Linux commands

Here are some important Linux commands that are widely used for file management, system navigation, user management, and system administration:

1. File and Directory Management

• ls: Lists files and directories in the current directory.

  • Example: ls -l (detailed list), ls -a (includes hidden files)

• cd: Changes the current directory.

  • Example: cd /home/user (navigate to /home/user)

• pwd: Prints the current working directory.

  • Example: pwd

• mkdir: Creates a new directory.

  • Example: mkdir new_directory

• rmdir: Removes an empty directory.

  • Example: rmdir empty_directory

• rm: Removes files or directories.

  • Example: rm file.txt, rm -r directory_name (removes directory with content)

• cp: Copies files or directories.

  • Example: cp file1.txt file2.txt, cp -r dir1 dir2

• mv: Moves or renames files or directories.

  • Example: mv oldname.txt newname.txt

• touch: Creates an empty file or updates file timestamp.

  • Example: touch file.txt

• cat: Displays content of a file.

  • Example: cat file.txt

• nano, vim: Opens file in text editors.

  • Example: nano file.txt, vim file.txt

• find: Finds files and directories.

  • Example: find / -name filename.txt

• grep: Searches for patterns within files.

  • Example: grep 'pattern' file.txt, grep -r 'pattern' /path/to/directory

2. File Permissions and Ownership

• chmod: Changes file permissions.

  • Example: chmod 755 file.txt, chmod u+x script.sh

• chown: Changes file ownership.

  • Example: chown user:group file.txt

• chgrp: Changes the group ownership of a file.

  • Example: chgrp groupname file.txt

3. Process Management

• ps: Displays currently running processes.

  • Example: ps aux, ps -ef

• top: Displays real-time system processes and resource usage.

• kill: Terminates a process by its process ID (PID).

  • Example: kill 12345, kill -9 12345 (force kill)

• pkill: Terminates processes by name.

  • Example: pkill firefox

• bg / fg: Sends jobs to background (bg) or foreground (fg).

4. Disk and System Information

• df: Displays disk space usage.

  • Example: df -h

• du: Shows the size of files and directories.

  • Example: du -sh directory_name

• free: Displays memory usage.

  • Example: free -h

• uname: Displays system information.

  • Example: uname -a

• uptime: Shows how long the system has been running.

• dmesg: Prints kernel and boot messages.

• who: Shows who is logged in.

• w: Displays system uptime and logged-in users.

5. Networking

• ifconfig: Displays network interfaces and IP addresses.

  • Example: ifconfig eth0

• ping: Sends ICMP echo request to a host.

  • Example: ping google.com

• netstat: Displays network connections, routing tables, and interface statistics.

• ssh: Securely connects to a remote machine.

  • Example: ssh user@hostname

• scp: Copies files between local and remote systems.

  • Example: scp file.txt user@remote:/path/to/destination

• wget / curl: Downloads files from the web.

  • Example: wget http://example.com/file, curl -O http://example.com/file

• ip: Shows/manages network configurations.

  • Example: ip a, ip link show

6. User Management

• useradd: Adds a new user.

  • Example: sudo useradd username

• passwd: Changes the password for a user.

  • Example: passwd username

• usermod: Modifies an existing user account.

  • Example: usermod -aG sudo username (add user to sudo group)

• userdel: Deletes a user account.

  • Example: userdel username

• groupadd: Creates a new group.

  • Example: groupadd groupname

• groups: Displays group memberships of a user.

  • Example: groups username

7. Archiving and Compression

• tar: Archives files into a tarball (optionally compressed with gzip or bzip2).

  • Example: tar -cvf archive.tar file1 file2, tar -xvf archive.tar

  • Example with compression: tar -czvf archive.tar.gz directory/

• gzip: Compresses files.

  • Example: gzip file.txt, gunzip file.txt.gz

• zip / unzip: Compresses and extracts ZIP archives.

  • Example: zip archive.zip file.txt, unzip archive.zip

8. Package Management (Depends on the Distribution)

• For Debian/Ubuntu-based systems:

  • apt-get install: Installs a package.

    • Example: sudo apt-get install package_name

  • apt-get update: Updates the package index.

    • Example: sudo apt-get update

  • apt-get upgrade: Upgrades installed packages.

    • Example: sudo apt-get upgrade

• For Red Hat/CentOS-based systems:

  • yum install: Installs a package.

    • Example: sudo yum install package_name

  • yum update: Updates the package index and upgrades packages.

    • Example: sudo yum update

9. System Monitoring

• htop: Interactive process viewer.

