Basic Unix/Linux Command Reference For Absolutely Beginners

File Commands for Ubuntu or Any Linux Distro

Written by Knight

1. ls – directory listing
2. ls -al – formatted listing with hidden files
3. cd dir – change directory to dir
4. cd – change to home
5. pwd – show current directory
6. mkdir dir – create a directory dir
7. rm file – delete file
8. rm -r dir – delete directory dir
9. rm -f file – force remove file
10. rm -rf dir – force remove directory dir *
11. cp file1 file2 – copy file1 to file2
12. cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it doesn’t exist
13. mv file1 file2 – rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
14. ln -s file link – create symbolic link link to file
15. touch file – create or update file
16. cat > file – places standard input into file
17. more file – output the contents of file
18. head file – output the first 10 lines of file
19. tail file – output the last 10 lines of file
20. tail -f file – output the contents of file as it grows, starting with the last 10 lines

Process Management

1. ps – display your currently active processes
2. top – display all running processes
3. kill pid – kill process id pid
4. killall proc – kill all processes named proc *
5. bg – lists stopped or background jobs; resume a stopped job in the background
6. fg – brings the most recent job to foreground
7. fg n – brings job n to the foreground

File Permissions

1. chmod octal file – change the permissions of file to octal, which can be found separately for user, group, and world by adding:
   ● 4 – read (r)
   ● 2 – write (w)
   ● 1 – execute (x)
2. Examples:
   ● chmod 777 – read, write, execute for all
   ● chmod +x filename – execute for filename
   ● chmod 755 – rwx for owner, rx for group and world. For more options, see man chmod.
   
   

SSH – Secure Shell

ssh user@host – connect to host as user

ssh -p port user@host – connect to host on port port as user

ssh-copy-id user@host – add your key to host for user to enable a keyed or passwordless login

Searching

grep pattern files – search for pattern in files

grep -r pattern dir – search recursively for pattern in dir

command | grep pattern – search for pattern in the output of command

locate file – find all instances of file

System Info

date – show the current date and time

cal – show this month’s calendar

uptime – show current uptime

w – display who is online

whoami – who you are logged in as

finger user – display information about user

uname -a – show kernel information

cat /proc/cpuinfo – cpu information

cat /proc/meminfo – memory information

man command – show the manual for command

df – show disk usage

du – show directory space usage

free – show memory and swap usage

whereis app – show possible locations of app

which app – show which app will be run by default

Compression

tar cf file.tar files – create a tar named file.tar containing files

tar xf file.tar – extract the files from file.tar

tar czf file.tar.gz files – create a tar with Gzip compression

tar xzf file.tar.gz – extract a tar using Gzip

tar cjf file.tar.bz2 – create a tar with Bzip2 compression

tar xjf file.tar.bz2 – extract a tar using Bzip2

gzip file – compresses file and renames it to file.gz

gzip -d file.gz – decompresses file.gz back to file

Network

ping host – ping host and output results

whois domain – get whois information for domain

dig domain – get DNS information for domain

dig -x host – reverse lookup host

wget file – download file

wget -c file – continue a stopped download

Installation

Install from source:

./configure

make

make install

dpkg -i pkg.deb – install a package (Debian)

rpm -Uvh pkg.rpm – install a package (RPM)

Shortcuts

Ctrl+C – halts the current command

Ctrl+Z – stops the current command, resume with

fg in the foreground or bg in the background

Ctrl+D – log out of current session, similar to exit

Ctrl+W – erases one word in the current line

Ctrl+U – erases the whole line

Ctrl+R – type to bring up a recent command

!! – repeats the last command

exit – log out of current session

* use with extreme caution.

Dangerous Command

rm -rf / -> This will destroy the whole Linux.

:(){ :|: & };: -> Dangerous function of Batch

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