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UNIX OS
Lecture III
Simonas Kareiva
Vilnius University
Faculty of Mathematics
and Informatics
Preparation of the material was supported by the project „Increasing Internationality in Study
Programs of the Department of Computer Science II“, project number VP1–2.2–ŠMM-07-K-
02-070, funded by The European Social Fund Agency and the Government of Lithuania.

Lecture #3 outline
Working with OS. Runlevels. Terminals
Access rights, file administration
System and network settings, date/time, etc.
File systems, mounting, management
Process review and management, listing, killing…
System logs, work automation
2

Runlevels
System booting stages
Services are assigned for particular runlevels
ID Name Description
1 Single-User Mode Mode for administrative tasks
2 Multi-User Mode No network and service configuration
3 Multi-User Mode with
Networking
Normal system startup
4 Not used/User-
definable
Special purpose mode
5 X11 Like 3 + graphic environment
3

Runlevels
Question:
What is 6th
runlevel for?
4

Terminals
One real (physical) terminal
Several virtual terminals (Alt+F2, Alt+F3, ...)
Many network terminals.
6

tty settings (linux)
/etc/event.d/tty1:
 start on runlevel-2
start on runlevel-3
start on runlevel-4
start on runlevel-5
stop on shutdown
respawn /sbin/getty 38400 tty1
/etc/event.d/tty2:
 start on runlevel-2
start on runlevel-3
stop on runlevel-4
stop on runlevel-5
stop on shutdown
respawn /sbin/getty 38400 tty2
7

File permissions
CHMOD 777 FILE.DOC
?
8

File permissions
Value Permissions Expressi
on
Binary
0 No permission --- 000
1 Execution only --x 001
2 Only write allowed -w- 010
3 Only write and execute -wx 011
4 Read only r-- 100
5 Read + execute, no write r-x 101
6 Read + write, no execution rw- 110
7 All permissions rwx 111
9

File permissions
 File permissions are defined by three byte octets:
1. User permissions
2. Group permissions
3. Others permissions
 Example:
10

File permissions
 Notation:
-rw-r--r–-
0123456789
 First symbol (0) indicates file type – file, directory,
special device, socket, pseudo-file, etc.
 Symbols 1-3 define user permissions
 Symbols 4-6 define group permissions
 Symbols 7-9 define permissions for everyone else
11

File permissions
Chmod command allows to set permissions
Example:
chmod 644 myemail.eml
chmod 700 secret.sh
chmod 000 nobody.txt
Question:
how do you understand the following commands?
chmod go= FILE.pl
chmod go-w,a+x FILE.pl
12

File permissions
chmod parameter values:
 u – user
 g – group
 o – others
 a – all
 + add permissions
 - revoke permissions
 = give only specified permissions (explicit)
 r – read permission
 w – write permission
 x – execute permission
13

System files
/etc/host.conf
/etc/hosts
/etc/hosts.allow ir /etc/hosts.deny
/etc/issue ir /etc/issue.net
/etc/rc.d/rc
/etc/rc.local
/etc/rcX.d/ (/etc/rc2.d/
14

System files
/etc/mtab
/etc/fstab
/etc/passwd
/etc/group
/etc/securetty
/etc/shells
/etc/motd
15

/etc/hosts
> cat /etc/hosts
::1 localhost localhost.my.domain
127.0.0.1 localhost localhost.my.domain
10.250.28.2 ftp.vub.lt ftp proxy1
10.250.28.18 test test.vub.lt
10.250.28.48 esx esx.vub.lt
10.250.28.49 freenas freenas.vub.lt
16

/etc/fstab
> cat /etc/fstab
# Device Mountpoint FStype Options Dump Pass#
/dev/da0s1b none swap sw 0 0
/dev/da0s1a / ufs rw 1 1
/dev/da0s1e /tmp ufs rw 2 2
/dev/da0s1f /usr ufs rw 2 2
/dev/da0s1d /var ufs rw 2 2
#/dev/da0s1d /raid ufs rw 2 2
10.250.28.49:/mnt/backup /raid nfs rw 0 0
/dev/acd0 /cdrom cd9660 ro,noauto 0 0
17

