UNIX NOTES
UNIX/Linux Notes:
Page 1
Professor: Michael P. Harris
v.20050412
UNIX is a multi-user, multi-tasking operating system originally developed at AT&T
Bell Laboratories. It provides programs for editing text, sending electronic mail, preparing
tables, performing calculations and many other specialized functions that require
separate application programs in other operating systems. One of the key identifying
features of UNIX is its standardized directory and file structure.
Typical UNIX/Linux root
/
Directory structure:
│
┌────┬────┬────┬────┬───────┬┴────────┬───┬───┬───┬────┐
bin etc dev mnt lib lost+found home tmp sys boot unix
│
│
│
default │(mounted
┌────┬────┬─┴───┬───┬───┬────┐
┌───┬┴──┐volumes)
mike teri ...
etc bin lib spool
hd0 fd0 sd0
(users home directories)
There are many different versions of UNIX. One of the most important is the line of UNIX
releases that started at AT&T, the latest being System V Release 4. Other important
UNIX versions have come from the University of California at Berkeley; the latest is called
BSD4.4. Microsofts Xenix, a early popular microcomputer implementation of UNIX was
originally based on an earlier AT&T release called System V. Linus is currently the
leading popular “Open Source” implementation of a Unix-like standard operating system.
POSIX is the validation standard, set for UNIX-like operating systems. Starting with
Windows 2000 Pro, Windows 2000, XP, and 2003 are all now POSIX compliant. Other
major versions of UNIX include SunOS, Solaris, SCO UNIX, AIX, HP/UX, ULTRIX,
NOVELL UNIX (Univel), and the various implementations of the popular Linux OS.
Since it started more than 35 years ago, UNIX has grown and changed in a different way
from most operating systems. Many early UNIX users were computer and scientific
professionals; more than a few of them extended UNIX by adding tools and functionality
to do what they needed. UNIX was also used to develop a lot of the powerful networking
systems that connect the world, such as Internet. So, whereas most operating systems
were typically developed and controlled by one corporation, UNIX has been developed
through a collective effort. This has meant more versions and somewhat more confusion
than "standardized" operating systems like MSDOS & Windows. But it has also helped to
make UNIX the flexible and incredibly rich and powerful operating system that it is today.
UNIX and its derivatives were not designed as "user-friendly" operating systems, in fact,
UNIX has, in the past, earned its label of "user-hostile." UNIX can be used the way it was
originally designed, on typewriter-like terminals (ttys). Most modern versions of UNIX can
also work with window system GUIs (Graphical User Interface) which allow each user to
have more than one "terminal" on a single display. The X Window System (called X for
short) is the most common UNIX window system. The appearance of X Windows may
vary between systems due to different window managers. Four of the most common
window managers are mwm (Motif Window Manager), olwm (Open Look Window
Manager), CDE (Common Desktop Environment) and the new Linux windows shells
Gnome, KDE, fluxbox, and others.
UNIX NOTES
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Getting Started:
UNIX can be overwhelming with its barrage of details. To get started though, all you need
to do is master just a few details:
o
o
o
o
o
How to Log in and out of your system
Understand the Shell and how to control the system with control characters
Learn the important UNIX specific directories and files
Manage UNIX files and directories, including listing, creating, copying, printing and
removing files, and moving in and out of directories
Work efficiently using UNIX pipes, filters, and multi-tasking.
Logging In:
Before you can start using UNIX and its facilities, the System Administrator has to set up
a UNIX account for you with your login name, password, and home directory. At many
sites, there will be a whole network of UNIX computers so you may also have to know the
hostname of the computer that has your account as well. When you turn on your terminal
you should see a message from the UNIX computer that looks something like:
login:
Logging in is the process of making your self know to the UNIX computer and getting into
your account. On remote systems you will need to run a remote login program like telnet,
rlogin, cu, or tip. In this case your login session might look similar to the following: (what
you type is in bold-italic)
telnet nutshell.ora.com
Sun Solaris OS
mercury.delmar.edu: Solaris UNIX version 9.00.10
login: mpharris
Password: ********
Last login: Wed Mar 29 14:34 CST 2005, from mercury.delmar.edu
motd:
The "crisis" of Today is the "joke" of Tomorrow
REMEMBER !!!
We will be shutting down at 4:30pm for system backups.
