[ _ = = oe N’T COPY MY NOT! = Chapter 2- 2— - Services & Q 1) Explain any six services of Operating S' Draw diagram of services of OS. Ans:- 1. User Interface: All operating systems users to communicate with the system. Three types of user interfaces are available: a. Command line interface (CLI) b. Batch interface 2. Program execution: The operating system provides an environment where the user can conveniently run programs. To run a program, the program is loaded into the main memory and then CPU is assigned to that process for its execution. It also performs other important tasks like allocation and de- | | | \ c. Graphical user interface (GUI) | allocation of memory, CPU scheduling etc. It also provides service to end \ process execution either normally or abnormally by indicating error 3. /O operations: When a program is running, it may require input/output resources such as a file or devices such as print} | Fors iff i ‘special functions may be required such as recording to 4 protection users usually cannot control I/O device system provides a service to do I/O. 4. File system manipulation: - Programs may Hééd't6 tS4d Apa Wit data from and to the files and directories. Operating system manages the secondary. storage. User gives a command for reading or writing to a file. Operating system makes it easier for user programs to accomplish their task such as opening a CH-2 (Make UR Own Style---Don’t copy My Notes;Processes that are executing on different compu computer network. Communication can be implementediviai or through message passing, in which packets of information are moved between processes by the operating system. 6. Error detection: The operating system needs to be constantly aware of possible errors. Errors can occur in: a) CPU and memory hardware such as a memory error or power failure b) I/O devices such as, a connection failure on a network or lack of paper in the printer. c) The user program such as an arithmetic overflow, an attempt to access an illegal memory location or a too-great use of CPU time. | running at the same time, resources must be alldcat ! BHANDA RY | OS manages resource allocation to the processes. These re | memory, file storage and I/O devices. For maximizing use of CPU, operating system | does CPU scheduling, Operating system contains routines to allocate printers, | modems, USB storage drives and other peripheral devices. {Make UR Own Style---Don’t copy My Notes;8. Accounting: Operating system keeps irack of usages of various computer resources allocated to users. This accounting is used for reconfiguration of system to improve compuiing services. 9. Protection & security: Owners of information| stored jd multiuses networked computer system want to control use tron ion. several separate processes execute concurrent (one. br interfere with the other processes or operating system itself. Protection || provides controlled access to system resources. Security is provided by user authentication such as password for accessing information. 5 hating system.The caller needs to know nothing about how the system calls implemented, Just needs to obey API and understand what OS will do as a result call. user application ‘open () user mode system call interface 7m open () i " | Implementation i} -_________» ofcpen(} system call return — kernel mode | | 4) Open ( ) system calll :- For most file systems, a program initializes access to a file ina file system using the open system call. This allocates resources associated to the file (the file descriptor), and returns a handle that the process will use to refer to | that file. Q 3) How parameters are passed to the OS using System Call ‘Ans: 1) Parameters can be passed in registers. :- System calls provide an interface between the process and the opétating system. System calls allow user-level processes to request some services from the | operating system which process itself is not allowed to do. System call provides basic functionality to user to operate operating system. {Make UR Own Style---Don’t copy My Notes; | CH-2| Q 5) Sta ) State any four types of system call provided by an operating syste” xecute, Create | .d, Resume, Ans:- | tne System calls related to Process Control: End, Abort Load, E a fee Terminate process, Ready process, Dispateh-process, uspeni et Process attribute, set attribute, Wait for tn yanerer event tonal § er tg l@Open file , Close set file attribute, System calls Related to File Management: Create file, dele file ,Create directory Read, Write, Reposition G fle tribut Create a link, Change the working directory. System calls Related to Device Management: Request: ice Release 4 device BHANDARKAR gg Ac jevice attribute System calls Related to Information Maintenance: Get Time or Date, Set Time oF | Date, Get System data, Set system data, Get process, file or device attributes, Set | Process, file or Device attributes. ion: create, delete communication connection System calls Related to Communicati tion, attach or detach remote devices | send, receive messages, transfer status informal Q6) Explain any four file related system calls. ‘Ans:- System