Tag etiopia

Latest posts for tag etiopia

2009-06-06 00:57:39+02:00

Procedure to check if all the services of Dream University are up and running

Tenth day in Addis

If a machine blocks pings, use arping instead.

  1. Test DHCP:

    $ sudo ifdown eth0
    $ sudo ifup eth0
    $ ifconfig
  2. Test the DNS:

    # See if the DNS machine is on
    # The network
    $ ping -n
    # See if the DNS resolves names
    $ host www.dream.edu.et
  3. Test the gateway:

    # Ping the gateway
    $ ping gateway
    # Ping an outside host
    $ ping -n
  4. Test the proxy:

    # Ping the proxy
    $ ping proxy
    # Open a web page and see if it displays
    # See if it caches
    http_proxy=http://proxy.dream.edu.et:3030/ wget -S -O/dev/null http://www.enricozini.org  2>&1 | grep X-Cache
  5. Test the mail server:

    $ ping smtp
    $ nmap smtp -p 25 |grep 25/tcp
    $ if nmap gateway -p 25 |grep 25/tcp | grep -q open ; then echo "It works"; fi
    $ send a mail and see if you receive it

To do more advanced network and service monitoring, try nagios:

New useful tools seen today

wget - The non-interactive network downloader.

Special devices

Example uses:

wget -O/dev/null http://www.example.org

dd if=/dev/zero of=testdisk bs=1M count=50
mke2fs testdisk
sudo mount -o loop testdisk  /mnt

Tiny little commands

Example uses:

Some more shell syntax

Some people run commands ignoring the standard error: command 2> /dev/null this causes unexpected error messages to go unnoticed: please do not do it.

What to check if a machine is very slow

More VIM command mode

Command mode allows to perform various text editing functions.

You work by performing operations on selected blocks of text.

Some common operations:

Some common blocks:


The best way to learn more vim is always to run vimtutor.

Installing squirrelmail

To install squirrelmail:

  1. apt-get install squirrelmail
  2. /usr/sbin/squirrelmail-config and configure IMAP and SMTP.

    In our case, since we use IMAPS, the IMAP server is imap.dream.edu.et, port 993, secure IMAP enabled and SMTP is smtp.dream.edu.et. 3. Read /usr/share/doc/squirrelmail/README.Debian.gz (with zless) for how to proceed with setup. A short summary: * link /etc/squirrelmail/apache.conf into the apache conf.d directory * customise /etc/squirrelmail/apache.conf for example setting up the virtual hosts, or running it only on SSL

To have different virtual hosts over HTTPS, you need to have a different IP for every virtual host: name based virtual hosts do not work on HTTPS.

You can configure multiple IP addresses on the same computer: use network interfaces named: eth0:1, eth0:2, eth0:3... These are called interface aliases.

You cannot setup interface aliases using the graphical network configuration and you need to add them in /etc/network/interfaces:

    iface eth0:1 inet static
    auto eth0:1

This is the trick commonly used to put different virtual HTTPS hosts on the same computer.


squid documentation:

Shell programming:

Performance analysis:

Setting up mail services:

eng etiopia pdo tips
2009-06-06 00:57:39+02:00

Fifth day in Addis


To get samba:

    apt-get install samba samba-doc smbclient

To get the Samba Web Administration Tool:

    apt-get install swat netkit-inetd

The configuration is in /etc/samba:

One could use swat at http://localhost:901/ but it does not work easily on Ubuntu.

To see what is shared:

    smbclient -L localhost

To access a share:

    smbclient //localhost/name-of-the-share

To add a new user:

    sudo smbpasswd -a username

To change the password of a user:

    sudo smbpasswd username

To test accessing a share as a user:

    smbclient //localhost/web -U yared


    man smb.conf

To force the user or group used to access a share:

    force user = enrico
    force group = www-data

To set the unix permissions for every created file:

    # For files
    create mask = 0664
    # For directories
    directory mask = 0775

Example share configuration for a webspace:

    mkdir /var/www/public
    chgrp www-data /var/www/public
    chmod 0775 /var/www/public

Then, in /etc/samba/smb.conf:

       comment = Webspace
       path = /var/www
       writable = yes
       public = no
       force group = www-data
       create mask = 0664
       directory mask = 0775

Example share configuration for a read only directory where only a limited group of people can write:

       comment = Documents
       path = /home/enrico/Desktop/documents
       force user = enrico
       public = yes
       writable = no
       write list = enrico, yared

Print server (CUPS)


    apt-get install cupsys


Example IPP URIs:


For example:


"This printer uri scheme can be used to contact local or remote print services to address a particular queue on the named host in the uri. The "ipp" uri scheme is specified in the Internet Print Protocol specifications and is actually much more free form that listed above. All Solaris and CUPS based print queues will be accessed using the formats listed above. Access to print queues on other IPP based print servers requires use of the server supported ipp uri format. Generally, it will be one of the formats listed above."

