1. Linux Architecture Overview 1

2. Initialization Uboot – hardware init, loads kernel Kernel – remaining initialization, calls “init” Init – 1 st process, executes startup script – /etc/init.d/rcS Run_flphone.sh – startup script Nano-X – the X-Windows server Nanowm – sets bg image 2

3. System Structure MicroKernel – minimal functionality – Interprocess communication (IPC) – Memory management Autonomous processes & co-routines – VFS – Network stack – Process manager – Device drivers Non-kernel – windowing system – compiler – shells – Editors – utilities 3

4. System Structure 4 Kernel + h/w related code System Call Interface User mode space Device drivers Kernel mode space

5. System Structure-2 5 Sockets VFSVmem Process Control NFS TCP, IP, etc Proc, sysfs File sys’s mmap MM Process memory IPC Char dev’s Block Devices cache Scheduler Net Mgmt Device Module Bus drivers Net drivers Block Drivers Memory access Interrupts swap Char Drivers System Calls get us to these functionalities Bus controller Net adapter Monitor, keybd Disk controller CPU circuits MMU, RAM

6. Structural Problems Erroneous co-routines can block system Formal interfaces slow down system 6

7. Directory structure 7

8. System directories /bin Essential user command binaries that need to be available also in single user mode. /sbinEssential system binaries (e.g. init, insmod, ifup) /libLibraries for the binaries in /bin and /sbin /usr/binNon-essential user command binaries that are not needed in single user mode /usr/sbinNon-essential system binaries (e.g. daemons for network- services) /usr/libLibraries for the binaries in /usr/bin and /usr/sbin /etcHost-specific system-wide configuration files /devDevice files /homeUser home directories (optional) /procVirtual file system documenting kernel and process status as text files 8

9. © 2004, D. J. Foreman9 Basic Transitions # ready queues may be >1

10. © 2004, D. J. Foreman10 Linux Process/Thread States Running Uninterruptible ReadyTerminated Interruptible Stopped* Any signal or event New H/W Signal * Requires action from another process waiting

11. © 2004, D. J. Foreman11 Windows Thread States CPU scheduled WaitingTerminated RunningReady Page/stack wait New preempted Block requested Block released Runnable Not runnable