calls Related to File management: | | | is used to create a new file in any application Create file: This system call Delete file: This system ¢ allis used to delete a specific ile from the given directory. | j existing file Open file: This system call is used to open an Close file: This system call is used to close an é Read file: This system call is used to read a file this system call any information which is desired ¢ Write file: This system call is used to write som RKAR hange the positioh ‘ofa file porn within the file. If | Reposition file: It means to cl ges in a file then we can move forward or backward to there are many numbers of pa: any position within that file. CH-2 |Make UR Own Style---Don’t copy My Notes)type, file_size, date] name, filet ue tem call we ca Get file attribute: A file has certain attributes like st of creation, modification, access permission etc: BY using this s¥ check any of the attributes of a particular file. il Bi] ang orth Set file attribute: With the help of this system © i], any\ot modified or changed can be “SET \| iL e attributes which can be | Q 7) List types of system call and explain the, Maintenance”. ANS:- Types of System calls are as follows: 4. Process or Job control 2. File Management 3. Device Management 4. Information Maintenance 5. Communications. Information Maintenance: The operating system keeps information about all its processes and provides system calls to access this information. Some system calls exist purely for transferring information | between | the user program and the operating system. Transferring information between the user program and the operating system requires system call. System information includes displaying current date and time, the number of current user, the version number of | the operating system, the amount of free memory or disk space and so on. System calls Related to Information Maintenance: 5 Get Time or Date, Set Time or Date © Get System data, Set system data 1 Get process, file or device attributes I 9 Set process, file or Device attributes BHANDARKAR fi Academy | | cH-2 {Make UR Own Style---Don’t copy My Notes) ¥! ocess Q 8) What i 8) What is process management? State any four functions of Pr management. OR Ans:- The operating system manages many kingy of abtivides ranging from user Explain Process management components cf [vas its activities. programs to System programs like printer spool namd servers, file ; of these activities is encapsulated in a process. 4 process includes the mplete execution context (code, data, PC, registers, OSesaurces inuse etc | The major activities/functions of an operating system irrregard {6 process management are: e_ B 4. Creation and deletion of user and system processes. 2. Suspension and resumption of processes. 3. Providing mechanism for process synchronization. 4. Providing mechanism for process communication. 5. Providing mechanism for for deadlock handling Q9) Explain main memory Management components of OS with its activities. Ans:- Main-Memory is a large array of words or bytes = Each word or byte has its own address. | © Main memory provides storage that can be access directly by the CPU. That is to say for a program to be executed, it must in the main memory. The major activities of an operating in regard to memory-management are: 5 Decide which processes are loaded into mem available. server etc. EachQ 10) Explain File Management components of OS with its activities. ANS:- A file is coilection of related information defined by its creator. commonly file | represents program and data. Files are normally organizediinto directories to easy their use. i1\ ve The major activities of an operating in regard file’ 1) Creating and Deleting files. 2) Creating and deleting directories. 3) Mapping file on secondary stirage. 4) Backing up files on storage media Q 11) Explain different activities of I/O system management components of OS Ans:- 1) I/O System: Input / Output device management provides an environment for| the better interaction between system and the | / O devices such as printers, scanners, tape drives etc. 2) To interact with 1/0 devices in an effective manner the operating system uses some special programs known as device driver. 3) The device drivers take the data that operating system has defined as a file and then translate them into streams of bits or a series of laser. A device driver is a | specific type of computer software that is developed to allow interaction with hardware devices 1 4)) Typically this continues an interface for communicating with the I/O device, through the specific computer bus or communication subsystem that the hardware is connected with. al 5)) The device driver is a specialized hardware enables another program, typically an operating a hardware device. Activities: i Providing interfaces to other system componéht$NPARKAR) J cos Managing devices 0 Transferring data 1 Detecting 1/0 completion CH-2 (Make UR Own Style---Don’t copy My Notes)ment? /| | Q 12) What are the activities involved in secondary storage manag Ans:. The three major activities of an operating