• iostat: Reports CPU, disk I/O, and network usage.

• vmstat: Reports virtual memory statistics.

• sar: Collects and reports system activity.

10. Shutdown/Restart

• shutdown: Shuts down or reboots the system.

  • Example: shutdown -h now (shutdown), shutdown -r now (reboot)

• reboot: Reboots the system immediately.

  • Example: sudo reboot

• halt: Halts the system immediately.

  • Example: sudo halt

11. Advanced File Operations

• stat: Displays detailed information about a file or file system.

  • Example: stat file.txt

• ln: Creates hard or symbolic links to files.

  • Example: ln file.txt link_to_file.txt (hard link), ln -s file.txt symlink.txt (symbolic link)

• basename / dirname: Extracts filename or directory path from a given path.

  • Example: basename /home/user/file.txt (outputs file.txt)

  • Example: dirname /home/user/file.txt (outputs /home/user)

12. Disk and Partition Management

• fdisk: Used to view and manage disk partitions.

  • Example: fdisk /dev/sda

• parted: Another tool for partition management, especially for large disks.

  • Example: parted /dev/sda

• mkfs: Formats a partition with a specified filesystem.

  • Example: mkfs.ext4 /dev/sda1

• mount / umount: Mounts or unmounts a file system.

  • Example: mount /dev/sda1 /mnt, umount /mnt

• blkid: Shows UUIDs and details about block devices.

  • Example: blkid /dev/sda1

• lsblk: Lists information about block devices (disks and partitions).

  • Example: lsblk

• df -i: Shows inode usage on filesystems (useful when df shows space available but file creation fails due to lack of inodes).

13. System Resource and Performance Monitoring

• iotop: Displays real-time disk I/O usage.

  • Example: sudo iotop

• strace: Traces system calls and signals used by a command.

  • Example: strace -p <PID>, strace ls

• lsof: Lists open files and the processes that opened them (useful for checking which files are in use).

  • Example: lsof | grep filename, lsof -i :80 (lists processes using port 80)

• ncdu: Disk usage analyzer, an easy-to-read alternative to du.

  • Example: ncdu /home

• sysctl: Views or modifies kernel parameters.

  • Example: sysctl -a (shows all kernel parameters), sysctl vm.swappiness=10 (changes swappiness parameter)

• watch: Runs a command repeatedly at regular intervals and displays the output.

  • Example: watch -n 5 df -h (runs df -h every 5 seconds)

14. Networking and Internet Tools

• traceroute: Tracks the route packets take to a network host.

  • Example: traceroute google.com

• nc (netcat): Reads and writes data across network connections (a Swiss-army knife for network-related tasks).

  • Example: nc -l 12345 (listens on port 12345), nc google.com 80 (connects to google on port 80)

• dig: DNS lookup utility (more advanced than nslookup).

  • Example: dig google.com

• hostname: Shows or sets the system's hostname.

  • Example: hostname, hostnamectl set-hostname newhostname

• arp: Shows the system's ARP (Address Resolution Protocol) table.

  • Example: arp -a

• ss: Displays socket statistics, more modern than netstat.

  • Example: ss -tuln (shows open ports and services)

15. System Logs and Debugging

• journalctl: Views system logs on systemd systems.

  • Example: journalctl -xe (view recent logs with errors), journalctl -b (view logs since last boot)

• tail: Displays the last lines of a file (often used for logs).

  • Example: tail -f /var/log/syslog (live view of log file)

• dstat: Combines the functionality of vmstat, iostat, and netstat in real-time.

  • Example: dstat

• last: Shows the login history of users.

  • Example: last

• logrotate: Rotates, compresses, and removes old logs automatically (usually run in cron jobs).

16. Scripting and Automation

• cron: Schedules tasks to run periodically (using crontab).

  • Example: crontab -e (edit user crontab), crontab -l (list cron jobs)

• at: Schedules a task to run at a specific time (only once).

  • Example: echo "shutdown -h now" | at 22:00

• alias: Creates shortcuts for long commands.

  • Example: alias ll='ls -lah'

• export: Exports an environment variable.

  • Example: export PATH=$PATH:/usr/local/bin

• source: Executes commands from a file in the current shell.

  • Example: source ~/.bashrc

• awk: A powerful text processing tool for extracting and manipulating text.

  • Example: awk '{print $1}' file.txt

• sed: Stream editor for filtering and transforming text.

  • Example: sed 's/oldtext/newtext/g' file.txt

17. Security and Permissions

• sudo: Runs a command as the superuser (root).

  • Example: sudo apt-get update

• su: Switches to another user.

