DOCSLIB.ORG

Processes – CSC252

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Processes – CSC252 Processes – CSC252 PROF. EARL Some slides adopted from Dr. John Carelli and Dr. Lisa Frye User • Programs that the user interacts with User vs or launches themselves Kernel Kernel • Provides services to user space. Space Manages hardware and resources for multiple users. User processes access this space through system calls Hardware Processes https://goo.gl/images/381BdN Processes A single process is the execution of command by the Linux Kernel Every process (besides init) has a Process ID (PID) and Parent Process ID (PPID) Processes are “spawned” from another System Calls Allow a program in user space to interact with the kernel fork() – Allows for a process to create a new sub-process (A child process) The PPID of the new process, would be the PID of the process that called fork() exec() – Execute a new command replace the process with the new one. Sessions The lifetime a user login process When a user logins into a linux machine, a new shell process is created job – A command pipeline ; - Separate Commands & - Run the command in the background Basic Process Commands history – log of past commands jobs – List of currently running jobs kill – Terminal a process fg,bg – Move a process to the foreground/background ps – List processes top – View top running processes uptime – View how long system has been running free – View available memory (RAM) pstree – Show process tree nohup – run command immune to hangups Review the student presentations as posted on D2L (except for ps) The Process Table Data structure that exists in Kernel Space Contains the following: Process ID Process Owner Process Priority Environment variables for each process The Parent Process Location of its code, data, stack, and user area Pending Signals The ps command UNIX command that allows you to view information from the process table. Some Examples: https://www.tecmint.com/ps-command-examples-for-linux-process-monitoring/ Process Initiation init - is the last step when booting a computer (Usually PID 0 or 1) fork(), exec() – Used to create the new processes getty - Create a terminal session login - Login a user Modes User – “Normal” user kernel - root Process Termination Two ways a process can terminate Normal – Process runs and exits normally Abnormal – Terminated via an external control wait() When a process spawns subprocesses, it has to wait until its child process(es) finish before ending Parent process suspends until children are done Zombie Process Terminated, but still in process table Exists so parent can read exit code Orphan Process Parent Terminated Gets handed over to the init process Process States When a process is created, it will exist in one of these states: Suspended / Exit Idle/Waiting Stopped The process is waiting on some event to happen internally Runnable/Ready Process is ready to run and is waiting Idle/Waiting Runnable to be scheduled by the kernel Running Zombie (for an event) / Ready Running Process is currently running Suspended/Stopped Stopped externally, usually by a Sleeping / signal Blocked Sleeping/Blocked Waiting for an Input/Output event or a resource in use by another process Exit Zombie See previous slide. Process Internals Scheduler Decides which processes to run and for how long uses preemptive multitasking – system decides Memory Manger virtual memory System looks like it has more actual memory Magic Number embedded near beginning of file – Indicates the file type Can use file to identify type Process Areas User Code Area - The instructions to run the program Data Area - Data associated with the program Stack Area - Program stack (manage function calls) User Area - Misc. stuff (Opened files, the current directory, etc.) Kernel Area Process Table Page Table – Keep track of where items are stored within memory Scheduling Jobs crontab Allows user to schedule a job Useful stuff man crontab crontab –e - Allows individual users to edit their cron at Allows for launching of a command at a specified time man at.
Load more

Recommended publications
  • Tutorials Point, Simply Easy Learning
    Tutorials Point, Simply Easy Learning UML Tutorial Tutorialspoint.com UNIX is a computer Operating System which is capable of handling activities from multiple users at the same time. Unix was originated around in 1969 at AT&T Bell Labs by Ken Thompson and Dennis Ritchie. This tutorial gives an initial push to start you with UNIX. For more detail kindly check tutorialspoint.com/unix What is Unix ? The UNIX operating system is a set of programs that act as a link between the computer and the user. The computer programs that allocate the system resources and coordinate all the details of the computer's internals is called the operating system or kernel. Users communicate with the kernel through a program known as the shell. The shell is a command line interpreter; it translates commands entered by the user and converts them into a language that is understood by the kernel. Unix was originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna. There are various Unix variants available in the market. Solaris Unix, AIX, UP Unix and BSD are few examples. Linux is also a flavour of Unix which is freely available. Several people can use a UNIX computer at the same time; hence UNIX is called a multiuser system. A user can also run multiple programs at the same time; hence UNIX is called multitasking. Unix Architecture: Here is a basic block diagram of a UNIX system: 1 | P a g e Tutorials Point, Simply Easy Learning The main concept that unites all versions of UNIX is the following four basics: Kernel: The kernel is the heart of the operating system.
