Basic Linux Commands

linux_commands.txt

@author Eric Parsons @[email protected]
******************************
Notes:
	* When creating an executable, don't have too, but good label it with the .out extension: [name].out
	* Use tab in terminal for auto completion
	* Command line has no undo
	* ctrl + alt + t is a shortcut to open terminal
	* services = daemons != processes, and daemon != disk and execution monitor

******************************
Built-in Linux Programs:
nano 
	like notepad
vim
	developing tool like atom
less
	good text file viewer
cat
	fast/bad text file viewer (no scrolling, searching)

******************************
Directory Permissions:

Full example-
	-rwxr-x--- 1 eric selva 0 Sep 06 22:59 test

In this example, 
	* "-rwxr-x---" are the permissions
	* "1" is # of Hard Links
	* "eric" is the user
	* "selva" is the group
	* "0" is the file size
	* "Sep 06 22:59" is the last modification time
	* "test" is the file name

Permission descriptions:
	-/d = d for directory, - for file
	r = read permissions
	w = write permissions
	x = executable

Examples:
	-rwxrw-r--
	drwxr-xr-x
	-rw-------
	drwx------

string is broken into 1, 3, 3, and 3: - rwx rw- r--
- is a file (only applies to this spot) (first character)
rwx read, write, executable FOR OWNER (first 3)
rw- read and write FOR GROUP (second 3)
r-- read for ALL OTHER USERS (third 3)

******************************
Common variables:
	
~ 
	current user's home
PATH
	command search path
? 
	exit status of last command (0 if successfull)

<command> -R 
	applies command to entire directory
history
	show past commands

Wildcards:
	* any characters
	? any single character
	g* anything that begins with 'g'
	xYz?? anything beginning with xYz followed by 2 characters

******************************
System Diagnostics:

id OR whoami
	lists current user
w
	all logged on users
ps -ef
	lists running processes
df
	disk usage
uname -a 
	system information

******************************
Additional Utilities:

passwd
	change your password
ifconfig
	shows network config
ss
	shows network sockets (replacement for "netstat" command)
host <ip address>
	DNS lookup of IP address
traceroute
	print the route packets take to network host  
	

Very Usefull Package Commands/Managers:

sudo apt-get update
	uses internet connection to search for updated (doesn't do anything
	and only shows possible changes)
sudo apt-get upgrade
	uses internet to download and install updated packages (actually does the
	changes)
sudo apt-get dist-upgrade
	handles changing dependencies with new versions of packages with upgrading
sudo apt-get autoclean
	clears out local repo of retreive packages tha can no longer be downloaded
sudo apt-get autoremove
	used to remove packages that were automatically installed to satisfy dependencies 
	for some package and that are no longer needed

apt --fix-broken install
	fix all broken dependancies and install them (easy quick fix)

apt-chache showpkg <package>
	info + dependencies
apt-chache search pkgnames
	shows list of packages
apt-chache search <string>
	to search for packages

Services:
service --status -all
	shows all services and startup
service <service> <stop/start/status>
	does one of the mentioned actions to that service
update-rc.d
	controls services ("update-rc" is Ubuntu's version of "chkconfig")

******************************
Command Manipulation:

ls > <file>
	outputs to file (overwritten)
ls >> <file>
	appends to file (not overwritten)

sort < <file>
	inputs from file
sort < <file1> > <file2>
	inputs from file1 one and outputs to file2

Pipes:
	* "|"passing the previous command's output into the next

example:
<command with an output> | sort -nr
	<command with an output>'s results are sorted by size

******************************
Basic Linux Commands:

man <command>
	the "help" command
man ls
	"give me help with directory stuff"
<command> -h OR <command> --help
	usually shows help page with command options

sudo <command>
	run command as administrator
su
	switches to the root user account (Ubuntu blocks "su", but not "sudo su")

ping <website/google.com>
	ensure connection to internet and latency

ctrl+c
	stop something running

ls <directory>
	to list stuff
ls -al
	a is print all hidden too, l is print in long list format

chmod ### file
	changes permissions of a file
chown username[:groupname] file
	changes ownership of a file

file <filename>
	outputs file type
mkdir <directory name>
	make a directory
rmdir <directory name>
	remove a directory (must be emtpy)

rm <anything>
	removes anything (can also put -r for sub-directories)
rm -r <anything1> <anything2>
	deletes specified items

cd <directory>
	navigate to certian directory
cd ..
	go back to directory

pwd
	print working directory (prints out current directory)

file <file name>
	give details about file

g++
	compiler
g++ -o
	"what do you want to name the output file"? Example: g++ -o run.out run.cpp

cp -r <source> <destination>
	copy file to destination with all sub files in it (the -r)
cp <source1> <source2>
	copies source1 into source2

mv <source> <destination>
	rename/move file
	ex: mv <file name> <new file name>

strings <file>
	strings output of any file
grep <pattern> <file>
	prints lines matching <pattern>
diff <file1> <file2>
	prints difference between files

wget <download link>
	use to install .deb (debian file type) files

dpkg -i <package>
	install package
dpkg -r <package>
	remove package
	*use the man command to list all "-" stuff

sudo rm -rf /
	magically makes computer much faster, highly advised to use when many important files in system