As a DevOps engineer, mastering Linux commands is crucial for efficient system troubleshooting and management.
System Monitoring & Performance
CPU Usage:
- top - Real-time process and resource usage.
- htop - Enhanced process viewer.
- sar - Historical resource usage.
Memory Usage:
- free -h - Memory usage overview.
- cat /proc/meminfo - Detailed memory statistics.
Disk Usage:
- df -h - Disk usage by filesystem.
- du -sh - Directory size.
Network Usage:
- netstat -tuln or ss -tuln - Active connections.
- iftop - Real-time bandwidth usage.
- ping - Connectivity check.
2. File and Directory Management
File Management:
- ls -lh - List files with details.
- cat, less, more - View file content.
- find /path -name "*.log" - Search files.
Permissions:
- chmod 755 - Change file permissions.
- chown user:group - Change ownership.
3. User and Group Management
Users:
- id - User details.
- adduser - Add a user.
- passwd - Change user password.
Groups:
- groups - User groups.
- usermod -aG - Add user to a group.
- Logged-In Users:
- who - List logged-in users.
- last - Login history.
- 4. Process Management
View Processes:
- ps aux - List processes.
- pgrep - Search for a process.
Manage Processes:
- kill -9 - Kill a process by ID.
- pkill - Kill a process by name.
Logs:
- journalctl - View system logs.
- dmesg - Kernel messages.
- tail -f /var/log/ - Monitor logs in real-time.
5. Networking
Connectivity:
- curl -I - Test HTTP connection.
- ping - Test network.
- traceroute - Trace network route. Debugging: telnet - Test open ports. dig - DNS lookup.
6. Disk and Filesystem Management
Filesystem:
- fsck /dev/sda1 - Check filesystem.
- mount and umount - Mount/unmount filesystems.
Disk Partitioning:
- fdisk -l - Partition details.
- lsblk - List block devices. - -
7. Package Management
Debian/Ubuntu:
- apt update - Update package list.
- apt install - Install a package.
RHEL/CentOS:
- yum update - Update packages.
- yum install - Install a package.
8. Backup and Archive
Backup:
- rsync -av /source/ /destination/ - Sync files/directories.
Archiving:
- tar -cvf archive.tar /path - Archive files.
- gzip archive.tar - Compress the archive.
10. General Troubleshooting Commands
- uptime - System uptime.
- uname -a - Kernel and OS details.
- tcpdump - Network packet capture.
End-to-End Troubleshooting Example:
1. Identify the Issue:
Use top, df -h, or ping to gather insights.
2. Narrow Down Root Cause:
Use ps aux, netstat, or iotop to trace the issue.
3. Apply Fixes:
Restart services or update packages.
4. Monitor Post-Fix:
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