    [Show full text]
  • Process Manager Ext2fs Proc Devfs Process Management Memory Manager Scheduler Minix Nfs Msdos Memory Management Signaling
    Embedded Systems Prof. Myung-Eui Lee (A-405) [email protected] Embedded Systems 1-1 KUT Linux Structure l Linux Structure proc1 proc2 proc3 proc4 proc5 procn User Space System Call Interface Filesystem Manager Process Manager Ext2fs proc devfs Process Management Memory Manager Scheduler minix nfs msdos Memory Management Signaling Buffer Cache Kernel Space Device Manager Network Manager char block Ipv6 ethernet Console KBD SCSI CD-ROM PCI network ….. Device Interface dev1 dev2 dev3 dev4 devn Embedded Systems 1-2 KUT Linux Structure l Linux Structure Applications: Graphics UI, Compilers, Media player UI Text UI = Shell: sh, csh, ksh, bash, tcsh, zsh Compiler libraries (libc.a) API System Shared Libraries (System Call Interface) Memory File Process management management management Kernel Device Drives BIOS Computer Hardware Embedded Systems 1-3 KUT System Call Interface Standard C Lib. System Call C program invoking printf() library call, API – System call – OS Relationship which calls write() system call ar –t /usr/lib/libc.a | grep printf /usr/src/linux-2.4/arch/i386/kernel/entry.S Embedded Systems 1-4 KUT System Call l System calls define the programmer interface to Linux system » Interface between user-level processes and hardware devices u CPU, memory, disks etc. » Make programming easier u Let kernel take care of hardware-specific issues » Increase system security u Let kernel check requested service via system call » Provide portability u Maintain interface but change functional implementation l Roughly five categories of system calls
    [Show full text]
  • Processes in Linux/Unix
    Processes in Linux/Unix A program/command when executed, a special instance is provided by the system to the process. This instance consists of all the services/resources that may be utilized by the process under execution. • Whenever a command is issued in unix/linux, it creates/starts a new process. For example, pwd when issued which is used to list the current directory location the user is in, a process starts. • Through a 5 digit ID number unix/linux keeps account of the processes, this number is call process id or pid. Each process in the system has a unique pid. • Used up pid’s can be used in again for a newer process since all the possible combinations are used. • At any point of time, no two processes with the same pid exist in the system because it is the pid that Unix uses to track each process. Initializing a process A process can be run in two ways: 1. Foreground Process : Every process when started runs in foreground by default, receives input from the keyboard and sends output to the screen. When issuing pwd command $ ls pwd Output: $ /home/geeksforgeeks/root When a command/process is running in the foreground and is taking a lot of time, no other processes can be run or started because the prompt would not be available until the program finishes processing and comes out. 2. Backround Process : It runs in the background without keyboard input and waits till keyboard input is required. Thus, other processes can be done in parallel with the process running in background since they do not have to wait for the previous process to be completed.
    [Show full text]
  • CENG251: Assignment #5
    Out: March 30, 2021 Due: Wed Apr 14, 2021 There are 30 marks. Please keep and submit a time log to account for what you’ve done. CENG251: Assignment #5 Part I: C Language Features (8 marks) In class we demonstrated re-entrant code by comparing the use of ctime vs ctime_r. We showed that ctime always returned the same memory location and that ctime_r avoided this problem by passing the memory to be filled which was then returned with a different result; Write a single small C program that 1. Demonstrates that getpwuid and getpwnam are not reentrant by calling each of these twice with different valid arguments and displaying the return address and the content of the passwd structure returned. Prepare your output string using fmemopen and then writing the output to a string using a file pointer before writing the string to the terminal. An example of using fmemopen can be found in the example program stringIODemo.c (3) 2. Continue the program and call getpwuid_r and getpwnam_r with correct arguments. Prepare your output string using sprintf and then display the string to the terminal. Examples of long structured format strings can be seen in the example program stringIODemo.c (3) 3. In ctimeDemo.c we demonstrated the use of strdup to preserve the result of ctime from one function call to the next. Use malloc and memcpy to do the same for getpwuid and show that this worked displaying the values from the copy. (2) Part II: Signals (8 marks) The following exercises should be done as a single program.