system in regard to secondary | | storage management are: — a. Managing the free space available on the al ee f en. Oy b. Allocation of storage space when new files A c. Scheduling the requests for memory acces: ia ; Q. Write two uses of following 0.S. tools (i) Device Management (ii) Task Scheduler Performance monitor Ans:- {i) Device management:- * Managing all the hardware or virtual devices of computer system. * Allow interaction with hardware devices through device driver _ ¢ Used to install device and component-level drivers as well as associated software. * Allocate devices to the process as per process requirement and priority. * Deallocate devices either temporarily or permanentiy depending on condition. ] * Keeping track of all device's data and location . * Monitoring device status like printers, storage drivers and other devices. * Used to enforce the predetermined policies ang the device when and for how long. Performance monitor :- 1. Monitor various activities on a computer such 8S G BHANDARI 2. Used to examine how programs running on their compute! | performance Ontsage Academy fect computer's | 3. Itis used to identify performance problems or bottleneck that affect operatin, ‘system or installed applications. a (Make UR Own Style---Don’t copy My Notes;4. Used to observe the effect of system configuration changes: 1. Assign processor to task ready for execution {| \ acer d 2. Executing predefined actions automatically w! ty ad | ting a user to deleting Ans:- a) User management:: It includes everything from cr ways on linux } auser on your system. User management can be done in three system. Following are the linux commands line tools for managing users and groups: 1) User add 2) User mod 3) User del. 4) Useradd:- creating new user Syntax:- useradd login_name Example:- useradd XYZ Passwd command:- Syntax:- password user_name Example:- passwd salim 2) Usermod:- modifying properties of user. Syntax:- usermod —c < ‘newName'> 3) Userdel:- Delete a user account. Syntax:- userdel —r B) Security Policy:- 4) Keep system updated 2) Use secure SSH (secure protocol) 3) Deactivate networking ports. 4) Lock and Unlock ee Leena 5) Turn off IPV6. 6) Enable IPtables(Firewall) 7) Use storage password policy 8) Use SFTP, not FTP. {Make9) Install Antimalware / Antivirus Software 10) Backup regularly. | C) Device Management. It is the process of managi All linux device files are located in the / part of the root (/) file system because tl the OS during the boot process. ANDARKAR| To monitor and debug linux system performance problems, some commands are used. 1) Top Command. 2) Vimstat. | E) Task Scheduler:- 1) Adding New task 2) Saving files.Ans:- A process is of work. The execution is an active entity. PCB:-Process Control BI related to it. The of the process table, etc. Q. Give differenc Ans:- Program Itis a series of instructions to perform a particular task Itis a passive (Static) entity. Itis stored in secondary storage it doesn't have a resource requirement It doesn't have a control block. It occupy fixed place in storage. |t requires memory space to store instructions. i @ program in execution, Proce: Is a Of a process must progres lock is a data structure that contains! Process control biock is also known as a ta Sin éf the process ontrol block, entry e between Program and Process. Process A program in execution is called as process, Itis an active(Dynamic) entity. Itis stored in memory, ithas a high resource requirement. It has its own control block, which is known as Process Control Block. | changes its state during execution it requires resources such as CPU, memory address, I/O during its working, [Make UR Own Style---Don’t copy My Notes]—Q | Q. Enlist different states of process and draw diagram of processstate | transitions. Ans ( new admitted interrupt exit terminated ) ON > a < ony > Gum D ew ee ee VO or event wait 'C or event completion waiting = 1) New: When a process enters into the system, it is in new state. In this The process is being created. In new state the process is in job pool 2) Ready: When the process is loaded into the main memory, it is ready for execution. In this state the process is waiting for processor allocation. 3) Running: When CPU is available, system selects one process from main memory and executes all the instructions from that process. So, when a process is in execution, it is in running state. In single user system, only one process can be in the running state. In multiuser system, there can be | multiple processes which are in the running state. 