Operating Systems and Using Linux

CMSC 104, Version 8/06 1L03OperatingSystems.ppt

Operating Systems and Using Linux

Topics

• What is an Operating System?• Linux Overview• Frequently Used Linux Commands

Reading

None.


What is an Operating System (OS)?

• A computer program

• Performs many operations, such as:

• Allows you to communicate with the computer (tell it what to do)

• Controls access (login) to the computer

• Keeps track of all processes currently running

• At this point, your main concern is how to communicate with the computer using the OS


What Is A Process?

• A process is a task or program that you have requested the operating system do on your behalf.

• That process is given an identifying number, called a PID (process ID).


How Do I Communicate With the Computer Using the OS?

• You communicate using the operating system’s user interface.

• Graphical User Interface (GUI) – Microsoft Windows, Linux KDE• Command-driven interface - DOS, UNIX, Linux, Microsoft Command Prompt

• We will be using the Linux operating system, which is very similar to UNIX.


How Do I Communicate With the Computer Using the OS? (con’t)

• When you log in to the Linux system here, a user prompt will be displayed:

linux#[1]% _

where # is the number of the Linux server that you have connected to. You may use any of the Linux servers.

• The number in the brackets will change as you work. It is the “number” of the command that you are about to type.

• If this prompt is not on the screen at any time, you are not communicating with the OS.


User Prompt

• While the normal (or default) prompt is: linux#[1]%you can change this.

• To learn Linux well enough to do this, we recommend that you take CMSC121, a one credit course.


Linux Overview

• Files and Filenames• Directories and Subdirectories• Frequently Used Commands


Files

• A file is a sequence of bytes.• It can be created by

o a text editor (xemacs or pico)o a computer program (such as a C program)

• It may contain a program, data, a document, or other information .

• Files that contain other files are called directories (sometimes called folders).


Linux Filenames

• Restrictionso May not contain blanks or other reserved characters.o Have a maximum length (however, make your

filenames long enough to be useful and short enough to type without making a mistake.

o Are case sensitive.• It is best to stick with filenames that contain letters

(uppercase or lowercase), numbers, and the underscore ( _ ) for now.

• Filenames that start with a period are hidden files, so that when see the files in a directory, they don’t show up.


Directories

• Directories contain files or other directories called subdirectories. They may also be empty.

• Directories are organized in a hierarchical fashion, or directories can contain other directories.

• They help us to keep our files organized.


Directories (con’t)

/afs/umbc.edu/users/j/d/jdoe28

junk recipes notes

pies cookies CMSC104

apple peach choc_chip



• One example is to have a directory for CMSC104.

• Inside you could have a directory for each project, and whatever.

• Rule of Thumb: Never have more files in one directory than fits on the screen when you list them.



• Your home directory is where you are located when you log in (e.g., /afs/umbc.edu/users/j/d/jdoe28).

• The current directory is where you are located at any time while you are using the system.

• Files within the same directory must be given unique names.

• Paths allow us to give the same name to different files located in different directories.

• Each running program has a current directory and all filenames are implicitly assumed to start with the name of that directory unless they begin with a slash.


Subdirectories

• Are used for organizing your files• For example,

o make a subdirectory for CMSC104o make subdirectories for each project

CMSC104

project1 project2 . . . project8


Moving in the Directory Tree

• . (dot) is the current directory.• . . (dot-dot) is the parent directory.• Use the Linux command cd to change

directories.• Use dot-dot to move up the tree.• Use the directory name to move down.• Use the complete directory name (path

name) to move anywhere.


Pathnames

• Pathnames that start at the beginning (and start with a /): /afs/umbc.edu/users/j/d/jdoe28are called absolute pathnames.

• Pathnames can be shorted, so that if jdoe28 is the current directory and we have a file in that directory call schedule, we can edit it with just the filename (a relative pathname):pico schedule


Permissions

• Files and directories have permissions.• There are three sets of permissions for

three groups:o Read, write, execute (or, if a directory, access)o User, group, other

• You are the user, and can set and change permissions.


