10 Common Errors in RHEL 8 and How to Fix Them

Posted December 28, 2024Dec 28

RHEL 8 (Red Hat Enterprise Linux) is a robust and secure operating system, but like any system, it can present challenges. Below, we explore ten common issues and provide actionable solutions with detailed explanations suitable for beginners.

1. Dependency Resolution Errors During Software Installation

Problem: When using dnf or yum, you might encounter errors like:

Error: Package dependency conflicts

Cause: Missing or conflicting dependencies in the repository.

Solution:

Clear the DNF or YUM cache and retry:
```
sudo dnf clean all
sudo dnf update
sudo dnf install <package>
```
This ensures that outdated or corrupted cache files are removed, allowing the package manager to start fresh.
Enable additional repositories if needed:
- If you don’t know the repository name, list available repositories:
```
sudo subscription-manager repos --list
```
- Common repositories in RHEL include:
  - rhel-8-for-x86_64-appstream-rpms for application streams.
  - rhel-8-for-x86_64-baseos-rpms for the base operating system.
- Enable the repository with the following command:
```
sudo subscription-manager repos --enable=<repo_name>
```
This step adds the necessary repository where the required packages are stored.
If the issue persists, check for alternative packages or versions:
```
sudo dnf provides <missing_dependency>
```

2. Failed to Start GNOME Display Manager

Problem: The graphical interface fails to load after boot.

Cause: Misconfigured display settings, missing packages, or driver issues related to your GPU or video hardware.

Solution:

Check Logs for Clues: Logs provide detailed error messages to help pinpoint the issue.
```
journalctl -xe | grep gdm
journalctl -b | grep 'graphics'
```
Look for errors related to the GNOME Display Manager (GDM) or graphics drivers.
Reinstall or Install Missing GNOME Packages: If the GNOME display manager is not installed or corrupted, reinstall it:
```
sudo dnf groupinstall "Server with GUI"
sudo systemctl set-default graphical.target
sudo systemctl restart gdm
```
This installs the GNOME environment and ensures it starts by default.
Verify and Update Graphics Drivers: If you're using dedicated GPU hardware (e.g., NVIDIA or AMD), ensure the drivers are correctly installed. For NVIDIA:
```
sudo dnf install nvidia-driver
sudo systemctl restart gdm
```
For open-source drivers:
```
sudo dnf install xorg-x11-drv-vesa xorg-x11-drv-evdev
```
This ensures compatibility with your video hardware.
Test Alternative Display Managers: If GDM fails to work, try an alternative display manager like LightDM:
```
sudo dnf install lightdm
sudo systemctl enable lightdm --force
sudo systemctl start lightdm
```
Fallback to Command Line for Recovery: If the graphical interface is entirely inaccessible, use TTY mode (Ctrl + Alt + F2) to log in and troubleshoot further:
```
sudo systemctl set-default multi-user.target
sudo systemctl restart gdm
```

3. SELinux Denying Legitimate Actions

Problem: SELinux blocks actions with errors like:

AVC denial: access denied

Cause: SELinux policies are too restrictive for the action being performed.

Solution:

Check SELinux Logs: Use ausearch to identify what SELinux blocked:
```
sudo ausearch -m avc -ts today
```
This command shows detailed logs of blocked actions.
Generate a Custom SELinux Policy: If SELinux is blocking a legitimate action, create a custom policy to allow it:
```
sudo ausearch -c '<command>' --raw | audit2allow -M mypolicy
sudo semodule -i mypolicy.pp
```
Replace <command> with the blocked command to generate and apply the policy module.
Temporarily Change SELinux Mode (Not Recommended for Production): For testing purposes, switch SELinux to permissive mode:
```
sudo setenforce 0
```
This disables enforcement but logs violations. Don’t forget to revert back:
```
sudo setenforce 1
```

4. Network Configuration Issues

Problem: Network interface fails to connect.

Cause: Incorrect or missing configuration in NetworkManager or physical hardware issues.