    [Show full text]
  • Unit-Iv Process,Signals and File Locking
    UNIT-IV PROCESS, SIGNALS AND FILE LOCKING III-I R14 - 14BT50502 PROCESS: When you execute a program on your UNIX system, the system creates a special environment for that program. This environment contains everything needed for the system to run the program as if no other program were running on the system. Whenever you issue a command in UNIX, it creates, or starts, a new process. When you tried out the ls command to list directory contents, you started a process. A process, in simple terms, is an instance of a running program. When you start a process (run a command), there are two ways you can run it − Foreground Processes Background Processes FOREGROUND PROCESSES: By default, every process that you start runs in the foreground. It gets its input from the keyboard and sends its output to the screen. Example: $ls ch*.doc When a program is running in foreground and taking much time, we cannot run any other commands (start any other processes) because prompt would not be available until program finishes its processing and comes out. BACKGROUND PROCESSES: A background process runs without being connected to your keyboard. If the background process requires any keyboard input, it waits. The advantage of running a process in the background is that you can run other commands; you do not have to wait until it completes to start another! The simplest way to start a background process is to add an ampersand (&) at the end of the command. Example: $ls ch*.doc & PROCESS IDENTIFIERS: The process identifier – normally referred to as the process ID or just PID, is a number used by most operating system kernels such as that of UNIX, Mac OS X or Microsoft Windows — to uniquely identify an active process.
    [Show full text]
  • Tutorial 2 : Process Management
    Tutorial 2 : Process Management August 20, 2019 Objective : • This assignment is intended to learn how to create, work with and ma- nipulate processes in Linux. You are expected to refer to the text book and references mentioned in the course website befor you start the lab. Some sample codes for process creation using fork system call have been provided for your reference. Instructions • You are expected to run all the sample codes provided in the Helpful Re- sources section. It will help you understand how OS virtualizes CPU and memory. Some of the codes are related to process creation and execution using Unix based system calls such as fork,exit,wait and exec Tutorials 1. Tut1 : Memory Virtualization : Physical memory model presents Memory as an array of bytes. The data stored at an address of memory can be read by providing the address of the location wehere the data resides. Similarly, while writing data to any address of a memory, one needs to specify the address for writing as well as the data to be written to the given address. Memory is accessed all the time when a program is running. A program keeps all of its data structures in memory, and accesses them through various instruction. In- structions themeselves reside in the memory which have to be fetched. Instructions : Execute the code mem.c from the Helpful Resources sec- tion. Make sure to include the common.h file in the same folder as the mem.c. To execute use the following commands : gcc mem.c ./a.out ox200000 The program does a couple of things.
    [Show full text]
  • Exec(“/Bin/Ls”) : Overwrites the Memory Code Image with Binary from /Bin/Ls and Execute
    Assignment 1 Υπεύθυνοι βοηθοί: Ειρήνη Δέγκλερη ( [email protected] ) Ηλίας Παπαδόπουλος ( [email protected] ) System Calls ■ If a process is running a user program in user mode and needs a system service, such as reading data from a file, it has to execute a trap instruction to transfer control to the operating system. Application – USER SPACE System Call KERNEL SPACE System Calls A system call is a request for service that a program makes of the kernel. The service is generally something that only the kernel has the privilege to do, such as doing I/O. Fork() ■ Fork creates a new process (child process). – It creates an exact duplicate of the original process, including all the file descriptors, registers—everything. ■ The fork is called once, but returns twice! – After the fork, the original process and the copy (the parent and child) go their separate ways. – The fork call returns a value, which is zero in the child and equal to the child's process identifier or PID in the parent. ■ Now consider how fork is used by the shell. When a command is typed, the shell forks off a new process. This child process must execute the user command. Fork() – PID (Process IDentity) ■ pid < 0 → the creation of a child process was unsuccessful. ■ pid == 0 → the newly created child. ■ pid > 0 → the process ID of the child process passes to the parent. Consider a piece of program: #include <unistd.h> P1 fork() C1 pid_t pid = fork(); PID:28 PID:34 printf(“PID: %d\n”, pid); …. The parent will print: PID: 34 And the child will always print: PID: 0 Fork() #define TRUE 1 while (TRUE) { /* repeat forever */ type_prompt(); /* display prompt on the screen */ read_command(command, parameters); /* read input from terminal */ if (fork() != 0) { /* fork off child process */ /* Parent code.
