Kernel Header Troubleshooting

In addition to the information on Host Requirements for Agent Installation, this page describes how the agent uses kernel headers and tips on troubleshooting, if needed.

About Kernel Headers and the Kernel Module

The Sysdig agent requires a kernel module in order to install successfully on a host. This can be obtained in three ways:

  1. Agent compiles the module using kernel headers.

    If the hosts in your environment already have kernel header files pre-installed, no special action is needed. Or you can install the kernel headers manually; see below.

  2. Agent auto-downloads precompiled modules from Sysdig's AWS storage location.

    If the headers are not already installed but the agent is able to auto-download, no special action is needed. If there is no internet connectivity, you can use method 3 (download from an internal URL).

  3. Agent downloads precompiled modules from an internal URL.

    Use the environment variable SYSDIG_PROBE_URL. See also Understanding the Agent Config Files. Contact Sysdig support for assistance.

To Install Kernel Headers

In some cases, the host(s) in your environment may use Unix versions that do not match the provided headers, and the agent may fail to install correctly. In those cases, you must install the kernal headers manually.

Debian-Style

For Debian-syle distributions, run the command:

apt-get -y install linux-headers-$(uname -r)

RHEL-Style

For RHEL-style distributions, run the command:

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

RancherOS

For RancherOS distributions, the kernel headers are available in the form of a system service and therefore are enabled using the ros service command:

sudo ros service enable kernel-headers-system-docker 
sudo ros service up -d kernel-headers-system-docker

NOTE: Some cloud hosting service providers supply pre-configured Linux instances with customized kernels. You may need to contact your provider's support desk for instructions on obtaining appropriate header files, or for installing the distribution's default kernel.

To Correct Kernel Header Errors in AWS AMI

During an agent installation in an Amazon machine image (AMI) you may encounter the following errors while the installer is trying to compile the Sysdig kernel module:

Errors

  • "Unable to find kernel development files for the current kernel version" or

  • "FATAL: Module sysdigcloud-probe not found"

This indicates your machine is running a kernel in an older AMI for which the kernel headers are no longer available in the configured repositories. The issue has to do with Amazon purging packages in the yum repository when new Amazon Linux machine images are released.

The solution is either to update your kernel to a version for which header files are readily available (recommended), or perform a one-time installation of the kernel headers for your older AMI.

Option 1: Upgrade Your Host's Kernel

First install a new kernel and reboot your instance:

sudo yum -y install kernel
sudo reboot

After rebooting, check to see if the host is reporting metrics to your Sysdig account. If not, you may need to issue three more commands to install the required header files:

sudo yum -y install kernel-devel-$(uname -r)
sudo /usr/lib/dkms/dkms_autoinstaller start
sudo service dragent restart

Option 2: Install Older Kernel Headers

Although it is recommended to upgrade to the latest kernel for security and performance reasons, you can alternatively install the older headers for your AMI.

Find the the AMI version string and install the appropriate headers with the commands:

releasever=$(cat /etc/os-release | grep 'VERSION_ID' | grep -Eo "[0-9]{4}\.[0-9]{2}")
sudo yum -y --releasever=${releasever} install kernel-devel-$(uname -r)

Issue the remaining commands to allow the Sydig Agent to start successfully:

sudo /usr/lib/dkms/dkms_autoinstaller start
sudo service dragent restart

Reference: Find Your AWS Instance Image Version

The file /etc/image-id shows information about the original machine image with which your instance was set up:

[ec2-user ~]$ cat /etc/image-id
image_name="amzn-ami-hvm"
image_version="2017.03"
image_arch="x86_64"image_file="amzn-ami-hvm-2017.03.0.20170401-x86_64.ext4.gpt"image_stamp="26a3-ed31"
image_date="20170402053945"
recipe_name="amzn ami"
recipe_id="47cfa924-413c-d460-f4f2-2af7-feb6-9e37-7c9f1d2b"

This file will not change as you install updates from the yum repository.

The file /etc/system-release will tell what version of the AWS image is currently installed:

[ec2-user ~]$ cat /etc/system-release
Amazon Linux AMI release 2017.03