Fri Apr 1 12:24:48 CST 2005
$_
UNIX NOTES
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The UNIX Shell:
Once you've logged into a UNIX computer, you're working with a program called the shell.
The shell interprets the commands you enter, runs the program you've ask for, and
generally coordinates what happens between you and the UNIX operating system. There
are three shells in common use: the Bourne shell, Korn shell, and C shell. For the novice
the differences are slight however some to run some software or execute some program
(especially shell scripts) you will need to know which shell you are using (ask your system
administrator). The only immediate difference you will see is that the Bourne, Korn, and
Bash shells prompt you with $_ while the C shell most often uses %_ as the prompt.
Certain keyboard commands (keystrokes) are interpreted by the shell, these are
commonly called control characters. The basic control characters are:
Ctrl-C or [DEL]
Ctrl-D
Ctrl-H or [BACKSPACE]
Ctrl-Q
Ctrl-S
Ctrl-U
Interrupt character (interrupts or cancel a command)
Returns you to UNIX command level. Used to signal end of
input. ** Also logs you off of most UNIX systems
Erase character to left of cursor
Restart output after paused by Ctrl-S
Pauses output to the screen
Erase the whole input line so you can start over
UNIX vs. MSDOS
The UNIX operating system has been around much longer than MSDOS. While MSDOS
owes much of its original heritage to a single-user operating system named CP/M,
MSDOSevolved gaining more and more UNIX like capability. MSDOS is not case
sensitive meaning that commands can be typed in either upper or lower case and
MSDOS treats them all as if they were typed in UPPER CASE. UNIX is case sensitive
meaning that there is a difference between a command typed in upper or lower case. The
UNIX standard is that commands are typed in lower case. A brief comparison of MSDOS
and UNIX command equivalents follows:
CD
CD DIRNAME
CHKDSK
COPY FILE1 FILE2
COPY FILE1 + FILE2 FILE3
COPY FILENAME PRN
DIR
DIR /W
DIR /P
DEL FILENAME
MD DIRNAME
REN FILE1 FILE2
RD DIRNAME
TYPE FILENAME
pwd
cd dirname
fsck
cp file1 file2
cat file1 file2 >file3
pr filename | lpr
ls
ls -C
ls | more
rm filename
mkdir dirname
mv file1 file2
rmdir dirname
cat filename
UNIX NOTES
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File Access and Permissions
An important point to always remember is that in UNIX everything is a file. The textbook
definition of UNIX usually goes something like this...
UNIX - a multi-user/multi-tasking interactive operating system developed by AT&T. UNIX has
a directory structure that is tree-like with files containing all the information that is part of the
system.
Most people familiar with microcomputers and MSDOS are familiar with the tree-like
directory structure with directories, sub-directories and pathnames. But in UNIX the
directory structure and file system are the heart of the system. UNIX is also device
independent there for no duplication of commands is necessary for different devices such
as the screen, printer, or disk drives.
For example, UNIX always keeps the files in its directory structure is a sorted order, there
for to rename a file is really moving that file within the directory structure. To copy that file
to another directory, to the screen, or to a floppy disk drive is the same command
because UNIX is device independent, everything is a file, the destination directory, the
screen, the auxiliary storage device are all files to UNIX. This concept may take a little
getting used to before all that is means sets in.
To log into a UNIX system your terminal must be described to the system. In the directory
/dev the system device files (files that contain the hardware interfacing information UNIX
needs) are contained. In addition, your terminal type is stored in /etc/ttytype, your
terminal speed in /etc/ttys, and your terminal setup and capabilities data in
/etc/termcap. The advantage of this system is obvious, if you change your terminal or
enhance its capabilities, your just edit the system files. In addition you can have multiple
definitions and settings for multiple different users.
The UNIX executable commands are kept in a the /bin directory with miscellaneous
system data files kept in the /etc directory. Unix commands are usually short and terse
and most always in lower case. UNIX filenames may include A-Z, a-x, 0-9, . and _. After
UNIX boots from the kernel code stored in /unix directory, the /etc/rc startup file is
executed. This (reboot cold) startup file would be the equivalent of the
MSDOSCONFIG.SYS and AUTOEXEC.BAT files. The system default setup information
is stored in the /etc/default file.