Frequently Used Linux Commands

• passwd, man, lpr• pwd, ls, cat, more, cd, cp, mv, rm• mkdir, rmdir• ctrl-c, ctrl-z

References:• Linux man pages• Links from the 104 homepage• Books and the Internet


Linux Command Format

• Fromat: cmd options arguments• Options and arguments are optional.• Options start with - or - -• Options are different for each command.• Arguments are different for each command.• When in doubt, look up the command in the

on-line help, man.


man

• On-line help.• Argument is the command you wish to have

help for.• Option –k is most common, which looks for

a description that contains the argument.• When the description of a command takes

more than one screen to display, press the space bar for more information and q to quit.


man (cont’d)

• Example:[burt@linux1 ~]$ man -k passwd

htpasswd htpasswd (1) - Create and update user authentication fileskpasswd kpasswd (1) - change a user's Kerberos password

mkpasswd mkpasswd (1) - generate new password, optionally apply it to a user

passwd.nntp passwd.nntp (5) - passwords for connecting to remote NNTP servers

saslpasswd saslpasswd (8) - set a user's sasl passwordsaslpasswd2 saslpasswd2 (8) - set a user's sasl password

v5passwd v5passwd (1) - change a user's Kerberos password


passwd

• Used to change your password.NAME passwd - update a user's authentication tokens(s)

SYNOPSIS passwd [-k] [-l] [-u [-f]] [-d] [-n mindays] [-x

maxdays] [-w warndays] [-i inactivedays] [-S] [username]


lpr

• Used to print something on the printer.• You must pay per page.• Pick up your print-out at ECS-019.


cd

• Change directory.• With no argument, it will take you back to

your home directory.• With a argument, it will set that directory to

be your current working directory, assuming you have permission to access the directory.


pwd

• Print the current working directory.• Helpful when you forget where you are.• Has no options or arguments.


ls

• Lists the names of files in a directory.• Arguments are name(s) of file(s) and/or

director(ies).• Normally, when you specify a directory, you

get the contents of the directory.


ls Options

• -a all (including hidden files)• -d just show the directory, not the files in the

directory• -F classify files as ordinary, directory (/), or

executable (*)• --color classify with color• -l long format• -r show in reverse order• -R recursive, show the contents of all subdirectories.


cat

• Used to display the contents of a file.• If there is too much to fit on the screen, the

first part scrolls off and leaves only the last screenful.

• Argument is the name of a file or files.• Useful option is –n (or –number) to show

the line numbers.


more

• More shows a screen full of a file at a time. SYNOPSIS more [-dlfpcsu] [-num] [+/ pattern] [+ linenum] [file]

DESCRIPTION More is a filter for paging through text one

screenful at a time. This version is especially primitve. Users should realize that less(1) provides more(1) emulation and extensive enhancements.

• Less is a similar command with more features.


cp

• This allows you to create a new copy of an existing file.

• Two mandatory arguments, source and destination.o Source is the name of the existing file.o Destination is the name for new file.

• If you change the contents of the new file, you do not change the contents of the old file.


ln

• Allows you to create two names for one file by “linking” them, similar to a shortcut in Microsoft Windows.

• Two mandatory options are the source and destination, just like for cp.

• If you change the new version, you change the old version.


mv

• This allows you to rename a file and/or move it to a new location.

• Two mandatory arguments, source and destination.o Source is the name of the existing file.o Destination is the new name and/or location for

the existing file.• At completion, there is only one file.


rm

• Allows you to remove or delete a file.• Normally, once a file is removed, it is gone

forever!• (UMBC has changed this and it moves the

file to a backup directory, where you can recover it, if necessary. However, this is not a long-term option!)


rm (cont’d)

• The argument(s) are a list of files to remove.• Options include:

o -i interactive, ask first (UMBC has set this as the default)

o -r recursive, delete the files in the subdirectories and the subdirectories.

• NOTE: rm –r directory will remove directories that are not empty!


mkdir

• Used to create a new directory.• Argument(s) is/are the name(s) of the new

directory(ies).


Wildcard Characters

• You will find wildcard characters useful when manipulating files (e.g., listing or moving them).

• The wildcard characters are * and ?• ? is used to represent any single character.• * is used to represent 0 or more characters.

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