osy_unit_2.pptxservices and components of OS

Chapter 2
Services and Components of Operating System
By
Ms. H. C Kunwar
Lecturer
RAISONI GROUP OF INSTITUTIONS

Operating System Services
• Operating systems provide an environment for execution of programs and
services to programs and users
1. User interface : -
Almost all operating systems have a user interface (UI) Varies between
Command-Line (CLI), Graphics User Interface (GUI), Batch
2. Program execution :-
The system must be able to load a program into memory and to run that
program, end execution, either normally or abnormally (indicating error).
3. I/O operations : -
A running program may require I/O, which may involve a file or an I/O device
4. File-system manipulation :-
The file system is of particular interest. Programs need to read and write files
and directories, create and delete them, search them, list file Information,
permission management.

Operating System Services (Cont.)
5. Communications :–
Processes may exchange information, on the same computer or between
computers over a network Communications may be via shared memory or
through message passing (packets moved by the OS)
6. Error detection :–
OS needs to be constantly aware of possible errors
• May occur in the CPU and memory hardware, in I/O devices, in user
program
• For each type of error, OS should take the appropriate action to
ensure correct and consistent computing
• Debugging facilities can greatly enhance the user’s and programmer’s
abilities to efficiently use the system

Operating System Services (Cont.)
6. Resource allocation :-
When multiple users or multiple jobs running concurrently, resources must be
allocated to each of them Many types of resources - Some (such as CPU cycles, main
memory, and file storage) may have special allocation code, others (such as I/O
devices) may have general request and release code
7. Accounting :-
To keep track of which users use how much and what kinds of computer resources
8. Protection and security:-
The owners of information stored in a multiuser or networked computer system may
want to control use of that information, concurrent processes should not
interfere with each other
• Protection involves ensuring that all access to system resources is controlled
• Security of the system from outsiders requires user authentication, extends
to defending external I/O devices from invalid access attempts

A View of Operating System Services

System Calls
• System call is an interface between a running program and operating system. It
allows user to access services provided by operating system. This system calls are
procedures written using C,C++ and assembly language instructions.
• The interface between a process and an operating system is provided by system
calls.
• Each operating system has its own name for each system call.
• Each system call is associated with a number that identifies itself
• System calls are usually made when a process in user mode requires access to a
resource. Then it requests the kernel to provide the resource via a system call.

System Call Implementation
• Typically, a number associated with each system call System-call interface
maintains a table indexed according to these numbers.
• The system call interface invokes intended system call in OS kernel and
returns status of the system call and any return values.
• The caller need know nothing about how the system call is implemented
• Just needs to obey API and understand what OS will do as a result
call.
• Most details of OS interface hidden from programmer by API.

How System Call Implemented

Types of System Calls
• Process control
– end, abort
– load, execute
– create process, terminate process
– get process attributes, set process attributes
– wait for time
– wait event, signal event
– allocate and free memory
• File management
– create file, delete file
– open, close file
– read, write, reposition
– get and set file attributes

Types of System Calls (Cont.)
• Device management
– request device, release device
– read, write, reposition
– get device attributes, set device attributes
– logically attach or detach devices
• Information maintenance
– get time or date, set time or date
– get system data, set system data
– get and set process, file, or device attributes
• Communications
– create, delete communication connection
– send, receive messages
– transfer status information
– attach and detach remote devices

Examples of Windows and
Unix System Calls

Operating System Components
• Process Management
• Main Memory Management
• Secondary-Storage Management
• I/O System Management
• File Management

Process Management
• A process is a program in execution. A process needs certain resources,
including CPU time, memory, files, and I/O devices, to accomplish its task.
• The operating system is responsible for the following activities in
connection with process management.
– Process creation and deletion.
– process suspension and resumption.
– Provision of mechanisms for:
• process synchronization
• process communication

Main-Memory Management
• Memory is a large array of words or bytes, each with its own
address. It is a repository of quickly accessible data shared by the
CPU and I/O devices.
• Main memory is a volatile storage device. It loses its contents in the
case of system failure.
connections with memory management:
– Keep track of which parts of memory are currently being used
and by whom.
– Decide which processes to load when memory space becomes
available.
– Allocate and deallocate memory space as needed.

Secondary-Storage Management
• Since main memory (primary storage) is volatile and too small to
accommodate all data and programs permanently, the computer
system must provide secondary storage to back up main memory.
• Most modern computer systems use disks as the principle on-line
storage medium, for both programs and data.
connection with disk management:
– Free space management
– Storage allocation
– Disk scheduling

I/O System Management
• The I/O system consists of:
– A buffer-caching system
– A general device-driver interface
– Drivers for specific hardware devices

File Management
• A file is a collection of related information defined by its creator.
Commonly, files represent programs (both source and object forms) and
data.
connections with file management:
– File creation and deletion.
– Directory creation and deletion.
– Support of primitives for manipulating files and directories.
– Mapping files onto secondary storage.
– File backup on stable (nonvolatile) storage media.

Use of Operating System Tools
Following are the operating tools:
 User Management
 Security policy
 Device Management
 Performance Monitor
 Task Scheduler

Use of Operating System
Tools(cont..)
1. User Management:
• User management includes everything from creating a user to deleting a user on
your system. User management can be done in three ways on a Linux system.
• Command line tools include commands like useradd, userdel, usermod, passwd,
etc. These are mostly used by the server administrators.
• Useradd: With useradd commands you can add a user.
• Syntax: useradd -m -d /home/ - c ""
• Example: useradd -m -d /home/xyz -c "xyz" xyz

Tools(cont..)
2. Device Management:
• Device management is the process of managing the implementation, operation and
maintenance of a physical and/or virtual device.
• All Linux device files are located in the /dev directory, which is an integral part of
the root (/) file system because these device files must be available to the operating
system during the boot process.
• Example: ls –l /dev
• Above example gives the list of device file from kernel.

Tools(cont..)
3. Performance Monitor:
• It is very tough job for every system or network administrator to monitor and debug
Linux System Performance problems every day.
• The commands discussed below are some of the most fundamental commands
when it comes to system analysis and debugging Linux server issues such as:
• vmstat: Virtual memory statistics
• The vmstat command reports information about processes, memory, paging, block
IO, traps, and cpu activity.
• Eg. $ vmstat 3

Tools(cont..)
3. Security Policy:
• Security policies cover all preventative measures and techniques to ensure the
safeguarding of an OS, the network it connects to, and the data which can be
stolen, edited or deleted.
• OS security policies and procedures cover a broad area (i.e. from threats to
attacks), there are many ways to address them.
• Some of these areas include:
• Ensuring systems are patched or updated regularly.
• Installing and updating anti-virus software.
• Installing a firewall and ensuring it is configured properly to monitor all
incoming and outgoing traffic.
• Implementing user management procedures secure user accounts and
privileges.

Tools(cont..)
3. Task Scheduler:
• The Task Scheduler is a tool included
with Windows that allows predefined
actions to be automatically executed
whenever a certain set of conditions is
met.
• For example, you can schedule a task to
run a backup script every night, or send
you an e-mail whenever a certain system
event occurs

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