Rate limit outgoing emails from PHP web applications using postfix and policyd

One of the worst things a webmaster or a anyone else that runs some web application can do, is to constantly send “informative newsletters” to people. Most CMS applications make it really easy to send such emails. These are 99% spam, and as such there are many good reasons that you should limit the amount of such outgoing “newsletters” coming out of your email server. Else there’s a good chance you might get added to a blacklist, and you don’t want your legitimate clients to have their emails blocked because of some irresponsible people. I recently had to deploy such a solution to a hosting server that serves multiple (>300) domains. The server already ran postfix, so I had to implement something useful around it.

The problem with postfix is that you can’t really rate-limit the outgoing queue per sender domain/address. There are only generic settings that control the general mail server’s capabilities of sending emails. What I wanted though is to have the ability to restrict specific domains to some specific email message count per day. This is something that a postfix addon named postfix-policyd can do by deferring/greylisting, but still just on the incoming queue. One would think that the problems would be solved by just applying this, but truth is that they don’t. Applying a defer/greylisting policy on the incoming queue is fine while the client on the remote side is another SMTP server that can happily store the deferred email on its queue and retry some minutes/hours later. What happens though if the SMTP client is a PHP application that connects through the mail() function ? There you have no queue and if you defer a message at the SMTP server it will get forever lost, PHP can’t resend it. So the solution would be to apply an intermediate SMTP queue between PHP and the primary SMTP server, that is another local postfix installation that would only serve as a queue that relays emails to the primary.

Using a “simple” diagram sending an email from PHP should follow this path upon a successful installation:

PHP mail() –(sendmail binary)–> intermediate_POSTFIX –(SMTP relay)–> POSTFIX –(smtpd_sender_restrictions)–> POLICYD –(pickup)–> POSTFIX –(SMTP)–> REMOTE SERVER

Here are the steps I took on a Debian Squeeze server to install this little monster.

1. Create a new postfix configuration directory for the new intermediate postfix instance
I named my intermediate postfix config dir as postfix2525, name comes from the port that it will listen on but you can definitely be more creative.

# mkdir /etc/postfix2525
# cp -av /etc/postfix /etc/postfix2525

Remove everything from /etc/postfix2525/main.cf and just add the following lines:

data_directory = /var/lib/postfix2525
queue_directory = /var/spool/postfix2525
relayhost =

This defines a new data and queue directory and instructs this postfix to relay all emails through another one that listens on the localhost, the primary one, on port 12525. More about this port later when you will create some special config on the primary postfix.

Remove previous contents of /etc/postfix2525/master.cf and just add these lines:      inet  n       -       -       -       2       smtpd
        -o syslog_name=postfix2525
pickup    fifo  n       -       -       60      1       pickup
cleanup   unix  n       -       -       -       0       cleanup
qmgr      fifo  n       -       n       300     1       qmgr
#qmgr     fifo  n       -       -       300     1       oqmgr
tlsmgr    unix  -       -       -       1000?   1       tlsmgr
rewrite   unix  -       -       -       -       -       trivial-rewrite
bounce    unix  -       -       -       -       0       bounce
defer     unix  -       -       -       -       0       bounce
trace     unix  -       -       -       -       0       bounce
verify    unix  -       -       -       -       1       verify
flush     unix  n       -       -       1000?   0       flush
proxymap  unix  -       -       n       -       -       proxymap
proxywrite unix -       -       n       -       1       proxymap
smtp      unix  -       -       -       -       -       smtp
# When relaying mail as backup MX, disable fallback_relay to avoid MX loops
relay     unix  -       -       -       -       -       smtp
        -o smtp_fallback_relay=
#       -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq     unix  n       -       -       -       -       showq
error     unix  -       -       -       -       -       error
retry     unix  -       -       -       -       -       error
discard   unix  -       -       -       -       -       discard
local     unix  -       n       n       -       -       local
virtual   unix  -       n       n       -       -       virtual
lmtp      unix  -       -       -       -       -       lmtp
anvil     unix  -       -       -       -       1       anvil
scache    unix  -       -       -       -       1       scache

Obviously the most important part here is the first line. It defines that this postfix instance will listen for SMTP connections on localhost, port 2525 and it’s syslog output name will be postfix2525 so that it’s easier to tell apart which SMTP instance spits which errors.

After this is done you need to run the following command that will create all necessary directories with their proper permissions.

# postfix -c /etc/postfix2525/ check

Also make sure you add the following line to the main.cf file of your main postfix installation:
alternate_config_directories = /etc/postfix2525

You will also need a new init script. Since the script by itself is quite big and there are only a few lines that actually differ, I will post my diff here:

--- /etc/init.d/postfix  2011-05-04 21:17:47.000000000 +0200
+++ /etc/init.d/postfix2525  2011-12-19 19:22:09.000000000 +0100
@@ -17,8 +17,10 @@
 # Description:       postfix is a Mail Transport agent
+DAEMON_OPTIONS="-c /etc/postfix2525"
 unset TZ
@@ -28,13 +30,13 @@
 test -f /etc/default/postfix && . /etc/default/postfix
-test -x $DAEMON && test -f /etc/postfix/main.cf || exit 0
+test -x $DAEMON && test -f /etc/postfix2525/main.cf || exit 0
 . /lib/lsb/init-functions
 #DISTRO=$(lsb_release -is 2>/dev/null || echo Debian)
 running() {
-    queue=$(postconf -h queue_directory 2>/dev/null || echo /var/spool/postfix)
+    queue=$(postconf -c $CONFDIR -h queue_directory 2>/dev/null || echo /var/spool/postfix2525)
     if [ -f ${queue}/pid/master.pid ]; then
   pid=$(sed 's/ //g' ${queue}/pid/master.pid)
   # what directory does the executable live in.  stupid prelink systems.
@@ -66,7 +68,7 @@
       # see if anything is running chrooted.
-      NEED_CHROOT=$(awk '/^[0-9a-z]/ && ($5 ~ "[-yY]") { print "y"; exit}' /etc/postfix/master.cf)
+      NEED_CHROOT=$(awk '/^[0-9a-z]/ && ($5 ~ "[-yY]") { print "y"; exit}' /etc/postfix2525/master.cf)
       if [ -n "$NEED_CHROOT" ] && [ -n "$SYNC_CHROOT" ]; then
     # Make sure that the chroot environment is set up correctly.
@@ -111,7 +113,7 @@
     umask $oldumask
-      if start-stop-daemon --start --exec ${DAEMON} -- quiet-quick-start; then
+      if start-stop-daemon --start --exec ${DAEMON} -- ${DAEMON_OPTIONS} quiet-quick-start; then
     log_end_msg 0
     log_end_msg 1
@@ -123,7 +125,7 @@
   log_daemon_msg "Stopping Postfix Mail Transport Agent" postfix
   if [ -n "$RUNNING" ]; then
-      if ${DAEMON} quiet-stop; then
+      if ${DAEMON} ${DAEMON_OPTIONS} quiet-stop; then
     log_end_msg 0
     log_end_msg 1

If everything went well up to now you should be able to start your new postfix instance and check that it is actually running.

# /etc/init.d/postfix2525 start
# netstat -antp | grep 2525
tcp        0      0*               LISTEN      6138/master

2. Configure main postfix to accept emails from the intermediate
Edit /etc/postfix/master.cf and add this line at the bottom: inet n - - - - smtpd  -o smtp_fallback_relay= -o smtpd_client_restrictions=  -o smtpd_helo_restrictions=  -o smtpd_recipient_restrictions=permit_mynetworks,reject  -o smtpd_data_restrictions=  -o receive_override_options=no_unknown_recipient_checks

This defines a special port for the main postfix instance that has (or maybe it hasn’t actually) some special restrictions.
Actually you will have to change this line later on upon installing postfix-policyd, but this should be good enough for now, in order for you to do some testing.
Restart postfix

# /etc/init.d/postfix restart
# netstat -antp | grep 2525
tcp        0      0*               LISTEN      26799/master    
tcp        0      0*               LISTEN      6138/master   

The intermediate postfix listens on and the main one has another special listening port on

3. Test your intermediate postfix instance
You can do this in a gazillion different ways. One of my favorite ways to test SMTP connectivity is through telnet (—> shows data entry):

# telnet localhost 2525
Connected to localhost.
Escape character is '^]'.
220 server.mydomain.gr ESMTP Postfix
---> EHLO koko.gr
250-SIZE 10240000
250 DSN
---> MAIL FROM: lala@koko.gr
250 2.1.0 Ok
---> RCPT TO: koko@destination.gr
250 2.1.5 Ok
---> DATA
354 End data with <CR><LF>.<CR><LF>
---> .
250 2.0.0 Ok: queued as C41E21C84FF
---> quit

If you were keeping an eye on syslog messages you should have seen some connection messages both from postfix2525 and from postfix. If everything went well your email _should_ have arrived at it’s destination. If this is true then your primary postfix instance now works as a relay for your intermediate queue.

Don’t read the next parts of this post if you haven’t previously managed this step!

4. Install and configure postfix-policyd

# aptitude install postfix-policyd

To run policyd you need to create a database and import policyd SQL schema to it. Your distro has probably already taken care of the previous step, if it hasn’t…do it manually and think about changing distro!
Then edit the config file usually located at /etc/postfix-policyd.conf. The options I chose to play with were the following:

Since all emails will be relayed through localhost there’s no point in throttling per host, what is needed is throttling per envelope sender.
You should manually review your desired limits though. I won’t post mine here because everyone has different needs and there’s no sane config for everyone.

Start postfix-policyd
# /etc/init.d/postfix-policyd start

If you get weird startup errors like:
postfix-policyd: fatal: didn't find priority 'LOG_IFOO', exiting
Edit /etc/postfix-policyd.conf, find the following line:
and change it to (mind the removed spaces):

5. Configure main postfix instance to use postifix-policyd
Edit /etc/postfix/main.cf and add this:
webclient_restrictions = check_policy_service inet:

Then edit /etc/postfix/master.cf again and change the line you had previously added to the bottom of the file with this: inet n - - - - smtpd  -o smtp_fallback_relay= -o smtpd_client_restrictions=  -o smtpd_helo_restrictions=  -o smtpd_recipient_restrictions=permit_mynetworks,reject  -o smtpd_data_restrictions=  -o receive_override_options=no_unknown_recipient_checks -o smtpd_sender_restrictions=${webclient_restrictions}

The difference is
-o smtpd_sender_restrictions=${webclient_restrictions}
which practically instructs postfix to use postfix-policyd for emails that arrive on port 12525, which is the port that the intermediate postfix instance uses to relay all emails.

6. Test your intermediate postfix instance again
If everything went well, the main postfix instance should now be able to enforce sender policies. Try sending a new email through the intermediate postfix again, yes using telnet, and you should pickup some new log lines at your syslog:

Dec 19 21:56:40 myserver postfix-policyd: connection from: port: 45635 slots: 0 of 4096 used
Dec 19 21:56:40 myserver postfix-policyd: rcpt=5, greylist=new, host= (unknown), from=lala@koko.gr, to=koko@lalala.gr, size=348
Dec 19 21:56:40 myserver postfix/smtpd[9168]: NOQUEUE: reject: RCPT from unknown[]: 450 4.7.1 : Sender address rejected: Policy Rejection- Please try later.; from= to= proto=ESMTP helo=
Dec 19 21:56:40 myserver postfix/smtp[8970]: C41E21C84FF: to=, relay=[]:12525, delay=20, delays=20/0/0.01/0, dsn=4.7.1, status=deferred (host[] said: 450 4.7.1 : Sender address rejected: Policy Rejection- Please try later. (in reply to RCPT TO command))

The above means that greylisting through policyd works.

7. make PHP use your new intermediate postfix instance
PHP on linux by default uses the sendmail binary to send emails via the mail() function. That would use the main postfix instance though, so one needs to edit /etc/php/apache2/php.ini and change the following line:
sendmail_path = "sendmail -C /etc/postfix2525 -t -i"

The -C directive instructs sendmail to use the alternate config dir, so that emails will be sent to the new intermediate postfix instance and then to the main one, passing through policyd of course.

To check the queue size of the intermediate postfix:
# postqueue -p -c /etc/postfix2525/

If any PHP applications that are hosted have explicit SMTP server/port directives, then be sure to notify your clients/developers that they _MUST_ use localhost:2525 to send their emails to and not the default localhost:25. This is one of the shortcomings of the above method, if someone manually sets up his application to use the default localhost:25 his emails will get right through. But being a good sysadmin, you should monitor such behavior and punish those users accordingly!

That’s about it…with the above configuration and some tweaking to the thresholds you have very good chances of avoiding getting blacklisted because someone decided to send a few thousand spams emails. And most importantly, your normal mail service will continue to work flawlessly, no matter how big the queue of the intermediate mail server is.


Reference for policyd: http://policyd.sourceforge.net/readme.html

Handling right clicks on a macbook running Linux – The 2011 Awesome Edition

2 years ago I had written a post about handling right clicks on a macbook running linux. Along with changing my window manager of choice, I think I’ve found a better/more elegant solution to that problem.

