DOCSLIB.ORG

Bca-404 Unix and Shell Programming (Unit-Iii)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Bca-404 Unix and Shell Programming (Unit-Iii) BCA-404 UNIX AND SHELL PROGRAMMING (UNIT-III) General Purpose Utilities Calendar The cal command to see the calculator of any specific month or a complete year. Syntax: cal [[ month ] year ] ECHO echo is one of the most commonly and widely used built-in command for Linux bash and C shells, that typically used in scripting language and batch files to display a line of text/string on standard output or a file. Syntax: echo [OPTION]... [STRING]... Printf: Display text in formatted %s String %30s print space in a 30 characters wide %d decimal %o octal %x Hexadecimal %f Floating point number Example : $ printf "%s\n" "hello printf" "in" "bash script" hello printf in bash script bc - Unix calculator bc is a unix command which stands for bench calcultor. Depending on the way we use it, it can either look like a programming language or as a interactive mathematic shell. Let us see in this article how to use bc to do some simple arithmetic. passwd ---- Assigning password passwd username who are the users w ---- to know who are the users connected who am i Uname: features of operating system. uname -a ----- all the details uname -r ---- kernel version DATE : Displaying the System Date you can display the current date with date command, which shows the date and time to nearest second. Syntax: date Process states and Transitions in a UNIX Process Process A process is an instance of a program in execution. A set of processes combined together make a complete program. There are two categories of processes in Unix, namely User processes: They are operated in user mode. Kernel processes: They are operated in kernel mode. Process States The states that a Process enters in working from start till end are known as Process states. These are listed below as: Created-Process is newly created by system call, is not ready to run User running-Process is running in user mode which means it is a user process. Kernel Running-Indicates process is a kernel process running in kernel mode. Zombie- Process does not exist/ is terminated. Preempted- When process runs from kernel to user mode, it is said to be preempted. e-notes by Naveen Kumar Gupta Page 1 BCA-404 UNIX AND SHELL PROGRAMMING (UNIT-III) Ready to run in memory- It indicated that process has reached a state where it is ready to run in memory and is waiting for kernel to schedule it. Ready to run, swapped– Process is ready to run but no empty main memory is present Sleep, swapped- Process has been swapped to secondary storage and is at a blocked state. Asleep in memory- Process is in memory(not swapped to secondary storage) but is in blocked state. Process Transitions The working of Process is explained in following steps: 1. User-running: Process is in user-running. 2. Kernel-running: Process is allocated to kernel and hence, is in kernel mode. 3. Ready to run in memory: Further, after processing in main memory process is rescheduled to the Kernel.i.e.The process is not executing but is ready to run as soon as the kernel schedules it. 4. Asleep in memory: Process is sleeping but resides in main memory. It is waiting for the task to begin. 5. Ready to run, swapped: Process is ready to run and be swapped by the processor into main memory, thereby allowing kernel to schedule it for execution. 6. Sleep, Swapped: Process is in sleep state in secondary memory, making space for execution of other processes in main memory. It may resume once the task is fulfilled. 7. Pre-empted: Kernel preempts an on-going process for allocation of another process, while the first process is moving from kernel to user mode. 8. Created: Process is newly created but not running. This is the start state for all processes. 9. Zombie: Process has been executed thoroughly and exit call has been enabled.The process, thereby, no longer exists. But, it stores a statistical record for the process. This is the final state of all processes. Manipulation of a process address space The region table entry contains the following information: The i-node of the file from which the region was initially loaded The type of the region (text, shared memory, private data, or stack) The size of the region The location of the region in physical memory. The state of the region: locked, in demand, being loaded into memory, valid, loaded into memory The reference count, giving the number of processes that reference the region e-notes by Naveen Kumar Gupta Page 2 BCA-404 UNIX AND SHELL PROGRAMMING (UNIT-III) The operations that manipulate regions are: lock a region unlock a region allocate a region attach a region to the memory space of a process change the size of a region load a region from a file into the memory space of a process free a region detach a region from the memory space of a process, and duplicate the contents of a region sleep process in unix sleep command is used to create a dummy job. A dummy job helps in delaying the execution. It takes time in seconds by default but a small suffix(s, m, h, d) can be added at the end to convert it into any other format. This command pauses the execution for an amount of time which is defined by NUMBER. Syntax: sleep NUMBER[SUFFIX]... Process creation in unix A process is simply a running program. A process is said