An Introduction to Operating Systems
Using UNIX
CMSC 104, Lecture 03 1

• A computer program
• Performs many operations:
• 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
CMSC 104, Lecture 03 2

How Do I Communicate With the
Computer Using the OS?
• You communicate using the particular OS’s user interface
• Graphical User Interface (GUI) - Windows
• Command-driven interface - DOS, UNIX,
Linux
• We will be using Linux, which is very similar to
UNIX
CMSC 104, Lecture 03 3

How Do I Communicate With the
Computer Using the OS?
• When you log in to the Linux system here, a user prompt will be displayed: linux1[#]% _ where # 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
CMSC 104, Lecture 03 4

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Files
Directories
Commands
Resources o books o links from course homepage
CMSC 104, Lecture 03 5

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A file is a sequence of bytes
Created by text editor (emacs, pico)
Created by other programs
May contain a program, data, a document, or other information (but all are text)
Files which contain other files are called
“directories” (sometimes called folders)
CMSC 104, Lecture 03 6

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Restrictions o no blanks, no metacharacters , length o case sensitive
Wildcards : * ?
CMSC 104, Lecture 03 7

• Directories can contain files or other directories called subdirectories
• Directories are organized in a hierarchical fashion
• They help us to keep our files organized
CMSC 104, Lecture 03 8

/afs/umbc.edu/users/b/o/bob junk pie recipes cookie apple peach choc_chip
CMSC 104, Lecture 03 9

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• Your home directory is where you are located when you log in
The current directory is where you are located at any time while you are using the system
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• 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
CMSC 104, Lecture 03 10

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Organizing your files
For example o make a subdirectory for CS104 o make subdirectories for each project
CMSC 104, Lecture 03 11

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(dot) is the current directory
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(dot-dot) is the parent directory
UNIX command cd “change directory”
Use dot-dot to move up the tree
Use directory name to move down
Use complete directory name (path name) to move anywhere
CMSC 104, Lecture 03 12

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• cp, mv, ls, rm, more, cat, cd, pwd mkdir, rmdir, passwd, man, lpr redirection: | < > ctl-c, ctl-d
CMSC 104, Lecture 03 13