UNIX (Linux) Introduction Module-1

OS Kernel In computing, the kernel is the central component of OS. It is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources (the communication between hardware and software components).

CPU It runs the operating system and applications, constantly receiving input from the user or active software programs.operating systemapplicationsinput It processes the data and produces output, which may stored by an application or displayed on the screen.output The world's first CPU was introduced by Intel in The Intel 4004 was a 4-bit CPU, clocked at 740 KHz and capable of executing up to 92,600 instructions per second. Five months after the Intel 4004, the Intel 8008 was introduced. This was the world's first 8-bit microprocessor. INTEL (x86) SPARC IBM POWER AMD

Open Source? Software & Source code available to all Freedom to distribute software and source code Ability to modify and create derived works Integrity of author’s code FEDOROA Project community support Personal systems RHEL (Red hat Enterprise Linux) Stable, thoroughly tested software Professional support servers Centralized Management tools for large networks

UNIX Principles Everything is a file (including hardware) Small, single purpose programs Ability to chain programs together to perform complex tasks Configuration data stored in text

Logging in to a Linux System Two types of login screens: Virtual consoles (Text based) & Graphical logins (display managers) RHEL use GNOME/KDE display manager Run-level -3 is a text based Up-to 6 virtual consoles & one graphical console Switch among the virtual consoles ( Ctrl-Alt-F[1-6]) Access the graphical console by typing Ctrl-Alt-F7

Root User: Special administrative account Also called super user Root has complete control over system How to login as root: SU creates new shell as root SUDO commands runs command as root command shows who you are?

Editing text files: Nano Gedit Vim Gvim VI

Important Directories Home Directory - /root, /home/ User Executables - /bin, /usr/bin,/usr/local/bin System Executables - /sbin, /usr/sbin, /usr/local/sbin Other mounts - /media, /mnt Configuration - /etc Temporary files - /tmp Kernels & boot loader - /boot Server Data - /var, /srv System information - /proc, /sys Shared libraries - /lib,/usr/lib, /usr/local/lib

Run Levels A run-level is a system state that is defined by the services listed in /etc/rc.d. Configuration file to update runlevel $ vi /etc/inittab  update line “ id:3:initdefault: To check which run level your are now $ Who -r You can change the run level just by typing # init0 or init6 # init 5 LEVELNAMEDESCRIPTION 0Halt Immediately shuts down system and powers it off, if it can 1Single user Brings system to a bare essentials mode for maintenance 2User-definedCustom 3 Multi-user with console only All services are running but X11 4User-definedCustom 5 Multi-user with display and console All services are running including X11 (or GUI) 6RebootReboots the machine

Login to running server: (Things to check) Server Name OS Patch level Run level OS release Memory /SWAP CPU count/type Harddiks Any one logged in ? Hardware detail? ……continue

Login to running server: (Things to check) File system detail Any volume manager? Logical volumes? Physical volumes? What process running? System load? IP address?

RHEL Versions: