Updated: 2015-09-06 01:35 EDT
The final exam schedule is posted on the Course Home Page. Your final exam is three hours long, starting at 8am, in T117/119. It will be 180 multiple-choice questions. There will be a set of practice questions, and a quiz on those questions, posted before the exam.
Check the due date for each assignment and put a reminder in your agenda, calendar, and digital assistant.
The worksheets are available in four formats: Open Office (ODT), PDF, HTML, and Text. Only the Open Office format allows you “fill in the blanks” in the worksheet. The PDF format looks good but doesn’t allow you to type into the blanks in the worksheet. The HTML format is crude but useful for quick for viewing online.
Do NOT open the ODT files using any Microsoft products; they will mangle the format and mis-number the questions. Use the free Libre Office or Open Office programs to open these ODT documents. On campus, you can download Libre Office here.
PS1, cd, find, less, ls, man, mkdir, passwd, pwd, rmdir
cat, clear, cp, find, grep, history, less, man, mv, rm, sleep, touch
date, head, nl, tail, tr, wc
Some students triggered a CLS security alert because they were trying to solve assignment tasks using privileged commands found in Internet searches:
UNAUTHORIZED use of SUDO: COMMAND=/bin/mv /home/idallen/cst8207/14f/assignment04/maze mazeinfo.txt
You are wasting a lot of your own time if you are searching the entire Internet for the solutions to your assignments. (You also waste my time if you try things that trigger security alerts.)
The only commands you need to know in this course are listed each week in the page List of Commands You Should Know that is in the list of weekly Readings, above. They are the same commands you used in the Worksheets and the same commands I put as examples in all the course notes.
Stop wasting your own time searching the Internet; Read All The Words.
After the power failure on Wednesday, private connections to the Course Linux Server were failing and resetting, and long file transfers (e.g. the hourly backup to my desktop machine) were also failing or terminating in the middle. Connections to the public IP address worked fine. I went on a diagnostic mission. Indeed, long file transfers to the private address would “stall” in the middle, sometimes finishing and sometimes not. Sometimes, trying to connect to the private address gave “connection timed out”. A
PuTTY session to the private address would either not connect or would abort in the middle.
What finally clued me in to the problem was watching a running
ping trace where I saw the
TTL jump from
63 and then back to
127 again. I ran an
nmap scan of the IP address when it had one
TTL, and then another
nmap scan when it flipped back. Here is the result of that diagnostic, an email message to the IT department:
From: Ian! D. Allen Subject: duplicate DHCP IP for 10.50.254.149 Date: Thu, 23 Oct 2014 08:45:37 -0400 To: Algonquin College Help Desk Cc: Todd Kelley, Wenjuan Jiang There may be a rogue machine using IP 10.50.254.149. The DHCP server at 10.254.21.74 handed this IP to my Linux server, but some other machine was already using it. The result was intermittent connection failure to my server, icmp misdirects, and failure of long file transfers. You can see the result here from two successive nmap requests to the same IP address. One connects to some probably-Microsoft machine, and the next nmap a few seconds later connects to my Linux server: Starting Nmap 5.21 ( http://nmap.org ) at 2014-10-23 08:29 EDT Nmap scan report for idallen-cls-alg.dyndns.org. (10.50.254.149) Host is up (0.00025s latency). Not shown: 994 filtered ports PORT STATE SERVICE 80/tcp open http 135/tcp open msrpc 445/tcp open microsoft-ds 3389/tcp open ms-term-serv 49153/tcp open unknown 49154/tcp open unknown Nmap done: 1 IP address (1 host up) scanned in 5.18 seconds Starting Nmap 5.21 ( http://nmap.org ) at 2014-10-23 08:30 EDT Nmap scan report for idallen-cls-alg.dyndns.org. (10.50.254.149) Host is up (0.00084s latency). Not shown: 992 closed ports PORT STATE SERVICE 22/tcp open ssh 25/tcp open smtp 80/tcp open http 110/tcp open pop3 443/tcp open https 995/tcp open pop3s 2222/tcp filtered unknown 8080/tcp filtered http-proxy Nmap done: 1 IP address (1 host up) scanned in 1.32 seconds You can see the same thing when running ping to the IP address; it switches machines in the middle (the TTL changes): 64 bytes from 10.50.254.149: icmp_seq=42 ttl=126 time=0 ms 64 bytes from 10.50.254.149: icmp_seq=43 ttl=126 time=0 ms 64 bytes from 10.50.254.149: icmp_seq=44 ttl=126 time=0 ms 64 bytes from 10.50.254.149: icmp_seq=45 ttl=62 time=0 ms 64 bytes from 10.50.254.149: icmp_seq=46 ttl=62 time=0 ms 64 bytes from 10.50.254.149: icmp_seq=47 ttl=62 time=0 ms I've DHCP released that bogus IP address and obtained a new one. You might find out why the DHCP server gave my machine an IP address that was already in use, or track down why that machine is using that IP instead of getting it properly from the DHCP server.
Linux doesn’t have a way to say “don’t ask DHCP for this IP address”, but I know enough about how Linux
DHCP works to know that the previous IP address obtained by
DHCP is cached in the file
/var/lib/dhcp/dhclient.eth0.leases and that Linux will ask for this address again even if you release the IP and re-request a new address via
DHCP. So I shut down the
eth0 interface, which released the current IP address, edited the file to cache a different IP address (I picked
10.50.254.160 at random), and then brought up the interface. Linux asked for
10.50.254.160 and the
DHCP server acknowledged that. So now the CLS has its own IP that isn’t in conflict with that other machine at
This is what sysadmin do.
Author: | Ian! D. Allen - firstname.lastname@example.org - Ottawa, Ontario, Canada | Home Page: http://idallen.com/ Contact Improv: http://contactimprov.ca/ | College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/ | Defend digital freedom: http://eff.org/ and have fun: http://fools.ca/
Author Ian! D. Allen