to be born when the program starts execution and remains alive till the process is active. After the execution the process is said to be died.A process in a Unix system is created by fork system call. Every process except process 0 is created. The process that invokes the fork system call is parent process and the newly created process is the child process. Every process has one parent process but a parent can have many child process. The kernel identifies it process by its process identification number (PID). Process 0 is a special process created "by hand" when the system boots. There are 3 distinct phase in mechanism of process creation and uses 3 system calls: fork(), exec() and wait(). fork(): Creates a child process. A new process is created because an existing process creates an exact copy of itself. This child process has the same environment as its parent but only the PID is different. This procedure is known as forking. exec(): After forking the process, the address space of the child process is overwritten by the new process data. This is done through exec call to the system. No new process is created over here. The PID & PPID remains unchanged. wait(): The parent then executes wait system call to wait for the child process to complete its execution. The important attributes that are inherited by the child process from its parents are: Real UID and GID, PGID, Nice value, Environment setting, Current working directory, memory segments etc. When the process dies it immediately moves to the zombie state and remains in that state until the parent picks it up to exit status. A zombie is the harmless dead child. Process termination in unix Process termination occurs when the process is terminated The exit() system call is used by most operating systems for process termination. Some of the causes of process termination are as follows − A process may be terminated after its execution is naturally completed. This process leaves the processor and releases all its resources. A child process may be terminated if its parent process requests for its termination. A process can be terminated if it tries to use a resource that it is not allowed to. For example - A process can be terminated for trying to write into a read only file. If an I/O failure occurs for a process, it can be terminated. For example - If a process requires the printer and it is not working, then the process will be terminated. In most cases, if a parent process is terminated then its child processes are also terminated. This is done because the child process cannot exist without the parent process. If a process requires more memory than is currently available in the system, then it is terminated because of memory scarcity. The user-id of a process Every process has a real user ID (the UID), an effective user ID (the EUID), a real user group ID (the GID), and an effective user group ID (the EGID). The user group ID is distinct from the process group ID. The real IDs are used for accounting and user-user communication, while the effective IDs are used to control access to files and control signal sending. e-notes by Naveen Kumar Gupta Page 3 BCA-404 UNIX AND SHELL PROGRAMMING (UNIT-III) A user ID is associated with each user login name in the password file /etc/passwd. This is assigned to the user's shell as its UID and EUID, and is inherited by processes spawned from the shell. The user IDs can be accessed with the system calls: int getuid(void) which gets the UID of the process, and int geteuid(void) which gets the EUID of the process. Each entry in /etc/passwd also has a group ID which is given to the shell as its initial GID and EGID. The group IDs can be accessed with the system calls: int getgid(void) which gets the GID of the process and int getegid() which gets the EGID of the process.
Load more

Recommended publications
  • Process Text Streams Using Filters
    Process Text Streams Using Filters OBJECTIVE: Candidates should should be able to apply filters to text streams. 1 Process Text Streams Using Filters KeyKEY knowledge KNOWLEDGE area(s): AREAS: Send text files and output streams through text utility filters to modify the output using standard UNIX commands found in the GNU textutils package. 2 Process Text Streams Using Filters KEY FILES,TERMS, UTILITIES cat nl tail cut paste tr expand pr unexpand fmt sed uniq head sort wc hexdump split join tac 3 cat cat the editor - used as a rudimentary text editor. cat > short-message we are curious to meet penguins in Prague Crtl+D *Ctrl+D - command is used for ending interactive input. 4 cat cat the reader More commonly used to flush text to stdout. Options: -n number each line of output -b number only non-blank output lines -A show carriage return Example cat /etc/resolv.conf ▶ search mydomain.org nameserver 127.0.0.1 5 tac tac reads back-to-front This command is the same as cat except that the text is read from the last line to the first. tac short-message ▶ penguins in Prague to meet we are curious 6 head or tail using head or tail - often used to analyze logfiles. - by default, output 10 lines of text. List 20 first lines of /var/log/messages: head -n 20 /var/log/messages head -20 /var/log/messages List 20 last lines of /etc/aliases: tail -20 /etc/aliases 7 head or tail The tail utility has an added option that allows one to list the end of a text starting at a given line.
