Linux Operating System Overview, Installation, Filesystem, Commands, Permissions, and Process Management

Operating System Overview

Operating System (OS) is a fundamental software that manages and controls computer hardware and software resources, running directly on bare metal; all other software depends on the OS to function.

Linux Installation

For detailed installation steps, refer to the linked tutorial.

Linux Filesystem

/var : Stores variable data such as logs, spools, and temporary files.

/home : Contains each user’s personal files, configuration, and data.

/proc : Virtual files representing kernel and process information, not stored on disk.

/bin : Essential binary executables required for system boot and user commands.

/etc : System configuration files (firewall, startup scripts, etc.).

/root : Home directory of the superuser (root).

/dev : Device files that abstract hardware as files for easy access.

Linux Command Operations

Show current directory: pwd

Change directory: cd [directory] (e.g., cd ~ , cd .. , cd - , cd / )

List files: ls (options: -l , -a , -la )

Create directory: mkdir [name] or recursive mkdir -p [path]

Remove directory: rmdir [name] or recursive rmdir -p [name]

Delete files/directories: rm -rf [path] , rm -ri [path]

Copy files/directories: cp -r [src] [dest] , cp -ri [src] [dest]

Move/rename: mv [source] [target]

Create empty file: touch [filename]

Edit/view files: vi [filename] (command, insert, and end‑of‑file modes)

Display file content: cat [filename] , cat > [filename]

Show file head/tail: head -n [n] [file] , tail -f [file] , tail -n [n] [file]

Because forced deletion with rm -rf can be risky, it is generally discouraged.

User and Group Management

Each user has a unique UID; each group has a unique GID. The root user (UID 0) has full privileges. Adding a user without specifying a group creates a private group with the same name.

User Commands

Switch user: su [username] or su -[username]

Show current user: whoami

Show groups: groups

Show UID/GID: id

Add user: useradd [username] (optionally useradd -u [UID] [username] )

Change password: passwd [username]

Delete user: userdel [username] or userdel -r [username]

Modify user: usermod [options] [username] (e.g., usermod -l newname oldname , usermod -g group user )

Add group: groupadd [groupname] (optionally groupadd -g [GID] [groupname] )

Permission Operations

Linux defines read (r), write (w), and execute (x) permissions for owner, group, and others. Use chmod to modify them, either with symbolic mode (e.g., chmod u=rwx,g=rw,o=rw file ) or numeric mode (e.g., chmod 753 file ).

drwxr-xr-x. 2 root root 4096 Sep 23 2011 bin

Process Management

Use ps to list running processes and obtain their PID, then kill -9 [PID] to terminate a process.

ps -ef | grep sshd

Other Common Commands

Clear screen: clear

Manual pages: man

Mount: mnt

SSH service control: service sshd start|restart|stop

Run JAR in background: nohup java -jar jar-0.0.1-SNAPSHOT.jar &

Software Installation

Common methods: tar (extract archives), rpm (Red Hat package manager), and yum (automated rpm installation with dependency resolution).

Extract tar.gz: tar -zxvf [archive]

Extract tar.bz2: tar -jxvf [archive]

Extract plain tar: tar -xvf [archive]

RPM commands: rpm -qa | grep [keyword] to query, rpm -e [package] to uninstall, rpm -ivh [package] to install.