On my computer’s workspaces one will normally find one or two browser windows open, some instant messaging applications (skype,pidgin), an mp3 player (audacious2) and terminals. Lots of them. I need them to ssh to the servers I monitor/administer and for coding (with vim of course!). I even use one for my email client (mutt). So I need my terminals to be as efficient as possible. After many trials over the years I’ve decided on using urxvt as my terminal of choice.

About a month ago I gave awesome a try and since then it’s been my window manager of choice instead of fluxbox. The reason behind this is mostly fluxbox’s inability to tile terminal (call me urxvt) windows efficiently while changing resolutions. I mostly use my laptop with an external 23” monitor but I wanted to be able to tile my terminals independently of using only my laptop’s screen or both laptop’s and the external one. In fluxbox you can make a window appear on specific area of the screen, so I could open 3-4 terminals on a specific workspace/monitor. Resizing though one of them to fit some monitoring program more efficiently didn’t resize the others ‘automagically’ as well. So, I had to manually resize all open windows of that workspace. Yes, this is horrible from a usability point of view, luckily I didn’t have to do it that frequently. So, I gave awesome a try for its tiling features. I really miss though fluxbox’s tabbing features that I constantly used along with it’s amazing keybindings flexibility (Rant: isn’t it stupid that you have to write your keybindings in lua for awesome and in haskell for xmonad ?) but the tiling capabilities of awesome are currently more important to me.

So while my previous solution for right clicking without a mouse worked pretty well for fluxbox, in my new awesome world I’ve replaced it with xautomation tools. First of all, one needs to install xautomation tools

aptitude install xautomation

Then find clientbuttons configuration part in the default ~/.config/awesome/rc.lua and add this line to it:

awful.button({ modkey }, 2, function () awful.util.spawn("xte 'mouseclick 3'") end)

restart awesome and try modkey + 3 finger tap on your touchpad. You should be seeing a right click “menu”.
If you don’t know what 3 finger tap is or how to configure it, read the 2009 article.

That’s it, no more xbindkeys + xvkbd for awesome.

my past 2 articles for LinuxInside

Following my first article on the Greek Linux Magazine called LinuxInside about IPv6, I uploaded my past 2 articles for it. Both articles are in Greek of course.

The first one is about debugging network connectivity issues using the command line on Linux. It was published on the 2nd issue of LinuxInside.
Εντοπίζοντας ένα πρόβλημα δικτύωσης

The other one is an introduction to Zsh. It was published on the 3rd issue of LinuxInside.
Κατακτήστε το Z shell

If you haven’t read the magazine already, feel free to download those pdfs and read them.
All my presentations/articles can be found at: Articles/Presentations

0x375 – 0x07 – Security Considerations for a brave new (IPv6) World

I finally had the chance to present something at the Thessaloniki Tech Talk Sessions also known as 0x375. The people over there have done a great job, and I truly mean that, bringing tech people together. Almost once a month 2 speakers can present a tech topic they like at an open auditorium inside the Aristotle University of Thessaloniki. On those events people from Thessaloniki, but also from nearby cities, gather and have a great time, not only during the presentations but afterwards as well. I won’t spoil the events that take place during the tech talks, because you should definitely go if you are curious, but I can tell you that it’s not uncommon for as many as 15 to 20 people to go for beers after the talks!

So, the past Friday (25/11/2011), me and @apoikos traveled from Athens to Thessaloniki to present at 0x375. My presentation was about some security concepts on IPv6 networks, how old attacks of the IPv4 world transform to new ones on the IPv6 world and about some new ones that will appear on local networks sooner or later. I also had prepared some small live demos, but as always it’s very hard to succeed in a live demo if you don’t quite control the environment. At least some of the stuff I wanted to show were successful, and I’m happy with those. (Thanks to Nuclear for booting his OS X guinea pig)

Some apologies…When giving a presentation on IPv6, in an event that has no other introductory IPv6 presentations, I always face the same problem, most people are not very well aware of how different this protocol is from IPv4. When I ask the audience how well do they know IPv6, most people are embarrassed to say they have never actually used it, so the audience stays very, VERY silent. This means that I have to put around 15-20 slides to make a “quick introduction to IPv6”, and this unfortunately takes usually over 30′ of presentation time. Some techy/advanced people might be bored with this, but there’s no other way to overcome this “issue”. If you go straight to the point and start discussing about ND ICMPv6 messages most people won’t be able to keep up…so I’m sorry if I made some of the audience get bored by my first slides. I promise that my next talk on 0x375, cause there will surely be a next one, will be less boring for you 🙂

Thank you all for coming there, I hope you enjoyed it as much as I did!

You can find the slides and my live demo notes here:
0x375 – 0x07 – kargig – Security Considerations for a brave new (IPv6) World (pdf)
0x375 – 0x07 – kargig – Security Considerations for a brave new (IPv6) World – live demo notes (txt)

P.S. I’ve started collecting some interesting (for me) presentations regarding IPv6 topics at void.gr/kargig/ipv6/. Check them out if you like.

GrRBL goes django

I’ve had this thought for some time now, I needed a nice interface for GrRBL so that it would make it easier for others, read more, people to contribute. Many people have been, politely, complaining about lack of features, policy and so on.

Right now most people use either the submission form or they bounce their emails to grrbl [at] void [dot] gr. Then their emails get manually processed, filtered and if everything goes well the “useful” parts of their email end up in the DNS RBL or the email address blacklist. This process is not automated at all, entries are manually added to a database, and is therefore quite time consuming. What’s worse is that people who are listed don’t have an ‘easy’ way to opt-out, apart from emailing us. The algorithm of adding someone to these lists is also not well-defined. The main rule that is followed is that an IP or email address is added to these lists when at least 3 people have submitted them on different days.

Hopefully this is about to change soon (I don’t know how soon, but soon!). During the past month I’ve been trying to code an interface in django, even though I had no prior experience in it. It’s mostly a self educating process and I like it very much. This django application will be generic enough to cover submissions and listings for IPs, emails and possibly URLs.

  • Short term goals:
  • Anonymous users will only get to see details about an IP they search for. People though will be able to register and add their own entries to a database. These registered users will be able to see the complete listings. Each user will belong to a group and every group will have a different weight which will depend on his ‘expertise’ (I know this is broad, but read on). For example, the group of the individual users will certainly have less weight than the group of the postmasters of Greek ISPs (yeap there are some who regularly contribute). Using their weights users will be able to vote on each entry that’s inside the database. Upon a certain score these entries will be flagged as eligible to be on the blacklist. Listed people will be able to opt-out but this process will be moderated by the superusers, that means that spammers like the infamous sofokleous10 will never get a chance to opt-out even for a single second.
    Most of this functionality is already coded and is working quite well.

