This handbook serves as a comprehensive guide to understanding and using Linux commands effectively. It covers basic, advanced, and administrative commands, along with examples and outputs, to help users navigate and manage Linux systems efficiently.
Most input lines entered at the shell prompt have three basic elements:
- Command: The name of the program or utility you are executing.
- Options: Usually starts with one or two dashes (e.g.,
-por--print) and modifies the behavior of the command. - Arguments: Specifies the target or input for the command.
Some commands may not require options or arguments.
-
cat: Used to display the contents of a file or concatenate multiple files.- Example:
cat file.txt - Output: Displays the content of
file.txt.
- Example:
-
head: Displays the first few lines of a file.- Example:
head file.txt - Output: Shows the first 10 lines of
file.txt.
- Example:
-
tail: Displays the last few lines of a file.- Example:
tail file.txt - Output: Shows the last 10 lines of
file.txt.
- Example:
-
man: Displays the manual or documentation for a command.- Example:
man ls - Output: Opens the manual page for the
lscommand.
- Example:
-
pwd: Prints the current working directory.- Example:
pwd - Output:
/home/user
- Example:
-
ls: Lists the contents of the current directory.-
Example:
ls -
Output: Lists files and directories in the current directory.
-
Options:
-a: Lists all files, including hidden files (those starting with.).- Example:
ls -a - Output:
. .. file1 file2 .hiddenfile
- Example:
-R: Recursively lists directories and their contents.- Example:
ls -R - Output: Displays all files and subdirectories.
- Example:
-
-
tree: Displays the directory structure in a tree-like format.- Example:
tree - Output:
. ├── file1 ├── file2 └── file3 └── subdir
- Example:
-
cd: Changes the current directory.- Example:
cd /home/user - Output: Changes the working directory to
/home/user.
- Example:
-
mkdir: Creates a new directory.- Example:
mkdir new_folder - Output: Creates a directory named
new_folder.
- Example:
-
rmdir: Removes an empty directory.- Example:
rmdir empty_folder - Output: Deletes the directory
empty_folder.
- Example:
-
touch: Creates an empty file.-
Example:
touch file.txt -
Output: Creates a file named
file.txt. -
Hidden File: Prefix the filename with a dot (
.) to create a hidden file.- Example:
touch .hiddenfile - Output: Creates a hidden file named
.hiddenfile.
- Example:
-
-
mv: Moves or renames files.- Example:
mv file.txt /home/user - Output: Moves
file.txtto/home/user.
- Example:
-
cp: Copies files.- Example:
cp file.txt /home/user - Output: Copies
file.txtto/home/user.
- Example:
-
clear: Clears the terminal screen.- Output: Clears all text from the terminal.
-
history: Displays the list of previously executed commands.- Output:
1 ls 2 cd /home 3 pwd
⚠️ Caution: Avoid entering sensitive information, such as passwords, directly into the terminal. Commands entered in the terminal are saved in the history file, which could be accessed by others with sufficient permissions, posing a security risk. - Output:
-
echo: Prints text to the terminal.- Example:
echo Hello - Output:
Hello
- Example:
-
printf: Prints formatted text to the terminal. - Example:printf "This is a ball.\n"- Output:This is a ball.
-
chmod: Changes file permissions.The
chmodcommand is used to modify the permissions of a file or directory. Permissions determine who can read, write, or execute a file.-
Permission Breakdown:
-
Each file or directory has three permission groups:
- Owner: The user who owns the file.
- Group: Other users in the same group as the owner.
- Others: All other users.
-
Each group has three types of permissions:
r→ Read (4 in binary).w→ Write (2 in binary).x→ Execute (1 in binary).-→ No permission (0 in binary).
-
Permissions are represented as a combination of these values:
rwx→ Read, Write, Execute (4 + 2 + 1 = 7).rw-→ Read, Write (4 + 2 = 6).r--→ Read only (4).