When users log into a UNIX system, there access is controlled by password and access
information stored in the /etc/passwd and /etc/group files. Once logged in users
are met by the users login message-of-the-day stored in the /etc/motd file and then the
users personal startup and setup commands are executed from their own
private .profile file stored in their /home/username login/home directory.
UNIX NOTES
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One logged into the UNIX system file access is controlled by the standard UNIX
permissions: r w x -. The permission settings are for Read, Write (or change), eXecute,
and permission denied (-). The permissions are grouped into a set of three rwxrwxrwx
where the first three are the permissions for the user/owner of the file, the second three
are the permissions for members of the group assigned to the file and the last three
permissions are for all others who may wish access to the file. The command chown is
used to change the owner of the file. The command chgrp will change the group
assigned to the file. And the command chmod (for change access mode) will change the
file permissions. Of course, you must have write permission to change the owner, group
assignment, or permissions to a file.
As an example, assume the ls command (list single file) gave you the following
permission settings for the file /etc/motd...
rwxr-x--x
These permission settings would indicate that the owner (usually supervisor) has Read,
Write, and eXecute permissions to the file. Those who have the assigned group access
permissions can Read and eXecute the file, all others may only eXecute the file.
When changing permissons to your files with the chmod command, you have the options
of a, u, g, and o (for All, User/owner, Group, and Others) the syntax is:
chmod options filename
where options can include:
(1) a, u, g, o
(2) + or and (3) r, w, x
in any combination.
For example: chmod g+rx myfile
would add Read and eXecute to the group portion of the permission settings.
Alternate Input / Output, Piping, and Redirection
The Unix commands for redirecting Input and Output are:
>
>>
|
For example:
redirect output
redirect output append
pipe (output into input)
<
<<
tee
redirect input
redirect input append
split output into two streams
who | sort > wholist
would execute the who command (generate a list of who is currently logged on to the
system) and pipe the output into the input of the sort command (alphabetize) and the
sorted list would be written to the file wholist.
and...
banner < wholist >>register
the file contents of wholist would be fed into the command banner (which generates large
bannerized letters from file contents) and add this output to the end of the file register.
UNIX NOTES
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UNIX DIRECTORY GUIDE
Typical UNIX/Linux root
/
Directory structure:
│
┌────┬────┬────┬────┬───────┬┴────────┬───┬───┬───┬────┐
bin etc dev mnt lib lost+found home tmp sys boot unix
│
│
│
default │(mounted
┌────┬────┬─┴───┬───┬───┬────┐
┌───┬┴──┐volumes)
mike teri ...
etc bin lib spool
hd0 fd0 sd0
(users home directories)
/
UNIX root directory
/bin
UNIX Commands (binary files)
/boot
UNIX file system bootstrap loader programs
/etc
miscellaneous system data files
/etc/default
system default setup files
/dev
peripheral device control files
/lib
libraries for the 'C' compiler
/lost+found
depository for misplaced files
/mnt
empty directory to mount file systems
/sys
code for UNIX kernel (operating system)
/tmp
temporary files (may be auto deleted)
/home
users master/personal directory (or /usr, or /user)
/ home /bin
more commands usually user created
/ home /lib
more language libraries and data files
/ home /spool
print spooler master directory
/ home /tmp
users temporary files
/ home /asm
administration accounting files
/unix
executable code for UNIX kernel
UNIX NOTES
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UNIX FILE GUIDE
.
name of current directory
..
name of current directory's parent
.profile
set up environment at login (personal startup file)
/etc/group
designate group 'names'
/etc/logbook
logbook of installed software
/etc/motd
(message of the day) login message for users
/etc/passwd
define system users and access
/etc/rc
define system initialization and startup commands
/etc/systemid
define system name
/etc/termcap
define standard terminal setup information and capabilities
/etc/ttys
define terminal port status/speed
/etc/ttytype
define default terminal type
/ home /lib/crontab
time & date for auto execution
/ home /adm/messages
record of console messages
Sample UNIX / home directory with subdirectories:
/
│
home
┌─────────────┬──────────────┬┴─────────────────┬─────────┐
adam
betty
edward
mark
...
