Linux OS " Commands For Trouble Shooting "

 

When troubleshooting on a Linux OS, several commands can help diagnose and resolve issues. Here's a list of essential commands categorized by common troubleshooting areas:

1. System Monitoring

• top: Displays running processes and system resource usage (CPU, memory).
• htop: An enhanced version of top with a more user-friendly interface.
• vmstat: Provides system performance information, such as processes, memory, paging, block I/O, traps, and CPU activity.
• uptime: Shows how long the system has been running, the number of users, and load averages.
• dmesg: Displays system messages and logs from the kernel ring buffer.
• iostat: Provides CPU and I/O statistics for devices and partitions.
• free: Displays memory usage, including total, used, and available memory.
• sar: Collects and reports system activity information.

2. Disk Usage and File System

• df -h: Shows disk space usage in a human-readable format.
• du -sh *: Displays the disk usage of files and directories.
• lsblk: Lists information about all available or the specified block devices.
• fdisk -l: Lists the partition tables for the specified devices.
• mount: Displays all currently mounted filesystems.
• umount: Unmounts filesystems.
• fsck: Checks and repairs a Linux filesystem.

3. Network Troubleshooting

• ifconfig: Displays network interfaces and their status.
• ip addr show: Shows IP addresses and network interfaces.
• ping: Checks connectivity to a remote host.
• traceroute: Traces the route packets take to a network host.
• netstat: Displays network connections, routing tables, and interface statistics.
• ss: A modern replacement for netstat, showing more detailed information about network connections.
• nslookup: Queries DNS servers for domain name or IP address mapping.
• dig: Performs DNS queries.
• tcpdump: Captures and analyzes network packets.
• nmap: Scans networks for open ports and services.

4. Process Management

• ps aux: Lists all running processes.
• kill PID: Terminates a process by its PID (Process ID).
• pkill process_name: Kills processes by name.
• killall process_name: Kills all instances of a process.
• systemctl: Manages system services (start, stop, restart, enable, disable).

5. Log Management

• tail -f /var/log/syslog: Continuously monitors the system log file.
• tail -f /var/log/messages: Continuously monitors the messages log file.
• journalctl: Views logs collected by the systemd journal.
• last: Displays the last logins of users.
• who: Shows who is currently logged into the system.

6. User and Permission Issues

• whoami: Displays the current user’s name.
• id: Displays user identity, including UID, GID, and groups.
• groups username: Lists the groups a user belongs to.
• passwd: Changes a user's password.
• chown: Changes file ownership.
• chmod: Changes file permissions.
• usermod: Modifies user accounts.

7. Package Management

• apt-get update && apt-get upgrade: Updates package lists and upgrades all packages (Debian/Ubuntu).
• yum update: Updates all packages (CentOS/RHEL).
• rpm -qa: Lists all installed RPM packages.
• dpkg -l: Lists all installed DEB packages.
• apt-cache search package_name: Searches for a package (Debian/Ubuntu).

8. Service Management

• systemctl start service_name: Starts a service.
• systemctl stop service_name: Stops a service.
• systemctl restart service_name: Restarts a service.
• systemctl status service_name: Displays the status of a service.

9. Miscellaneous

• uname -a: Displays system information (kernel version, etc.).
• hostname: Shows or sets the system's hostname.
• date: Displays or sets the system date and time.
• crontab -e: Edits the cron jobs for the current user.

These commands are the starting points for troubleshooting most issues in a Linux environment.