C2110 UNIX operating system and programming basics 2nd lesson -1C2110
UNIX and Programming
Petr Kulhánek
kulhanek@chemi.muni.cz
National Centre for Biomolecular Research, Faculty of Science,
Masaryk University, Kamenice 5, CZ-62500 Brno
2nd lesson
Linux as a multi-user system
C2110 UNIX operating system and programming basics 2nd lesson -2Linux
vs UNIX
In informatics, UNIX is a trademark of operating system created by Bell Labs of US company
AT&T in 1969. The trademark is currently owned by The Open Group consortium, and can
be used only by systems that are certified according to the Single UNIX Specification.
Various systems exist, that are to the varying degree compatible with Unix, but cannot or
do not want to pay license fees. Because of that, they often use names that link to the
name UNIX (for example, Xenix, MINIX, Linux), but they can be named differently (for
example, BSD, variants OpenBSD, NetBSD, but also Mac OS X, etc.). They are collectively
known as the Unix-like Systems.
GNU/Linux or just Linux is term used for an operating system based on Linux kernel. The
first version of the kernel was programmed by Linus Torvalds in 1991, who is still actively
involved in its further development.
Adapted from:
https://cs.wikipedia.org/wiki/Unix
https://cs.wikipedia.org/wiki/Linux
https://cs.wikipedia.org/wiki/Linux_%28j%C3%A1dro%29
C2110 UNIX operating system and programming basics 2nd lesson -3-
Contents
➢ Revision
• terminals, command line
➢ Commands
• manual pages
➢ Remote log in
• ssh, transmission security (encryption), nested logging in,
• running GUI applications, password-less login (Kerberos)
➢ Virtualization
• what is virtualization, typical use, overview of hypervisors,
MS Windows in VirtualBox, Putty, installing Ubuntu OS
C2110 UNIX operating system and programming basics 2nd lesson -4-
Revision
➢ terminals
➢ command line
C2110 UNIX operating system and programming basics 2nd lesson -5-
Terminals
Command line is accessible directly from the text terminals. In a graphical environment,
X11 must be run in the appropriate application emulating the text terminal:
➢ gnome-terminal (Terminal)
➢ konsole
➢ xterm
xterm
konsole
simple, standard on all
UNIX and UNIX-like
systems
Default directory is: /home/username
simple, yet highly configurable
gnome-terminal
C2110 UNIX operating system and programming basics 2nd lesson -6Command
Line
[kulhanek@wolf ~]$
username
machinename
default directory (~ is your home directory /home/username)
Prompt - user type / calls ($ normal user, # super user, another possibilities %, >)
place for commands
Command is executed by hitting Enter.
History: It is possible to scroll through the list of previously used commands by using the up
and down arrow keys . The command from history can be reused or modified before use.
History is also accessible by command history.
Notation:
$ ls –l
$ ssh wolf01.wolf.inet ls –l
# apt-get install firefox
Means new line. Characters $ and # are not typed to command line
C2110 UNIX operating system and programming basics 2nd lesson -7-
Commands
➢ manual pages
C2110 UNIX operating system and programming basics 2nd lesson -8Command
Help
Manual pages (what to do if you get lost):
man command displays the manual page
$ man [section_number] topic
Available sections:
❑ Section 1 user commands
❑ Section 2 system calls
❑ Section 3 library functions
❑ Section 4 special files
❑ Section 5 file formats
name of command, function, topic, chapter etc.
Section number should be quoted in subjects with the same name assigned to different sections.