    [Show full text]
  • A Brief Introduction to Unix-2019-AMS
    Brief Intro to Linux/Unix Brief Intro to Unix (contd) A Brief Introduction to o Brief History of Unix o Compilers, Email, Text processing o Basics of a Unix session o Image Processing Linux/Unix – AMS 2019 o The Unix File System Pete Pokrandt o Working with Files and Directories o The vi editor UW-Madison AOS Systems Administrator o Your Environment [email protected] o Common Commands Twitter @PTH1 History of Unix History of Unix History of Unix o Created in 1969 by Kenneth Thompson and Dennis o Today – two main variants, but blended o It’s been around for a long time Ritchie at AT&T o Revised in-house until first public release 1977 o System V (Sun Solaris, SGI, Dec OSF1, AIX, o It was written by computer programmers for o 1977 – UC-Berkeley – Berkeley Software Distribution (BSD) linux) computer programmers o 1983 – Sun Workstations produced a Unix Workstation o BSD (Old SunOS, linux, Mac OSX/MacOS) o Case sensitive, mostly lowercase o AT&T unix -> System V abbreviations 1 Basics of a Unix Login Session Basics of a Unix Login Session Basics of a Unix Login Session o The Shell – the command line interface, o Features provided by the shell o Logging in to a unix session where you enter commands, etc n Create an environment that meets your needs n login: username n Some common shells n Write shell scripts (batch files) n password: tImpAw$ n Define command aliases (this Is my password At work $) Bourne Shell (sh) OR n Manipulate command history IHateHaving2changeMypasswordevery3weeks!!! C Shell (csh) n Automatically complete the command
    [Show full text]
  • How the /Etc/Passwd File Relates to the Laua User
    Page 1 (2) System Foundation 9.0 laua User and Group How the /etc/passwd File Relates to the laua User Scenario Most users who need access to the Lawson environment will need to have a user account set up on the Operating System where Lawson System Foundation 9.0 has been installed. Users will need resources allocated to run their jobs and space in the directory structure to store their print files. The user account on the Operating System is what allows the allocation of resources and space. In the example presented in this session, users are associated to the Unix Operating System and setup via the /etc/passwd file. The information stored on the user account in the file is used by Lawson’s Legacy Security System, laua. This scenario will present the /etc/passwd file and highlight the important parts of the user represented in the file and how it relates to user setup. Workflow Step 1 of 3: To verify that a user has an account on the Unix Operating System where the Lawson server resides, view the /etc/passwd file on the Lawson server. To do so, you must first access a command line which can be done either through LID (Lawson Insight Desktop) or through lawterminal which is command line access through the Lawson portal. This demonstration will use LID. First access your command line. Action: Type in 'cd /etc' and press the 'Enter' key. © Copyright Lawson Learning 2008 Page 2 (2) Step 2 of 3: You can use any method you choose to view the file.