4) Waiting State: When a process is in execution, it may request for /O resources. If the resource is not available, process goes into the waiting state. When the resource is available, the process goes back toready state > ~ 5) Terminated State: & When the process completes its execution Srginated'state. In & Explain PCB with diagram. Ans:- Each process is represented as a process bon system. It contains information associated with specific. process Process State: It indicates current state of a process. Process st running, waiting and terminated. ; - : Process number: Each process is associated with a unique number which is known process identification number. [Make UR Own Style---Don’t copy My Notes]Program Cot unter: It ind | process, licates the address of the next instruction to be executed for the puter ointer@yand general CPU Registe rs: architecture. Re a registers vary in number and type depending o, purpose 1gisia gister includes accumulators, index fegisters, staci "8 plus any condition code information) \ informetjon such as , depending-on the }) value of money faerie eee page tables, t tabi Accounting Information: This information incuc a Pirates account holders, job or process number and soon, I ronan Buudee infomation about listed 1/0 devices allocated to 1 dusigned . Each PCB gives information about a particular process for w! Memory Mana: . igement Information(Memory Limits} : It/inlad nl used, time prdeéds such as list hich it is process state process number program counter registers memory limits ‘Ans:- Scheduling queues refers to queues of processes, ‘enters into the system, then this process is put into qjpb qyeue. The operating system also maintains other queues is a queue for which multiple processes are waiting This figure shows the queuing diagram of process Queue is represented by rectangular box. SHANDAREA © The circles represent the resources that serve the queues, J The arrows indicate the process flow in the system Academy Queues are of two types * Ready queue Device queue A newly arrived process is put in the ready queue. Processes waits in ready queue for CH-3 [Make UR Own Style- Don’t copy My Notes]a a ——— a gornark allocating the CPU A i \— Onoe the CPU is ‘assigned to a process, then that process wil exacute, While executing the process, any one of the following events can occur. * The process could issue an /O request and then * The process could create new sub process and will W/ | The process could be removed forcibly from the CPU, a in the ready queue Ready queue: The processes that are residing ip waiting to execute are kept on a list called the ready queue Job queue: As processes enter the system they-aré-put Int) job queue. i Device queue: The list of processes waiting for a’particulak VO ge Nicelis'cailed a device queue. aca ~ =a ready queve | ———_____{ cpu] _ | { wel —I nae vo }-—{ woqueva “)[+-—|_vo request bmasica = 1, __ expired | cnila fork a excoutes | chi JC imerrupt wait for any \ / interrupt oceurs, | @ State and describe types of scheduler. ‘Ans:- There are three types of scheduler: + Long term scheduler , Short term scheduler and Medium term scheduler 4) Long term scheduler 4 F + It'selects programs from job pool and Ip + Itcontrols the degree of multiprogramr) * The degree of multiprogramming is| (existing) into the main memory. System contains /Obound processes 4 An I/O bound process spends more tiie CPU bound process spends more time Ir doin with the CPU So It is the responsibility of long term Scheduler t6 Jon the system by loading some /O bound and some CPU bound processed into the main memory. + Long term scheduler executes only when a process leaves the system, so it executes less frequently. : * When long term scheduler selects a process from job pool, the state of process changes from new to ready state. : [Make UR Own Style---Don’t copy My Notes]2) Short term scheduler: * Its also known as CPU scheduler. This scheduler selects processes that are reacy for execution from the ready quous-andhallogates,the CPU to the selected process, ’ Frequency of execution of short t schedulers When short term scheduler selects a from ready to running state 3) Medium term scheduler: When a process is in running state, due.to,some interrupt, jt is blocked. ‘System swaps out blocked process and store it into ablocked and swapped Out process queue. Whe space is available in the main memory, the operating system: looks at the list of swapped out but ready processes. 7 The medium term scheduier selects one process from that list and loads it into the ready queue. The job of medium term scheduler is to select a process from swapped out Process queue and to load it into the main memory. This scheduler works in close communication with long term scheduler for loading process into the main memory. Dig:- Refer Class Notebook andles process scheduling in various ways. Scheduler is the system program whith schedules processes from the scheduling queues. Their main task is to select the jobs to be submitted into the J} system and to decide which process to run. ae Schedulers are of three types: 1) Long Term Scheduler ike UR Own Style---Don’t copy My Notes]2) Short Term Scheduler 3) Medium Term Scheduler Tong term scheduler | Medium term = scheduler __ Tage’ itis ajob scheduler Itis a process swaping”) if a scheduler —__ em | 2 | Itselects processes from | It selects a process, ftom! seleg SS, | ob pool and loads them. | swanped-out process. | readymueue Which #2 ready | poe into memory for to execute and allocates ‘ecution CPU to one of them.