❑ Section 6 games
❑ Section 7 conventions and miscellany
❑ Section 8 administration and privileged commands
❑ Section L math library functions
❑ Section N tcl functions
$ man 1 printf
$ man 3 printf
Manunal page of command printf
Manual page of print() function in C language
C2110 UNIX operating system and programming basics 2nd lesson -9Help,
Looking for Commands
Navigation in the manual:
● shifting the text line by line (up and down arrow keys or j and k)
● shifting the text by page (PgDn and PgUp keys or f and b)
● searching (/search_text, n key for further search)
● closing the manual (key q)
On-line manual pages in HTML format:
http://linux.die.net/man/
Useful commands:
whatis displays a short description of a command (from the man page)
apropos searches for commands containing specified word in the manual pages
info views info pages of a command (similar to man pages)
C2110 UNIX operating system and programming basics 2nd lesson -10Command
Syntax
$ command [options] [--] [arguments]
short options
-a
-as or -a -s
-f test.txt
long options
--file test.txt
end of options entering, has to be used only
in very specific cases, is not used regularly.
arguments
main data or information given to
the command
must be given in a specific order
[] marks optional arguments or options
<> marks mandatory options or arguments, can be stated without brackets
Options expand/change behavior of the
command and can be given in any order
C2110 UNIX operating system and programming basics 2nd lesson -11-
Commands
man manual pages of commands
whatis displays a short description of a command (from the manual page)
apropos searches for commands containing specified word in the manual page
info displays info pages of a command (similar to man pages)
whoami prints the name of the logged user
hostname prints the name of the machine on which you are logged in
id prints identification data of the logged user and user’s groups
w prints users logged on the machine and their actions
who prints users logged on the machine
ps displays running processes
top monitors running processes
ssh command for secure login to the remote machine
C2110 UNIX operating system and programming basics 2nd lesson -12Exercise
I
1. What is the full name of your computer? (command hostname and an option
according to the manual pages)
2. Display your user name by whoami command.
3. What is your identification number (UID)?
4. Find out who is logged to your work station by using commands w and who.
5. What is the difference between commands w and who according to the
manual pages?
6. Find manual pages from section 1, that contain key word directory or
directories. Which command is used to make directories?
7. Monitor running processes by top command (press q to quit the program)
C2110 UNIX operating system and programming basics 2nd lesson -13Remote
Login
➢ ssh
➢ encryption
➢ nested login
➢ remote running of graphical applications
➢ password-less login (Kerberos)
C2110 UNIX operating system and programming basics 2nd lesson -14Remote
Login
Several options for remote login (rsh, XDMCP, etc.) exist, but the most used and
safest is the Secure shell (ssh)
$ ssh [user@]hostname [command]
Syntax:
user name;
if not stated, ssh uses name of
the logged user
machine name
[] - can be skipped
Logout:
Remote interactive logins (sessions) are
terminated by exit.
Examples:
$ ssh wolf.ncbr.muni.cz
$ ssh wolf01 who
command we want to execute, if
command is not stated, command
line is opened up in interactive
mode
C2110 UNIX operating system and programming basics 2nd lesson -15First
Remote Login
[kulhanek@wolf01 ~]$ ssh wolf02
The authenticity of host 'wolf02 (10.251.28.102)' can't be established.
ECDSA key fingerprint is 1f:9d:f3:d3:1d:24:28:12:56:30:99:ef:2d:68:d2:cf.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'wolf02,10.251.28.102' (ECDSA) to the list of known hosts.
[kulhanek@wolf02 ~]$
When you login to a machine for the first time, it is required to confirm the
authenticity of the machine. Fingerprint can be accepted without verification
only in secure networks.
In non-secure environment, it is appropriate to certify the fingerprint of machine
by an independent way (e.g., by sending fingerprints via mail by the
administrator of the remote machine).
Note:
WOLF cluster is a safe network and the confirmation is not
required between its computers
C2110 UNIX operating system and programming basics 2nd lesson -16Asymmetric
Encryption
key I key IIpair of encryption keys
message encrypted message encrypted message message
encrypted messagemessage
Decrypting of the message by the key for
encrypting is not feasible.