    [Show full text]
  • The AWK Programming Language
    The Programming ~" ·. Language PolyAWK- The Toolbox Language· Auru:o V. AHo BRIAN W.I<ERNIGHAN PETER J. WEINBERGER TheAWK4 Programming~ Language TheAWI(. Programming~ Language ALFRED V. AHo BRIAN w. KERNIGHAN PETER J. WEINBERGER AT& T Bell Laboratories Murray Hill, New Jersey A ADDISON-WESLEY•• PUBLISHING COMPANY Reading, Massachusetts • Menlo Park, California • New York Don Mills, Ontario • Wokingham, England • Amsterdam • Bonn Sydney • Singapore • Tokyo • Madrid • Bogota Santiago • San Juan This book is in the Addison-Wesley Series in Computer Science Michael A. Harrison Consulting Editor Library of Congress Cataloging-in-Publication Data Aho, Alfred V. The AWK programming language. Includes index. I. AWK (Computer program language) I. Kernighan, Brian W. II. Weinberger, Peter J. III. Title. QA76.73.A95A35 1988 005.13'3 87-17566 ISBN 0-201-07981-X This book was typeset in Times Roman and Courier by the authors, using an Autologic APS-5 phototypesetter and a DEC VAX 8550 running the 9th Edition of the UNIX~ operating system. -~- ATs.T Copyright c 1988 by Bell Telephone Laboratories, Incorporated. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopy­ ing, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America. Published simultaneously in Canada. UNIX is a registered trademark of AT&T. DEFGHIJ-AL-898 PREFACE Computer users spend a lot of time doing simple, mechanical data manipula­ tion - changing the format of data, checking its validity, finding items with some property, adding up numbers, printing reports, and the like.
    [Show full text]
  • Basic Unix/Linux Commands
    Unix/Linux Basic commands Learn the basics of grep, sed, awk, find, sort, uniq, cut, cat, etc We will study them using sample requirements 1. Determine all the users that are having at least two first names. Using /etc/passwd file as an input. 2. Replace all the bash shells with csh in the /etc/passwd file. Eg. /bin/bash should be replaced with /bin/csh. 3. Replace all the home directories with /home/missing in the same /etc/passwd file. 4. Count the number of lines in a file. 5. Count the number of words starting with letter b/B in /etc/passwd file. 6. Determine the most popular family name found in the /etc/passwd file. 7. Display all text file names in the current directory ordered by their name. 8. Display all the files having more than 100 bytes. 9. Display all the files that the current user has at least read permission. 10. Sort the content of the /etc/passwd file ascending/descending by the fifth column. 11. Display the first 25 lines from the /etc/passwd file. 12. Display the last 30 lines from the /etc/passwd file. 13. If a file has N lines display the lines between N/2 and N/2+10. 14. Display all the unique parent directories from the /etc/passwd file. Eg. on the sixth column we have the home directory, like: /home/scs/master/an1/gr246/abicr2020, from this we will consider the /home/scs/master/an1/gr246/ as the parent directory. 15. Display the first 10 characters from each line of /etc/passwd file.
    [Show full text]
  • Manipulating Files and Directories
    MANIPULATING FILES AND DIRECTORIES At this point, we are ready for some real work! This chapter will introduce the following commands: z cp—Copy files and directories. z mv—Move/rename files and directories. z mkdir—Create directories. z rm—Remove files and directories. z ln—Create hard and symbolic links. These five commands are among the most frequently used Linux com- mands. They are used for manipulating both files and directories. Now, to be frank, some of the tasks performed by these commands are more easily done with a graphical file manager. With a file manager, we can drag and drop a file from one directory to another, cut and paste files, delete files, and so on. So why use these old command-line programs? www.it-ebooks.info The answer is power and flexibility. While it is easy to perform simple file manipulations with a graphical file manager, complicated tasks can be easier with the command-line programs. For example, how could we copy all the HTML files from one directory to another—but only those that do not exist in the destination directory or are newer than the versions in the destination directory? Pretty hard with a file manager. Pretty easy with the command line: cp -u *.html destination Wildcards Before we begin using our commands, we need to talk about the shell fea- ture that makes these commands so powerful. Because the shell uses file- names so much, it provides special characters to help you rapidly specify groups of filenames. These special characters are called wildcards.