LDAP Lightweight Directory Access Protocol


    apt-get install ldap-utils slapd

The configuration is in /etc/ldap.

To access a ldap server:

    apt-get install gq

Various LDAP HOWTOs:


The configuration file is in /boot/grub/menu.lst.

The documentation can be accessed as info grub after installing the package grub-doc.

Quick list of keys for info:

Grub trick to have a memory checker:

  1. apt-get install memtest86+
  2. Add this to /boot/grub/menu.lst:
    title Memory test
        root (hd0,5)
        kernel /boot/memtest86+.bin


With iptables:

    man iptables
    # Only allow in input the network packets
    # that are going to the web server
    iptables -P INPUT DROP
    iptables -A INPUT --protocol tcp --destination port 80 -j ACCEPT
    # To reset the input chain as the default
    iptables -F INPUT
    iptables -P INPUT ACCEPT

Some links:



    apt-get install squid

The configuration is in /etc/squid/squid.conf.

To allow the local network to use the proxy:

    # Add this before "http_access deny all"
    acl our_networks src
    http_access allow our_networks

To use a parent proxy:

    cache_peer proxy.aau.edu.et     parent    8080  0  proxy-only no-query

Pay attention because /var/spool/squid will grow as the cache is used. The maximum cache size is set in the directive cache_dir.

Information about squid access control is at http://www.squid-cache.org/Doc/FAQ/FAQ-10.html

To check that the configuration has no syntactic errors: squid -k parse.

To match urls:

    acl forbiddensites url_regex [-i] regexp

For info about regular expressions:

    man regex

Example filtering by regular expression:

    acl skype url_regex -i [^A-Za-z]skype[^A-Za-z]
    http_access deny skype

Transparent proxy setup: http://www.tldp.org/HOWTO/TransparentProxy.html

Problems found today

Hiccups of the day:

Update: Marius Gedminas writes:

I think it would be a good idea to mention that running

     iptables -P INPUT DROP

in the shell is a Bad Idea if you're logged in remotely via SSH.

eng etiopia pdo tips
2009-06-06 00:57:39+02:00

Seventh day in Addis

Setting up a mail server


Some terminology:

With SMTP you connect to a server and send two things: envelope and message.

The envelope looks like this:

MAIL FROM: <enrico@enricozini.org>
RCPT TO: <rms@fsf.org>
RCPT TO: <linus@linux.org>

The message looks like this:

From: <enrico@enricozini.org>
To: <rms@fsf.org>
Cc: <linus@linux.org>
Message-ID: <1234567@enricozini.org>
Subject: Test mail

Hi Richard,

this is a test mail.  I'm also writing
Linus to show how to send to more people.



There is no authentication.

There is no encryption.

Two usual types of access control:

  1. Outbound e-mail is normally only accepted from an internal network
  2. Inbound e-mail is normally accepted from anywhere

The DNS is used to find the SMTP server to use to send a message:

$ host -t MX yahoo.com
yahoo.com MX 10 smtp1.yahoo.com
yahoo.com MX 20 smtp2.yahoo.com
yahoo.com MX 20 smtp3.yahoo.com

The process of sending an E-Mail:

  1. Enrico writes an E-Mail:

    From: Enrico Zini <enrico@enricozini.org>
    To: Richard Stallman <rms@fsf.org>
    Subject: Hello from Addis
    Hi Richard,
    Addis is a wonderful city, even if
    it rains a lot.
    Bye,  Enrico
  2. Enrico's MUA connects to the SMTP server (for example, port 25 of smtp.aau.edu.et):

    HELO enricozini.org
    200 OK Hello enricozini.org
    MAIL FROM: <enrico@enricozini.org>
    200 OK Mail from enrico@enricozini.org
    RCPT TO: <rms@fsf.org>

    Here, the SMTP server performs relay control: "do we relay mail to rms@fsf.org?":

    • Outbound e-mail is normally only accepted from an internal network
    • Inbound e-mail is normally accepted from anywhere

    A target address could be refused:

    413 ERR I don't relay for rms@fsf.org

    In this case, the destination is not local but the recipient is accepted because I'm inside the local network:

    200 OK Destination rms@fsf.org
    200 OK Please send message body
    From: Enrico Zini <enrico@enricozini.org>
    To: Richard Stallman <rms@fsf.org>
    Subject: Hello from Addis
    Date: Mon, 17 Jul 2006 09:49:45 +0300
    Message-ID: <124372643@enricozini.org>
    Hi Richard,
    Addis is a wonderful city, even if
    it rains a lot.
    Bye,  Enrico
    200 OK Message accepted
    200 OK Bye.
  3. The SMTP server needs to find out where to send the message, using the DNS:

