Working with Older Kernel Versions on CentOS 7: Challenges and Solutions

Introduction

When developing or testing kernel-related code on CentOS 7 systems, working with older kernel versions presents unique challenges. This document outlines solutions specifically validated on CentOS 7.9 (Final).

Challenges with Older Kernels on CentOS 7

1. Header Availability Issues

   • Missing headers in default installations

   • Version mismatches between installed headers and running kernel

   • Deprecated interfaces in newer kernel-devel packages

2. Toolchain Compatibility

   • CentOS 7’s default GCC 4.8.5 may be too old/new for certain kernels

   • SELinux context requirements for system headers

   • Potential need for Developer Toolset (devtoolset) packages

3. Dependency Management

   • Requires kernel-devel package matching running kernel version

   • Potential conflicts with elfutils-libelf-devel versions

   • EPEL repository often needed for additional dependencies

Case Study: LTP Build System Header Missing Issue

The Problem

On CentOS 7.9, the LTP build system failed because:

• Required kernel headers were missing (syscall.h not found)

• Installed kernel-devel package didn’t match running kernel version

• Build system expected legacy header locations

CentOS 7 Solution Approach

1. Verify and Install Correct Headers

   # Check running kernel version
   uname -r
   # Install matching headers
   sudo yum install kernel-devel-$(uname -r)
   # Install base development tools
   sudo yum groupinstall "Development Tools"
   sudo yum install elfutils-libelf-devel
   

2. Header Linking Workaround

   # Create necessary symbolic links
   cd /usr/include/asm && sudo ln -sf ../asm-generic/unistd.h unistd.h
   # Verify SELinux context
   sudo restorecon -v /usr/include/asm/unistd.h
   

3. Validation

   # Verify headers are accessible
   ls -l /usr/include/asm/unistd.h
   # Check build environment
   make --version
   gcc --version
   

Best Practices for CentOS 7

1. Environment Isolation

   • Use yum history to track changes

   • Consider Docker containers with CentOS 7 base image

2. Version Management

   • Maintain multiple kernel-devel RPMs in local repository

   • Use yum versionlock to prevent unwanted updates

3. Documentation

   • Record exact kernel and package versions

   • Document all symbolic links created

4. Cleanup Procedures

   # Remove symbolic links
   sudo rm -f /usr/include/asm/unistd.h
   # Verify system integrity
   sudo rpm --verify kernel-devel
   

CentOS 7 Specific Notes

• Tested on CentOS 7.9 with kernel versions 3.10.0-1160 through 3.10.0-1160.76.1

• Requires EPEL repository for some dependencies:

  sudo yum install epel-release
  

• For newer toolchains:

  sudo yum install centos-release-scl
  sudo yum install devtoolset-9
  

Conclusion

Working with older kernels on CentOS 7 requires careful version management and understanding of RHEL-based system conventions. The presented solution provides a stable foundation for LTP development while maintaining system integrity.

Version History

• 2023-11-15: Initial version validated on CentOS 7.9.2009

• 2023-11-16: Added devtoolset and EPEL notes