Working with the Unix OS

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Introduction to kernel ... C runtime library open(char *name, int mode) { place parameters in registers. execute trap instruction, switching to kernel code return result of system call } Kernel system call vector table ... address of kernel close() address of kernel open() address of kernel write() ... ----------------------------------- kernel system call code kernel code for open() { manipulate kernel data structures ... return to user code and user mode } The scheduler will not assign the CPU to another process during the execution of a system call. i.e. when a process performs a system call, it cannot be "preempted". System calls that make I/O requests from a device, may take time to complete. To avoid leaving the CPU idle, the kernel puts the process to sleep and wakes it with a hardware interrupt signalling I/O completion. Interrupts highest priority 0 1 2 3 4 Interrupt vector table hardware errors clock disk I/O keyboard traps S/W interrupts pointers to kernel interrupt handlers lowest priority current process suspend resume ----------------------------> - - - - - - - - - - - - - - - -------------------------------> | | | keyboard interrupt handler | |----------------------------------------------->| keyboard interrupt completed When an interrupt occurs, the current process is suspended and the kernel determines the source of the interrupt. It then examines the interrupt vector table to find the location of the code to process the interrupt. If a higher priority interrupt than the current arrives, the lower priority interrupt handler is suspended until the higher priority interrupt completes. Critical sections of kernel code protect themselves from interrupts by temporarily disabling interrupts. … 89
Introduction to kernel File System regular files - contain data – standard I/O system calls directory files - backbone of fs – directory system calls special files - peripherals – standard I/O system calls ! Disk architecture cylinders tracks sectors blocks 4K bytes ! Interleaving 1:1 interleave - logically contiguous blocks 3:1 interleave - e.g. 8 sectors, blocks 1 4 7 2 5 8 3 6 ! Fragmentation loss of storage due to under-use of last block ! Scattered file blocks are rarely contiguous ! Block I/O To read the first byte of data from a file, using the read system call, the device driver issues an I/O request to the disk controller to read the first 4K block into a kernel buffer, then copies the first byte to your process. ! Inodes Index Node to store information about each file. The Inode of regular or directory file contains the location or its disk blocks, the inode of special file contains peripheral device information. type of file file permissions user and group ids hard link count last modified, last accesses times location of blocks or major and minor numbers symbolic link ! Block Map Only the first 10 blocks of a file are stored directly in the inode. Larger files use indirect addressing schemes. File System Layout The first logical block of disk is the "boot block". The second logical block is the superblock, contains information about disk. Followed by the inode list, each block holding about 40 inodes. The remaining blocks store directory and user files. Superblock - Total number of blocks in file system - Number of inodes in inode free list - Free block bitmap - linear sequence of bits, one per disk block, 1 indicates it is free - Size of block in bytes - Number of free blocks - Number of used blocks ! Bad blocks mkfs - location of all bad blocks on disk inode number 1 90
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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 $append then tee -a
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C Programming - Basics main() { int
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C Programming - Basics e.g. i += 2
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External Variables A C program cons
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C Programming - Basics main.c #incl
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C Programming - Basics default: pri
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C Programming - Basics struct tnode
Page 41 and 42: Unix Tools 4. UNIX TOOLS Tools of t
Page 43 and 44: Unix Tools Korn shell ! .profile HI
Page 45 and 46: Unix Tools grep "$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 and 84: Introduction to kernel 7. INTRODUCT
Page 85 and 86: 82 Introduction to kernel Programs
Page 87 and 88: Introduction to kernel } { printf("
Page 89 and 90: Introduction to kernel The kernel r
Page 91: Introduction to kernel UNIX Interna
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
Page 135 and 136: Processes II { } char process_name[
Page 137 and 138: Processes II - Pipe in a single pro
Page 139 and 140: Processes II System V IPC - message
Page 141 and 142: 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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