    [Show full text]
  • A. -D B. -L C. -1 D. -I E. -A A
    Ian! D. Allen − Fall 2012 -1- 45 minutes Ian! D. Allen − Fall 2012 -2- 45 minutes 7. [61/123] If I am in my home directory named /home/me and mt is an empty sub- Test Version: ___ Print Name: directory,what is true after this command line: touch ./foo ; mv ./mt/../foo ../me/bar Multiple Choice - 52 Questions - 15 of 15% a. the directory mt nowcontains only a file named bar 1. Read all the instructions and both sides (back and front) of all pages. b. there is a second copyofthe file named foo in the file named bar 2. Put the Test Version above into NO. OF QUESTIONS and NO. OF STUDENTS c. the command fails because path ./mt/../foo does not exist 3. Answer the questions you know, first. One Answer Only per question. d. the command fails because path ../me/bar does not exist 4. Manage your time when answering questions on this test! e. the directory mt/.. nowhas a file named bar in it 8. [63/125] In the output of ls -a,the one-character name . signifies what? 1. [49/126] If my current directory is /bin,which of these pathnames is equivalent to the file name /bin/ls? a. Acurrent file. a. ../bin/ls/. b. /root/bin/ls c. ls/. b. The current directory. d. ./bin/ls e. ../../bin/ls c. The parent directory. d. Aname that is hidden. 2. [52/125] If my current working directory is /home,and my home directory is e. Aname with an unprintable character. /home/ian,which command copies file /bin/ls into my home directory under the name me? 9.
    [Show full text]
  • Linux File System and Linux Commands
    Hands-on Keyboard: Cyber Experiments for Strategists and Policy Makers Review of the Linux File System and Linux Commands 1. Introduction Becoming adept at using the Linux OS requires gaining familiarity with the Linux file system, file permissions, and a base set of Linux commands. In this activity, you will study how the Linux file system is organized and practice utilizing common Linux commands. Objectives • Describe the purpose of the /bin, /sbin, /etc, /var/log, /home, /proc, /root, /dev, /tmp, and /lib directories. • Describe the purpose of the /etc/shadow and /etc/passwd files. • Utilize a common set of Linux commands including ls, cat, and find. • Understand and manipulate file permissions, including rwx, binary and octal formats. • Change the group and owner of a file. Materials • Windows computer with access to an account with administrative rights The Air Force Cyber College thanks the Advanced Cyber Engineering program at the Air Force Research Laboratory in Rome, NY, for providing the information to assist in educating the general Air Force on the technical aspects of cyberspace. • VirtualBox • Ubuntu OS .iso File Assumptions • The provided instructions were tested on an Ubuntu 15.10 image running on a Windows 8 physical machine. Instructions may vary for other OS. • The student has administrative access to their system and possesses the right to install programs. • The student’s computer has Internet access. 2. Directories / The / directory or root directory is the mother of all Linux directories, containing all of the other directories and files. From a terminal users can type cd/ to move to the root directory.
    [Show full text]
  • Permissions and Ownership
    Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ Objective 1 Understand User and Group Configuration Files Information on users and groups on a Linux system is kept in the following files: ■ /etc/passwd ■ /etc/shadow ■ /etc/group Whenever possible, you should not modify these files with an editor. Instead, use the Security and Users modules in YaST or the command line tools described in the next objective, “Manage User Accounts and Groups from the Command Line” on 7-12. Modifying these files with an editor can lead to errors (especially in /etc/shadow), such as a user—including the user root—no longer being able to log in. To ensure consistency of these files, you need to understand how to ■ Check /etc/passwd and /etc/shadow ■ Convert Passwords to and from Shadow /etc/passwd The file /etc/passwd stores information for each user. In the past, UNIX and Linux users were handled in a single file: /etc/passwd. The user name, the UID, the home directory, the standard shell, and the encrypted password were all stored in this file. The password was encrypted using the function crypt (man 3 crypt). In principle, the plain text password could not be deciphered from the encrypted password. 7-2 Version 2 Use the Command Line Interface to Administer the System However, there are programs (such as john) that use dictionaries to encrypt various passwords with crypt, and then compare the results with the entries in the file /etc/passwd. With the calculation power of modern computers, simple passwords can be “guessed” within minutes.