-___ . |3 | Access job pool ana | Access process from cess ready queue and leone” | ready queue | swapped out process | CPU. | __| queue. — | 4 litexecutes much less Itexecuted whenever _| frequently select a new | Ipeeww | frequently when ready | swapped queue contains | process for the CPU, at least | queue has space to ‘a swapped out process. | once every100 milliseconds | accommodate new | [process 7 = 5 | Speed is less than short | Speed is in between | ‘Speed is fast | eet term scheduler both short and long term Se a | scheduling | ae 6 | It is almost absent or It is a part of time Itis also minimal in time | minimal in time sharing | sharing system sharing system |__| system | oo — 7 | It controls the degree of | It reduces the degree of | it provides lesser control over | deg multiprogramming | multiprogramming | degree of multiprogramming | | sa ming __ ero ‘Ans:- 1) Context Switching involves storing the co: can be reloaded when required and execution ca 2) This is a feature of a earlier. 4)The context switch represented with PCB. 5) Saves context of old process in its PCB and loads context of new process schedule to tun. Context switch time is pure overhead. 6) Diagram demonstrates context switching is as follows: CH-3 [Make UR Own Style---Don’t copy My Notes]In the below diagram, initially Process PO is running Process P1 is switched in because of an interrupt i involves saving the state of Proce: into PCBOja from PCB1 PO into process P, operating system process P, ‘stort or system call owcutrg | ‘av stale nto PCB, | (ead tate om PCE] ‘ce ntanrapto¢ system call executing | -G, With neat diagram explain inter process com: ni aon el. wars ANS:- In general, Inter Process Communication is a type of mechanism usually provided by the operating system (or OS). The main aim or goal of this mechanism is to provide communications in between several processes. In short, the intercommunication allows a process letting another process know that some event has occurred. Describe with suitable diagram shared memory system. Also write two advantages of each sysi Inter-process communication (IPC) is a mechanism that allows processes to ‘communicate with each other and synchronize their actions. CH-3 [Make UR Own Style---Don’t copy My Notes]The communication between these processes can be seen as a method of e2-00 between them. Processes can communicate with each other throug! 1. Shared Memory 2, Message passing 1) Shared ‘memory: * In this model, a region of the memory Process creating a shared memory seg} rocesses who want to communicate w! ‘+ All the processes using the shared mer tach to the address space of the shared memory. BHANDARKAS, * All the processes can exchange information by reading and/or writing data in shared memory segment. * The form of data and location are determined by these processes who want '0 communicate with each other. These processes are not under the control Of the operating system. * The processes are also responsible for ensuring that they are not writing to the same location simultaneously. * After establishing shared memory segment, all accesses to the shared memory segment are treated as routine memory access and without assistance of kemel Advantages of Shared Memory: * Fast * Coping of message is eliminated, = * Reading and Writing is easy, _ [Make UR Own Style---Don’t copy My Notes]1) Message Passing: - . m this meas communication takes place by exchanging mes cooperating processes. eee ee It allows processes to communicate an cone ar Seay wi sharing the same address space. ‘ * tis particularly useful in a distributed e! Process may reside on a different com) * Communication requires sending and r kernel * The processes that want to communica| en as communication link between them. — PHANDAKA ink exiét + Between each pair of processes exactly one communication lin! - | sages between Advantages cf Massage Passing: * Explicit sharing | «Less error prone * Easier to build parallel hardware. Process P1 M Process P2 Message Passing System QDefine thread? Ans:- A thread is a lightweight process that can bi Scheduler. It improves the application performance using pai a subpart of a large process. In a process, all the threads withi other. A typical thread contains some information like data se ‘This information is being shared to their peer threads during independently by a llelism. A thread is basically in it are interrelated to each gment, code segment, etc, execution.CH-3 ference between Process and Thread: Process Process means Program is in execution Process is heavyweight process Ittakes more time for creation, Controlled by Operating system. Process has overhead New Process creation is time consuming. Process are independent. Assystem call is involved in it. The process has its own Process Control Block, Stack, and Address Space. Ifa process gets blocked, remaining processes can continue execution. IHANDARK AR re fakes tess tim Controlled by programmer in program. Thread has no overhead A thread needs less time for creation. Threads are dependent. No system call is involved, it is created using APIs. Ifa user level thread gets blocked, all of its peer threads also get blocked [Make UR Own Style---Don’t copy My Notes]» Explain user thread and kernel threads nsi- User-Level Threads: know ; ; . ne ore evel thread approach the cost of a db text sivitch Betwase” threads less Since the operating system itself does not nec lo beAnvdive system calls are required, A user-level thread is represented by a progra Kad sirall thread control block (TCB), Programmers typically use a thread library to'sitipity MGHABGAABHEGF threads within a process. Creating a new thread, switchi Gone via function cal! stopping threads, as ing between threads, and synchronizing threads are 's into the library. This provides an interface for creating and well as control over how they are scheduled. 