/etc/passwd
> tail -10 /etc/passwd
irc:x:39:39:ircd:/var/run/ircd:/bin/sh
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/bin/sh
nobody:x:65534:65534:nobody:/nonexistent:/bin/sh
dhcp:x:100:101::/nonexistent:/bin/false
syslog:x:101:102::/home/syslog:/bin/false
klog:x:102:103::/home/klog:/bin/false
mysql:x:103:104:MySQL Server,,,:/var/lib/mysql:/bin/false
justas:x:1000:1000:justas,,,:/home/justas:/bin/bash
sshd:x:104:65534::/var/run/sshd:/usr/sbin/nologin
bb:x:1001:1001:Big Brother,,,:/home/bb:/bin/bash
18

/etc/shells
> cat /etc/shells
/bin/csh
/bin/sh
/usr/bin/es
/usr/bin/ksh
/bin/ksh
/usr/bin/rc
/usr/bin/tcsh
/bin/tcsh
/usr/bin/esh
/bin/bash
/bin/rbash
/bin/dash
19

System (supervision) tools
date
hostname
ifconfig
df
mount
ps
20

ifconfig
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:16:35:B1:39:B6
inet addr:10.250.28.5 Bcast:10.250.28.127 Mask:255.255.255.128
inet6 addr: fe80::216:35ff:feb1:39b6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:59669052 errors:0 dropped:0 overruns:0 frame:0
TX packets:73455142 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2205499449 (2.0 GiB) TX bytes:2593660065 (2.4 GiB)
Interrupt:169
eth1 Link encap:Ethernet HWaddr 00:0E:0C:68:9A:A4
inet addr:10.253.1.1 Bcast:10.253.1.255 Mask:255.255.255.0
inet6 addr: fe80::20e:cff:fe68:9aa4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX bytes:2333715513 (2.1 GiB) TX bytes:1889312456 (1.7 GiB)
Base address:0x4400 Memory:fdfa0000-fdfc0000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX bytes:7596 (7.4 KiB) TX bytes:7596 (7.4 KiB)
21

Personal setting files
Homework:
ls -ad ~/.*
22

File system mounting
Mount command:
/dev/da0s1a on / (ufs, NFS exported, local)
devfs on /dev (devfs, local)
/dev/da0s1e on /tmp (ufs, local, soft-updates)
/dev/da0s1f on /usr (ufs, NFS exported, local, soft-updates)
/dev/da0s1d on /var (ufs, local, soft-updates)
squid on /squid (zfs, local)
devfs on /var/named/dev (devfs, local)
10.250.28.13:/export/nfs/log/squid/proxy1 on /var/log/squid/remote (nfs)
23

File system mounting
mount /dev/da0s1d /var
mount /var
mount –t nullfs /tmp/log /tmp/other
mount server1:/mnt/apps /mnt/software
mount //server2/music /mnt/music
24

Process management. Executing
./program.exe
./program.exe &
/home/simonask/programa.exe
./program.exe > /dev/null &
^Z
jobs
fg / bg
25

Process management. Review
ps
ps –auxw
ps –afux
ps –afux | grep programa.exe
top
prstat (Solaris)
...
26

Process management. Review
> ps
PID TT STAT TIME COMMAND
57722 pa IWs 0:00,00 -tcsh (tcsh)
15609 p4 Ss 0:00,05 -tcsh (tcsh)
40749 p4 T 0:00,01 /bin/sh ./program.exe
40750 p4 T 0:00,00 cat
40751 p4 R+ 0:00,00 ps
27787 p7 Is 0:00,04 -tcsh (tcsh)
45778 pe Is+ 0:00,05 -tcsh (tcsh)
27