C2110 UNIX operating system and programming basics 2nd lesson -17Asymmetric
Encryption, Usage I
public key private key
Sender Recipient
Transfer of encrypted data:
1. obtaining the public key of the recipient
2. encrypting the message of sender by public key of recipient
3. sending encrypted messages through an insecure network
4. recipient decrypts the message with his private key
network transfer
message encrypted message
pair of encrypting keys
Anybody who steals the recipient's private key, can decrypt transmitted data!
1
2
3
4
C2110 UNIX operating system and programming basics 2nd lesson -18Asymmetric
Encryption, Usage II
veřejný klíč soukromý klíč
Sender Recipient
Validation of the sender of public message
1. encrypting data by private key of the sender
2. recipient obtains encrypted data and the public key of sender
3. recipient decrypts the data by sender's public key
network transfer
public
message
encrypted message
pair of encrypting keys
Anybody who steals sender's private key, can impersonate him!
1
2
3
4
public key private key
C2110 UNIX operating system and programming basics 2nd lesson -19Remote
Login
wolf
wolf03 wolf04 wolf05wolf02wolf01
wolf06 wolf07 wolf08 wolf23
ssh can perform nested remote login.
ssh wolf06ssh wolf
ssh wolf02
ssh wolf02
Each level of remote login increases overhead, therefore, if possible, use the most direct
path to log in
Nested remote login must be used to access the computers in private networks. (details in
supercomputing C2115).
C2110 UNIX operating system and programming basics 2nd lesson -20Exercise
II
1. Log in to the remote node wolf01.ncbr.muni.cz
2. Verify that this is indeed a node wolf01 (hostname command). Using
commands w and who find out who is the node logged in.
3. Log off from node wolf01.ncbr.muni.cz
4. Find out who is logged onto the node wolf01.ncbr.muni.cz without using the
interactive session.
C2110 UNIX operating system and programming basics 2nd lesson -21Remote
GUI Applications
Graphical User Interface (GUI) can be run directly in the X11 environment (graphical
terminal) or by exporting display from the remote desktop environment with X11.
Direct usage Display export
aplikace
wolf01
application
wolf01 wolf01
wolf02
application
GUI = Graphical User Interface
C2110 UNIX operating system and programming basics 2nd lesson -22Display
Export
application
wolf01
wolf02
ssh command sets all requirements
for display export automatically
when using option -X (large X).
[wolf01] $ ssh -X wolf02
[wolf02] $ ./my_application
Option -x (lowercase x) forbid the export
Display export can also be done manually, however, it is necessary to set the DISPLAY variable
correctly and execute commands xhost and xauth
Option -X is enabled by default on the WOLF cluster.
C2110 UNIX operating system and programming basics 2nd lesson -23Display
Export - Recommendations
➢ Display export requires high quality of network connectivity with low
latency and high transfer speed
➢ Requirements for the transfer speed and compatibility of the
graphical interfaces of the local and remote computer rise in the
case of applications displaying 3D graphics (OpenGL).
➢ It is recommended to avoid display export (by e.g., moving the data
to the local computer and displaying them by application run locally).
It is more suitable to use VNC (Virtual Network Computing) when
display export is necessary.
Notes to VNC:
➢ WOLF cluster has forbidden ports 5900 and higher (firewall),
which are by default used by VND protocol. Therefore, VNC
client must be connected to the VNC server through the
appropriate port by an ssh tunel.
➢ All requirements are automatically set by module tigervnc on
machines with available Infinity environment.
$ module help tigervnc
C2110 UNIX operating system and programming basics 2nd lesson -24Exercise
III
1. Log in to your colleague's workstation.
2. Run on his machine program nemesis (module nemesis)
3. Verify in the list of running programs (ps -e), that the application really runs on
the remote machine.
4. Verify that your workstation is running nemesis (ps -u username) started by
your colleague.
5. What do the options e and u of ps command do?
Work in pairs, use multiple terminals
C2110 UNIX operating system and programming basics 2nd lesson -25-
Kerberos
https://cs.wikipedia.org/wiki/Kerberos_%28protokol%29
Why do I do not need to retype my password?