    [Show full text]
  • User Accounts User Accounts User Info /Etc/Passwd User Info /Etc
    User Accounts Even a single-user workstation (Desktop Computer) uses multiple accounts. Such a computer may have just one user account, but several system accounts help keep the computer running. Accounts enable multiple users to share a single computer without causing each other too much trouble. User Accounts The Users in a Linux system are stored in the /etc/passwd file. If you are on your own VM - somewhere near the bottom you should see yourself and joe. On a brand new install you will see many users listed. Of course if you recall, we only added ourselves and joe. So what are all these other users for? These users are added because we don’t want to give sudo power to all of our programs. So each program installed gets its own user with its own limited permissions. This is a protection for our computer. User Info /etc/passwd Examine the /etc/passwd file using cat or less . Here is what we are seeing: It is colon : separated. So each : denotes a new column. username password The x is just a place-holder. The password is not really in this file User ID (UID) Just like every computer needs a unique ip address, every user needs a unique id. User Info /etc/passwd Group ID (GID) Every user belongs to its own group, with its own group id Comment field This is the Full name, phone number, office number, etc. It is okay if it is blank. Home Directory This is the location of the users home directory - This is how we can know the full path of any users home directory - /home/smorgan vs /home/s/smorgan.
    [Show full text]
  • Unix Commands (09/04/2014)
    Unix Commands (09/04/2014) • Access control – login <login_name> – exit – passwd <login_name> – yppassswd <loginname> – su – • Login as Super user – su <login> • Login as user <login> • Root Prompt – [root@localhost ~] # • User Prompt – [bms@raxama ~] $ On Line Documentation – man <command/topic> – info <command/topic> • Working with directories – mkdir –p <subdir> ... {-p create all directories in path if not present} mkdir –p /2015/Jan/21/14 will create /2015, Jan, 21 & 14 in case any of these is absent – cd <dir> – rm -r <subdir> ... Man Pages • 1 Executable programs or shell commands • 2 System calls (functions provided by the kernel) • 3 Library calls (functions within program libraries) • 4 Special files (usually found in /dev) • 5 File formats and conventions eg /etc/passwd • 6 Games • 7 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7) • 8 System administration commands (usually only for root) • 9 Kernel routines [Non standard] – man grep, {awk,sed,find,cut,sort} – man –k mysql, man –k dhcp – man crontab ,man 5 crontab – man printf, man 3 printf – man read, man 2 read – man info Runlevels used by Fedora/RHS Refer /etc/inittab • 0 - halt (Do NOT set initdefault to this) • 1 - Single user mode • 2 - Multiuser, – without NFS (The same as 3, if you do not have networking) • 3 - Full multi user mode w/o X • 4 - unused • 5 - X11 • 6 - reboot (Do NOT set init default to this) – init 6 {Reboot System} – init 0 {Halt the System} – reboot {Requires Super User} – <ctrl> <alt> <del> • in tty[2-7] mode – tty switching • <ctrl> <alt> <F1-7> • In Fedora 10 tty1 is X.
    [Show full text]
  • Basic Unix Command
    Basic Unix Command The Unix command has the following common pattern command_name options argument(s) Here we are trying to give some of the basic unix command in Unix Information Related man It is used to see the manual of the various command. It helps in selecting the correct options to get the desirable output. Just need to give man command finger Getting information about a local and remote user. Sometimes you may want to know what all user are currently logged into the Unix system then this will help passwd Changing your password for the user. If you are logged in, then enter passwd,it will change the password for the current user. From root login you can change password for any user by using passwd who Finding out who is logged on which find the source directory of the executable being used uname print name of current system. On Solaris uname -X will give the cpu and various other informations uptime Time since the last reboot File listing and directory manipulation command ls List contents of Directory(s) Syntax: ls options OPTIONS The following options are supported:-a Lists all entries, including those that begin with a dot (.), which are normally not listed. -d If an argument is a directory, lists only its name (not its contents); often used with -l to get the status of a directory. -n The same as -l, except that the owner's UID and group's GID numbers are printed, rather than the associated character strings. -r Reverses the order of sort to get reverse alphabetic or oldest first as appropriate.
    [Show full text]