Understanding Troubleshooting Modes

The boot procedure can be interrupted in various ways:

• Kernel Arguments can be used to within the Grub2 Menu
• The Kernel Argument rd.break can be used to interrupt the boot process right after the kernel and drivers are loaded
• Systemd can be replaced with init=/bin/bash
• The system can be booted into the Emergency Target right before the basic operating system is loaded
• The system can be booted into the Rescue Target before the network services are loaded

Kernel arguments should be used to interrupt the boot process if there is an issue loading the current kernel version

If the kernel is loading, but it is necessary to load the system right after the kernel is loaded, use rd.break

If there is an issue with loading into a target, use either emergency.target or rescue.target

Changing the Root Password

• Reboot system
• Select Up Arrow or Down Arrow to interrupt automatic boot
• Hover over kernel entry and select e
• Locate line ending in rhgb and add the following to the end of the line:

rd.break enforcing=0

• Select Ctrl +X
• Remount the sysroot directory using mount as Read/Write:

mount -oremount,rw  /sysroot

• Mount the sysroot directory as the root directory using chroot:

chroot /sysroot

• Pass the passwd command to change the root password
• Create the /.autorelabel file for SELinux:

touch /.autorelabel

• Exit chroot and sysroot to reboot:

sh-4.2# exit
exit

• Once the system boots, open a terminal and run:

restorecon /etc/shadow

setneforce 1

Troubleshooting Filesystem Issues

Real filesystem corruption does occur, but most often automatically fixed

Problems occur when making typo’s in /etc/fstab

To repair these type of issues, remount the filesystem in a read/write state and edit /etc/fstab by booting into the Emergency Target

Fragmentation can be fixed by:

• xfs_fsr: The XFS Filesystem organizer that optimizes XFS filesystems
• e4defrag: Used to defragment Ext4 Filesystems

Troubleshooting Networking Issues

Common Network Issues

• Wrong subnet mask
• Wrong router
• DNS is not working

Use ip a to check the current DNS configuration on the system network devices

Use ip a d [IP_ADDRESS] dev [DEVICE_NAME] to remove any unwanted IP Addresses

Use ip a a dev [DEVICE_NAME] [IP_ADDRESS] to add an IP Address

Use ip route show to list the current network routes, and ip route add default via [IP_ADDRESS] to add a default route

To make changes persistently, use nmtui

Use dhclient to renew the IP Address from the DHCP server

Troubleshooting Performance Issues

Focus on the four key area’s of performance:

• Memory
• CPU Load
• Disk Load
• Network

Utilize top to obtain an overview of the system’s overall health, and either renice or kill processes