How to Diagnose and Fix Common Linux Boot, Network, and Disk Failures

Linux System Boot Failures

Four common causes and their remediation steps.

1. /etc/fstab misconfiguration or loss

Diagnosis: Boot stops after the "starting system logger" message and the log shows errors related to /etc/fstab.

Solution: Boot into rescue mode, mount the root filesystem, and recreate /etc/fstab with correct device and mount‑point definitions.

2. Root filesystem corruption after abrupt shutdown

Sudden power loss can corrupt ext3/ext4 filesystems. Example error output:

checking root filesystem
/dev/sdb5 contains a file system with errors, check forced
Unattached inode 68338812
... FAILED

Solution: Unmount the affected partition and run fsck to repair it.

# umount /dev/sdb5
# fsck.ext3 -y /dev/sdb5

3. Missing or corrupted kernel files in /boot

If /boot/vmlinuz or /boot/initrd.img are absent, the bootloader cannot load the kernel, resulting in errors such as "error: file '/vmlinuz' not found".

Solution: Use a live rescue medium to mount the /boot partition, copy the missing kernel or initramfs files from backup or installation media, and update grub.cfg to reference the correct files.

4. Hardware failures

Faulty motherboard, power supply, or disk can also prevent booting. Replacing the defective component typically resolves the issue.

Linux Network Fault Diagnosis

A five‑step checklist to isolate network problems.

Check network hardware – verify NICs, cables, switches, and routers are functional.

Confirm NIC driver loading – use ifconfig or ip addr to ensure the interface appears.

Inspect IP configuration – ensure IP address, netmask, and gateway are correct and do not conflict with other hosts.

Test LAN connectivity – ping other hosts and the default gateway.

Verify routing table – check route -n or ip route. Example to replace an incorrect default route:

# route delete default
# route add default gw 10.10.1.254

MBR Sector Failure Recovery

Symptoms include "Operating system not found" or a black screen after power‑on.

Typical causes: malware, improper partitioning, or disk write errors.

Recovery procedure:

Add a new virtual disk (if using a VM), list partitions with fdisk -l, create a new partition using fdisk /dev/sdb, and format it.

Mount the new partition and copy needed data.

Backup the original MBR: dd if=/dev/sda of=mbr.backup bs=512 count=1.

Boot into rescue mode, restore the MBR with dd if=mbr.backup of=/dev/sda bs=512 count=1, then reboot.

GRUB Bootloader Fault

When the system stops at a grub> prompt, two main reasons are common:

Incorrect entries in /boot/grub2/grub.cfg.

Missing GRUB configuration files.

Fix for misconfiguration: Boot from a rescue medium, mount /boot, edit the menuentry lines so that the linux and initrd lines point to the correct vmlinuz and initrd.img, then reboot.

Fix for missing files: Re‑install GRUB to the disk MBR:

# grub2-install /dev/sda

Forgotten Linux Root Password

Method 1 – Rescue mode password reset

sh-4.2# chroot /mnt/sysimage
# passwd root
# exit
# reboot

Method 2 – Single‑user mode

At the GRUB menu edit the kernel line, append single, and boot. The system drops to a root shell where passwd can be used to set a new password. Return to multi‑user mode with init 3 if desired.

Read‑Only Filesystem Errors

Symptoms: commands such as cp, mv, tar fail with "Read‑only file system".

Common causes: filesystem corruption, disk hardware problems, or incorrect /etc/fstab entries.

Remediation steps:

Remount the filesystem as read‑write: mount -o rw,remount /system If the filesystem is damaged, unmount it and run fsck:

nohup fsck -y /dev/VolGroup00/LogVol00 > /dev/shm/fscklog &

Replace failing hardware or, if the disk is still usable, back up data via a live CD and reinstall the operating system.