    $ host -t MX fsf.org
    fsf.org MX 10 mail.fsf.org
    fsf.org MX 20 mail.gnu.org
  4. So the SMTP server tries the first one and connects to port 25 of mail.fsf.org:

    HELO smtp.aau.edu.et
    200 OK Hello smtp.aau.edu.et
    MAIL FROM: <enrico@enricozini.org>
    200 OK Mail from enrico@enricozini.org
    RCPT TO: <rms@fsf.org>

    The destination is accepted because it's for a local user::

    200 OK Destination rms@fsf.org
    200 OK Please send message body
    From: Enrico Zini <enrico@enricozini.org>
    To: Richard Stallman <rms@fsf.org>
    Subject: Hello from Addis
    Date: Mon, 17 Jul 2006 09:49:45 +0300
    Message-ID: <124372643@enricozini.org>
    Received: by mail.aau.edu.et
      on Mon, 17 Jul 2006 09:55:53 +0300
    Hi Richard,
    Addis is a wonderful city, even if
    it rains a lot.
    Bye,  Enrico
    200 OK Message accepted
    200 OK Bye.
  5. Now, mail.fsf.org will invoke a MDA to write the mail in Richard Stallman's mailbox.

Example of problems with mail handling:

RFC-822 is the original standard for E-mail. RFCs are standard Internet documents. Have a look at RFC documents released the 1st of April.


Common setup: "Internet site with smarthost".

More difficult to maintain: "Internet site".

A smarthost is a machine that will relay e-mail for you.

Questions asked with "Internet site with smarthost":

To test a mail server::

$ telnet localhost 25
MAIL FROM: <a@b.c>
RCPT TO: <mail@of.a.local.user>


By default, you find locally delivered mail in /var/mail/username.

Postfix configuration files:

To rewrite addresses:

  1. In /etc/postfix/main.cf::

    canonical_maps = hash:/etc/postfix/canonical
  2. Then in /etc/postfix/canonical you can add the rewrite rules, like::

    enrico   enrico@enricozini.org
  3. When /etc/postfix/canonical is modified you need to regenerate the index::

    sudo postmap canonical

    (same is when you change the alias file: sudo postalias /etc/aliases)

(see file:///usr/share/doc/postfix/html/ADDRESS_REWRITING_README.html)

Manipulating the message queue:

mailq - List the mail queue.



postqueue - Postfix queue control


    # Like mailq
    postqueue -p

    # Tries to send every message in the queue
    postqueue -f

    # Tries to send every message in the queue for that site
    postqueue -s site

postsuper - Postfix superintendent


    # Deletes one message
    sudo postsuper -d 7C4D2EC0F5D

    # Deletes all messages held in the queue for later delivery
    sudo postsuper -d ALL deferred

Different mail queues in postfix:

Mail logs are in::


Mail delivery

Mailbox formats:

Alternate MDA: procmail: allows to filter mail automatically into different folders.

Mail forwarding with ~/.forward: allows to redirect mail to a different address: just put the address you want to send to in the file ~/.forward.

POP or IMAP server


apt-get install dovecot

Configuration is in::


The main thing that is needed is to enable the mail protocols you want::

protocols = imaps

Server monitoring

To make all sorts of graphs::

apt-get install munin munin-node

Example: http://munin.ping.uio.no

To compute more statistics:

Monitor system logs: logcheck:

Filtering viruses and spam

clamav - Virus scanner

Virus scanning:

spamassassin - Spam filter

Spam scanning:

Man pages and sections

Man pages are divided in sections:

Authentication and encryption with SMTP (update by Marius Gedminas)

You can have authentication and encryption with SMTP:

Cheat sheet

Setting up the client (I assume Ubuntu)

  # vi /etc/postfix/main.cf

      relayhost = [hostname.of.your.ISPs.smtp.server]
      smtp_use_tls = yes
      smtp_enforce_tls = yes
      smtp_tls_enforce_peername = no
      smtp_sasl_auth_enable = yes
      smtp_sasl_password_maps = hash:/etc/postfix/smtp_auth
      smtp_sasl_security_options = noanonymous

  # vi /etc/postfix/smtp_auth

      [hostname.of.your.ISPs.smtp.server] username:password

  # chmod 600 /etc/postfix/smtp_auth
  # postmap /etc/postfix/smtp_auth
  # postfix reload

(It would be a good idea to make the client verify the server's certificate to prevent man-in-the-middle attacks, but I haven't figured out that part yet...)