  • Mid term goals:
  • Various export formats will be supported (BIND/RBLDNSD, Spamassassin/Postifix/Exim/sendmail/etc). Selective/custom export of entries will be provided. Users will be able to select if they want to export/use a strict blacklist, that is hosts that are scored very high, a moderate one and a very broad/risky one. Levels have yet to be defined. An API will be published so that entries can be re-used in other applications (json format ?)

  • Long term goals:
  • A method/interface that someone would copy/paste their email and it would automagically parse it, provide the user with the discovered malicious entries (IP, emails, URLs) and propose him to add them to the database. Maybe automate this even further so that they are added on a separate moderated queue without user interaction, that would be suitable for submitting entries via email plugins for clients such as mutt/thunderbird/etc.

  • The code:
  • The django application code resides in github for now: https://github.com/kargig/grrbl_django. Everyone is welcome to submit ideas (as issues) and code! Feel free to download, test and provide feedback.

  • Greek Adblock Plus Filter
  • Since the code is very flexible I am thinking whether Greek Adblock Plus Filter can also be benefited by this voting system. It probably can, so expect some changes to that list as well. One interface to rule them all.

    Many thanks go to @apoikos who has been helping me a lot with the tons of questions I still have on django stuff.

    Notes on HP raid controllers

    Lately I had to deal with some HP raid controllers and I’ve gathered some notes on them. I’ll post them here so I won’t forget about them.

    First of all, don’t even think on using them without a battery pack. Seriously DON’T. The performance degradation is humongous. Without a battery pack the controllers were giving me 1/20th of the results with a battery pack. If you want to quickly test them, try iozone using the following options: iozone -t4 -I

    Installing hpacucli is a also a must if you want to monitor or configure the controllers from within your OS. Be sure to add the repositories from HWraid to your system and then issue: aptitude install hpacucli (you are using Debian, arent’ you?). That reminds me that I am using those repositories on so many systems I manage that I must send a donation to the people at hwraid to thank them.

    Below are some commands using hpacucli that I used.
    # Show everything about your raid controllers
    # hpacucli controller all show config detail

    Cache Board Present: True
    Cache Status: OK
    Accelerator Ratio: 25% Read / 75% Write
    Drive Write Cache: Enabled
    Total Cache Size: 512 MB
    Battery Pack Count: 1
    Battery Status: OK
    SATA NCQ Supported: True

    What you must take notice here is the Accelerator Ratio, Drive Write Cache and Battery Pack Count.
    if you have a battery pack installed but your Drive Write Cache is still shown as “Disabled”, you can enable it using the command:
    # hpacucli controller slot=X modify dwc=enable
    You’ll know what to put instead of “slot=X” from the output of the previous command (show config detail).

    To modify Accelerator Ratio (read/write):
    # hpacucli controller slot=X modify cacheratio=25/75

    To enable Array Acceleration for one of your logical drives use:
    # hpacucli controller slot=X logicaldrive Y modify aa=enable

    If you happen to face the following error while opening hpacucli, don’t worry. You don’t need to reboot your machine as I’ve seen in various blogs.

    Error: Another instance of ACU is already running (possibly a service). Please
    terminate the ACU application before running the ACU CLI. Press ENTER to

    What you need to do is delete the shared IPC that hpacucli left when it got killed for some reason.
    To see all your ipcs:

    # ipcs
    ------ Shared Memory Segments --------
    key        shmid      owner      perms      bytes      nattch     status      
    ------ Semaphore Arrays --------
    key        semid      owner      perms      nsems     
    0xffffffff 32768      root       0          1         
    ------ Message Queues --------
    key        msqid      owner      perms      used-bytes   messages    

    Then use ipcrm to remove the array with the semid you want:
    # ipcrm -s 32768

    and try to start hpacucli again.

    1. http://www.datadisk.co.uk/html_docs/redhat/hpacucli.htm
    2. http://people.freebsd.org/~jcagle/hpacucli-readme

    Block Greek ads with Internet Explorer 9+

    Greek Adblock Plus filter list has more than 3500 regular unique (as per IP) subscribers daily. The majority of them uses some Mozilla-based browser (Firefox/Iceweasel). An increasing number of users has started using Chrome along with the Chrome Adblock Extension and Opera. Thanks to Panagiotis Dimopoulos, Greek Adblock Plus filter has now been converted to a Tracking Protection List for Internet Explorer 9+.

    To load the protection list visit the url: Greek Adblock Tracking Protection List for Internet Explorer 9+

    For more details about using Greek Adblock Plus filter on various browsers please visit: Greek Adblock Plus Filter.

    Don’t forget to send in comments and URLs to block. If you are using Firefox’s addon, please use the “Report Issue on this page…” feature of it by right clicking on the status icon of adblock.

    Why vacation auto-reply messages can sometimes be bad

    Say that a user has an email account at the company he works for. Before going on vacation he activates his cool “vacation auto-reply” feature that adds

    Out of Office – I will be back from holidays at the end of July.

    on the top and then quotes the email he was sent.

    During his vacation, he receives a call and he is told he has to urgently sent an email about some financial updates. He rushes to an internet cafe and sends the email. He makes a mistake though and mistypes one of the email addresses of the recipients. Instead of sending the email to “user@domain.com” he sends it at “usar@domain.com”.

    His company’s SMTP server though receives the following error message from the remote SMTP server while trying to deliver the email:

    <usar@domain.com>: host mx.domain.com[] said: 550 5.1.1
       <usar@domain.com>... User unknown (in reply to RCPT TO command)

    This means that his SMTP server will then send an email to him informing him about the error and quoting parts if not all of the email he had previously sent. The email will likely appear to be from “postmaster@company.com” or “do-not-reply@company.com” or something similar.
    It will look like this:

    This is the mail system at host mail.company.com.
    I'm sorry to have to inform you that your message could not
    be delivered to one or more recipients. It's attached below.
    For further assistance, please send mail to postmaster.
    If you do so, please include this problem report. You can
    delete your own text from the attached returned message.
                      The mail system
    <usar@domain.com>: host mx.domain.com[] said: 550 5.1.1
       <usar@domain.com>... User unknown (in reply to RCPT TO command)
    Reporting-MTA: dns; mail.company.com
    X-Postfix-Queue-ID: AE4812AE328
    X-Postfix-Sender: rfc822; employee1@company.com
    Arrival-Date: Thu,  5 May 2011 20:05:27 +0200 (CEST)
    Final-Recipient: rfc822; usar@domain.com
    Original-Recipient: rfc822;usar@domain.com
    Action: failed
    Status: 5.1.1
    Remote-MTA: dns; mx.domain.com
    Diagnostic-Code: smtp; 550 5.1.1 <usar@domain.com>... User unknown
    From: Loyal Employee <employee1@company.com>
    Date: July 5, 2011 9:05:29 PM GMT+03:00
    To: User User <usar@domain.com>
    Subject: Re: Financial updates
    Financial data goes here

    But the user has still his vacation auto-reply turned on, so when the automatic postmaster’s email reaches his mailbox, the system will automatically reply back to the “postmaster@company.com” quoting the previous email and adding his auto-reply message:

    Out of Office – I will be back from holidays at the end of July.

