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It's happened again! I have 4 servers which are crashing periodically, and there is no information printed to the system logs or the serial console.

In addition, the Linux kdump service isn't writing core dumps to the default location of /var/crash.

  • Can you help me figure out why?
  • Does it matter if my root filesystem is a LVM volume?

Here is what I've tried.

  1. My system is Scientific Linux 6.5 with the latest kernel.

    [root@host1 ~]# uname -r 2.6.32-431.11.2.el6.x86_64 [root@host1 ~]# cat /etc/issue Scientific Linux release 6.5 (Carbon)

  2. The file /etc/kdump.conf is the vanilla file containing the default settings. Most lines are commented out, there are only two active lines for path and core_collector.

    #net my.server.com:/export/tmp #net [email protected] path /var/crash core_collector makedumpfile -c --message-level 1 -d 31 #core_collector scp

  3. I ensure that the kdump service is running, and that kdump doesn't need to rebuild my initrd.

    [root@host1 ~]# chkconfig --list kdump kdump 0:off 1:off 2:off 3:on 4:on 5:on 6:off [root@host1 ~]# /etc/init.d/kdump restart Stopping kdump: [ OK ] Starting kdump: [ OK ] [root@host1 ~]#

  4. Then, I force a Kernel crash using these commands borrowed from the RHEL6 Deployment Guide: Chapter 29. The kdump Crash Recovery Service:

    Then type the following commands at a shell prompt:

    echo 1 > /proc/sys/kernel/sysrq echo c > /proc/sysrq-trigger

    This will force the Linux kernel to crash

  5. The system crashes. I can view the progress on my serial console. I see the message Saving to the local filesystem UUID=e7abcdeb-1987-4c69-a867-fabdceffghi2, but immediately after that I see the strange message of Usage: fsck.ext4, which sort of looks like something is accidentally calling fsck instead of whatever it should be doing. I see no mention of an out-of-memory error or anything.

    host1.example.org login: SysRq : Trigger a crash BUG: unable to handle kernel NULL pointer dereference at (null) ... ... skipping 50 lines of output ... Creating block device ram8 Creating block device ram9 Creating Remain Block Devices Making device-mapper control node Scanning logical volumes Reading all physical volumes. This may take a while... No volume groups found No volume groups found Activating logical volumes No volume groups found No volume groups found Free memory/Total memory (free %): 58272 / 116616 ( 49.9691 ) Saving to the local filesystem UUID=e7abcdeb-1987-4c69-a867-fabdceffghi2 Usage: fsck.ext4 [-panyrcdfvtDFV] [-b superblock] [-B blocksize] [-I inode_buffer_blocks] [-P process_inode_size] [-l|-L bad_blocks_file] [-C fd] [-j external_journal] [-E extended-options] device Emergency help: -p Autom

  6. And then the system reboots (which is the default).

  7. When the system comes back online, there is nothing in /var/crash. I assume that the crash dump was not written.

    [root@host1 ~]# ls -lA /var/crash/ total 0 [root@host1 ~]#

  8. I know that crash dumps can work in general. If I tell kdump to copy the core dump to another system with the following configuration, kdump will successfully write the core dump to another host:

    path vmcore ssh [email protected] sshkey /root/.ssh/kdump_id_rsa

  9. If I set default shell in /etc/kdump.conf and rebuild initrd, and then crash the system again I get a slightly more informative error about mount: can't find /mnt in /etc/fstab

    Free memory/Total memory (free %): 58272 / 116616 ( 49.9691 ) Saving to the local filesystem UUID=e720481b-1987-4c69-a867-f2b4cba3b312 Usage: fsck.ext4 [-panyrcdfvtDFV] [-b superblock] [-B blocksize] [-I inode_buffer_blocks] [-P process_inode_size] [-l|-L bad_blocks_file] [-C fd] [-j external_journal] [-E extended-options] device Emergency help: -p Automatic repair (no questions) -n Make no changes to the filesystem -y Assume "yes" to all questions -c Check for bad blocks and add them to the badblock list -f Force checking even if filesystem is marked clean -v Be verbose -b superblock Use alternative superblock -B blocksize Force blocksize when looking for superblock -j external_journal Set location of the external journal -l bad_blocks_file Add to badblocks list -L bad_blocks_file Set badblocks list mount: can't find /mnt in /etc/fstab dropping to initramfs shell exiting this shell will reboot your system /sys/block #

  10. But now, I'm stuck.

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10
  • What is the make/model of the server? Commented Jun 6, 2014 at 21:57
  • This is a Supermicro with a X9DRW4 motherboard, and the latest bios. Commented Jun 6, 2014 at 22:03
  • Bummer. I'm having a similar crash on HP ProLiants with the newest RHEL6 kernel. I'm wondering if it's a deeper issue. Commented Jun 6, 2014 at 22:14
  • 1
    Hi. Did you resolve this issue? I'm facing very similar problem. Commented May 31, 2015 at 2:13
  • 1
    This is may be due to the if you try to generate the core on the LVM partition. Did you check the generate the core on the normal file system? Also another could be the array controller card, which might not be able to initialize when system boot on minikernel. Commented Sep 17, 2016 at 10:41

2 Answers 2

Reset to default
5

A little late to the game but if you need to configure kdump for the future:

I think the path directive designates a path from the partition or file system designated. By default this is the root FS. If you have a separate partition in /etc/fstab for /var it will obfuscate the crash directory when your system is booted normally. ie if you were to boot normally and unmount /var you would see the crash/[UniqCoreDir]. You can adjust this by adding an ext4 /PATH/TO/DEVICE directive in kdump.conf. Also you could use a different path that won't be mounted over.

Just a guess but might have a number of vmcores burried under /var.

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2

Pull apart your kdump initrd in /boot/ check to to see the final path that its trying to dump to.

  • I think the "path" option is a little weird, I'd probably leave it to the default or set it explicitly to /var/crash

  • Do you have some kind of watchdog rebooting the machine ? this may also prevent the core being created by rebooting the machine before the is started.

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3
  • I'll check out the initrd and see what I find. The path option in #2 is the default path (/var/crash). Commented Jun 20, 2014 at 5:35
  • No I do not have a watchdog rebooting the machine. Turns out that the LSI controller + Samsung SSDs are periodically freezing for reasons that we don't totally understand. Commented Jan 22, 2015 at 0:16
  • Did you get any feedback, because that is pretty crazy, maybe a power draw problem dropping the voltage too low ? Commented Apr 20, 2015 at 12:49

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