00:00:80 systemd 1062 > 08:00:00 (sd-pam) 1074 ttyl 00:20:00 zsh 3) 7a: It shows the processes of alll users. Example: $ ps -a PID TTy TIME CMD 27011 pts/a 60:00:08 man 27016 pts/@ 00:00:00 1 27499 pts/1 00:00:80 ek Pee eet] “ksoftirqd/o Lae Acre) ae Cet ett tts rcu_bh Don’t copy My Notes]Q. Write use of following system calls. 1)fork() 2)exec() 3) abort() 4) end( ) Ans.- yith anew 2. exec( ) This system call is used to replace the prd rogram. It loads a binary fle into memory and start 3. abort( ) This system call is used to halt process ¢ 4. end () This system call is used to halt process e: ANS:- A thread, sometit A traditional (or fa process has Imes called a lightweight process, is a basic unit of CPU utilization. heavyweight) process has a single thread of control. Multiple threads of control, it can do more than one task at’a time, ‘The benefits of using threads: 1. Responsiveness:- Multi. Utilizati i , oe ae of multiprocessor architectures: - The benefits of multithreading fanning hoa 2804 In @ multiprocessor architecture, where threads may De ing in parallel on different processors. A si can only run on one CPU, no matter how many are availal lt-CPU machine increases concutrency. Q. In Message Passing system. describe the foll i) Naming (ii) Synchronization (iii) Buffering ANS:. (i) Namin, BHANDARKAR fi Acaden Processes which wish to communicate with each other need to know each other with the name for identification. There are two types of communications : 1. Direct Communication 2. indirect Communication * Indirect communication each process that want to communicate must be explicitly use name for the sender as well as receiver while communication. In this type the send{ ) and receive( ) primitives are defined as follows: ‘+ Send(P,message) — Send message to process P * Receive (Q, message) ~ Receive a message from process Q. > Inan indirect communication the messages could be send or receive from mailboxes or ports. > Amailbox can be viewed as an object in which messages could be kept or even removed > Each mailbox is associated with the unique number. > In this type the send( ) and receive( ) primitives are defined as follows: Send(A.message) ~ Send message to mailbox A. Receive (A, message) ~ Receive a message from mailbox A. (ii) Synchronization: > © Communication between the processes takes place through the system calls. OS has to maintain proper synchronization between the sondiag apcuteceiving: processes. y + To send{ ) and receive( ) primitives, a special bt} implementation of these primitives. These are asynchronous communication. ) Buffering: > The communication could be direct or indirect communicating processes resides or stores in a > The OS will buffer the messages into the puree Hake & Address space. > Asender’s message will be copied from the sender's address space to thé next free slot in the system buffers. > From this system buffer, the messages will be delivered to the receiver process in FCFS order when receiver process executes receive calls. hariged bythe ue | jedi tHe systemQ Describe Process in memory with diagram. 4 Ans:- ition needs re * Process is program in execution. A process in execu memory, VO Current machines allow several processes to Processor is shared among many processes. Process is a program in execution. A process Could contain some part called as text section| 't may contain the current activity, represente & the contents of CPU register. émporat Another part of process is stack. Stack is basi aa al Papionless. values, That values can be parameter or return yal [ues oF fufctions, lo addresses of the retum values etc. There is another part called data section. Data section stores the global variable. Global variables are accessible sources like CPU, a Ss or Static BHANDARKARBM Academy =also maintains for is information counting user area: In addition to the text, data, and stack segment, the OS Mh process a region called the u area (User Area). The u area contain’ afc to the process (e.g. open fiies, current directory, and signal action, 2 formation) and a system stack segment for process, 7 If the process makes a system call function in main), the stack frame information for t segment. Again, this information is kept by the OS it normally have access to. ‘Thus, if this information is needed, t to access it. Like the process itself, the contents of tf in and out by the OS. NE we a sin@ Don't copy My Notes] as [Make UR Own Styl