Linux is a powerful and reliable operating system, but even seasoned users encounter unexpected problems. Whether it’s a deleted file, a forgotten root password, or a sluggish system, knowing how to troubleshoot efficiently is key to becoming a true Linux expert.

This guide presents real-world Linux problem-solving scenarios along with step-by-step solutions, which are common among system administrators, developers, and everyday Linux users.

Scenario 1: You Accidentally Deleted an Important File

You accidentally deleted an important file using the rm command, and now you need to recover it. Unlike Windows and macOS, Linux does not have a built-in “Recycle Bin” for files deleted from the terminal.

Your recovery options depend on the filesystem in use.

For EXT3/EXT4 Filesystems

Use extundelete, which is an open-source utility designed to recover deleted files from ext3 and ext4 filesystems in Linux.

sudo apt install extundelete  # Debian-based  
sudo yum install extundelete  # RHEL-based  

Before attempting recovery, unmount the partition to prevent further writes that could overwrite deleted data:

sudo umount /dev/sdX

Next, run the following command to recover the deleted file and make sure to replace /dev/sdX with the actual partition where the file was deleted.

sudo extundelete /dev/sdX --restore-all

For XFS, Btrfs, or NTFS Filesystems

If your system uses XFS, Btrfs, or NTFS, the testdisk tool is a better option.

sudo apt install testdisk  # Debian-based  
sudo yum install testdisk  # RHEL-based  

Run testdisk and follow the interactive prompts to restore lost files.

sudo testdisk

Prevention Tips:

• • Use trash-cli: Instead of rm, use trash-cli to send files to a recoverable trash bin.

sudo apt install trash-cli  
trash-put myfile.txt  

• Enable regular backups: Set up rsync or Timeshift to automatically back up important files.

Scenario 2: Recovering a Forgotten Root Password

You forgot your root password and can’t perform administrative tasks, which means you can’t install software, change system settings, or access critical files.

You can reset the root password by booting into recovery mode or modifying the GRUB bootloader.

Using Recovery Mode (Ubuntu/Debian)

First, reboot your system and hold Shift during startup to access the GRUB menu, then select “Advanced options” → “Recovery mode” and choose “Drop to root shell prompt“.

Here, remount the root filesystem as writable and reset the root password.

mount -o remount,rw /
passwd root

Reboot the system.

reboot

Using rd.break (RHEL/CentOS/Fedora)

First, reboot your system, press e at the GRUB menu and find the line starting with linux and add rd.break at the end.

Next, mount the root filesystem and reset the root password.

mount -o remount,rw /sysroot  
chroot /sysroot  
passwd root  

Finally, exit and reboot.

exit  
reboot  

Prevention Tips:

• Create a passwordless sudo user to avoid being locked out of root access.
• Use SSH keys instead of passwords for authentication.

Scenario 3: You Installed a Package, but It’s Not Working

You installed a package, but it says “command not found” when you try to run it, which usually happens when the binary isn’t in your system’s PATH, the package isn’t installed correctly, or there’s a missing dependency.

The solution is, first you need to verify that the package is installed or not.

dpkg -l | grep package-name  # Debian-based  
rpm -qa | grep package-name  # RHEL-based  

If it’s missing, reinstall it:

sudo apt install package-name  
sudo yum install package-name  

Next, check if the command is in your system PATH.

which package-name  
echo $PATH

If the binary is in a non-standard location, add it to PATH:

export PATH=$PATH:/usr/local/bin  

Prevention Tips:

• Restart the terminal or run hash -r after installing new packages.
• Use package managers like Snap or Flatpak, which handle dependencies better.

Scenario 4: Your System is Running Out of Disk Space

Your system displays a “No space left on device” error, preventing software updates, logging, and normal operations.

Here’s how to reclaim disk space and keep your system running smoothly.

Step 1: Check Disk Usage

The solution is, first you need to check how much space is used on each partition on your system using the df command.

df -h

Step 2: Find and Delete Large Files

Next, locate the largest files consuming space by running du command, which will scan your system and list the top 10 largest files or directories. Delete unnecessary files using rm or move them to an external drive.

du -ah / | sort -rh | head -10

Step 3: Remove Unnecessary Logs

Logs are essential for troubleshooting and monitoring system activity, but they can grow rapidly and consume a significant amount of disk space.

Over time, old logs may no longer be needed, making them prime candidates for cleanup.

sudo journalctl --vacuum-time=2d  # Deletes logs older than 2 days  
sudo apt autoclean                # Removes outdated package files  

Step 4: Remove Old Kernels (Ubuntu/Debian)

When you update your system, especially on Ubuntu or Debian-based distributions, new versions of the Linux kernel are often installed.

However, the old kernels are not automatically removed and over time, these old kernels can accumulate and take up a significant amount of disk space.

Removing them is a safe and effective way to free up space without affecting your system’s functionality.

sudo apt autoremove --purge  

Prevention Tips:

• Set Up Log Rotation: Use logrotate to automatically manage log file sizes and retention periods.
• Monitor Disk Usage: Install tools like ncdu to track disk usage and identify space hogs.
• Regular Cleanups: Schedule periodic cleanups to remove temporary files, caches, and unused packages.

Scenario 5: Your Server is Suddenly Unresponsive

You are managing a Linux server, and suddenly, it stops responding and you try connecting via SSH, but the connection times out or refuses to establish. You might even notice that the server is still powered on, but it doesn’t react to any commands.

This situation can be caused by various issues, including:

• High CPU or memory usage due to runaway processes.
• Disk I/O bottlenecks, where the system is overloaded with read/write operations.
• Kernel panics or system crashes.
• Network failures, preventing remote access.

To restore control, follow these troubleshooting steps.

Step 1: Access the Server Locally or via TTY

If SSH isn’t working, try accessing the server directly or through a TTY session:

• On a physical machine, use the local console.
• On a virtual machine, use the hypervisor’s console.
• For Linux systems, switch to another TTY session using Ctrl + Alt + F2 (or F3, F4, etc.).

Step 2: Check System Load

Once logged in, check the system’s load and resource usage, which will show the system’s load averages over 1, 5, and 15 minutes. A load value higher than the number of CPU cores indicates high demand.

uptime  

Next, use top or htop to monitor processes in real time:

top  
Or
htop

Look for processes consuming excessive CPU or memory.

Step 3: Identify and Kill Runaway Processes

To identify the most resource-intensive processes, run:

ps aux --sort=-%cpu | head  

This lists the top CPU-consuming processes, where you can find a problematic process, and terminate it using:

kill -9 PID  

Replace PID with the process ID of the problematic application.

Step 4: Check System Logs

If the system is still responsive, check logs for errors:

sudo tail -f /var/log/syslog  
Or
sudo dmesg | tail  

These commands display recent system messages and kernel logs, which can help identify hardware or software issues.

Step 5: Reboot Safely Using SysRq

If the system is completely frozen, use the SysRq key combination to reboot safely:

echo b > /proc/sysrq-trigger  

This triggers a safe reboot, ensuring data integrity by syncing disks and unmounting filesystems.

Conclusion

Troubleshooting is an essential skill for every Linux user. Whether it’s recovering deleted files, resetting passwords, or fixing system errors, knowing the right commands can save time and frustration.

Do you have your own troubleshooting tips? Share them in the comments! Let’s build a helpful Linux community together.

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