    [Show full text]
  • Assignment 1
    Assignment 1 Teaching Assistant: Michalis Pachilakis ( [email protected]) System Calls If a process is running a user program in user mode and needs a system service, such as reading data from a file, it has to execute a trap instruction to transfer control the operating system. Application –USER SPACE System call KERNEL SPACE System Calls A system call is a request for service that a program makes of the kernel. The service is generally something that only the kernel has the privilege to do, such as doing I/O. SYSTEM CALLS PROCESS CONTROL fork(), wait(), exec(),exit() FILE open(), close(), MANIPULATION read(), write() DIRECTORIES mkdir(),rmdir(), MANAGEMENT mount(),link() OTHER chdir(),chmod(), kill(),time() Fork() Fork creates a new process(child process). It creates an exact duplicate of the original process, including all the file descriptors, registers etc. The fork is called once, but returns twice! After the fork, the original process and the copy(the parent and the child) go their separate ways. The fork call returns a value, which is zero in the child and equal to the child’s process identifier (PID) in the parent. Now consider how fork is used by the shell. When a command is typed, the shell forks off a new process. This child process must execute the user command. Fork() – PID (Process IDentity) pid < 0 the creation of a child process was unsuccessful. pid == 0 the newly created child. pid > 0 the process ID of the child process passes to the parent Consider the program: #include <unistd.h> P1 fork() C1 PID:28 PID:34 pid_t pid = fork(); printf(“PID:%d\n”,pid); … The parent will print: PID:34 The child will always print: PID:0 Fork() #define TRUE 1 while (TRUE) { /* repeat forever */ type_prompt(); /* display prompt on the screen */ read_command(command, parameters); /* read input from terminal */ if (fork() != 0) { /* fork off child process */ /* Parent code.
    [Show full text]
  • Digital Notes on Linux Programming (R17a0525)
    DIGITAL NOTES ON LINUX PROGRAMMING (R17A0525) B.TECH III YEAR - I SEM (2019-20) DEPARTMENT OF INFORMATION TECHNOLOGY MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, INDIA. Linux Programming Page 1 MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY III Year B.Tech IT – I Sem L T /P/D C 4 - / - / - 4 (R17A0525)LINUX PROGRAMMING Objectives: To develop the skills necessary for Unix systems programming including file system programming, process and signal management, and interprocess communication. To make effective use of Unix utilities and Shell scripting language such as bash. To develop the basic skills required to write network programs using Sockets. UNIT I Linux Utilities-File handling utilities, Security by file permissions, Process utilities, Disk utilities, Networking commands, Filters, Text processing utilities and Backup utilities. Sed-Scripts, Operation, Addresses. Awk- Execution, Fields and Records, Scripts, Operation, Patterns, Actions. Shell programming with Bourne again shell(bash)- Introduction, shell responsibilities, pipes and Redirection, here documents, running a shell script, the shell as a programming language, shell meta characters, file name substitution, shell variables, shell commands, the environment, quoting, test command, control structures, arithmetic in shell, shell script examples. UNIT II Files and Directories- File Concept, File types, File System Structure, file metadata- Inodes, kernel support for files, system calls for file I/O operations- open, create, read, write, close, lseek, dup2,file status information-stat family, file and record locking-lockf and fcntl functions, file permissions - chmod, fchmod, file ownership- chown, lchown, fchown, links-soft links and hard links – symlink, link, unlink.
    [Show full text]
  • Basic Multiprocessing in UNIX
    BasicBasic MultiprocessingMultiprocessing inin UNIXUNIX WithWith ExamplesExamples ParallelParallel ApplicationsApplications ModernModern computerscomputers havehave multiplemultiple CPUCPU corescores (and/or(and/or multiplemultiple CPUs)CPUs) onon boardboard WeWe havehave toto bebe ableable toto utilizeutilize thethe computingcomputing powerpower byby parallelizingparallelizing ourour taskstasks CPUCPU InformationInformation LinuxLinux computer:computer: /proc//proc/cpuinfocpuinfo CatCat /proc//proc/cpuinfocpuinfo example:example: processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 65 model name : Dual-Core AMD Opteron(tm) Processor 8220 stepping : 3 cpu MHz : 2800.000 cache size : 1024 KB physical id : 0 siblings : 2 core id : 0 cpu cores : 2 fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm 3dnowext 3dnow pni cx16 lahf _lm cmp_legacy svm extapic cr8_legacy bogomips : 5625.16 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: ts fid vid ttp tm stc ProcessesProcesses inin UNIXUNIX UNIXUNIX isis nativelynatively parallelparallel operatingoperating systemsystem AA processprocess isis anan instanceinstance ofof runningrunning aa programprogram EachEach processprocess hashas aa uniqueunique processprocess idid ShellShell commandcommand ““psps”” givesgives thethe listlist ofof allall runningrunning
    [Show full text]
  • Lecture 3 : Process Management
    Lecture 3 : Process Management INSTRUCTOR : DR. BIBHAS GHOSHAL ([email protected]) 1 Lecture Outline What is Process? Process States Process Creation Process Address Space Creating a process by Cloning Process Termination Zombie Process Orphans Process Process Address Map in xv6 2 Process Program in Execution Process Comprises of: #include<stdio.h> . Code int main(){ . Data In User space of process Char str[] = “Hello World!\n”; . Stack Printf(“%s”,str); . Heap } . State in OS . $ gcc hello.c Kernel stack In Kernel space of process ELF Process Executable(a.out) $ ./a.out Program Process . Code + static & global data . Dynamic instantiation of code + data + heap + stack + process . One program can create several state processes . A process is unique isolated entity 3 Data Structure of Process Stack Recursive calls Attributes of a Process . Process Id Heap Dynamic allocation of data structures . Program counter . Static Variable Process State . & Once created, it will be there for lifetime Priority . Global Variable General Purpose Register . List of open files Executable a.out . List of open devices . Protection While executing a process, you are restricted to process boundary or else segmentation fault will occur. Heap grows upwards while Stack grows downwards. 4 Process State Process Scheduled Exit NEW READY RUN Terminate ◦ Created I/O Request over I/O Request WAIT Running: In the running state, a process is running on a processor. This means it is executing instructions. Ready: In the ready state, a process is ready to run but for some reason the OS has chosen not to run it at this given moment. Wait: In the blocked state, a process has performed some kind of operation that makes it not ready to run until some other event takes place.
    [Show full text]
  • Introduction To
    UNIVERSITY OF ENGINEERING AND TECHNOLOGY, TAXILA FACULTY OF TELECOMMUNICATION AND INFORMATION ENGINEERING SOFTWARE ENGINEERING DEPARTMENT OPERATING SYSTEM LAB #05 System Calls In UNIX System Call: A system call is just what its name implies—a request for the operating system to do something on behalf of the user’s program. fork() wait() exec() exit() fork() When the fork system call is executed, a new process is created which consists of a copy of the address space of the parent. The return code for fork is zero for the child process and the process identifier of child is returned to the parent process. On success, both processes continue execution at the instruction after the fork call. On failure, -1 is returned to the parent process. fork()—Sample Code Operating System 4th Semester-2k11-SE UET Taxila UNIVERSITY OF ENGINEERING AND TECHNOLOGY, TAXILA FACULTY OF TELECOMMUNICATION AND INFORMATION ENGINEERING SOFTWARE ENGINEERING DEPARTMENT Implementing fork() system call using C program #include<stdio.h> #include <unistd.h> /* contains prototype for fork */ #include <sys/types.h> main() { pid_t pid; pid = fork(); if (pid == 0) printf("\n I'm the child process"); else if (pid > 0) printf("\n I'm the parent process. My child pid is %d", pid); else perror("error in fork"); } /* Note: pid_t is a data type defines in types.h. Q: pid_t is a signed integer type only. Then why should we use pid_t? A: We don't have to know what type of integer (an int, short int, or long int ) the implementation uses for a pid value. So we use pid_t.
    [Show full text]