-
-
How the Permission Number is Generated:
-
Permissions are represented as a three-digit number, where:
- The first digit represents the owner's permissions.
- The second digit represents the group's permissions.
- The third digit represents others' permissions.
-
Each digit is the sum of the binary values for
r,w, andx. -
Example:
chmod 754 file.txt:7→ Owner: Read (4) + Write (2) + Execute (1) =rwx.5→ Group: Read (4) + Execute (1) =r-x.4→ Others: Read (4) =r--.
-
-
Example Command:
chmod 755 file.txt- Explanation:
- Owner:
rwx(7). - Group:
r-x(5). - Others:
r-x(5).
- Owner:
- Output: Updates the permissions of
file.txtto allow the owner full access, while the group and others can only read and execute.
- Explanation:
-
Special Cases:
-
If the file starts with
d, it is a directory.- Example:
ls -ldrwxr-xr-x 2 user group 4096 Oct 10 12:00 my_directory- The
dat the beginning indicates thatmy_directoryis a directory. - To change the permissions of this directory:
chmod 755 my_directory- Explanation: Grants the owner full access (
rwx), and read/execute permissions (r-x) to the group and others.
- Example:
-
If the file starts with
-, it is a regular file.- Example:
ls -l-rw-r--r-- 1 user group 1024 Oct 10 12:00 my_file.txt- The
-at the beginning indicates thatmy_file.txtis a regular file. - To change the permissions of this file:
chmod 644 my_file.txt- Explanation: Grants the owner read/write permissions (
rw-), and read-only permissions (r--) to the group and others.
- Example:
-
-
Chmod Calculator:
- Use Chmod Calculator to easily calculate permissions.
-
-
top: Displays real-time system processes and resource usage.- Example:
top - Output: Displays CPU, memory usage, and running processes.
- Example:
-
ps: Displays information about running processes.-
Example:
ps -
Output:
PID TTY TIME CMD 1234 pts/0 00:00:01 bash 5678 pts/0 00:00:00 ps -
Options:
-
-a: Shows all processes associated with terminals.- Example:
ps -a - Output:
PID TTY TIME CMD 1234 pts/0 00:00:01 bash 5678 pts/0 00:00:00 ps 9101 pts/1 00:00:02 vim
- Example:
-
-ef: Displays detailed information about all processes.- Example:
ps -ef - Output:
UID PID PPID C STIME TTY TIME CMD root 1 0 0 10:00 ? 00:00:01 init user 1234 1 0 10:01 pts/0 00:00:01 bash user 5678 1234 0 10:02 pts/0 00:00:00 ps
- Example:
-
-
-
kill: Terminates a process by its PID.- Example:
kill 1234 - Explanation: The PID (Process ID) can be obtained using commands like
psortop. For example, runningpswill list the currently running processes along with their PIDs. - Output: Terminates the process with PID
1234.
- Example:
-
vim: Opens a file in the Vim text editor.- Description: Vim (Vi IMproved) is a highly configurable and powerful text editor used for efficiently creating and editing text files. It is widely used by developers and system administrators due to its versatility and extensive features.
- Note: Vim needs to be installed before use.
- Installation Command:
sudo apt install vim
- Installation Command:
- Example:
vim file.txt - Usage:
- Press
ito enter insert mode. - Press
Escto exit insert mode. - Type
:wqto save and exit. - Type
:qto exit without saving.
- Press
-
sudo: Executes commands with administrative privileges.- Example:
sudo apt update - Output: Updates the package index.
- Example:
-
su: Switches to another user account.- Example:
su username - Output: Switches to the specified user.
- Example:
-
sudo su: Temporarily switches to the root user.- Example:
sudo su - Output: Grants root access.
- Example:
-
apt: Manages software packages.- Examples:
sudo apt update: Updates the package index.sudo apt upgrade: Upgrades all installed packages.sudo apt install packageName: Installs the specified package.sudo apt remove packageName: Removes the specified package.sudo apt purge packageName: Removes the package and its configuration files.sudo apt autoremove: Removes unnecessary dependencies.
