Frequently Used Linux Commands for Server Administration

1. Navigation and Filesystem

Command	Description
`ls`	Lists files and directories.
`cd`	Changes the current directory.
`pwd`	Displays the current directory.
`mkdir`	Creates a new directory.
`rm`	Deletes files or directories (`rm -r` for directories).
`cp`	Copies files or directories (`cp -r`).
`mv`	Moves or renames files.
`find`	Searches for files based on criteria.
`df -h`	Displays disk space usage of filesystems.
`du -sh`	Shows the size of a directory.

2. User and Permission Management

Command	Description
`whoami`	Displays the current user.
`id`	Displays user and group information.
`adduser`	Creates a new user.
`usermod`	Modifies user accounts (e.g., adding to groups).
`passwd`	Changes a user's password.
`chmod`	Changes file permissions.
`chown`	Changes the owner of a file or directory.
`groups`	Lists groups of the current user.

3. Network Management

Command	Description
`ip a`	Displays network configurations.
`ping`	Checks the reachability of a host.
`traceroute`	Shows the path a packet takes to a destination.
`netstat -tuln`	Displays open ports and connections.
`ss -tuln`	Displays detailed network connections.
`curl`	Executes HTTP requests.
`wget`	Downloads files from the internet.
`scp`	Copies files between hosts.
`rsync`	Synchronizes files between hosts.

4. Process and System Monitoring

Command	Description
`top`	Displays running processes and resource usage.
`htop`	Interactive process viewer.
`ps aux`	Lists all processes.
`kill`	Terminates processes by PID.
`uptime`	Displays system uptime.
`free -h`	Shows memory usage.
`vmstat`	Displays real-time system statistics.

5. Package Management

Debian-based Systems (e.g., Ubuntu)

Command	Description
`apt update`	Updates the package list.
`apt upgrade`	Installs available updates.
`apt install <package>`	Installs a package.
`apt remove <package>`	Removes a package.
`dpkg -l`	Lists installed packages.

RHEL-based Systems (e.g., CentOS, Fedora)

Command	Description
`dnf update`	Performs system updates.
`dnf install <package>`	Installs a package.
`dnf remove <package>`	Removes a package.
`rpm -qa`	Lists installed RPM packages.

6. Security

Command	Description
`ufw status`	Displays the status of the firewall (Ubuntu).
`ufw allow <port>`	Allows incoming traffic on a port.
`iptables`	Configures advanced firewall rules.
`fail2ban-client status`	Displays the status of Fail2ban.
`rkhunter --check`	Checks the system for rootkits.
`ssh-keygen`	Generates SSH key pairs.
`ssh-copy-id`	Copies SSH keys to a remote host.

7. Log and Error Analysis

Command	Description
`journalctl`	Displays system logs.
`dmesg`	Shows kernel messages.
`tail -f /var/log/syslog`	Monitors log files in real-time.
`grep <word>`	Searches files for a specific term.

8. Backup and Restoration

Command	Description
`tar -czvf <file>.tar.gz <folder>`	Creates a compressed archive.
`tar -xzvf <file>.tar.gz`	Extracts an archive.
`rsync -av <source> <destination>`	Synchronizes files.
`dd if=<source> of=<destination>`	Creates exact copies of disks.

Conclusion

This is a collection of the most commonly used commands for Linux server administration. These commands will help you manage, troubleshoot, and optimize your system effectively.