Solution:

Verify Connection Details: List active connections:
```
sudo nmcli connection show
```
If your desired connection isn’t active, bring it up manually:
```
sudo nmcli connection up <connection_name>
```
Restart Network Services: Sometimes restarting the network manager resolves transient issues:
```
sudo systemctl restart NetworkManager
```
Check IP Configuration: Verify if the interface has a valid IP address:
```
ip addr show
```
If not, troubleshoot the DHCP configuration or assign a static IP address.
Test Connectivity: Use ping to check the connection:
```
ping 8.8.8.8
```
If this works but domain names fail, investigate DNS settings.
Inspect Hardware: Check the physical connection and ensure the network card is recognized:
```
lspci | grep Ethernet
```

5. Kernel Panic on Boot

Problem: System halts with a kernel panic, often accompanied by cryptic error messages.

Cause: Corrupt kernel, incompatible kernel modules, or hardware issues.

Solution:

Boot into an Older Kernel: During boot, access the GRUB menu and select a previous kernel version.
Reinstall the Kernel: If the kernel is corrupted, reinstall it:
```
sudo dnf reinstall kernel
```
Update GRUB Configuration: Ensure GRUB is properly configured to boot the updated kernel:
```
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
```
Check Hardware: Run a memory and hardware test to ensure physical components aren’t failing.

6. Time Synchronization Issues

Problem: System time is incorrect or out of sync.

Cause: Misconfigured chronyd service or missing NTP servers.

Solution:

Verify chronyd Status: Check if the service is running:
```
sudo systemctl status chronyd
```
Sync Time Manually: Force a synchronization:
```
sudo chronyc makestep
```

Edit Configuration: Update /etc/chrony.conf with the correct NTP servers:

server 0.centos.pool.ntp.org iburst
server 1.centos.pool.ntp.org iburst

Restart the Service: Apply changes by restarting the service:
```
sudo systemctl restart chronyd
```

7. Filesystem Corruption

Problem: System reports errors when accessing files or directories.

Cause: Power failure or improper shutdown.

Solution:

Run fsck: Boot into single-user mode and repair the filesystem:
```
sudo fsck -y /dev/<partition>
```
Backup Critical Data: Always back up important files before attempting repairs.
Use Journaled Filesystems: Ensure your partitions are using ext4 or another journaled filesystem to reduce future risks.

8. YUM/DNF Lock Error

Problem: You see errors like:

Another app is currently holding the yum lock

Cause: Another process is using dnf or yum.

Solution:

Kill the Offending Process: Identify and terminate the process:
```
sudo ps aux | grep dnf
sudo kill -9 <PID>
```
Remove Lock Files: Clear any lingering lock files:
```
sudo rm -f /var/run/dnf.pid
```
Retry the Operation: Restart your package manager command.

9. Service Fails to Start

Problem: A service doesn’t start, with errors like:

Job for <service>.service failed

Cause: Misconfiguration, missing dependencies, or permission issues.

Solution:

Check Service Status: Review the service details:
```
sudo systemctl status <service>
```
Inspect Logs: Look for error messages:
```
journalctl -xe
```
Reconfigure the Service: Edit the service configuration files or reinstall the associated package:
```
sudo dnf reinstall <package>
```
Verify Dependencies: Ensure all required dependencies are installed.

10. Authentication Issues with SSH

Problem: Cannot log in via SSH.

Cause: Incorrect configuration in sshd_config or permission issues.

Solution:

Verify Configuration: Check the SSH configuration file:
```
sudo nano /etc/ssh/sshd_config
```
Ensure settings like PermitRootLogin and PasswordAuthentication are configured correctly.
Restart SSH Service: Apply changes by restarting SSH:
```
sudo systemctl restart sshd
```
Correct File Permissions: Ensure proper permissions for the .ssh directory and files:
```
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
```
Test Connectivity: Use verbose mode to troubleshoot:
```
ssh -vvv user@hostname
```

By addressing these common RHEL 8 issues, you can maintain a stable and secure environment. Bookmark this guide for quick reference or share it on your forum to help others.

CodeName: Jessica

💻 Linux Enthusiast | 🌍 Adventurer | 🦄 Unicorn
🌐 My Site | 📢 Join the Forum

Sign In

10 Common Errors in RHEL 8 and How to Fix Them

Featured Replies

1. Dependency Resolution Errors During Software Installation

2. Failed to Start GNOME Display Manager

3. SELinux Denying Legitimate Actions

4. Network Configuration Issues

5. Kernel Panic on Boot

6. Time Synchronization Issues

7. Filesystem Corruption

8. YUM/DNF Lock Error

9. Service Fails to Start

10. Authentication Issues with SSH

Please sign in to comment

Important Information

Account

Navigation

Messages

Notifications

Search