General Topics






Tips and How-To


DiskTester Command Line

This is not a tutorial on using a command line interface, but see this page for getting started.

Abbreviations and units

Abbreviations available for conveniently specifying quantities and positions are shown in the table below. Please note that DiskTester considers one Kilobyte to be 1024 bytes, not 1000 bytes.   A Megabyte is 1024 Kilobytes, etc.  All rates shown in DiskTester results are calculated using these units.

Abbreviation Units
b bytes
K, KB kilobyte (1024 bytes)
M, MB megabytes (1024 kilobytes = 1024 X 1024 bytes)
G, GB gigabytes (1024 megabytes = 1024 X 1024 X 1024 bytes)
T, TB terabytes (1024 terabytes = 1024 X 1024 X 1024 X 1024 bytes)
max maximum size (--test-size option only)
start, middle, end test areas of 0%, 50%, 100% (--test-area option only)

Stopping a command line test

To stop an in-progress test, use control-c (you must be in the Terminal window with the running disktester process).  Hold down the control key and press 'c'.   The control key is the key labeled “control” on the standard Apple US keyboard; it’s right next to the “option” key.

A control-c sends a “signal” to disktester that it needs to quit.  You should immediately see a message similar to this one:

Caught signal 2 (SIGINT)
Program should respond within a few seconds.
Test canceled by user request.

In most cases, disktester will quit within a second or two, though it might take longer with certain tests and/or very large chunk sizes.

If you do not see something like the above immediately (ie nothing at all), it means that disktester has “hung”, typically within a MacOS file-manager call.  DiskTester no longer has control and isn’t running in the sense that it is waiting for a request to finish and no longer has any control over what happens.   This can be caused by hardware problems of various kinds, such as a bad cable, driver bug, bad drive, etc.  It could also be caused by an operating system bug (rare) or driver bug or hardware bug.  In such cases, disktester typically is using 0% CPU time (you can check using Activity  Monitor).

If DiskTester has not responded to control-c, you can try control-z, which means “stop the process (disktester) from running”.  Always try control-c first!  After typing control-z, you should see something like the following:


Now you can attempt to kill the running 'disktester' process.  The “kill” command means what it says: the “-9” part means to do it with no warning to the program, and the “%1” part means “job number 1”:

llcMP:~ lloyd$ kill -9 %1
[1]+ Stopped /disktester run-async-test X8

What the above output is saying is that the program is stopped; sometimes it can’t actually be killed until it is told to run again (after issuing the “kill” command).  Use the “fg” command  If successful, you’ll see something like the following:

llcMP:~ lloyd$ fg
-bash: fg: job has terminated

If none of the above works, you can try waiting a minute or so to see if there is any change (unlikely); if not it’s “pull the power plug” time. But first, if possible, save any unsaved files and quit open programs.  (This may or may not be possible

Previous article: dgl
Next article: Troubleshooting