Scenario / Questions

I have some dedicated server hosted by a OVH (French service provider).
OS : Ubuntu 12.04 x64

A few months ago, one of my server crashed.
The only weird thing was some “ASCII NUL” caracters in the syslog :

^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@

With the help of my service provider, we checked :

  • The RAM
  • The CPU
  • The DISKS

Everything was ok, so my service provider recommended to change the motherboard of the server and update the kernel (which we did).
But since, this server crashed two more times, with the same caracters in the syslog.

Without any more explanation, we decided to change this server (this is planned in a few weeks).

BUT, problem is, this night, this happened to another server.
Same crash, same caracters in the syslog, no explanation.

Does anybody have any clue of what we should check ?
Is it a hardware or a software problem ?

Find below all possible solutions or suggestions for the above questions..

Suggestion: 1

I’ll share more widely the great answer given by @n-st:

NUL bytes in the syslog are a common effect of a crash that prevented the system from cleanly syncing and unmounting the filesystem. They don’t give an indication of what actually triggered the crash.

Indeed, I have often seen that behavior after a server crash: those characters are NULL (\0) characters that may represent a recovered block that was filled with zeros by some recover process.

As for the cause of the crash, that’s a whole different question – you’d need to provide way more information for a diagnostic to even begin. I would recommend opening a different question about this if you still have the problem.

Suggestion: 2

If you are using a text-editor to view the log files, that could be the cause;

  • the “^@” characters may indicate that a line is too long (eg: in vim, turn on wrapping)
  • The encoding is mismatched; either use a different text-editor to view the file, or change the encoding used by syslog.