session-13.txt

Linus File system heirarchy

/bin -> essential user binaries/softwares/commands
/boot -> OS booting process commands or files
/dev -> devices. everything in Linux is file including keyboard, mouse, disk, USB, etc.
/etc -> extra configuration. Configurations related to system or user installed packages are here
/home -> any user related directories are here, /home/<username>
/lib and /lib64 -> all required libraries are here..
/media -> removable disks like usb, DVD, etc, are mounted here automatically in desktop environments
/mnt -> used to mount extra disks in linux server are here for temp purpose
/opt -> optional. when you installed a software manually you do it here. /opt/roboshop, /opt/tomcat, /opt/jobss etc.
/proc -> processor information, /proc/cpuinfo, /proc/meminfo. running process info is here related to kernel
/root -> root user home directory
/run -> running process information 
/sbin -> essential root user binaries/softwares/commands
/srv -> service, data related to system like HTML directory, NFS directory, etc.
/swap -> virutal RAM. swap usage is more means system is under stress
/sys -> kernel sub systems
/tmp -> temporary directory in linux
/usr -> user related commands and libs are here
/var -> variable files, continously growing files are here

Hard Disk vs Network Disk
=========================
hard disk near to comupter
network disk, any where in the internet like google drive, MS drive, S3, etc..

OS, DB always should be in HD, HD latency is less
normal files and objects are stored in network storages

at a time one HD can be mounted to only one computer.
Network storages can be attached to multiple computers


How to add extra disk to Linux server
=====================================
1. create EBS volume
2. attach to the instance, EBS volume should in the same AZ as EC2

nvme0n1 -> root disk -> OS default purpose
nvme1n1 -> new disk -> database data, imp files and configurations are stored here..

3. list the block devices, you can see newly attached disk
4. create partition from the disk
sudo parted /dev/nvme1n1 --script mklabel gpt mkpart primary 0% 100%

/var/lib/mysql -> mysql data is stored here
/data -> redis


UUID="0683949b-ce15-4d77-b202-4d47ee2a863a"

UUID=0683949b-ce15-4d77-b202-4d47ee2a863a   /data   xfs   defaults,nofail   0   2


memory usage commands
===================
df -hT -> disk information
free -m -> RAM usage

top 10 usages
ps aux --sort -rss | head -10

du -sh *
memory occupied by files and folders

growpart nvme1n1 1

xfs_growfs /data

tomorrow topics
===============
inode, hardlink and symlink
Shell scripting