Troubleshooting kernel issues

1.5 hours
  • 2 Learning Objectives

About this Hands-on Lab

In this lesson, you will enable kernel dumps and give `cloud_user` the ability to run a `SystemTap` module.

*This course is not approved or sponsored by Red Hat.*

Learning Objectives

Successfully complete this lab by achieving the following learning objectives:

Enable kernel dumps.

Note: The hypervisor used by EC2 prevents kdump from being engaged. Forcing a kernel crash will simply prevent you from logging back in for 3-4 miniutes. No crash will be present in /var/crash.

Start and enable the kdump service:

systemctl start kdump && systemctl enable kdump

You’ll notice kdump doesn’t start. Install necessary packages:

yum --enablerepo=rhel-7-server-rhui-debug-rpms install -y kexec-tools crash kernel-debug kernel-debuginfo-$(uname -r)

Modify /etc/default/grub to set crash memory to 128M.

Install the new Grub config:

grub2-mkconfig -o /boot/grub2/grub.cfg
Permit cloud_user to run the example.stp via SystemTap.

Install SystemTap:

yum install -y systemtap kernel-devel-$(uname -r)

Run the example script: /root/example.stp

stap /root/example.stp

Compile the script as a module:

stap -p 4 -v -m stap_example example.stp

Create a systemtap directory for the module:

mkdir /lib/modules/$(uname -r)/systemtap

Move the module into the new directory:

mv stap_example.ko /lib/modules/`uname -r`/systemtap/

Run the module:

staprun stap_example

Add cloud_user to the stapusr group:

usermod -aG stapusr cloud_user

Verify cloud_user can run the module:

runuser -l cloud_user -c 'staprun stap_example'

Additional Resources

Configure the system to perform a kernel dump upon a crash, using no more than 128 MB for the crash kernel.

Permit cloud_user to run /root/example.stp as a module stap_example.

What are Hands-on Labs

Hands-on Labs are real environments created by industry experts to help you learn. These environments help you gain knowledge and experience, practice without compromising your system, test without risk, destroy without fear, and let you learn from your mistakes. Hands-on Labs: practice your skills before delivering in the real world.

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