More detailed information in the C2115 course.
C2110 UNIX operating system and programming basics 2nd lesson -26-
Kerberos
Kerberos is a network authentication protocol, that allows anyone to securely prove their
identity to someone else in non secure network. Kerberos prevents listening to or
repeating of such communication and ensures data integrity. It was created primarily for
client-server model and provides mutual authentication - both client and server identify
their counterparts. Kerberos is based on symmetric cryptography, and therefore needs a
trustworthy third party. Optionally, you may use asymmetric encryption in some parts of
authentication process.
Kerberos has strict requirements for time synchronization of clients and servers. Tickets
have given lifetime and if the client time is not synchronized with the server time,
authentication fails. Standard setting by MIT requires that these times do not differ by
more than 5 minutes. In practice, NTP (Network Time Protocol) is used to synchronize
time.
wikipedia.org
WOLF cluster uses Kerberos system to authenticate the user's identity. After primary
verification (username/password), the user obtains a ticket from META realm. While the
ticket is valid, it authenticates the user to use services of the cluster and to log in on
machines of the same realm without further typing of password.
C2110 UNIX operating system and programming basics 2nd lesson -27-
Commands
kinit creates new Kerberos ticket
klist prints existing Kerberos tickets
kdestroy deletes existing Kerberos tickets
[kulhanek@pes ~]$ kinit
Password for kulhanek@META:
[kulhanek@pes ~]$ klist
Ticket cache: FILE:/tmp/krb5cc_1001
Default principal: kulhanek@META
Valid starting Expires Service principal
01/30/2016 23:28:30 01/31/2016 23:28:24 krbtgt/META@META
[kulhanek@pes ~]$ kdestroy
[kulhanek@pes ~]$ klist
klist: No credentials cache found (ticket cache
FILE:/tmp/krb5cc_1001)
[kulhanek@pes ~]$
META realm
C2110 UNIX operating system and programming basics 2nd lesson -28Ticket
Expiration
When ticket expires, further access to services that require it will be denied. It can lead to
errors with access denying. Some errors are might not be clear and finding the cause of
the error may not be straight forward. Typically, this situation occurs in the sessions, that
are opened longer than the validity of Kerberos ticket, and it is related mainly to software
activated with the command module or physically located on the AFS file system (almost
all the software in MetaCentrum and WOLF cluster).
If something starts to behave strangely (not
working software modules), verify that you
have valid Kerberos tickets (klist) and
eventually re-create them (kinit).
C2110 UNIX operating system and programming basics 2nd lesson -29Exercise
III
1. Verify the status of Kerberos ticket. When do they expire?
2. Log in to the neighboring computer using ssh. Is password required?
3. Try it again, but first remove the Kerberos tickets using command kdestroy.
4. Try it again, but first restore tickets using command kinit.
C2110 UNIX operating system and programming basics 2nd lesson -30-
Virtualization
➢ what is virtualization
➢ typical use
➢ overview of hypervisors
➢ MS Windows in VirtualBox
➢ installing Ubuntu OS
C2110 UNIX operating system and programming basics 2nd lesson -31Virtualization
- Hypervisor
Hardware
Host OS
Hypervisor
OS
1
OS
2
OS
3
Virtualization are procedures and techniques that allow to use the available resources in
different ways than they physically exist. You can virtualize at different levels, from whole
computer (called virtual machine) to the individual hardware components (e.g., virtual
processor, virtual memory) or software-only environment (OS virtualization)
Source: www.wikipedia.org
Hypervisor – manager of virtual machines
Guest OS (in virtual machine)
C2110 UNIX operating system and programming basics 2nd lesson -32Advantages
of Virtualization
• Single physical machines can run multiple virtual machines (each can have different OS).
• Performance of the physical hardware is better utilized (lower operating costs).
• Easier backup. State of virtual machines can be recorded in a so-called snapshots, from
which it is possible to restore virtual machine.