  • Example: su - username

• umask: Sets default permissions for newly created files and directories.

  • Example: umask 022

• setfacl / getfacl: Manages Access Control Lists (ACLs) for fine-grained file permissions.

  • Example: setfacl -m u:username:rwx file.txt, getfacl file.txt

18. Backup and Recovery

• rsync: Synchronizes files and directories between two locations efficiently.

  • Example: rsync -avh /source/ /destination/

• dd: Copies and converts files at a low level, often used for backups or disk cloning.

  • Example: dd if=/dev/sda of=/path/to/backup.img bs=64K

• fsck: Checks and repairs file system consistency.

  • Example: fsck /dev/sda1

19. Virtualization and Containers

• docker: Manages containerized applications.

  • Example: docker run -it ubuntu bash, docker ps (list running containers)

• virt-install: Installs virtual machines via command line (for libvirt/KVM).

  • Example: virt-install --name vm1 --ram 1024 --vcpus 1 --disk path=/var/lib/libvirt/images/vm1.img,size=10

• vagrant: Automates the setup of virtualized development environments.

  • Example: vagrant up, vagrant ssh

20. System Control and Administration

• systemctl: Manages systemd services (starting, stopping, enabling, disabling services).

  • Example: systemctl start apache2, systemctl enable apache2, systemctl status apache2

• timedatectl: Configures date, time, and timezone settings.

  • Example: timedatectl set-timezone America/New_York

• hostnamectl: Changes the system hostname and related settings.

  • Example: hostnamectl set-hostname newhostname

• modprobe: Loads or unloads kernel modules.

  • Example: modprobe module_name

• sysfs: Interacts with system hardware information exposed through /sys.

  • Example: cat /sys/class/net/eth0/speed

21. Networking Tools

• mtr: Combines the functionality of traceroute and ping to diagnose network issues.

  • Example: mtr google.com

• iftop: Displays bandwidth usage by network interface.

  • Example: sudo iftop -i eth0

• tcpdump: Captures and analyzes network packets.

  • Example: sudo tcpdump -i eth0, tcpdump port 80

• iptraf-ng: An interactive, real-time network monitoring utility.

• ethtool: Displays or changes network interface card (NIC) settings.

  • Example: sudo ethtool eth0

• ufw: Manages uncomplicated firewall settings (commonly used in Ubuntu).

  • Example: sudo ufw allow 22, sudo ufw enable

• firewalld: Firewall management tool used in RedHat/CentOS.

  • Example: sudo firewall-cmd --permanent --add-port=8080/tcp

22. Filesystem and Storage Management

• lsattr: Lists attributes of files and directories.

  • Example: lsattr file.txt

• chattr: Changes file attributes, for example, to make a file immutable.

  • Example: chattr +i file.txt

• xfs_admin: Manages XFS file systems (resizing, repairing, etc.).

  • Example: xfs_admin -L new_label /dev/sda1

• quota: Displays disk quotas and user limits on filesystems.

  • Example: quota -u username

• lvm: Logical Volume Manager commands like lvcreate, vgextend, etc.

  • Example: lvcreate -L 10G -n lv_data vg1, lvextend -L +5G /dev/vg1/lv_data

• cryptsetup: Sets up encrypted filesystems using LUKS (Linux Unified Key Setup).

  • Example: cryptsetup luksFormat /dev/sda1, cryptsetup luksOpen /dev/sda1 secure_drive

23. Development and Debugging Tools

• gdb: GNU Debugger, used for debugging programs.

  • Example: gdb ./program, gdb --pid=<PID>

• objdump: Displays detailed information about binary files.

  • Example: objdump -d binary_file

• ldd: Displays shared library dependencies for executable files.

  • Example: ldd /bin/ls

• valgrind: A tool for memory debugging, memory leak detection, and profiling.

  • Example: valgrind ./program

• nm: Displays symbols from object files.

  • Example: nm a.out

• strace: Tracks system calls and signals a process makes.

  • Example: strace -p <PID>

24. Package Management Tools

• dpkg: Low-level package management for Debian-based distributions (like Ubuntu).

  • Example: dpkg -i package.deb, dpkg -l (list installed packages)

• rpm: Low-level package management for Red Hat-based distributions.

  • Example: rpm -ivh package.rpm, rpm -qa (list installed packages)

• yum: High-level package manager for Red Hat/CentOS (predecessor of dnf).

  • Example: yum search package_name, yum remove package_name

• dnf: Modern package manager for Red Hat/CentOS/Fedora.

