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Linux System Commands for System Engineers

System Information Commands

uname -a - Displays system information.
hostname - Displays or sets the hostname.
uptime - Shows how long the system has been running.
who - Displays who is logged in.
id - Shows user ID and group ID information.
arch - Displays the system architecture.
lsb_release -a - Displays Linux Standard Base distribution information.

File and Directory Management

ls - Lists files and directories.
cd <directory> - Changes the current directory.
pwd - Prints the current working directory.
mkdir <directory> - Creates a new directory.
rmdir <directory> - Removes an empty directory.
rm <file> - Removes a file.
cp <source> <destination> - Copies files or directories.
mv <source> <destination> - Moves or renames files or directories.

File Viewing and Editing

cat <file> - Displays the content of a file.
less <file> - Allows viewing of a file one screen at a time.
head <file> - Displays the first 10 lines of a file.
tail <file> - Displays the last 10 lines of a file.
nano <file> - Opens the file in the Nano text editor.
vi <file> - Opens the file in the Vi text editor.

Process Management

ps - Displays active processes.
top - Displays real-time system and process information.
htop - Interactive process viewer (if installed).
kill <PID> - Kills a process by its PID.
killall <process_name> - Kills all processes with the specified name.
bg - Resumes a job in the background.
fg - Resumes a job in the foreground.

Disk Usage and Storage

df -h - Displays disk space usage in a human-readable format.
du -sh <directory> - Displays the size of a directory.
mount - Lists mounted filesystems or mounts a device.
umount <device> - Unmounts a device.
lsblk - Lists information about block devices.
blkid - Displays information about block devices and their UUIDs.

Network Commands

ifconfig - Displays or configures network interfaces.
ip addr - Displays IP addresses and network interfaces.
ping <host> - Checks connectivity to a host.
netstat -tuln - Displays network connections.
ss -tuln - Displays listening ports and connections.
curl <URL> - Fetches data from a URL.
wget <URL> - Downloads a file from a URL.

User Management

whoami - Displays the current user.
adduser <username> - Adds a new user.
passwd <username> - Changes a user's password.
deluser <username> - Deletes a user.
groups <username> - Displays the groups a user belongs to.

Permissions and Ownership

chmod <mode> <file> - Changes file permissions.
chown <user>:<group> <file> - Changes file ownership.
ls -l - Displays file permissions in a detailed format.
umask - Displays or sets default file permissions.

Package Management (Debian-based systems)

apt update - Updates the package list.
apt upgrade - Upgrades installed packages.
apt install <package> - Installs a package.
apt remove <package> - Removes a package.

Package Management (Red Hat-based systems)

dnf update - Updates all installed packages.
dnf install <package> - Installs a package.
dnf remove <package> - Removes a package.

System Monitoring

free -h - Displays memory usage.
vmstat - Displays system performance metrics.
iostat - Displays CPU and I/O statistics.
sar - Collects and reports system activity.
dmesg - Displays kernel messages.

Backup and Archiving

tar -cvf <archive.tar> <directory> - Creates a tar archive.
tar -xvf <archive.tar> - Extracts a tar archive.
rsync -av <source> <destination> - Synchronizes files/directories.

Search and Find

find <directory> -name <pattern> - Searches for files matching a pattern.
grep <pattern> <file> - Searches for a pattern in a file.
locate <file> - Quickly finds a file (requires updatedb).
which <command> - Shows the path of a command.

Shutdown and Reboot

shutdown -h now - Shuts down the system immediately.
reboot - Reboots the system.
halt - Halts the system.