│
┌───┼────┐
┌──┴─┬────┐
┌─────┴┬────┬────┐
├demo1 memo etc letter util fax pgms news
bin fax make
└demo2
│
│
│
│
│
├mm1
├let1
├fax1
├jan
├mod1.c
└mm2
├let2
└fax2
├feb
└mod2.c
└let3
└mar
all users have a .profile file in / home /username/.profile
UNIX NOTES
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ALPHABETICAL LIST OF UNIX COMMANDS
The commands in the Basic System are listed below in alphabetical order.
asktime
assign
at
atq
atrm
awk
banner
bc
bdiff
bfs
cal
cat
cd
chgrp
chmod
chown
chroot
cmp
comm
copy
cp
cpio
cron
crypt
csplit
cu
date
dc
devnm
df
diff
diff3
dircmp
dirname
disable
dtype
du
echo
ed
egrep
enable
env
ex
expr
set system date and time
assign a device to a user
execute commands at a later time
examine the "at" job queue
remove a job from the "at" job queue
pattern scanning and processing language
print large letters
arbitrary-precision arithmetic language
compare very large files
scan big files
print calendar
concatenate and print files
change working directory
change group
change mode (change access permissions)
change file owner
change the process root directory
compare two files (any type)
select or reject lines common to two sorted files
copy groups of files
copy
copy file archives in and out
execute commands at specified times
encode or decode a file
split files according to context
call the UNIX system
print and set the date
desk calculator
identify device name
report the number of free disk blocks
compare two text files
compare three text files
compare directories
deliver the directory part of a path name
turn terminal use off
print disk type (such as Xenix, msdos, tar)
summarize disk use
echo arguments
invoke text editor (line editor)
search a file for a pattern
turn terminal use on
set or print the environment for command execution
text editor (line editor)
evaluate arguments as an expression
UNIX NOTES
false
fgrep
file
find
finger
fsck
grep
grpcheck
haltsys
hd
head
id
join
kill
l
lc
learn
line
ln
login
logname
look
lpr
ls
mail
mesg
mkdir
mkfs
mknod
mkuser
more
mount
mv
newgrp
nice
pack
passwd
pr
ps
pstat
pwcheck
pwd
quot
random
remote
restor
rm
Page 9
provide truth value by returning with a nonzero exit code
search a file for a pattern
determine file type
find files
find information about users
check file system for consistency and repair if necessary
search a file for a pattern
check group file
shut system down
give hex dump of a file
give first few lines of a file
print user and group ID and name
join two relations
terminate a process
list directory contents in long form (equivalent to ls -1)
list directory contents in columns
give computer-aided instruction about UNIX
read one line
make a link to a file
give access to the system
get login name
find files in a sorted list
send files to the line printer queue for printing
list the contents of a directory
send, receive, or dispose of mail
permit or deny messages sent to a terminal
make a directory
make a file system
make a special file
add a new user account
display a file one screen at a time
attach a file system to a directory on the root subtree
move or rename files and directories
log into a new group
run a command at a different priority
compress files
change login password
print a file
report process status
print system facts
check the password file
print the name of the working directory
summarize file system ownership
generate a random number
execute commands on another machine
invoke incremental file system restorer
remove a file
UNIX NOTES
rmail
rmdir
rmuser
rsh
sdiff
sed
setmnt
settime
sh
shutdown
sleep
sort
split
stty
su
sum
sysadmin
tail
tar
tee
test
touch
tr
true
tset
tty
unmask
unmount
uname
uniq
uucp
uulog
uux
vi
vsh
wait
wall
wc
what
who
whodo
write
xargs
yes
Page 10
send mail among users
remove a directory
remove a user
invoke a restricted a shell
compare two files side by side
invoke stream editor
establish a mount table (/etc/mnttab)
change file access and modification dates
invoke the Bourne shell
shut down the system
suspend execution for an interval
sort or merge files
split a file into pieces
set terminal options
make the user root or another user temporarily
calculate checksum and count blocks in a file
perform file system backup and restore
deliver last part of a file
archive files
create a tee in a pipe to save intermediate output
test conditions
update file access and modification times
translate characters
return with a zero exit value
set terminal type
get terminal name
set default file creation mask
detach a file system from the root directory
print the current UNIX name
report repeated lines in a file
copy files from UNIX to UNIX
copy files from UNIX to UNIX
execute commands on remote UNIX
invoke a screen-display editor based on ex
invoke the visual shell
wait for background jobs to finish
write to all users
count lines, words, and characters
identify files
list users currently logged on
show who is doing what
send a message to a user's terminal
construct argument lists and execute commands
print string repeatedly