How to Diagnose and Fix Common Linux Boot, Network, and File‑System Failures

Linux System Boot Failure

Common boot problems stem from four main causes:

Incorrect or missing /etc/fstab – mis‑configured file‑system entries prevent the system from mounting partitions. Recover the file by booting into rescue mode and rebuilding it.

Root‑filesystem corruption after illegal shutdown – sudden power loss can leave the ext3/ext4 file system inconsistent. The system drops to a maintenance shell showing messages such as checking root filesystem and UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY. Run fsck -y /dev/sdX after unmounting the affected partition.

Missing kernel or initramfs files – the boot loader cannot find vmlinuz or initrd.img in the /boot partition. Restore the files from installation media or a backup and update grub.cfg.

Hardware failure – defective motherboard, power supply, or disk can also stop booting; replace the faulty component.

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

Always unmount the partition before running fsck.

Linux Network Failure

Network issues are tackled in four steps:

Verify physical hardware (NIC, cables, switch, router) and replace if defective.

Check that the NIC driver is loaded using ifconfig or ip a. Use ethtool to inspect link speed and status.

Confirm correct IP configuration and ensure no address conflicts.

Inspect the routing table; a wrong default route (e.g., pointing to a LAN‑only subnet) can block external access. Adjust with route delete default and route add default gw 10.10.1.254.

# route delete default
# route add default gw 10.10.1.254

Check DNS resolution by reviewing /etc/host.conf and /etc/nsswitch.conf (e.g., hosts: files dns).

MBR Sector Failure

Symptoms include “Operating system not found” and boot interruption. Recovery steps:

Add a new virtual disk, partition it (e.g., fdisk -l, fdisk /dev/sdb), format, and mount it.

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

In rescue mode, restore the MBR using the backup file.

GRUB Boot Failure

Two typical causes:

Incorrect grub.cfg entries – the kernel or initramfs paths are wrong, leading to “error: you need to load the kernel first”. Fix by editing /boot/grub2/grub.cfg to point to the correct files.

Missing GRUB files – the boot loader cannot locate its modules. Reinstall GRUB with grub2-install /dev/sda and regenerate the config.

# grub2-install /dev/sda
# grub2-mkconfig -o /boot/grub2/grub.cfg

Forgot Linux Root Password

Two recovery methods:

Rescue mode reset – boot from rescue media, chroot into the system ( chroot /mnt/sysimage) and run passwd root to set a new password.

Single‑user mode – at the GRUB menu press e, append single to the kernel line, boot, then change the password with passwd.

# chroot /mnt/sysimage
# passwd root
# exit
# reboot

Read‑Only File System Error

When commands such as cp, mv, or chmod fail with “Read‑only file system”, possible causes are file‑system damage, disk errors, or a wrong /etc/fstab entry.

Remount the filesystem read‑write: mount -o rw,remount /system.

If the FS is corrupted, run fsck on the unmounted device.

Hardware failure may require disk replacement.

# mount -o rw,remount /system
# fsck -y /dev/VolGroup00/LogVol00