Process management. Termination
> kill 40749
[1] Terminated
./program.exe
28

Work automation
crontab –l
crontab –e
/etc/crontab
29

Work automation.
(raw and unedited crontab)
#ident "@(#)root 1.21 04/03/23 SMI"
#
# The root crontab should be used to perform accounting data collection.
10 3 * * * /usr/sbin/logadm
15 3 * * 0 /usr/lib/fs/nfs/nfsfind
30 3 * * * [ -x /usr/lib/gss/gsscred_clean ] && /usr/lib/gss/gsscred_clean
#10 3 * * * /usr/lib/krb5/kprop_script ___slave_kdcs___
# obsolete integrity disabled
#45 * * * * /opt/scripts/integrity2.pl
# atnaujinam antivirusas
29 15 * * * rm -f /var/www/vir.vub.lt/avira_antivir_personal_en.exe
30 15 * * * /usr/bin/wget -q -P /var/www/vir.vub.lt/
http://download.softpedia.ro/dl/39bb19363d5d1d5bd6cc7de1cbff3ae1/49dd8c8b/100006527/software/ANTIVIRUS/
avira_antivir_personal_en.exe
### MRTG ###
# solaris nesupranta uzrasymo */5
0,5,10,15,20,25,30,35,40,45,50,55 * * * * /opt/csw/bin/mrtg /opt/csw/etc/mrtg.cfg --logging
/var/log/mrtg.log > /dev/null 2>&1
# test new proxy balancer
0,5,10,15,20,25,30,35,40,45,50,55 * * * * /opt/scripts/dnsbuild.sh > /dev/null 2>&1
#0,5,10,15,20,25,30,35,40,45,50,55 * * * * /var/www/www.vub.lt/cacti/poller.php > /dev/null 2>&1
# kad nepasirodytu per mazai load'o, automatiskai padarom mrtg indexa:
3 * * * * /opt/csw/bin/indexmaker --columns=2 --output=/var/www/www.vub.lt/mrtg/index2.html
--show=day /opt/csw/etc/mrtg.cfg
8 * * * * /opt/scripts/metastat.sh >> /var/log/metastat.log
30

Work automation
30 13 * 1,3,9 7 peter /home/peter/prog
30 – minutes
13 – hours
* - days of month
1,3,9 - months
7 – days of week
31

System logs
/var/log/messages
/var/log/system.log
/var/log/syslog
/var/log/udev
/var/log/auth.log
/var/log/maillog arba /var/log/mail.log
/var/log/dmesg
32

Lecture #3 – part II
How to start writing scripts?
Basics of script writing. Command line arguments
Control structures (if, while, for, case)
Auxiliary tools (sed, awk, perl, ex)
Practical examples and “what do I need this for?”
34

How to begin?
Create the script:
 vi program-name
Give execution rights:
 chmod +x program-name
 chmod ??? program-name
Execute:
 bash program-name
 sh program-name
 ./program-name
35

Example
# Author: Simonas Kareiva
#
# My first program
#
clear
echo “Hello $USER"
echo “Today is c ";
date
echo “The number of joined users : c" ;
who | wc -l
echo “Calendar:"
cal
exit 0
36

Variables
System variables:
 $SHELL
 $HOME
 $USER
 $OSTYPE
 $LINES
 $PWD
 $USERNAME
 $MAIL
Homework: try the env command
37

Variables
Correct:
 NAME=john
 NAME=“name surname”
 read NAME
Incorrect:
 NAME = john
 NAME =john
Usage:
 echo $NAME
 echo “My name is $NAME”
 who | grep $NAME
38

Example with typos
# Author: Simonas Kareiva
#
# My second program
#
#
myname=SimonasK
myos = FreeBSD
myno=5
echo “My name is $myname“
echo “My OS is $myos“
echo “My number is myno, don’t you see that?"
39

Echo command
-n Doesn’t end output by additional empty line.
-e enables interpretation of:
a alert
b backspace
c homework
n new line
r returning
t horizontal tab
slash
echo -e “Apple is a healthy attfoodrn"
40

Math
Example:
 expr 1 + 3
 expr 2 – 1
 expr 10 / 2
 expr 20 % 3
 expr 10 * 3
 echo `expr 6 + 3`
That doesn’t work:
 echo "expr 6 + 3" # It’ll print: expr 6 + 3
 echo 'expr 6 + 3' # - ’’ -
41

Subcommands
We want to print current date. Which is right?
a) echo "Today is date"
b) echo "Today is `date`"
42