- Examples:
-
ping: Tests the reachability of a host on a network.- Example:
ping google.com - Output:
PING google.com (142.250.190.78): 56 data bytes 64 bytes from 142.250.190.78: icmp_seq=0 ttl=118 time=14.2 ms - Explanation: Sends ICMP echo requests to the specified host and measures the response time.
- Example:
-
ifconfig: Displays or configures network interfaces.- Example:
ifconfig - Output:
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 192.168.1.10 netmask 255.255.255.0 broadcast 192.168.1.255 - Explanation: Shows details about the network interfaces, such as IP address and netmask.
- Example:
-
netstat: Displays network connections, routing tables, and interface statistics.- Example:
netstat -tuln - Output:
Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN udp 0 0 0.0.0.0:68 0.0.0.0:* - Explanation: Lists active network connections and listening ports.
- Example:
-
curl: Transfers data from or to a server using various protocols.- Example:
curl http://example.com - Output: Displays the HTML content of the specified URL.
- Example:
-
wget: Downloads files from the web.- Example:
wget http://example.com/file.zip - Output: Downloads
file.zipto the current directory.
- Example:
-
df: Displays disk space usage.- Example:
df -h - Output:
Filesystem Size Used Avail Use% Mounted on /dev/sda1 50G 20G 30G 40% / - Explanation: Shows the available and used disk space in a human-readable format.
- Example:
-
du: Displays disk usage of files and directories.- Example:
du -sh /home/user - Output:
1.2G /home/user - Explanation: Shows the total size of the specified directory.
- Example:
-
mount: Mounts a filesystem.- Example:
mount /dev/sdb1 /mnt - Output: Mounts the device
/dev/sdb1to the/mntdirectory.
- Example:
-
umount: Unmounts a filesystem.- Example:
umount /mnt - Output: Unmounts the filesystem mounted at
/mnt.
- Example:
-
fdisk: Partition management tool.- Example:
fdisk /dev/sda - Output: Opens an interactive session to manage partitions on
/dev/sda.
- Example:
-
tar: Archives files into a single file.- Example:
tar -cvf archive.tar file1 file2 - Output: Creates an archive named
archive.tarcontainingfile1andfile2.
- Example:
-
gzip: Compresses files.- Example:
gzip file.txt - Output: Compresses
file.txtintofile.txt.gz.
- Example:
-
zip: Compresses files into a zip archive.- Example:
zip archive.zip file1 file2 - Output: Creates a zip archive named
archive.zipcontainingfile1andfile2.
- Example:
-
unzip: Extracts files from a zip archive.- Example:
unzip archive.zip - Output: Extracts the contents of
archive.zipinto the current directory.
- Example:
-
uptime: Displays system uptime and load average.- Example:
uptime - Output:
10:00:00 up 5 days, 3:42, 2 users, load average: 0.00, 0.01, 0.05 - Explanation: Shows how long the system has been running and the average system load.
- Example:
-
free: Displays memory usage.- Example:
free -h - Output:
total used free shared buff/cache available Mem: 8.0G 2.5G 4.0G 500M 1.5G 5.0G Swap: 2.0G 0.5G 1.5G - Explanation: Shows the total, used, and available memory in a human-readable format.
- Example:
-
vmstat: Displays system performance statistics.- Example:
vmstat 1 - Output:
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 1 0 0 4000M 1000M 2000M 0 0 0 0 100 200 5 1 94 0 0 - Explanation: Provides real-time statistics on CPU, memory, and I/O usage.
- Example:
-
Absolute Path: Starts with
/and specifies the full path.- Example:
/home/user/file.txt
- Example:
-
Relative Path: Does not start with
/and is relative to the current directory.- Example:
file.txt
- Example:
$: Represents a regular user.#: Represents a super user (root user).