  • Example: dnf install package_name, dnf update

• snap: Manages snap packages, often used for containerized applications.

  • Example: snap install package_name, snap list

• flatpak: Another framework for distributing desktop applications in containers.

  • Example: flatpak install package_name

25. Containers and Virtualization

• virsh: CLI interface for managing virtual machines using libvirt.

  • Example: virsh list --all, virsh start vm1

• kvm: Manages kernel-based virtual machines.

  • Example: kvm -hda disk.img -m 512 -net nic -net user

• docker-compose: Manages multi-container Docker applications using YAML configuration files.

  • Example: docker-compose up, docker-compose down

• podman: A daemonless container engine that is compatible with Docker.

  • Example: podman run -it fedora, podman ps

• lxc: Linux Containers toolset, alternative to Docker for containerization.

  • Example: lxc-create -n container -t download, lxc-start -n container

26. Performance Monitoring

• perf: Performance analysis tool for Linux, particularly useful for kernel developers.

  • Example: perf top, perf record -a

• sar: Collects and reports system activity information.

  • Example: sar -u 1 3 (CPU utilization over 1-second intervals)

• iotop: Real-time disk I/O monitoring by process.

  • Example: iotop

• latencytop: Identifies latency issues in your system.

• dstat: A versatile resource monitoring tool that combines features of vmstat, iostat, and netstat.

  • Example: dstat --cpu --io --net

27. Security and Cryptography

• fail2ban: Protects your server from brute-force attacks by blocking IP addresses.

  • Example: sudo fail2ban-client status, sudo fail2ban-client set sshd banip <IP>

• gpg: GNU Privacy Guard for encrypting and signing files or messages.

  • Example: gpg --gen-key, gpg -e -r recipient file.txt

• openssl: Toolset for SSL/TLS, certificates, and cryptography functions.

  • Example: openssl genpkey -algorithm RSA -out private.pem

• nmap: A powerful network scanning tool for security auditing and network exploration.

  • Example: nmap -A 192.168.1.1

28. Miscellaneous

• tldr: Displays simplified and practical examples of common commands.

  • Example: tldr tar

• bc: A command-line calculator supporting floating-point arithmetic.

  • Example: echo "scale=2; 10/3" | bc

• yes: Continuously outputs a string until terminated.

  • Example: yes "I agree"

• shuf: Generates random permutations from input lines.

  • Example: shuf -n 1 file.txt (outputs a random line from a file)

• units: Converts between different units of measurement.

  • Example: units '10 miles' 'kilometers'

• tree: Displays a directory structure in a tree-like format.

  • Example: tree /path/to/directory

• alias: Defines a shortcut for a command.

  • Example: alias ll='ls -la'

30. Specialized File Management Commands

• split: Splits a file into smaller chunks.

  • Example: split -b 100M largefile.bin part_ (splits a file into 100 MB chunks)

• shred: Securely deletes a file by overwriting it multiple times.

  • Example: shred -u file.txt

• rev: Reverses the characters in each line of a file.

  • Example: echo "hello" | rev (outputs olleh)

• rename: Renames multiple files using a regular expression.

  • Example: rename 's/\.txt$/.bak/' *.txt (renames .txt files to .bak)

• xxd: Converts a file to hexadecimal and back.

  • Example: xxd file.txt, xxd -r file.hex

31. Advanced Scripting and Text Processing

• xargs: Constructs argument lists and passes them to a command.

  • Example: find . -name '*.txt' | xargs rm (removes all .txt files)

• tee: Reads from standard input and writes to both standard output and a file.

  • Example: echo "hello" | tee output.txt (writes "hello" to both terminal and file)

• paste: Merges lines of files horizontally.

  • Example: paste file1.txt file2.txt (merges lines from both files side-by-side)

• comm: Compares two sorted files line by line.

  • Example: comm file1.txt file2.txt

• tac: Displays the contents of a file in reverse order (last line first).

  • Example: tac file.txt

• expr: Evaluates expressions (useful in shell scripts for arithmetic).

  • Example: expr 1 + 2

• bc: Command-line calculator.

  • Example: echo "2^10" | bc

• tr: Translates or deletes characters in input.

  • Example: echo "HELLO" | tr 'A-Z' 'a-z' (converts to lowercase)

32. Terminal Utilities and Shortcuts

• tmux: Terminal multiplexer to manage multiple terminal sessions.

  • Example: tmux (starts a new session), tmux attach (reattaches to an existing session)

• screen: Another terminal multiplexer, similar to tmux.

  • Example: screen (starts a new session), screen -r (reattaches to a session)

• reset: Resets the terminal display and clears any weird states.

