# Linux Command Line Cheat Sheet : 75 Essential Linux Commands The command line is where you get real control in Linux. It lets you dig into the system, automate tasks, and solve problems directly. This guide includes a hand-picked list of fundamental Linux commands, grouped by category. You’ll find commands for managing files, users, hardware, networking, and more. ## System-Based Commands * `uname` - Displays system information: kernel version, machine type, and more. * `uname -r` - Displays the running Linux kernel's release version. * `uptime` - Shows current time, system uptime, users, and load averages. * `hostname` - Shows the system hostname. * `hostname -i` - Displays the IP address of the current host. * `last reboot` - Shows last reboot times and durations in logs. * `date` - Displays the current date and time information. * `timedatectl` - Displays detailed system clock and time zone information. * `cal` - Displays a simple calendar of the current month. * `w` - Shows who is logged on and their activity. * `whoami` - Displays the username of the current user. * `finger username` - Displays information about a user named `username`. ## Hardware-Based Commands * `dmesg` - Displays messages from the kernel's ring buffer. * `cat /proc/cpuinfo` - Displays detailed information about the CPU. * `cat /proc/meminfo` - Displays detailed system memory usage information. * `lscpu` - Lists information about the CPU. * `lshw` - Lists detailed hardware configuration of the system. * `lsblk` - Lists information about all available block devices. * `free -m` - Shows system memory usage in megabytes. * `lspci -tv` - Displays PCI devices in tree format, verbosely. * `lsusb -tv` - Shows USB devices as a tree, verbosely. * `dmidecode` - Displays hardware information from system BIOS. * `hdparm -i /dev/sda` - Displays information of disk `/dev/sda`. * `badblocks -s /dev/sda` - Checks `/dev/sda` for bad blocks, showing progress. ## User Management Commands * `id` - Displays the user's UID, GID, and groups. * `last` - Shows list of last logged-in users. * `who` - Displays who is currently logged in. * `groupadd admin` - Creates a new user group named `admin`. * `adduser Sam` - Creates a new user account named `Sam`. * `userdel Sam` - Deletes the user account named `Sam`. * `usermod` - Modifies properties of an existing user account. ## File Commands * `ls -al` - Lists all files, with detailed information, in long format. * `pwd` - Displays the present working directory's path. * `mkdir dir1` - Creates a new directory named `dir1`. * `rm file1` - Deletes the file named `file1`. * `rm -f file2` - Forcefully deletes the file named `file2`. * `rm -r dir1` - Recursively removes directory `dir1` and its contents. * `rm -rf dir1` - Forcefully deletes directory `dir1` and its contents. * `cp file1 file2` - Copies `file1`, creating or overwriting `file2`. * `cp -r dir1 dir2` - Copies `dir1` to `dir2`, including subdirectories. * `mv file1 file2` - Renames or moves `file1` to `file2`. * `ln -s /path/to/file_name link_name` - Creates symbolic link named `link_name` to `file_name`. * `touch file1` - Creates an empty file named `file1`. * `cat > file1` - Creates or overwrites `file1`, awaiting standard input. * `more file1` - Displays `file1` content, paginating through output. * `head file1` - Displays the first ten lines of `file1`. * `tail file1` - Displays the last ten lines of `file1`. * `gpg -c file1` - Encrypts `file1` with a symmetric cipher using a passphrase. * `gpg file2.gpg` - Decrypts `file2.gpg`, prompting for the passphrase. * `wc` - Counts words, lines, and characters in files. * `xargs` - Executes commands with piped or file-provided arguments. ## Network Commands * `ip addr show` - Displays all network interfaces and their information. * `ip address add 192.168.0.1/24 dev eth0` - Assigns IP address `192.168.0.1` to interface `eth0`. * `ifconfig` - Shows network interfaces and their configuration. * `ping host` - Sends ICMP packets, measures round-trip time to `host`. * `whois domain` - Retrieves and displays a domain's registration information. * `dig domain` - Queries DNS, provides domain's DNS information. * `dig -x host` - Resolves IP address to hostname, shows reverse DNS info. * `host google.com` - Performs an IP lookup for the domain name. * `wget file_path` - Downloads file from the specified path. * `netstat` - Displays various network-related information and statistics. * `ss` - Displays information about network sockets. ## Compression / Archive Commands * `tar -cf backup.tar /home/ubuntu` - Creates a tar archive of the `/home/ubuntu` directory. * `tar -xf backup.tar` - Extracts files from the `backup.tar` archive. * `tar -zcvf backup.tar.gz /home/ubuntu` - Creates compressed `backup.tar.gz` archive of `/home/ubuntu`. * `gzip file1` - Compresses `file1` into `file1.gz`; original file is removed. ## Install Packages Commands * `rpm -i pkg_name.rpm` - Installs the package `pkg_name.rpm` using RPM. * `rpm -e pkg_name` - Uninstalls the specified RPM package. * `dnf install pkg_name` - Installs the specified package using DNF. * `pacman -S pkg_name` - Installs the specified package using Pacman. ## Install from Source (Compilation) * `./configure` - Checks system compatibility and generates Makefile. * `make` - Compiles code using the Makefile. * `make install` - Installs compiled code into appropriate system locations. ## Search Commands * `grep pattern file` - Searches for a given `pattern` within the specified file. * `grep -r pattern dir1` - Recursively searches for `pattern` in directory `dir1`. * `locate file` - Finds files named `file` using a prebuilt index database. * `find /home -name index` - Searches `/home` for files named `index`. * `find /home -size +10000k` - Finds files over 10,000 KB in `/home`. ## Login Commands * `ssh user@hostname` - Initiates SSH connection to specified host. * `ssh -p port_number user@hostname` - Connects over SSH using a specific port. * `ssh hostname` - Connects to `hostname` using SSH on port 22. * `telnet host` - Connects to `host` via Telnet on port 23. ## File Transfer Commands * `scp file.txt remoteuser@remote_host:/remote/directory` - Copies `file.txt` to a remote directory. * `rsync -a /home/ubuntu /backup/` - Synchronizes `/home/ubuntu` to `/backup/`, preserving attributes. * `rsync -a /var/www/web/ user@remote_host:/backup/web_backup/` - Syncs local directory to remote backup. ## Disk Usage Commands * `df -h` - Shows human-readable disk space usage. * `df -i` - Shows inode usage for all mounted filesystems. * `fdisk -l` - Lists all partitions and information for all drives. * `du -sh /dir1` - Displays total disk usage of `/dir1` in human-readable form. * `findmnt` - Lists all mounted filesystems and their properties. * `mount device-path mount-point` - Mounts a device to the specified mount point. ## Directory Traversal Commands * `cd ..` - Navigates to the parent directory. * `cd` - Changes the current directory to the user's home. * `cd /mnt` - Changes the current directory to `/mnt`.