    So the postmaster@company.com currently has all the financial details that he shouldn’t!

    Apart from the fact that the user was sending financial data to somebody else in a clear text email instead of an encrypted one, the second biggest mistake that the user has made was that he has enabled vacation auto-replies that quote the email he was previously sent. That’s very very wrong. If you don’t want sensitive stuff ending at the postmaster’s inbox avoid quoting previous emails in your auto-replies by all means.

    Based on a true story 🙂

    please use indexes in your database tables

    I don’t know how many times I’ve heard a sysadmin swearing at a web/application developer that has “forgotten” to add proper index to their database tables. Please dear developers, add those indexes, it’s not that hard!

    Today I had to do it on a table for a xoops module. A single query could keep mysql very very busy…how busy ? the query could take more than 2 minutes, unless it was already cached! I’ll post the way I solved it as an example. It is actually usually quite easy to solve these kind of issues.

    1) How to spot the problem
    Your application is slow and your server’s “top” shows mysql running constantly at full load.

    2) Find the problematic query. Login to mysql and run a ‘show processlist;’

    mysql> show processlist;
    | Id   | User         | Host      | db                 | Command | Time | State          | Info                                                                                                 |
    | 1792 | admin        | localhost | aaa                | Sleep   |    0 |                | NULL                                                                                                 | 
    | 4790 | user         | localhost | bbb                | Query   |    0 | Sorting result | SELECT * FROM foobar WHERE (com_rootid = '22797' AND com_id >= '22797') ORDER BY com_id              | 
    | 4791 | user         | localhost | bbb                | Query   |    0 | Sorting result | SELECT * FROM foobar WHERE (com_rootid = '22797' AND com_id >= '22797') ORDER BY com_id              | 
    | 4817 | admin        | localhost | NULL               | Query   |    0 | NULL           | show processlist                                                                                     | 
    4 rows in set (0.00 sec)

    3) Take a closer look at the structure of the table

    mysql> describe foobar;
    | Field        | Type                  | Null | Key | Default | Extra          |
    | com_id       | mediumint(8) unsigned | NO   | PRI | NULL    | auto_increment | 
    | com_pid      | mediumint(8) unsigned | NO   | MUL | 0       |                | 
    | com_rootid   | mediumint(8) unsigned | NO   |     | 0       |                | 
    | com_modid    | smallint(5) unsigned  | NO   |     | 0       |                | 
    | com_itemid   | mediumint(8) unsigned | NO   | MUL | 0       |                | 
    | com_icon     | varchar(25)           | NO   |     |         |                | 
    | com_created  | int(10) unsigned      | NO   |     | 0       |                | 
    | com_modified | int(10) unsigned      | NO   |     | 0       |                | 
    | com_uid      | mediumint(8) unsigned | NO   | MUL | 0       |                | 
    | com_ip       | varchar(15)           | NO   |     |         |                | 
    | com_title    | varchar(255)          | NO   | MUL |         |                | 
    | com_text     | text                  | NO   |     | NULL    |                | 
    | com_sig      | tinyint(1) unsigned   | NO   |     | 0       |                | 
    | com_status   | tinyint(1) unsigned   | NO   |     | 0       |                | 
    | com_exparams | varchar(255)          | NO   |     |         |                | 
    | dohtml       | tinyint(1) unsigned   | NO   |     | 0       |                | 
    | dosmiley     | tinyint(1) unsigned   | NO   |     | 0       |                | 
    | doxcode      | tinyint(1) unsigned   | NO   |     | 0       |                | 
    | doimage      | tinyint(1) unsigned   | NO   |     | 0       |                | 
    | dobr         | tinyint(1) unsigned   | NO   |     | 0       |                | 
    20 rows in set (0.01 sec)

    4) run EXPLAIN on the problematic query

    mysql> explain SELECT * FROM foobar WHERE (com_rootid = '17536' AND com_id >= '17536') ORDER BY com_id;
    | id | select_type | table              | type | possible_keys         | key  | key_len | ref  | rows  | Extra                       |
    |  1 | SIMPLE      | foobar             | ALL  | PRIMARY               | NULL | NULL    | NULL | 18271 | Using where; Using filesort | 
    1 row in set (0.02 sec)

    If “type” is “ALL”, like the case above, then you have a problem. This is the worst “type” you could have. The query above scans the whole table and has to go through 18271 rows and then has to do a filesort on these rows.

    5) Look at indexes, if there are any….

    mysql> show index from foobar;
    | Table              | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
    | foobar             |          0 | PRIMARY    |            1 | com_id      | A         |       18272 |     NULL | NULL   |      | BTREE      |         | 
    | foobar             |          1 | com_pid    |            1 | com_pid     | A         |           1 |     NULL | NULL   |      | BTREE      |         | 
    | foobar             |          1 | com_itemid |            1 | com_itemid  | A         |          18 |     NULL | NULL   |      | BTREE      |         | 
    | foobar             |          1 | com_uid    |            1 | com_uid     | A         |           6 |     NULL | NULL   |      | BTREE      |         | 
    | foobar             |          1 | com_title  |            1 | com_title   | A         |       18272 |       40 | NULL   |      | BTREE      |         | 
    5 rows in set (0.00 sec)

    6)Create necessary new index

    ALTER TABLE  `DB`.`foobar` ADD INDEX `com_id_rootid` (  `com_id` ,  `com_rootid` )

    7) Explain the query again

    mysql> explain SELECT * FROM foobar WHERE (com_rootid = '17536' AND com_id >= '17536') ORDER BY com_id;
    | id | select_type | table              | type | possible_keys          | key           | key_len | ref   | rows | Extra                       |
    |  1 | SIMPLE      | foobar             | ref  | PRIMARY,com_id_rootid  | com_id_rootid | 3       | const |    1 | Using where; Using filesort | 
    1 row in set (0.00 sec)

    now the query is of type “ref” and it only fetches 1 row!
    If the query could be optimized even more by the developer and he/she could replace ‘>=’ with ‘=’ then it would make us even happier

    mysql> explain SELECT * FROM foobar WHERE (com_rootid = '17536' AND com_id = '17536') ORDER BY com_id;
    | id | select_type | table              | type  | possible_keys         | key     | key_len | ref   | rows | Extra |
    |  1 | SIMPLE      | foobar             | const | PRIMARY,com_id_rootid | PRIMARY | 3       | const |    1 |       | 
    1 row in set (0.00 sec)

    the type would now be ‘const’, which is the best type we could have.

    The problem got fixed with just one command! Now the queries take milliseconds to finish and the web application is as fast as ever. The server load dropped from 2.5 to 0.4 with just this tiny addition to the indexes.

    CPU load drops dramatically after adding the proper index to the table

    CPU Load

    So dear developers, please run EXPLAIN to your queries before you submit your applications and if you find queries with type=ALL try to add indexes! It saves all of us a loooooot of trouble!

    For anyone who wants to read a nice blog post about EXPLAIN and what each part of the output means, I recommend that he/she reads this: MySQL Explain – Reference

    Resolving OSSEC active response iptables issues

    The past few days some of my servers are having difficult times due to the increase of spam by some botnet(s). From around 600-700 emails per day for unknown addresses/recipients on local domains, this number reached a peak of 8.000 emails 2 days ago. In order to reduce further botnet attempts I’m having ossec to engage, which in turn tries to firewall hosts.

    That worked quite ok for a while but then I’ve started seeing errors in the active-response.log like the ones below:

    Unable to run (iptables returning != 3): 1 – /var/ossec/active-response/bin/firewall-drop.sh delete – 1310919172.51029 31106
    Unable to run (iptables returning != 1): 1 – /var/ossec/active-response/bin/firewall-drop.sh delete – 1310919524.52191 3302
    Unable to run (iptables returning != 1): 2 – /var/ossec/active-response/bin/firewall-drop.sh delete – 1310919524.52191 3302
    Unable to run (iptables returning != 1): 3 – /var/ossec/active-response/bin/firewall-drop.sh delete – 1310919524.52191 3302
    Unable to run (iptables returning != 1): 4 – /var/ossec/active-response/bin/firewall-drop.sh delete – 1310919524.52191 3302
    Unable to run (iptables returning != 1): 5 – /var/ossec/active-response/bin/firewall-drop.sh delete – 1310919524.52191 3302
    Unable to run (iptables returning != 4): 1 – /var/ossec/active-response/bin/firewall-drop.sh add – 1310969220.1045522 3302

    Obviously iptables is busy doing something else at the time, adding or deleting some other rule, so the loop inside firewall-drop.sh sometimes fails. That was a bit worrying, I had to fix ossec so one way or another so that iptables rules would eventually be applied. I’ve faced the same issue with iptables in the past, trying to simultaneously add multiple (>5) iptables rules at exactly the same time is very error prone, there’s no way to tell which of those rules will be applied. In order to circumvent the issue, I added locking to the active response script.

    Whenever it comes to locking with shell scripts I am using a set of four functions inside a file that I source when I need to. I place this file usually inside /usr/local/bin/ under the lock.sh filename.

    lockme () {
        if [ -z "$1" ];then
            echo " o Use an argument to lock"
            return 1
        if [ -z "$2" ];then
        if [ -f $LOCK_PID_FILE ];then
            sleep 1
            echo " o Lock file found"
            if [ ! -d /proc/`cat $LOCK_PID_FILE 2>/dev/null` ];then
                echo " o Stale lock file ignoring..."
                rm -f $LOCK_PID_FILE
                return 1
        #temp file
        echo -n $PID > $LOCK_PID_FILE.$PID
        ln -s $LOCK_PID_FILE.$PID $LOCK_PID_FILE && return 0
        rm -f $LOCK_PID_FILE.$PID
        return 1
    lockme_wait () {
        if [ -z "$1" ];then
            echo " o Use an argument to lock"
            return 1
        if [ -z "$2" ];then
        while [ 1 ];do
            lockme $1 $PID && break
            sleep 4
        return 0
    unlockme () {
        if [ -z "$1" ];then
            echo " o Use an argument to unlock"
            return 1
        #remove pid file
        rm -f /var/lock/$1.`cat /var/lock/$1 2>/dev/null`
        rm -f /var/lock/$1
        return 0
    kill_locked () {
        if [ -z "$1" ];then
            echo " o Use an argument to kill_locked"
            return 1
        if [ -e /var/lock/$1 ]; then
            kill `cat /var/lock/$1 2>/dev/null`
        rm -f /var/lock/$1.`cat /var/lock/$1 2>/dev/null`
        rm -f /var/lock/$1

    You can also use %s/var\/lock/tmp/g if you prefer having the locks on the /tmp which is usually ramfs, partition.

    Afterwards I edited /var/ossec/active-response/bin/firewall-drop.sh to just add 3 lines. (I only edited the relevant Linux section of the script, since I haven’t tested, or don’t even know if it’s needed on the BSD, SunOS sections, I left those unedited):

  • Add . /usr/bin/lock.sh right after the “# Checking for an IP” section (around line 45)
  • Right after “# Executing and exiting” add lockme_wait active-response (around line 75)
  • Right after the second while loop finishes, after “done” and before “exit 0” add unlockme active-response (around line 110)
  • That’s it…just 3 lines added and the errors have completely stopped since then.

    P.S. Yes, I could have used lockfile-progs to achieve the same result, but I (also) use lock.sh file in embedded systems when needed, and it’s far more portable and easy.

    World IPv6 Day – The Future is Forever

    It’s time!

    Tomorrow is the World IPv6 Day and in order to celebrate it in Athens, we are having an IPv6 Party at hackerspace.gr!
    I’ll do a small introductory presentation about the basics of IPv6 Protocol and how’s Linux doing with it. After the presentation there will be an open discussion regarding IPv6 … drinking beer.

    Everyone’s invited! Be there!

    WORLD IPV6 DAY is 8 June 2011 – The Future is Forever

    End Users IPv6 Training by Hellenic IPv6 Task force

    Today the Hellenic IPv6 Task force organized a training day for end users. Most of the presentations were entry level, since they were targeting end users, but most of them were very interesting. I was happily surprised by Cosmote‘s presentation on their mobile IPv6 tests using native IPv6 and NAT64.

    My presentation was about what is architecturally different inside an IPv6-enabled CPE. I tried to present topics like WAN addressing, LAN addressing, auto-configuration (SLAAC), DHCPv6 as well as some migration/tunneling techniques. There were lots of comments, a lot of interesting questions and I was happy to “provoke” an interesting exchange of ideas/perceptions on IPv4 NAT mainly due to the previous to last slide of my presentation 🙂

    At the end of the event there was a draw and people got 4 IPv6-enabled CPEs produced by the company I work for (Gennet), 4 DSL accounts by OTE ready to use for OTE’s pilot IPv6 program and 5 IPv6 related books generously provided by Cisco.

    My presentation: Defining an IPv6-ready CPE
    All presentations: IPv6 End Users Training Day (2011)

    On Friday(s) 27/05 and 03/06 I’ll be giving two more IPv6 presentations at University of Pireus: [oss-unipi] Event #26: Introduction to TCP/IP and IPv6. The first one will be introductory and the second one will be more technical and maybe workshop based. In the same day(s) there will also be in-depth technical IPv4 presentations by Apollon Oikonomopoulos. Be there if you like technical presentations!

    Fosswar 2011 – How we did it

    As said in my previous post about Fosscomm 2011, during the conference there was a wargame consisting of 5 challenges. We played in a team consisting mainly of the following members: manji/manjiki, trelo_mpifteki, mickflemm and me. Along with us was maisk mainly acting as our manager (!!) shouting at us when we did something he did not like. He was of course a great help (sometimes :P).

    Few words about the team
    As most people who regularly read this blog already know, I consider myself a sysadmin even though I currently work at a company that produces Linux based xDSL routers where I do most of the things required about networking and system interaction like QoS, VoIP, IPv6, firewall, etc. My coding is confined among the realms of scripting languages. Manji is also a sysadmin who has lately started to mess with VoIP. Trelo_mpifteki is mostly a java developer and so is maisk. mickflemm is a coder and a very good one, frequently messing with Linux kernel’s wireless driver support. Obviously, we are certainly not the typical wargame players…

    The challenges
    Be sure to download the challenges from: http://patras.fosscomm.gr/fosswar/

    As soon as the wargame was on we split the challenges among us. Since mickflemm was the only coder he started to mess with challenge number 5 (reverse engineering). Me and trelo_mpifteki started to look at challenge number 1 (networking) while manji started poking at challenge number 3 (networking).

    Challenge 1:
    Type: Networking
    Players: kargig, trelo_mpifteki
    The first challenge said just this:

    Connect to the elite port and find the secret message.

    Everyone knows that elite = 31337
    So we just did a nc X.Y.Z.W 31337 (where X.Y.Z.W is the IP address of the server) and the following message appeared:

    IP protocol = 1
    id = 1337
    seq = 0xCAFE
    orig = 0xDEAD

    As it is easily understood one must create a packet, the problem is what kind of packet. And then was when I did a huge mistake stalling my team for more than 10 mins by insisting that Protocol 1 is IP. So we started trying to create an IP packet using scapy. Obviously we hit lots of problems because IP’s header clearly misses most of the above options, especially timestamp. Our next idea was to create a TCP packet in order to embed some of the options. This also lead to a dead end. The I looked again at my /etc/protocols file and I saw that Protocol 1 is ICMP. Timestamp is type 13, code 0 and the rest are just options. So our solution was this:

    >>> packet_2= IP(dst='X.Y.Z.W')/ICMP(type=13, id=1337, seq=0xcafe, ts_ori=0xdead)
    >>> send(packet_2)

    Using Wireshark we captured the response packet which looked like this (this setup is on my box atm):

    One can see the message: feedadeadface in it.

    If you need to compile listenicmp.c yourself you have to do something like this:

     # aptitude install libpcap-dev
    # gcc -o listenicmp listenicmp.c -lpcap

    Challenge 2:
    Type: Steganography
    Players: kargig,trelo_mpifteki,maisk
    For this challenge the organizers gave us a hint what we needed to find was close to the end of the image.jpg and after “BAADF00D”.

    # hd image.jpg | tail -n 4
    000152a0  d4 4d 77 22 b9 9a 68 ba  ad f0 0d 78 9c 0b c9 c8  |.Mw"..h....x....|
    000152b0  2c 56 00 a2 44 85 e2 d4  e4 a2 d4 12 85 dc d4 e2  |,V..D...........|
    000152c0  e2 c4 f4 54 3d 00 72 da  08 ef                    |...T=.r...|

    so we found “ba ad f0 0d” and the next characters were “78 9c”. We googled those and came up with the result that it was the magic of zlib compression. So what we had to do was get the rest of the file after “ba ad f0 0d” and then uncompress that. To get the rest of the file we found the size of the file and subtracted the bytes (31) that were of interest to us:

    # du -b image.jpg
    86730  image.jpg
    # split -b 86699 image.jpg koko
    # mv kokoab final

    Then we run python to decompress “final” file.

    >>> import zlib
    >>> ourfile=file('final')
    >>> ourfile
    <open file 'final', mode 'r' at 0xb7473020>
    >>> chunk=ourfile.read()
    >>> chunk
    >>> zlib.decompress(chunk)
    'This is a secret message.'

    Challenge 3:
    Type: Networking
    Players: manji,maisk,kargig

    While me and trelo_mpifteki were trying to solve challenges 1 and 2, manji was looking into challenge 3 pcap file for weird things. Once again we were given a hint that we needed to look at strange headers. Finding strange headers in a 800+ kb pcap file is not an easy task though. At a point manji was looking for very big sequence numbers…and then we got another hint, that we shouldn’t look at those big numbers at all. When me and trelo_mpifteki finished the other two challenges we started looking at Wireshark.
    We applied the following filter:
    (ip.host == && ((tcp.seq == 0) || (tcp.seq ==1))
    And the we had the following results in front of us:

    Since we knew that the message was sent to “” we needed to look at packets originating from “”. The first thing I noticed were packets with strange TTLs, they were going up and down..so I made a guess that the secret message could be hidden there. Transforming those TTL values to ASCII was a dead end. Then we started to look closer at every packet that sent to and we grouped them by destination port. There was clearly something going on with destination port 58900. A careful eye will also notice that packets towards port 58900 don’t have an MSS set while others mostly do. So, we expanded our filter with packets that also had destination port 58900:
    ((ip.host == && ((tcp.seq == 0) || (tcp.seq ==1))) && (tcp.dstport == 58900)
    and came up with this:

    If you look closely at the selected packet from Wireshark, you’ll see that the sequence number while set to 0 (zero) contains the letter ‘r’ inside it. The next packet contained the letter ‘o’ and the next one the letter ‘t’. Writing all these letters down we had this sequence:



    That was a rot13 encrypted message! with google’s help we found a rot13 decryptor. The decrypted message was:
    D E A D B E E F

    That’s it! we had 3 out of 5 while no other team had more than 2. So we had wooooon! Congrats to everyone on our team!

    Fosscomm 2011 – My review

    Generic comments
    I just got back home from Fosscomm 2011 and I must admit it has been one of the best organized events of this kind I’ve seen in Greece ever. The single most important fact was that presentations and workshops were always _on time_. They started on time, they finished on time. The organizers had to face even a power cut by the national energy company but they still managed not to fall behind on schedule. My only remark would be about the selection of the presentations that took place in the big room (called BA). Most of them gathered far less people than other presentations which took place in smaller rooms (B3 for example) and those rooms got extremely crowded from time to time. Maybe the organizers thought that generic open source presentations would attract more people than the technical ones but, unfortunately for them, and fortunately for “the greater good”, they were very wrong. This doesn’t reduce their achievement though. Another thing I would like to see on the next Fosscomm is less material given out to participants and instead spend this money on paying for travel expenses of people coming to speak on Fosscomm from abroad. Giving one (or even more) of the phones that HTC kindly provided to the voted by the participants best talk/presentation/workshop would also be very nice. My sincere congratulations to the organizing committee.

    My IPv6 workshop
    On my application to Fosscomm I had asked for one presentation and a separate workshop. This unfortunately wasn’t accepted, probably due to the large amount of other presentations/workshops, so I was given the first workshop on the very first day of Fosscomm, about “Using IPv6”- on Linux. Since I only had one hour, my original plans were to do a quick 15 min introductory presentation on IPv6 and then a 45 min hands-on lab. Since University of Patras could not provide IPv6 connectivity to the Lab, my other option was to have some remote VMs that would have upstream IPv6 connectivity and people on the Lab would ssh to. These VMs were kindly provided to us by Grnet and I have to publicly thank them one more time. My planning was bad though, people had far more questions about introductory IPv6 issues than I expected and the intro presentation was not finished until more than 35 mins had passed. This lead to the unfortunate result that the workshop could not be completed as I had planned. I am glad though that almost everyone logged into the VMs and had the chance to at least set up an IPv6 IP manually as well as an IPv6 default route. They also had their first ping6s. Some got even further by setting up ip6tables rules…What I definitely wanted to have shown during the workshop, and I didn’t have enough time to, was auto-configuration (SLAAC) which I consider to be one of the most intriguing features of IPv6. Next time I am doing either a presentation or a hands-on workshop, definitely not both in one session. Lesson learned.

    Presentation/Workshop material:
    Quick Intro to IPv6
    Using IPv6 on Linux (workshop notes)

    Talks I attended
    All the talks I attended were very interesting, I probably did a very good job picking them 🙂 The ones I attended were:
    a) “A unified user account manager using LDAP/KRB5/CIFS” by Giorgos Mamalakis, Chariton Karamitas
    b) “Network Exploitation with Ncrack” by Fotis Chatzis
    c) “Wargames” by Patroklos Argyroudis, Fotis Chatzis, Chariton Karamitas
    a) “Intro to Arduino” by Pierros Papadeas, Kostas Antonakoglou
    b) “Φωνή VoIPόντως εν τη ερήμω” by Effie Mouzeli
    c) “Bright side of the Darknets” by Athanasios Kostopoulos
    d) “Automated Testing Framework” by Giorgos Keramidas
    e) “Performing Digital Forensics with Open Source tools” by Dimitrios Glynos
    f) “Patras Heap Massacre” by Chariton Karamitas, Patroklos Argyroudis

    I consider the most well presented one being: “Performing Digital Forensics with Open Source tools” while the one with the best slides was definitely: “Patras Heap Massacre”. If you weren’t there to see them, definitely try and find at least the slides if not the video.

    I had never participated before in any wargames because I considered that to be out of my league. That’s the reason I had not even registered for Fosscomm’s wargame called “fosswar”. I was curious though about what it’s like, so me and 3-4 more friends decided to stand in line and enter the room among the other people. The Lab room was crowded, really crowded. At first I thought that one reason for this would be the prize for the winner, an Android phone donated by HTC. I was later proven wrong though. Fosswar started and the organizers presented us with the 5 challenges. Two of those had to do something with networking…so I said to my self that I would be lucky even if I understood what one of those asked. Another challenge had to do with steganography, another one with exploiting a vulnerability in C and the last one was about reverse engineering. While this game could only have one winner, since me and my friends were not actually interested about the prize we decided to work as a team and see whether we can solve anything. Me and a friend looked at the first challenge, another 1 was looking at the third while 2 more were each looking at the fourth and fifth. During the wargame HTC asked for the names of people that wanted to take part in the competition, there nobody actually wanted to give his name. Most of them were there “just for the kicks”. That was even more exciting! HTC then told us that if nobody wanted to give his name the phone would be given on a lottery…so 10-15 people decided to give our names so the phone would “stay” at the fosswar. After solving the first challenge we got so excited that we just had to try the others, we couldn’t give up. So, after 3 hours of thinking and coding, the result was that our team managed to solve 3 of the five challenges, the details on what the challenges were and how we dealt with them will follow in a separate blog post, and we ended up being the winners because no other team had solved more than two. Yes, we had won! We had managed to solve the two networking challenges and the steganography one. That was soooo unexpected!

    My pictures from Fosscomm 2011 are at: https://picasaweb.google.com/kargig/2011050720110508Fosscomm2011#

    My conclusion
    Fosscomm this year definitely showed a trend. People don’t need generic presentations about open source any more, they know what it is, they believe in it, they use it. People really ask for technical presentations, and we need more of them.

    Whoever couldn’t manage to attend Fosscomm 2011, should definitely attend Fosscomm 2012. I am certainly looking forward to it!

    IPv6 workshop at Fosscomm 2011

    This weekend, 7-8 May 2011, I’ll be doing a workshop about “IPv6 usage on Linux” at Fosscomm 2011 conference. Fosscomm is the biggest Greek Open Source conference with lots of interesting presentations, workshops and events. In the spirit of enabling IPv6 wherever possible, I am very happy to have managed to enable IPv6 connectivity for the website of Fosscomm this year!

    During the workshop I will try to show the necessary tools to use, debug network problems and configure various services for IPv6. My goal is to explain to participants the abolishment of NAT, introduce the concepts of SLAAC and DHCPv6 and show them how to configure their networks to effectively use IPv6. If there’s enough time some issues related to IPv6 security will also be discussed. Target audience is people who are not afraid of the command line, have basic networking skills and are eager to learn things regarding IPv6!

    Unfortunately it was impossible to have IPv6 upstream connectivity at the LAB, so participants will be testing everything on an IPv6 enabled remote infrastructure. Due to the limited number of LAB computers and Virtual Machines available, only 35, there is a registration form for participants to fill in. Please take the time to fill in the form any specific topics that you would like the workshop to pay attention to.

    The workshop is taking place on Saturday 07/05/2011 and it will start _exactly_ at 10:45 in order to take full advantage of the time given to us by Fosscomm’s organizers.

    Workshop is supported by the Greek IPv6 Taskforce and there miiiight be IPv6-related material distributed to the participants.

    Please don’t forget to fill in the registration form!!!