System Monitoring & Performance | Linux

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:

---