Re: md5sum freezes system

[Philip Rowlands]

On Sat, 15 Jul 2006, Daniel wrote:

> If I run md5sum on big files (>700MB) it freezes the system. There are 
> no logs, no panic, nothing. It only shows the last screen.

This will be difficult to diagnose if the problem occurs only on your 
system. Are you able to reproduce it on another computer?

When you say freeze, is the computer entirely unresponsive? Can you 
interrupt (Ctrl-C) md5sum to get back to the shell prompt?

700MB is a reasonably large amount of data, which might longer than 
you'd expect to process on an older system, say, with slow disk.

> I runned md5sum with strace and gdb because I want to know what 
> happens - but everything was fine and md5sum returns the hash.

Although I don't expect this is an md5sum bug, I'll need to convince you 
of that. Is 700MB the smallest file that breaks? Is it any 700MB file, 
or a specific one on your disk? The following commands may help narrow 
down the cause:

(I'm going to name the problematic 700MB file "badfile")
$ cat badfile > /dev/null
    (should return to the prompt with no output)

$ dd bs=1M count=700 if=/dev/zero | md5sum
700+0 records in
700+0 records out
734003200 bytes (734 MB) copied, 3.92202 seconds, 187 MB/s
7fe5ca2a051d6dbb9ef191fbee0af98c  -
    (tests md5sum handling 700MB of non-disk data)

$ dd bs=1M count=700 if/dev/zero > /tmp/bigfile
$ md5sum /tmp/bigfile badfile

> So, can anyone of you explain this behavior? What happens there? Why 
> is md5sum running fine if it is under control? Are there ways to get 
> some more informations?

The above tests should isolate whether it's md5sum or the specific file 
which triggers your problem.

> PS: it is _no_ hardware defect ;)

How can you be sure?


Cheers,
Phil