notes.txt

TCP/Inspection

OSI Layers:

1. Physical
2. Data
3. Netowrking
4. Transport
5. Session
6. Presantation
7. Application

ping/pong --> ICMP Echo/Reply

Linux dist = kernel + collections of software

----- Traps & Signals -----

kill -l --> list all the signals

SIGINT --> ctl + c

exit 1; --> terminates the scrit

----- Jobs managements -----

ps aux | grep <name of the job>
jobs --> list all jobs
job & --> run the job in the background

standart workarounds

jobs --> list backgound users jobs

pgrep <job-name>

ps aux | grep <job-name>

PID of the job and whatever you want
 
----- Permissions -----

file --> -
dire --> d

4 --> r
2 --> w
1 --> x

----- Redirections -----

stdin --> 0
stdout --> 1
stderr --> 2

ls -l output111111.txt > filename11111111111.txt 2>&1 --> try to list file that doesn't exist and print message in second file form 1 where 2 is redirected

exec 3<>log_file.txt

echo "Tesssttttt">&3 --> write output in log_file.txt e.g. 3 

exec3>&- unlink/bad file descriptor



----- Wildcards, Regex, finds, greps -----

find */ -name test.* --> will find every file named test no matter what extention in the next directory

find . -maxdepth 2 -iname *.py --> will find py file in 2 dir up

--------------------------------|
. --> level 1 			|
				|
/next/ --> level 2 		|--> maxdepth explain
				|
/next/onemore/ --> level 3	|
...etc				|
--------------------------------|

Examples:
---------------------------------------------------------------------------------------------------------
find . -iname *.py -o -iname *.sh --> find all files sh or py

find . -maxdepth 3  -iname "*.sh" -a -iname "*tests*" --> find file shell extention containing 'tests'

find . -maxdepth 2 -type d -name 'tests*' --> find a directory starts with tests*

find . -type f -iname '.vim*' --> find a hidden files of vim

find . -type f ! -perm 777 --> files that doesn't have permissions 777

sudo find /home -user hadoop --> find all files that belong to user hadoop 

find . -iname "*.py" | xargs ls -la {} \n; 
 
---------------------------------------------------------------------------------------------------------
Global Regular Expression Print(grep):

grep 'test' file.txt --> search for 'test' in file.txt
grep -r 'test' * --> search for 'test' recursively
grep -riv test * --> search for everything except 'test'
grep -c "test" file1.txt --> count "test" in file1.txt 
---------------------------------------------------------------------------------------------------------
AWK & SED

sed 's/,/-/g' <file_name> --> replace all ',' with '-' ;

awk syntax

BEGIN {
	# substitute space with a tab
	FS=" ";
	OFS="\t\t";
	print "Date\t\tPrice\t\tVolume";
	print "-----\t\t----\t\t------";
};
{
	print{$1, $2, $7}
};

Systems:

lscpu --> list cpu info
lsusb --> list usb

Glob and Expand
*: Match zero or more characters
?: Match any single characters (expect ".")
[]: Match any of the eclosed characters

{}: Expand contents
{A,B...}: Expand each alternatives
{A..B}: Expand each character in range


Mounting

fdisk -l

cd /etc/fstab

device 		point
/dev/xvdf1 	/var/www/html/images ext4 defaults 0 0 

mount -a

vim /etc/selinux -> disabel