1. ls
Lists the contents of a directory.
ls- Lists files and directories in the current directory.ls -l- Lists with detailed information including permissions, owner, size, and modification date.ls -a- Lists all entries including hidden files starting with..
2. cd
Changes the current directory.
cd /path/to/directory- Changes to the specified directory.cd ..- Moves up one directory level.cdorcd ~- Changes to the user's home directory.
3. pwd
Prints the current working directory.
pwd- Outputs the full path of the current directory.
4. cp
Copies files or directories.
cp source_file destination_file- Copies a file.cp -r source_directory destination_directory- Recursively copies a directory.
5. mv
Moves or renames files and directories.
mv source destination- Moves or renames files or directories.
6. rm
Removes files or directories.
rm file- Deletes a file.rm -r directory- Recursively deletes a directory and its contents.
7. mkdir
Creates a new directory.
mkdir directory_name- Creates a new directory.
8. rmdir
Removes empty directories.
rmdir directory_name- Removes an empty directory.
9. chmod
Changes the permissions of files or directories.
chmod 755 file- Changes the permissions of a file to read, write, and execute for the owner, and read and execute for others.
10. chown
Changes the owner and/or group of files or directories.
chown user:group file- Changes the owner and group of a file.
11. top
Displays running processes and system resource usage.
top- Opens an interactive monitor displaying system processes and resource usage.
12. df
Shows disk space usage.
df- Shows the amount of disk space used and available on all mounted filesystems.df -h- Displays the space in human-readable form (e.g., KB, MB, GB).
13. du
Shows the disk usage of files and directories.
du -sh directory- Shows the total size of a directory in a human-readable format.
14. grep
Searches for patterns in text.
grep "pattern" file- Searches for a pattern within a file and prints lines containing the pattern.
15. echo
Displays a line of text/string that is passed as an argument.
echo "Hello, World!"- Prints "Hello, World!" to the terminal.
16. cat
Concatenates and displays files.
cat file- Displays the contents of a file.
17. tail
Displays the last part of files.
tail file- Shows the last 10 lines of a file.tail -f file- Continuously monitors the end of a file, useful for logs.
18. head
Displays the first part of files.
head file- Shows the first 10 lines of a file.
19. man
Displays the manual pages for commands.
man command- Shows the manual for the specified command.
20. sudo
Executes a command with superuser privileges.
sudo command- Executes the command as the superuser.
These commands form the backbone of the Ubuntu command-line interface and are critical for daily operations and system management. Each command typically has a man page (e.g., man ls) which provides detailed usage information, options, and examples.