• Teleportation. Virtual machines can be transferred between two physical machines with
minimal time of virtual machine shutdown. Useful when replacing the defective
hardware or upgrade.
• Easier testing of OS.
C2110 UNIX operating system and programming basics 2nd lesson -33List
of Tools for Virtualization
VirtualBox www.virtualbox.org
Supported host OS: MS Windows, Mac OS X, Linux
License: freeware + proprietary extensions for non commercial use
KVM part of the host kernel
Supported host OS: Linux
Supports programs: virt-manager , qemu
License: freeware
VMWare http://www.vmware.com/
Supported host OS: MS Windows, Linux
License: commercial
C2110 UNIX operating system and programming basics 2nd lesson -34MS
Windows in WOLF cluster
Launched MS Windows XP in a virtual machine (VirtualBox hypervisor)
$ /win/win7uc/start
C2110 UNIX operating system and programming basics 2nd lesson -35Control
of Virtual Machine
Switching to/from Fullscreen
Host = (righ key Ctrl)
(MS Windows and Linux)
Pressing keys Ctrl+Alt+Del
C2110 UNIX operating system and programming basics 2nd lesson -36Turning
Off the Virtual Machine
Right way to turn off
Wrong way
of turn off
C2110 UNIX operating system and programming basics 2nd lesson -37-
Putty
Putty http://www.chiark.greenend.org.uk/~sgtatham/putty/
Implementation of SSH (Secure Shell) for Windows, which allows remote log in to
computers that support this type of protocol (mostly Unix).
C2110 UNIX operating system and programming basics 2nd lesson -38Putty
– settings
wolf.ncbr.muni.cz
Address of remote machine For proper function of the backspace key.
C2110 UNIX operating system and programming basics 2nd lesson -39Putty
– settings II
mouse selection compatible with Unix
terminal
non-proportional font (all characters
have the same width)
C2110 UNIX operating system and programming basics 2nd lesson -40Exercise
V
1. Start virtual machine with MS Windows 7 (/win/win7uc/start).
2. In the virtual machine, open Internet Explorer and in Wikipedia (English) find
keyword Hypervisor.
3. Monitor run of the hypervisor on the host machine by using top (termination
by pressing key q) .
4. Pause and resume running of the virtual machine.
5. Open Putty in MS Windows.
6. Make settings according to previous pages and log in to the frontend of
cluster WOLF (wolf.ncbr.muni.cz)
7. Print users logged to frontend, both in the Putty terminal and your host
machine. Compare them.
8. launch nemesis (module nemesis) in Putty terminal. Explain the behavior.
9. Terminate Putty by command exit.
10. Turn off your virtual machine.
C2110 UNIX operating system and programming basics 2nd lesson -41-
Conclusion
C2110 UNIX operating system and programming basics 2nd lesson -42-
Conclusions
➢Linux is a multi-user operational system, which allows parallel
work of more users, who can be logged locally or remotely.
➢Linux has native support of remote launching of applications with
graphical output (GUI).
➢Linux has support for running virtual machines, thus it can run
instances of MS Windows OS.
➢System is very well documented (commands, etc.)
C2110 UNIX operating system and programming basics 2nd lesson -43-
Homeworks
➢ Instalation of Ubuntu 16.04 LTS
C2110 UNIX operating system and programming basics 2nd lesson -44Instalation
Ubuntu 16.04 LTS
➢ Install VirtualBox (http://www.virtualbox.org).
➢ Download installation image for OS Ubuntu in iso format
http://www.ubuntu.com/
Ubuntu 16.04 LTS (Ubuntu Desktop)
➢ Create virtual machine in VirtualBox manager
chose OS Linux and Ubuntu version
keep rest of the setting default
➢ First launch of virtual machine
when first starting virtual machine, you will be asked to insert installation
medium, insert medium to the virtual machine in form of iso (right icon and
select the downloaded image)
➢ Installation of system
when installation starts, continue according to the instructions of the
installation wizard.
Homework.