Commands in Unix When Things Go Wrong
When working with Unix systems, encountering unexpected issues is common. Whether it’s system crashes, network failures, or corrupted files, Unix provides powerful commands to troubleshoot and resolve such problems. Here’s a comprehensive guide on essential Unix commands for handling issues efficiently.
1. Diagnosing System Performance Issues
top – Real-time Process Monitoring
- Displays CPU, memory usage, and running processes.
- Example usage:
top
Press q to exit.
htop – Interactive Process Viewer (better UI than top)
- Displays real-time CPU/memory usage with intuitive navigation.
- Install using:
sudo apt-get install htop # For Debian-based systems
vmstat – System Performance Overview
- Displays CPU, memory, and I/O performance details.
- Example usage:
vmstat 1 5 # Update every 1 second for 5 iterations
2. Analyzing Disk Space and Storage Issues
df – Disk Usage Information
- Shows available and used disk space.
- Example usage:
df -h
du – Directory Disk Usage
- Shows the size of files and directories.
- Example usage:
du -sh * # Summarizes space used by all files in the current directory
3. Finding and Terminating Problematic Processes
ps – Process Status
- Displays running processes and their details.
- Example usage:
ps aux | grep apache
kill – Terminate Processes
- Used to terminate problematic processes.
- Example usage:
kill -9 <PID> # Forcefully terminates the process with the given PID
pkill – Kill Processes by Name
- Example usage:
pkill -f "process_name"
xargs – Efficiently Handle Multiple Processes
- Example usage:
ps aux | grep python | awk '{print $2}' | xargs kill -9
4. Debugging Network Issues
ifconfig / ip a – Network Configuration
- Displays network interfaces and their status.
- Example usage:
ifconfig
ip a
ping – Test Network Connectivity
- Example usage:
ping 8.8.8.8
netstat – Display Network Statistics
- Example usage:
netstat -tuln
ss – Socket Statistics (Modern Alternative to netstat)
- Example usage:
ss -tuln
traceroute – Trace Network Route
- Example usage:
traceroute google.com
5. File System Recovery & Data Handling
fsck – File System Consistency Check
- Repairs and checks file system errors.
- Example usage:
sudo fsck /dev/sda1
mount / umount – Manage Mount Points
- Example usage:
mount /dev/sda1 /mnt
umount /mnt
lsof – List Open Files
- Example usage:
lsof | grep filename
6. Handling User and Permissions Issues
who – Show Logged-in Users
- Example usage:
who
last – Show Login History
- Example usage:
last
chmod / chown – Manage File Permissions
- Example usage:
chmod 755 filename
chown user:group filename
7. System Recovery Commands
reboot / shutdown – Restart or Shut Down System
- Example usage:
sudo reboot
sudo shutdown -h now
systemctl – Manage System Services
- Example usage:
systemctl restart apache2
systemctl status sshd
8. Log File Analysis for Troubleshooting
tail / less / cat – View Log Files
- Example usage:
tail -f /var/log/syslog
journalctl – Systemd Log Viewing
- Example usage:
journalctl -xe
9. Data Backup and Restoration
rsync – Sync Files and Directories
- Example usage:
rsync -av /source/ /destination/
tar – Archive Utility
- Example usage:
tar -czvf backup.tar.gz /folder_to_backup/
Conclusion
Mastering these Unix commands will help you quickly identify and resolve system issues, ensuring minimal downtime. Practice and familiarize yourself with these commands to enhance your troubleshooting skills.
