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Troubleshooting kernel issues

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.*

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Path Info

Clock icon Advanced
Clock icon 1h 30m
Clock icon Apr 04, 2019

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Table of Contents

  1. Challenge

    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
  2. Challenge

    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'

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