Overview

To troubleshoot a kernel crash, you will need to provide the core dumps to the support agent. This article explains the most common parameters to check if this file is not generating.

Solution

Kernel crashes are located in the /var/crash/ directory by default. If this directory is empty after a system crash, please check the settings using the steps below.

Check the Directory Configured to Save the Core Dump

The directory used to save the core dumps can be configured in /etc/kdump.conf. Please check if the default directory was changed. You will find the details in Chapter 7. Kernel Crash Dump Guide of the Kernel Administration Guide for RHEL 7. 

7.2.2.2. Configuring the kdump type

When a kernel crash is captured, the core dump can be either stored as a file in a local file system, written directly to a device, or sent over a network using the NFS (Network File System) or SSH (Secure Shell) protocol. Only one of these options can be set at the moment, and the default option is to store the vmcore file in the /var/crash/ directory of the local file system. To change this, as root, open the /etc/kdump.conf configuration file in a text editor and edit the options as described below.

To change the local directory in which the core dump is to be saved, remove the hash sign ("#") from the beginning of the #path /var/crash line, and replace the value with a desired directory path.

Check the User Max Core File Size

To see the limits associated with your login, use the command ulimit -a. If you are using a regular user account, you will likely see something like this:

$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 32767
max locked memory (kbytes, -l) 32
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 10240
cpu time (seconds, -t) unlimited
max user processes (-u) 50
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

If the core file size is set to zero, core dumps will not be allowed. If you need a core dump to debug problems, you would need to set your core file size to unlimited.

$ ulimit -c unlimited
$ ulimit -c
unlimited

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