specific amount of memory can be supplied as a number,

followed by a letter to indicate units:

· B or b - bytes

· K or k - kilobytes

· M or m - megabytes

· G or g - gigabytes

memtest used to assume megabytes if no letter was sup

plied. It now exits instead.

If memtest cannot allocate the amount of memory specified,

it will keep trying with smaller amounts until it succeeds.

If the option -l (or --log) is given, memtest will log to

the file memtest.log in addition to stderr. Any previous log

will be overwritten. If memtest fails to open its logfile it

will abort.

memtest will attempt to lock its pages into memory to in

crease the chances of testing a greater percentage of physical

memory. This typically requires the program to be run as root.

If it cannot lock its pages into memory due to a lack of permis

sions, it will issue a warning and continue with unlocked pages.

If it fails to lock pages because there are insufficient pages of

memory available to be locked, it will reduce its allocation and

try again.

Note that if memtest runs with unlocked pages, it may

start swapping. Since memtest spends virtually all of its time

accessing memory, this will slow down its operation by several

orders of magnitude. The best way to run memtest is to use the

largest value of memory to test which will allow it to lock its

pages into memory.

Building memtest

Simple -- just download, extract the tarball, and run

make. I've only tested it with the GNU toolchain, but it may

build with others as well.

RETURN VALUE

0 if it runs to completion, or receives one of SIGINT,

SIGTERM

-1 if it encounters an error and cannot run.

ERRORS

memtest will exit if it cannot allocate any memory, or if

it attempts to log to a file and cannot open its logfile.

EXAMPLES

· memtest 16m 2

Test 16MB of memory, run all tests twice, and log only

to stderr.

· memtest 2G --log

Test 2GB of memory, run until interrupted, and log to

stderr and memtest.log.

· memtest 1g 4 --log

Test 1GB of memory, run all tests four times, and log

to stderr and memtest.log.

FILES

memtest.log -- log file in current directory.

NOTES

If the machine you are testing on is an x86 clone, and you

can afford to take the machine down for an extended period, the

program memtest86 may be another option to consider. It is

available at http://reality.sgi.com/cbrady_denver/memtest86/.

CAVEATS

memtest by design is hard on the memory subsystem of a ma

chine. This can make the machine quite sluggish; it would be a

very poor idea to attempt to run memtest on a heavily loaded or

shared machine except for testing purposes, with small alloca

tions of memory.

Testing memory can be slow. Sample testing times for one

complete run of tests follow. If you have other examples, please

send them to me.

· Pentium 90MHz testing 24MB: ~30 minutes

· Sun UltraSparc 360MHz testing 1750MB: ~13 hours

DIAGNOSTICS

The program prints a small amount of information about how

it was invoked before running tests:

Successfully allocated 4194304 bytes. Aligning

memory...settling on 4190208 bytes at 0x400b7000... Proceeding

to lock pages...success. Starting tests...

memtest typically tests a slightly smaller amount of memo

ry than is specified on the commandline. This is because it

aligns its memory allocation to a page boundary before attempting

to lock its pages into memory. This is a requirement on some

Unix systems. With very small allocations of memory (typically

only used during debugging of memtest), it may fail to align to a

page boundary with a message similar to this:

Aligning memory...allocation too small to align to

pagesize of 4096 bytes. Failed to get sufficient memory.

Exiting...

If not run as root, the memlock will fail as follows:

Proceeding to lock pages...mlock failed: only root can

lock pages. Continuing with unlocked pages. Results are less

reliable.

Then, as the program runs through tests, it prints the

current `run' (cycle of tests) and test number and name. It also

prints status information on the progress of the tests. This

will look like the following:

Run 1:

Test 1: Random value:

Setting...Testing...Passed.

Test 2: XOR comparison:

Setting...Testing...Passed.

If one of the tests finds an error in memory, a message

like the following will be printed:

FAILURE: 0x5aa0f5c5 != 0x5aa0f585 at offset 0x0067f837.

Skipping to next test...

If the Stuck Address test finds a failure, it outputs a

slightly different message, to remind the user that other tests

are unreliable if an addressing problem exists:

FAILURE: possible bad address line at offset 0x004563f3.

At the end of each `run' it will print a summary of that

run as follows:

Run 1 completed in 114 seconds (2 tests showed errors).

When the program completes (is interrupted by a signal, or

finishes its last run, when a limit is specified on the command

line), it will print an overall summary:

2 runs completed. 2 errors detected. Total runtime: 235

seconds. Exiting...

BUGS

May or may not require GNU make, gcc or equivalent, etc.

Please let me know if memtest fails to build in your environment.

Known Bugs

The output examples in this manpage have fallen out of

sync with the software in minor ways.

How To Report Bugs

Bugs should be reported to <memtest@discworld.dyndns.org>.

If your problem is that memtest won't compile, please in

clude some information about your system (basic hardware type,

operating system type and version) and a log of the output of

'make clean; make all'.

If memtest builds and runs, but you feel it does not run

properly, please include the output log from memtest generated by

the --log option.

RESTRICTIONS

memtest, running in user space, cannot test all of physi

cal memory. The unswappable pages occupied by the kernel will

not be tested. memtest will also be limited to whatever per-pro

cess/per-user limitations you have imposed in your system.

AUTHORS

This software was written by Charles Cazabon <memtest@dis

cworld.dyndns.org>, based on the version 1 sourcecode by Simon

Kirby <sim@stormix.com>.

HISTORY

See the file CHANGELOG for details.

3rd Berkeley Distribution memtest version 2.93.1

MEMTEST(1)