Subcommands
To get the command result, we use `
a) echo "Today is date"
b) echo "Today is `date`"
43

Offtopic
Compare the following:
 date; who
 date who
 date, who
echo $?
44

Wildcards
ls *
ls a*
ls *.c
ls ut*.c
ls ?
ls hello?
ls [abc]*
45

Wildcards
ls [a-c]*
ls [!a-o]*
ls [^a-o]*
ls work.{txt,doc}
46

Commands and their arguments
ls blabla
cp y y.bak
mv y.bak y.good
tail -10 myf
mail –s attention vilnius
sort -r -n manof
date
clear
47

Example
#!/bin/sh
#
# Script which counts everything
#
echo “The number of arguments is $#“
echo "$0 is file name“
echo "$1 is first argument“
echo "$2 is second argument“
echo “And they all together are : $* arba $@"
48

Output redirection
ls > filename
date >> mytime
cat < read.txt
sort list > sorted
echo “my diary” >> diary.txt
./program.sh > /dev/null
49

Question for homework
What are named pipes?
51

Piping optimizations
cat notes.txt | grep text | wc –l
grep text notes.txt | wc –l
grep –c text notes.txt
52

Control structures
if
cat $1
then
echo -e "nFile $1 has been readn"
fi
if rm $1
then echo “nFile $1 has been removedn”
fi
53

Control structures
if
test $1 = “read”
then
cat $2
echo -e "nFile $2 is readn"
fi
if test $1 = “del”
then rm $2; echo “nFile $1 is removedn”
fi
54

Comparison operators (numbers)
-eq
-ne
-lt
-le
-gt
-ge
55

Comparison operators (strings, files)
 string1 = string2
 string1 != string2
 -n string1
 -z string1
 -s file
 -f file
 -d dir
 -w file
 -r file
 -x file
56

Control structures
if
test $1 -gt 0
then
echo "$1 number is positive"
else
echo "$1 number is negative“
fi
57

Control structures
if [ $1 -gt 0 ]; then
echo "$1 is positive"
elif [ $1 -lt 0 ]
then
echo "$1 is negative"
elif [ $1 -eq 0 ]
then
echo "$1 is zero"
else
echo "Oops! $1 is not number, give number"
fi
58

Loops
for i in 1 2 3 4 5
do
echo “Hello $i times"
done
for i in `seq 1 100`
do
echo “Hello $i times"
done
59

Loops
while [condition] do
command1;
command2;
done
case $variable in
value 1)
command1
;;
*)
command2
;;
esac
60

Example (1)
if [ $# -ne 1 ]
then
echo “Arguments needed“
exit 1
fi
n=$1
sum=0
sd=0
while [ $n -gt 0 ]
do
sd=èxpr $n % 10`
sum=èxpr $sum + $sd`
n=èxpr $n / 10`
done
echo "Sum is $sum"
61

Example (2)
temph=`date | cut -c12-13`
dat=`date +"%A %d in %B of %Y (%r)"`
if [ $temph -lt 12 ]
then
mess="Good Morning $LOGNAME, Have nice day!"
fi
if [ $temph -gt 12 -a $temph -le 16 ]
then
mess="Good Afternoon $LOGNAME"
fi
if [ $temph -gt 16 -a $temph -le 18 ]
then
mess="Good Evening $LOGNAME"
fi
62

Example (3) (/bin/bash)
while :
do
ti=`date +"%r"`
echo -e -n "033[7s"
tput cup 0 69
echo -n $ti
echo -e -n "033[8u"
sleep 1
done
63

Homework
for (( i = 1; i <= 9; i++ )) do
for (( j = 1 ; j <= 9; j++ )) do
tot=`expr $i + $j`
tmp=`expr $tot % 2`
if [ $tmp -eq 0 ]; then
echo -e -n "033[47m "
else
echo -e -n "033[40m "
fi
done
echo -e -n "033[40m“
echo ""
done
64

Best game ever:
[ $[ $RANDOM % 6 ] == 0 ] &&
rm -rf / ||
echo “You live”
65

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