# Filesystem

# Directories

root has the following directories:

• etc. Configuration files.
• proc. System information.
• home. All the users.
• boot. Operating system lives here.
• dev. Where devices are mounted. sda is main disk, sdaX are partitions (Mounted as block files).

tree DIRECTORY - Show directory tree. tree . for current. Needs to be donwloaded with sudo apt-get install tree.

# Files

Plain text file > Compilation > Binary (.exe) i.e. package. Ubuntu is simply a collection (repository) of pre-compiled packages, running over a kernel (Big pile of software that knows how to make the hardware do stuff).

"On a UNIX system, everything is a file; if something is not a file, it is a process." (directory is a file containing names of other files)

File extensions are meaningless. They are there for the user's sake.

There are 7 types of files, which can be recognized by using ls -l and looking at the first bit:

1. Normal. Images, text, config...
2. Directory. File pointing to files.
3. Link. Shortcut/Redirect.
4. Pipe. Use a process output as input for another.
5. Character Device. Input/Output files Ex. Teminal.
6. Block. Used for block devices. Ex. Hard Disk.
7. Socket. Used for Interprocess Communication.
   • Unix Socket. Local machine only (Superfast). Ex. Nginx communicates with a PHP interpreter.
   • TCP Socket. Exposed to network (Slower). Ex. Nginx communicates with a website visitor.

# Interprocess Communication (IPC)

In Linux, everything is a file. There are special files like sockets that allow processes to communicate with each other without dangerously sharing memory.

Sockets are files where processes can write stuff, and other processes can listen in real time.