12 thoughts on - System Unresponsive

• From the above description, I would normally say it sounds like hardware. However, why do you say the system is not dead when you plug in a console.. but there is nothing on the screen and it doesn’t respond to control-alt-delete. To me that sounds like ‘dead’. Usually the cpu is hardlocked or the hardware went into ‘over-heat’ and put everything in a deep sleep hoping it would cool down but never wake up.

• In the past I’ve found that the console may have blanked (due to time) and when the system locked up/hung it won’t unblank. Booting with
  “consoleblank=0” on the kernel command line will ensure that whatever is printed to the console (oops, panic, etc) will be there for you to see when you connect.

  I’ve had intermittent success in that type of situation with the SysRq key(s), see https://en.wikipedia.org/wiki/Magic_SysRq_key . They do require that you have it configured/enabled ahead of time. If you access the console over a BMC/IPMI KVM session it can be very difficult, if not impossible, to enter the keystroke as well.

  Good luck, Scott

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• I saw such an issue recently and never found out what happened and why.

  Regards, Simon

• Stephen John Smoogen wrote:
  It seems unlikely. It’s a 4U server, with 36 disks (and the dual root disks), in a machine room, and ipmitool sel list shows nada, nor are there any warnings, as I’ve seen on other systems occasionally, that the CPU is overheating, and is being throttled.

• Scott Silverman wrote:
  forgotten, never used it. I’ll try that if this happens again.

  mark

• Out of memory? We’ve definitely seen similar symptoms (it’s been a while, so I’m not sure they were identical) for compute nodes running large memory jobs.

  Noam

• Noam Bernstein via CentOS wrote:

  That seems unlikely. Foe one, I’ve seen that… but I *always* see entries in the log about the oom-killer being invoked. For another, this isn’t a compute node, it’s *only* a fileserver, serving projects, home directories, and backups (home-grown b/u, uses rsync), and backups don’t start until well after midnight, and as we’re business-hours only, there was less usage, and it does have 256G RAM….

  mark

• I would definitely start here.  If the system locks and there’s no oops printed to the screen, then you almost certainly have a hardware issue. 
  If there *is* an oops printed, you might still have a hardware issue, but the oops will probably give you some direction on tracking it down.

  At some point, you’ll probably want to schedule as many hours of down time as possible and run memtest86+

  If the console isn’t coming back on keyboard activity, then the system is probably hard-locked, and sysrq keys aren’t going to work.  Probably.

• If this is a recent sever (ivybridge/haswell/broadwell) then I’ve seen the
  “edac” kernel module prevent SEL from showing faults when a MCE/machine-check-exception occurs. Disable edac and poof server stops crashing and/or SEL shows something useful(ECC/MCE). Did you check
  /var/log/mcelog?

• I have two servers that would lock up like this occasionally, and if I let them sit at the console long enough sometimes they would give a login prompt. It took a lot of time and frustration (these are prod servers) but I tracked it down to a problem in the XFS driver, as it never occurred on the systems with EXT4 filesystems. The XFS driver would hang, preventing writes to the filesystem. I could identify exactly when that happened as all system logging would suddenly stop at the same second. Then OOMKiller would come in and start killing off processes but that wouldn’t be in the logs on disk because the file system couldn’t write. I rolled the servers back to a 5xx series kernel and the issue didn’t resurface. I recently let them boot the newer 9xx series kernels and I’m hoping the XFS issue is fixed.

• Jon Pruente wrote:

  I have no idea if that’s it… and the cluster nodes that would have it happen, a few years ago, were ext4.

  Crap – I just went to look on the system that died, and from sar, I see that it died between 18:10 and 18:20, and we found it unresponsive when I
  got in at 09:00. I’d think that was enuogh time to print something.

  mark

• You should be able to recognize or monitor this by configure the syslog to print everything on a specific TTY or use the remote logging functionality.

  Kind regards Thomas

  Am Do., 23. Mai 2019 um 18:31 Uhr schrieb Jon Pruente < jpruente@riskanalytics.com>: