Working with the Unix OS

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Introduction to kernel Desirable Features ! efficiency response time resource utilization throughput ! reliability OS should be error free able to handle all contingencies ! maintainability modular in construction clearly defined interfaces well documented ! small size memory space large systems more prone to error Architecture of UNIX OS File System ! Ordinary Files It is not possible to insert bytes into the middle of a file, or delete bytes from the middle - editor for example - just write a completely new file concurrent access - file locking - semaphores i-number is an index into an array of inodes kept at the file system ! Directories Inconvenient to refer to files by i-numbers, directories provide names to be used two column table, name & i-number-pair is called a link usr/ast/data usr ---> i-number to usr directory relative path OR absolute path begins with / when link count is zero the kernel discards the file directory entry: 14 bytes for file, 2 bytes for inode-number /usr ==> /usr/ast ==> /usr/ast/data ! Special Files some type of device: tty, disk, FIFO block & character devices kernel pool of buffers - are used to cache to speed up I/O disks are both char & block special files special files have an i-node, no data bytes just a device number and index to device drivers ! I-node When file opens the inode is kept in memory. 1, file type 9 rwx protection bits + few other bits 2, number of links 3, owner id 4, group id 5, file size in bytes 6, 13 disk addresses 7, time file last read 8, time file last written 9, time i-node last changed 13, disk addresses largest file = 1G byte for 512 byte blocks 10 disk addresses ==> direct blocks of 512 bytes 11 ==> indirect - points to 128 addresses - points to data blocks 12 ==> double indirect - points to 128 addresses - points to 128 addresses - points to data blocks 13 ==> triple indirect - points to 128 addresses - points to 128 addresses - points to 128 addresses - points to data blocks 81
82 Introduction to kernel Programs & Processes A program is a collection of instructions & data that are kept in an ordinary file on disk the file is marked executable, the contents have to obey rules text file --------> object file -----> bind with libraries compile linker To run program, the kernel has to create a new process (environment in which program executes) A process consists of - instruction segment - userdata segment - system data segment A process's system data includes attributes such as - current directory, - open file descriptors, - CPU time, A process uses system calls to access & modify attributes A process is created by the kernel on behalf of a currently executing process, which becomes the parent of the new child process. The child inherits most of the parents system data attributes. The UNIX Kernel User Level Kernel Level traps The system calls for controlling processes are: user programs libraries system call interface file subsystem process control subsystem interprocess communication buffer cache scheduler memory management character block device drivers hardware control Kernel Level Hardware Level hardware System calls interact with the file subsystem and process control system. The file subsystem manages files, allocating file space, administrating free space, controlling access to files, retrieving data for users. The file subsystem accesses file data using a buffering mechanism that regulates data flow between the kernel and secondary storage devices. Block I/O devices are random access storage devices, raw devices are called character devices. The process control subsystem is responsible for process synchronization, interprocess communication, memory management, and process scheduling. Processes interact with file subsystem via systems calls: open, close, read, write, stat, chown, chmod. fork, exec, exit, wait, brk, signal. Memory management - swapping and demand paging Scheduler - allocates the CPU to processes IPC - asynchronous signaling of events to synchronous transmission of messages between processes Hardware control is responsible for handling interrupts and communicating with the machine.
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UNIVERSITY OF ATHENS DEPARTMENT OF
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Figure 27. Driver Entry Points.....
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Introduction to Unix ! Execution ma
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Introduction to Unix It works in th
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Introduction to Unix * matches 0 or
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Introduction to Unix vi file-name s
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Introduction to Unix 1,$s/^/>>/ 1,$
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Introduction to Unix ! Special Devi
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Introduction to Unix Working with F
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Introduction to Unix ! Communicatio
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Unix Shells 2. UNIX SHELLS Back Quo
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Unix Shells ! CASE Statement case t
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Unix Shells two lines !Y@Y@Z@Z@ZY c
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Unix Shells if $append then tee -a
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C Programming - Basics main() { int
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C Programming - Basics e.g. i += 2
Page 33 and 34: External Variables A C program cons
Page 35 and 36: C Programming - Basics main.c #incl
Page 37 and 38: C Programming - Basics default: pri
Page 39 and 40: C Programming - Basics struct tnode
Page 41 and 42: Unix Tools 4. UNIX TOOLS Tools of t
Page 43 and 44: Unix Tools Korn shell ! .profile HI
Page 45 and 46: Unix Tools grep "$name" $PHONEBOOK
Page 47 and 48: Unix Tools awk '$3 > 0 { print $1,
Page 49 and 50: Unix Tools END { print max, maxline
Page 51 and 52: Unix Tools Let an example input fil
Page 53 and 54: Unix Tools Brown eqn 1 # output Jon
Page 55 and 56: Development Tools Make looks at the
Page 57 and 58: Development Tools /* compute size o
Page 59 and 60: Development Tools #endif #line cons
Page 61 and 62: Development Tools 1.1 5 lines Retri
Page 63 and 64: Development Tools In Emacs, you may
Page 65 and 66: Development Tools */ %{ #define YYS
Page 67 and 68: C Libraries 6. C LIBRARIES Input an
Page 69 and 70: C Libraries } while (!feof(fp1)) pu
Page 71 and 72: C Libraries } free(p); /* what is w
Page 73 and 74: C Libraries } if ((fp->flag&( _READ
Page 75 and 76: C Libraries /* dirwalk: apply fcn t
Page 77 and 78: C Libraries } switch (pid=fork()){
Page 79 and 80: C Libraries What is curses? - libra
Page 81 and 82: C Libraries } if ((fd=fopen(argv[1]
Page 83: Introduction to kernel 7. INTRODUCT
Page 87 and 88: Introduction to kernel } { printf("
Page 89 and 90: Introduction to kernel The kernel r
Page 91 and 92: Introduction to kernel UNIX Interna
Page 93 and 94: Introduction to kernel File System
Page 95 and 96: Introduction to kernel Every proces
Page 97 and 98: Processes I Process States 1. Execu
Page 99 and 100: Processes I } printf("%d %s\n", cnt
Page 101 and 102: Processes I dup (and other similar
Page 103 and 104: Processes I The u area contains - p
Page 105 and 106: Processes I The Context of a Proces
Page 107 and 108: Processes I Process Control use and
Page 109 and 110: Processes I Although the processes
Page 111 and 112: Processes I Handling Signals - proc
Page 113 and 114: Processes I USER=neville PATH=/user
Page 115 and 116: Processes I ! Shadow Password /etc/
Page 117 and 118: struct timeval { long tv_sec; /* se
Page 119 and 120: Processes I F_SETFL set status flag
Page 121 and 122: Processes I process is the child pr
Page 123 and 124: Processes I Rules about sharing of
Page 125 and 126: Processes II 9. PROCESSES (II) FORK
Page 127 and 128: Processes II /* background.c */ #in
Page 129 and 130: Processes II } while (1){ printf("p
Page 131 and 132: Processes II } /* child */ signal (
Page 133 and 134: Processes II int readline(int fd, c
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Processes II { } char process_name[
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Processes II - Pipe in a single pro
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Processes II System V IPC - message
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Processes II int msgctl(int msqid,
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Processes II For every semop operat
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Processes II /* client loop */ mesg
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I/O Subsystem Drivers frequently sl
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I/O Subsystem Terminal Drivers - In
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I/O Subsystem Canonical Mode algori
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I/O Subsystem Raw Mode Raw mode is
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Figure 43. Pushing a Module onto a
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Interprocess Communication } { ptra
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Interprocess Communication T ID KEY
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Interprocess Communication }; int m
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Interprocess Communication for (i=0
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Interprocess Communication /* struc
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Interprocess Communication ! Compar
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… connect(sockfd,(struct sockaddr
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Interprocess Communication Address
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Process Scheduling Page Tables and
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Figure 49. Tie breaker rule Process
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Process Scheduling Clock - restart
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Process Scheduling Figure 57. Mappi
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Figure 62. Sequence of Swapping Ope
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Buffer Cache The kernel takes buffe
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Buffer Cache The kernel places the
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Buffer Cache Process B will find th
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Unix Administration 14. UNIX ADMINI
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Unix Administration Example output
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Unix Administration *) IN=-mtime -2
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Unix Administration Load /Unix kern
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Unix Administration for (i=0; i&i d
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Unix Administration fi done echo $s
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Unix Administration New Software !
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Unix Security Example: group name:g
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Unix Security $ crypt < exam320.Z >
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Unix Security - exported filesystem
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Unix Security system(cmdstr); $ ech
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Unix Security - repairs damaged use
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Working with the Unix OS

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