3rd assignment

In the table below we summarize the more frequently used commands on a Unix system. In this table, as in general, for most Unix commands, file, could be an actual file name, or a list of file names, or input/output could be redirected to or from the command.
Unix Commands Command/Syntax What it will do
awk/nawk [options] file scan for patterns in a file and process the results
cat [options] file concatenate (list) a file
cd [directory] change directory
chgrp [options] group file change the group of the file
chmod [options] file change file or directory access permissions
chown [options] owner file change the ownership of a file; can only be done by the superuser
chsh (passwd -e/-s) username login_shell change the user's login shell (often only by the superuser)
cmp [options] file1 file2 compare two files and list where differences occur (text or binary files)
compress [options] file compress file and save it as file.Z
cp [options] file1 file2 copy file1 into file2; file2 shouldn't already exist. This command creates or overwrites file2.
cut (options) [file(s)] cut specified field(s)/character(s) from lines in file(s)
date [options] report the current date and time
dd [if=infile] [of=outfile] [operand=value] copy a file, converting between ASCII and EBCDIC or swapping byte order, as specified
diff [options] file1 file2 compare the two files and display the differences (text files only)
df [options] [resource] report the summary of disk blocks and inodes free and in use
du [options] [directory or file] report amount of disk space in use
echo [text string] echo the text string to stdout
ed or ex [options] file Unix line editors
emacs [options] file full-screen editor
expr arguments evaluate the arguments. Used to do arithmetic, etc. in the shell.
file [options] file classify the file type
find directory [options] [actions] find files matching a type or pattern
finger [options] user[@hostname] report information about users on local and remote machines
ftp [options] host transfer file(s) using file transfer protocol
grep [options] 'search string' argument

egrep [options] 'search string' argument

fgrep [options] 'search string' argument
search the argument (in this case probably a file) for all occurrences of the search string, and list them.
gzip [options] file

gunzip [options] file

zcat [options] file
compress or uncompress a file. Compressed files are stored with a .gz ending
head [-number] file display the first 10 (or number of) lines of a file
hostname display or set (super-user only) the name of the current machine
kill [options] [-SIGNAL] [pid#] [%job] send a signal to the process with the process id number (pid#) or job control number (%n). The default signal is to kill the process.
ln [options] source_file target link the source_file to the target
lpq [options]

lpstat [options]
show the status of print jobs
lpr [options] file

lp [options] file
print to defined printer
lprm [options]

cancel [options]
remove a print job from the print queue
ls [options] [directory or file] list directory contents or file permissions
mail [options] [user]

mailx [options] [user]

Mail [options] [user]
simple email utility available on Unix systems. Type a period as the first character on a new line to send message out, question mark for help.
man [options] command show the manual (man) page for a command
mkdir [options] directory make a directory
more [options] file

less [options] file

pg [options] file
page through a text file
mv [options] file1 file2 move file1 into file2
od [options] file octal dump a binary file, in octal, ASCII, hex, decimal, or character mode.
passwd [options] set or change your password
paste [options] file paste field(s) onto the lines in file
pr [options] file filter the file and print it on the terminal
ps [options] show status of active processes
pwd print working (current) directory
rcp [options] hostname remotely copy files from this machine to another machine
rlogin [options] hostname login remotely to another machine
rm [options] file remove (delete) a file or directory (-r recursively deletes the directory and its contents) (-i prompts before removing files)
rmdir [options] directory remove a directory
rsh [options] hostname remote shell to run on another machine
script file saves everything that appears on the screen to file until exit is executed
sed [options] file stream editor for editing files from a script or from the command line
sort [options] file sort the lines of the file according to the options chosen
source file

. file
read commands from the file and execute them in the current shell. source: C shell, .: Bourne shell.
strings [options] file report any sequence of 4 or more printable characters ending in or . Usually used to search binary files for ASCII strings.
stty [options] set or display terminal control options
tail [options] file display the last few lines (or parts) of a file
tar key[options] [file(s)] tape archiver--refer to man pages for details on creating, listing, and retrieving from archive files. Tar files can be stored on tape or disk.
tee [options] file copy stdout to one or more files
telnet [host [port]] communicate with another host using telnet protocol
touch [options] [date] file create an empty file, or update the access time of an existing file
tr [options] string1 string2 translate the characters in string1 from stdin into those in string2 in stdout
uncompress file.Z uncompress file.Z and save it as a file
uniq [options] file remove repeated lines in a file
uudecode [file] decode a uuencoded file, recreating the original file
uuencode [file] new_name encode binary file to 7-bit ASCII, useful when sending via email, to be decoded as new_name at destination
vi [options] file visual, full-screen editor
wc [options] [file(s)] display word (or character or line) count for file(s)
whereis [options] command report the binary, source, and man page locations for the command named
which command reports the path to the command or the shell alias in use
who or w report who is logged in and what processes are running
zcat file.Z concatenate (list) uncompressed file to screen, leaving file compressed on dislike

2nd Assignment

What is Operating System

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.
For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.
Operating systems can be classified as follows:
• multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.
• multiprocessing : Supports running a program on more than one CPU.
• multitasking : Allows more than one program to run concurrently.
• multithreading : Allows different parts of a single program to run concurrently.
• real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.
Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.
As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.

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