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commands in Linux/Ubuntu:
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
Text Editos
1-vi <file_Name>
it has 3 Modes:
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
2- nano <file_name>
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
default input for shell is Keyboard
default output for shell is monitor
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
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
ls *.txt >> list all .txt files
grep <option> <pattern> <file>
grep error *.log
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
We set rules of a group and another rules per specific user
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
Execute the directory means to open it
the need to create a file that can be read by all people but user and his group: VIRUS
change file Permissions:
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
change ownership:
chown -R Abdeen /home/myFolder #Makes Abdeen the new owner of all files in myFolder directory
Shell built-in commands:
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
type grep
.deb : debian is the software installer for debian
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
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>
Question: how to know block size in linux?
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...
File descriptor : contains file inode and something like a cursor(another pointer) to where the current cursor is..
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...