2. 11-2
INDEX
• History
• Design principals
• Components of linux system
• Kernel modules
• Process management
• Process and threads
• Scheduling in linux
• Process scheduling
• Memory management
• File systems
• I/O in linux
• Interprocess communication
• Linux networking structure
• Security
• Conclusion
4. 11-4
DESIGN PRINCIPLES
LINUX: A Multitasking, Multiuser and
full set of UNIX compatible tools.
It is capable of operating under 4Mb of
RAM
It contains POSIX standards.
It act as a interface for both the
programmer and the user.
5. 11-5
USER INTERFACE
Users operate linux through CLI and
GUI.
On desktop systems: KDE Plasma
Desktop,GNOME and Xfce.
Linux kernel and other components are
free and open source software.
6. 11-6
COMPONENTS OF LINUX SYSTEM
Linux system consists of three main bodies:
• The kernel
• The system libraries
• The system utilities
8. 11-8
PROCESS MANAGEMENT
Two different operations:
•The creation of process
•Running of new program
Terms in linux:
•Fork-a new process is created by fork system call.
•Execve-a new program is run after a execve call
•Clone-creates a new process sharing parent data structure
having it’s own identity.
9. 11-9
PROCESS MANAGEMENT
Process properties:
• Process identity:
a. Process ID(PID):
b. Credentials:
c. Personality:
• Process environment:
• Process context:
a. Scheduling context:
b. Accounting:
c. File table:
d. File system context:
e. Single handler table:
f. Virtual memory context:
10. 11-10
Processes and Threads
• Threads are light weight processes(LWPs)
• Processes are heavy weight processes(HWPs)
• Fundamental parts of process:
a. code(text)
b. data(vm)
c. stack
d. file I/O
e. signal table
• Threads: user level and kernel level
11. 11-11
PROCESSES AND THREADS
1. REPRESENT THE EXECUTION
OF SINGLE
PROGRAM
2. TWO SEPARATE
PROCESSES WILL HAVE
THEIR OWN INDEPENDENT
ADDRESS SPACE
1. REPRESENT SEPARATE ,
CONCURRENT EXECUTION
WITHIN SINGLE PROCESS
2. TWO THREADS WITHIN A
PROCESS SHARE SAME
ADDRESS SPACE
12. 11-12
SCHEDULING
• The linux scheduler is a pre-emptive , priority-based
algorithm
• Two separate priority ranges :
1. Real-time range( 0 to 99)
2. ice-value range (100 to 140)
• Once kernel code start running , then it is the only kernel
code till the following event occurs.
1. An interrupt
2. A page fault
3. A kernel code call to the scheduler function itself
13. 11-13
PROCESS SCHEDULING
Linux supports two process scheduling algorithms
• Time- sharing algorithm
• Real- time task algorithm
1.First-in first-out (FIFO)
2.Round Robin
14. 11-14
MEMORY MANAGEMENT
Two components in Memory management:
• Physical memory management
• Virtual memory
Physical memory management: This deals with allocation
and deallocation of pages, group of pages and blocks of memory.
Virtual memory: it is the memory mapped into the address
space of running process.
15. 11-15
PHYSICAL MEMORY MANAGEMENT
•Physical memory manager is a page allocator, which uses
“buddy heap” algorithm in order to keep track of available address
space .
Ex. Splitting of memory in buddy heap.
16 KB
8KB
8 KB
8 KB
4 KB
4 KB
16. 11-16
VIRTUAL MEMORY
• Virtual memory is responsible for maintaining the address
space visible to each process.
• There are two situations where the kernel creates a new
virtual address space
a) when a process runs a new program with the “exec”
system call.
b) When a new process is created by the “fork” system call.
17. 11-17
FILE SYSTEMS
• Linux file system retains UNIX’s features. here file can
be anything capable of handling I/O of stream of data.
• The virtual file system is designed using object oriented
principles. It consists of two components,
i. A set of definition which define what a file object is
allowed to look like.
ii. A layer of software to manipulate those objects.
3 main object defined by VTS are
i. Inode object
ii. File object structure
iii. File system object
18. 11-18
I/O IN LINUX
Linux splits all the I/O devices into three groups
a. Block devices
b. Character devices
c. Network devices
• Block devices include all devices that allow random
access like HDD, floppy disk & CD-ROMS.
• Character devices include other devices with the main
exception of network devices like Magnetic tap devices.
• Network devices are dealt differently from both devices.
user cannot transfer directly data to network devices
but communicate indirectly. Ex. Tty discipline.
20. 11-20
LINUX NETWORK STRUCTURE
Linux kernel is implemented using the
three layers of software internally-
• System call interface
• Protocol agnostic interface
• Network protocols
