cmds.txt

commands in Linux/Ubuntu:
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echo $SHELL --> echo shell path

ls -a --> list (a)ll files including hidden files

ls -l -->list all files with their information

ls -hl --> list all files with their information in a human readable format.

touch fileName.txt

pwd (print working directory): print current directory.

echo "mytext" > mytext.txt : insert text into mytext file.

history --> To list all commands ...

man <cmd> : to get cmd manual

man -k <word> EX: man -k list

apropos <keyword>: Search man pages by keyword EX: apropos ls
if you found a number like (2) that number indicates the section of this command in the manual

info <cmd>: Get command info EX: info ls

whatis <cmd>: Get a brief about a specific command and  returns its section in manual page (in circular braces () )EX: whatis ls

uname -a : Get full info about your device (After laptop name is the Kernel version)

uptime: Show you the time elapsed from the boot up till now

cd ~: change directory to home directory

cd - : change directory to the previous directory

There's no rename in linux we move the folder to the same directory with a different name = Rename :)

rm <Dir_Naem>: remove directory only if it's empty

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Text Editos
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1-vi <file_Name>

it has 3 Modes:
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1- Insert Mode: Press i then insert your text
2- Navigate
3- Command mode(One line Mode) (To exit: ESC then : then q ) (To exit and save: ESC then : then wq) w for write and q for quit
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2- nano <file_name>


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bash : is an implementation of shell

Fish : is an implementation of shell has an autocomplete feature...more or advanced GUI for shell

Power shell : is a linux shell implemented on windows

Note:
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default input for shell is Keyboard

default output for shell is monitor
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more ~/.bashrc
less ~/.bashrc
head -n <file_Name> : head -10 ~/.bashrc (echo the first 10 lines in that file)
tail -n <file_Name> : tail -10 ~/.bashrc (echo the last 10 lines in that file)
diff <file_One> <file_Two> : shows the difference between two files
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Wildcards(Globbing):
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to do an operation to a group of files at once
* is a wild card represents 0 or more character or number
? any character
[] range of characters EX ls [a-z]
{} group of wild cards

EX:
    ls *.txt >> list all .txt files
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grep <option> <pattern> <file>

EX:
  grep error *.log

clear
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29/11/2018
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Permissions:
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password in linux (passwd): hide the letters and password
Password is a file that contains user password and info...

>> cat /etc/passwd
| pipe sign will redirect the output of a command to be the input of another commands

>> cat /etc/passwd | grep "Amr Abdeen"

>> man <section_num> <cmd>
EX: man 5 passwd

password is saved in another file called shadow but it needs sudo

id >> returns the user ID
uid==> user id

whoami ==> return user fileName

exit ==> exit the terminal

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We set rules of a group and another rules per specific user
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Unix like OS : Follow Unix standard

sudo:super user do :gives the privileges of super user temporarily for 15 minutes

/etc/sudoers ---> contains super users names

su <user-name> : Switch user from terminal

change root user(super user) password: sudo passwd root

to exit root user : exit

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Execute the directory means to open it
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the need to create a file that can be read by all people but user and his group: VIRUS

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change file Permissions:
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chmod <Permissions> <files> : change Mode of a file

  chmod <digit1><digit2><digit3> <fileName> : each digit represents a rwx operations for each part (user,group,Others)

  chmod 777 fileName

  digit1=7=> 4+2+1 >read/write/execute

                    4= 0b100 >read
                    2= 0b010 >write
                    1= 0b001 >execute

digit2=7=> the same for group

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change ownership:
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chown -R Abdeen /home/myFolder #Makes Abdeen the new owner of all files in myFolder directory
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Shell built-in commands:
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sudo should execute a program (binary)

to know if the command is a program or a script use: type <cmd>

if its type in /bin directory it's a program
if it's hashed it means it's in a hash table
if it's shell builtin it means it's a program within the shell itself
....
....
....
EX:
    type grep
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.deb : debian is the software installer for debian
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cd - : change directory to previous directory (like back in windows)
cd is a builtin command so if you want to know its information you should use :
help cd #help is a program
NOTE: --->whatis will not work with cd
          info will not work with cd

*To make nested folders : cd -p {folderOne/folderTwo/folderThree}

* you can create multiple files @ once using : touch dirName/fileName{startNum..EndNum}.extension
                                          EX:  touch myDir/myFile{1..5}.txt


Home directory contains all users folders
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File hierarchy:
----------------
everything is a file

process is a task in the running state

Hard disk is a file
Device is a file

partition table : contains start/End of each partition

File System is methodology for storing the Permissions of files access/files numbers per partition/...etc
it consists of File system metadata and File System data.

File system is per each partition.

File system meta data consists of:

            1- inode(index-node) which is a part of file system metadata
              each inode (wit unique node ID) contains file creation ,file size , user Creator, modification , etc...
              each file is attached to a specific node...

            2- dentry(directory entery) Cache: contains file name , column ID in inode , file's parent
              *parent is a file that has a parent until ROOT which is the parent of itself.

-->To show ID for each file : ls -i or ls -il
-->To Show all information about that file: stat <fileName>
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Question: how to know block size in linux?
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File ID may be reused if the older file is deleted...

df --> list all partitions with their information

df -i | less : to list all partitions with their inodes data


*When moving a file from directory to another in the same partition the inode will be the same
but the dentry will be changed.

*when moving a file form file system to another file system it will copy the file itself , its inode , dentry , ...

*open: open a file inside C Program and returns File descriptor...

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File descriptor : contains file inode and something like a cursor(another pointer) to where the current cursor is..
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***************************************************************
Assignment: Links:Hard Link vs Symbolic
            Journal in Linux/Ubuntu
***************************************************************

Backward compatible: if newer version of a program it will support the previous versions of OS like 98,XP,Vista,7,...

Kernel contains a file system driver for each file system...

>> file <file_name> : list file information
>> xxd <file_name> : show HEX representation of a file

>> File Signature=magic number: found in file header indicates file extension...

>>
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