  • Example: reset

• script: Records a terminal session to a file.

  • Example: script session.txt

• yes: Repeats a string until terminated.

  • Example: yes "agree" (repeats "agree" until stopped with Ctrl+C)

33. System Monitoring and Information

• lsmod: Lists loaded kernel modules.

  • Example: lsmod

• uptime: Displays system uptime and load averages.

  • Example: uptime

• lshw: Lists detailed hardware information.

  • Example: sudo lshw

• inxi: Displays detailed system information (including CPU, GPU, RAM, etc.).

  • Example: inxi -Fx

• acpi: Displays battery status and thermal information (useful for laptops).

  • Example: acpi -b

• lsof: Lists open files and processes using them.

  • Example: lsof /dev/sda1

• dmesg: Displays kernel-related messages (especially useful for debugging hardware issues).

  • Example: dmesg | grep error

• vmstat: Reports virtual memory, process, and CPU activity.

  • Example: vmstat 5 (reports every 5 seconds)

• watch: Executes a command repeatedly and displays the output.

  • Example: watch -n 2 df -h (runs df -h every 2 seconds)

34. Networking and Connectivity Tools

• whois: Queries domain registration information.

  • Example: whois google.com

• host: Performs DNS lookups.

  • Example: host google.com

• iwconfig: Configures wireless network interfaces (similar to ifconfig but for wireless).

  • Example: iwconfig wlan0

• w: Displays who is logged into the system and their activities.

  • Example: w

• ip addr: Shows detailed network interface information (replacement for ifconfig).

  • Example: ip addr show

• ip route: Manages routing tables.

  • Example: ip route add 192.168.1.0/24 via 192.168.0.1

35. Process and System Control

• pkill: Sends a signal to a process by its name (alternative to kill).

  • Example: pkill firefox

• renice: Alters the scheduling priority of a running process.

  • Example: renice +5 -p <PID>

• fg: Brings a background process to the foreground.

  • Example: fg %1 (brings job 1 to the foreground)

• bg: Resumes a suspended job in the background.

  • Example: bg %1 (resumes job 1 in the background)

36. User and Group Management

• groups: Shows the groups a user is part of.

  • Example: groups username

• useradd: Adds a new user.

  • Example: sudo useradd -m username

• usermod: Modifies a user account.

  • Example: usermod -aG sudo username

• passwd: Changes a user's password.

  • Example: passwd username

• chage: Changes user password expiration information.

  • Example: sudo chage -l username

37. System Maintenance and Troubleshooting

• fsck: Checks and repairs file system inconsistencies.

  • Example: fsck /dev/sda1

• badblocks: Searches for bad sectors on a disk.

  • Example: sudo badblocks -v /dev/sda1

• smartctl: Monitors the health of hard drives and SSDs via S.M.A.R.T.

  • Example: sudo smartctl -a /dev/sda

• iotop: Displays disk I/O usage by processes in real time.

  • Example: iotop

38. Archiving and Compression

• tar: Archive files into a tarball or extract files.

  • Example: tar -czvf archive.tar.gz folder/, tar -xvzf archive.tar.gz

• gzip: Compresses or decompresses files.

  • Example: gzip file.txt, gunzip file.txt.gz

• bzip2: Compresses files using the Burrows-Wheeler block-sorting text compression algorithm.

  • Example: bzip2 file.txt

• xz: Compresses files with higher compression than gzip or bzip2.

  • Example: xz file.txt

• unzip: Extracts files from a ZIP archive.

  • Example: unzip archive.zip

39. Date and Time

• date: Displays or sets the system date and time.

  • Example: date, date --set="2024-10-11 10:30"

• cal: Displays a calendar.

  • Example: cal

• ntpq: Monitors NTP daemon and shows the status of time synchronization.

  • Example: ntpq -p

40. Miscellaneous Useful Commands

• flock: Manages file locking in shell scripts.

  • Example: flock /tmp/mylockfile command

• chroot: Changes the root directory for a process (used for system recovery and containers).

  • Example: chroot /mnt/recovery /bin/bash

• ncdu: Disk usage analyzer with a text-based user interface (faster alternative to du).

  • Example: ncdu /home

• hexdump: Displays file contents in hexadecimal, decimal

• uptime: Displays system uptime, load averages, and number of users logged in.

  • Example: uptime

• alias: Creates a shortcut for a command.

  • Example: alias ll='ls -la'

• bc: A command-line calculator.

  • Example: echo "5 * 7" | bc

• env: Displays environment variables.

  • Example: env