# Linux Commands In the dynamic world of DevOps, where speed, automation, and efficiency reign supreme, mastering the command line is an indispensable skill. Linux, with its powerful command-line interface, is at the heart of many DevOps workflows. In this blog post, we'll explore essential Linux commands that every DevOps professional should have in their toolkit. ### **File and Directory Operations:** 1. **ls** - List directory contents. ```bash ls -l /path/to/directory ``` 2. **cd** - Change directory. ```bash cd /path/to/directory ``` 3. **pwd** - Print working directory. ```bash pwd ``` 4. **touch** - Create an empty file. ```bash touch file.txt ``` 5. **cp** - Copy files or directories. ```bash cp sourcefile.txt destination/ ``` 6. **mv** - Move or rename files or directories. ```bash mv oldfile.txt newfile.txt ``` 7. **rm** - Remove files or directories. ```bash rm file.txt ``` 8. **find** - Search for files and directories. ```bash find /path/to/search -name "file.txt" ``` 9. **du** - Show directory space usage. ```bash du -sh /path/to/directory ``` 10. **df** - Display disk space usage. ```bash df -h ``` ### **Process Management:** 1. **ps** - Show information about running processes. ```bash ps aux ``` 2. **top** - Monitor system activity and processes in real-time. ```bash top ``` 3. **kill** - Terminate processes by process ID (PID). ```bash kill PID ``` 4. **pkill** - Terminate processes by name. ```bash pkill process_name ``` 5. **pgrep** - List processes by name. ```bash pgrep process_name ``` 6. **htop** - Interactive process viewer. ```bash htop ``` 7. **nice** - Run a command with a specified priority. ```bash nice -n 10 myprocess ``` 8. **renice** - Change the priority of a running process. ```bash renice -n 15 -p PID ``` 9. **systemctl** - Manage system services and units. ```bash systemctl status service_name ``` 10. **journalctl** - View and filter system logs. ```bash journalctl -xe ``` ### **Network and Connectivity:** 1. **ping** - Check network connectivity to a host. ```bash ping google.com ``` 2. **ifconfig/ip** - Display and configure network interfaces. ```bash ifconfig ``` 3. **netstat** - Network statistics and connection information. ```bash netstat -tuln ``` 4. **ssh** - Securely connect to remote servers. ```bash ssh user@remote_server ``` 5. **scp** - Securely copy files between hosts. ```bash scp file.txt user@remote_server:/path ``` 6. **curl** - Transfer data with URLs. ```bash curl ``` 7. **ss** - Display socket statistics. ```bash ss -tuln ``` 8. **nmap** - Network exploration tool and security scanner. ```bash nmap -p 80 example.com ``` 9. **traceroute** - Trace the route packets take to a network host. ```bash traceroute google.com ``` 10. **iptables** - Configure firewall rules. ```bash iptables -A INPUT -p tcp --dport 80 -j ACCEPT ``` ### **Package Management:** 1. **apt-get/apt** - Package management on Debian/Ubuntu. ```bash sudo apt-get install package_name ``` 2. **yum/dnf** - Package management on Red Hat/CentOS. ```bash sudo yum install package_name ``` 3. **dnf** - Improved package management for Fedora. ```bash sudo dnf install package_name ``` 4. **zypper** - Package management on openSUSE. ```bash sudo zypper install package_name ``` 5. **dpkg** - Debian package management (low-level). ```bash dpkg -i package.deb ``` 6. **rpm** - Red Hat Package Manager (low-level). ```bash rpm -i package.rpm ``` 7. **apt-cache search** - Search for packages on Debian-based systems. ```bash apt-cache search search_term ``` 8. **yum search/dnf search** - Search for packages on Red Hat-based systems. ```bash yum search search_term ``` 9. **rpm -qa** - List all installed RPM packages. ```bash rpm -qa ``` 10. **pip** - Package installer for Python. ```bash pip install package_name ``` ### **User and Permission Management:** 1. **useradd** - Add a new user. ```bash sudo useradd new_user ``` 2. **passwd** - Change user password. ```bash sudo passwd username ``` 3. **usermod** - Modify user attributes. ```bash sudo usermod -aG group_name username ``` 4. **userdel** - Delete a user account. ```bash sudo userdel username ``` 5. **chown** - Change file/folder ownership. ```bash sudo chown user:group file.txt ``` 6. **chmod** - Change file/folder permissions. ```bash chmod 644 file.txt ``` 7. **visudo** - Edit the sudoers file. ```bash sudo visudo ``` 8. **groups** - Show groups a user belongs to. ```bash groups username ``` 9. **id** - Display user and group information. ```bash id username ``` 10. **setfacl/getfacl** - Manage access control lists. ```bash setfacl -m u:username:rw file.txt ``` ### **System Monitoring and Performance:** 1. **free** - Display system memory usage. ```bash free -m ``` 2. **uptime** - Show system uptime and load averages. ```bash uptime ``` 3. **vmstat** - Virtual memory statistics. ```bash vmstat 1 ``` 4. **iostat** - Input/output statistics. ```bash iostat -d 1 ``` 5. **sar** - Collect and report system activity information. ```bash sar -u 1 5 ``` 6. **top/htop** - Real-time system resource monitoring. ```bash top ``` 7. **ps** - View process information and resource usage. ```bash ps aux ``` **lsof** - List open files and their associated processes. ```bash lsof ``` 8. **iotop** - Monitor I/O usage by processes. ```bash iotop ``` 9. **atop** - Advanced performance monitor. ```bash atop ``` ### **Backup and Restore:** 1. **tar** - Create and extract tar archives. ```bash tar -cvzf backup.tar.gz /path/to/backup ``` 2. **rsync** - Synchronize files and directories. ```bash rsync -av source/ destination/ ``` 3. **dd** - Copy and convert files. ```bash dd if=input_file of=output_file ``` 4. **dump** - Create filesystem backups. ```bash dump -0u -f /path/to/backup.dump /dev/sdX ``` **restore** - Restore files from backups. ```bash restore -r -f /path/to/backup.dump ``` **cron** - Schedule automated backups. ```bash crontab -e ``` **at** - Schedule one-time tasks. ```bash at now + 1 hour ``` 5. **rsnapshot** - Backup tool using rsync and hard links. ```bash rsnapshot daily ``` 6. **borg** - Deduplicating backup program. ```bash borg create backup::backupname /path/to/backup ``` 7. **duplicity** - Encrypted bandwidth-efficient backup. ```bash duplicity /source ssh://user@backup_server/destination ``` ### **Log and Troubleshooting:** 1. **tail** - Display the last part of a file (commonly used with log files). ```bash tail -f /var/log/syslog ``` 2. **grep** - Search for patterns in files. ```bash grep "error" /var/log/application.log ``` 3. **journalctl** - Query the systemd journal. ```bash journalctl -u service_name ``` 4. **dmesg** - Display kernel ring buffer messages. ```bash dmesg | grep error ``` 5. **strace** - Trace system calls and signals. ```bash strace -p PID ``` 6. **ltrace** - Library call tracer. ```bash ltrace command ``` 7. **nc/netcat** - Network utility for debugging and data transfer. ```bash nc -zv host port ``` 8. **tcpdump** - Network packet analyzer. ```bash tcpdump -i eth0 port 80 ``` 9. **ss** - Socket statistics. ```bash ss -tuln ``` **watch** - Execute a program periodically and display the output. ```bash watch -n 1 command_to_watch ```