Setting up the server

  # apt-get install sasl2-bin libsasl2-modules
  # saslpasswd2 -u hostname.of.the.server -c username1
  # saslpasswd2 -u hostname.of.the.server -c username2

        these commands create /etc/sasldb2

  # echo "pwcheck_method: auxprop" > /etc/postfix/sasl/smtpd.conf
  # touch /var/spool/postfix/etc/sasldb2
  # echo mount --bind /etc/sasldb2 /var/spool/postfix/etc/sasldb2 \
          > /etc/init.d/local-sasl-for-postfix
  # chmod +x /etc/init.d/local-sasl-for-postfix
  # ln -s ../init.d/local-sasl-for-postfix /etc/rc2.d/S19local-sasl-for-postfix
  # /etc/init.d/local-sasl-for-postfix
  # adduser postfix sasl

        these commands let postfix (which runs chrooted) access /etc/salsdb2

  # cd /etc/postfix
  # openssl req -new -outform PEM -out smtpd.cert -newkey rsa:2048 -nodes \
            -keyout smtpd.key -keyform PEM -days 365 -x509
  # chmod 600 smtpd.key

        these commands create a self-signed SSL certificate

  # vi main.cf

      smtpd_sasl_auth_enable = yes
      broken_sasl_auth_clients = yes
      smtpd_sasl_local_domain = hostname.of.the.server
      smtpd_recipient_restrictions = permit_mynetworks,
      smtpd_use_tls = yes
      smtpd_tls_cert_file = /etc/postfix/smtpd.cert
      smtpd_tls_key_file = /etc/postfix/smtpd.key

  # /etc/init.d/postfix restart
eng etiopia pdo tips
2009-06-06 00:57:39+02:00

Addis course Tasks & Skills questions

What does it do?

What command would you use to add a new username and password to /etc/apache2/students? (you can write the entire commandline if you know it, but just the name of the command is fine)

What are their advantages and disadvantages?

eng etiopia pdo
2009-06-06 00:57:39+02:00

Eight day in Addis

Useful things to keep in mind when setting up a service:

Example use of vim block selection:

To change network configuration with config files, edit:


To also setup DNS in /etc/network/interfaces, use dns-search and dns-nameservers (for this to work, you need to have the package resolvconf):

dns-search dream.edu.et

To make a router that connects to the internet on demand using a modem:

apt-get install diald

To see the path of network packets:


Basic NAT script:


modprobe iptable_nat
iptables -t nat -A POSTROUTING -o $OUT -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

What happens at system startup:

  1. the BIOS loads and runs the boot loader
  2. the boot loader loads the kernel and the inintrd ramdisk and runs the kernel
  3. the kernel runs the script 'init' in the initrd ramdisk
  4. the script 'init' mounts the root directory
  5. the script 'init' runs the command /sbin/init in the new root directory
  6. 'init' starts the system with the configuration in /etc/inittab

To install a new startup script:

sudo ln -s /usr/local/sbin/firewall /etc/init.d
sudo update-rc.d firewall defaults 16 75

Normally you can just do:

sudo update-rc.d [servicename] defaults

To have a look at the start and stop order numbers, look at /etc/rc2.d for other start scripts and /etc/rc0.d for other stop scripts

To test a proxy, low level way:

$ telnet proxy 8080
Connected to proxy.dream.edu.et.
Escape character is '^]'.
GET http://www.google.com HTTP/1.0 [press enter twice]
eng etiopia pdo tips
2009-06-06 00:57:39+02:00

First pratical lesson

Notes after today's training session.

Small index of most used shell commands:

Small index of commands useful for combining in pipelines:

Problems found during the lesson:

So apt-cache is a manipulator that doesn't manipulate. A possible improvement can be "query the APT package cache". * The language selector in Ubuntu Breezy doesn't really exit and keeps the package database locked. This seems to be fixed in Dapper, and probably had been fixed in some Breezy update. System updates here are a problem: my Dapper (with some Universe things in it) wanted to download more than 120Mb of data, and the Uni network was giving me 14Kbps. It's been a nice opportunity to teach about fuser -uva and kill. * dict, squid and many other packages from 'main' are not on the normal Ubuntu CDs: is there an easy way to build a CD with them? Or do Ubuntu CDs with extra packages already exist? I'll have to find out. * cupsys has documentation outside of /usr/share/doc, in /usr/share/cups/doc-root. * man works on all commands, except cd, which is an internal shell command and thus needs help instead of man. I should remember to ponder about autogenerating manpages from help output. * Is there an index-like manpage with a list of the core Unix commands and their short descriptions? It there's not, it's easy to generate:

    find $DIR | while read FILE
        if [ -x $FILE ] && ! [ -d $FILE ]
            LANG=C COLUMNS=2000 man `basename $FILE` | \
                     grep ^SYNOPSIS -B 100 | grep ^NAME -A 100 | \
                     tail -n +2 | head -n +2 | \
                     grep -v '^[ \t]*$'
    ) | sort | uniq | sed 's/^ \+//'

Try running it on /bin and /sbin: it's great!. Also, since it doesn't redirect stderr, it nicely exposes a number of manpage problems.

Lots of bugs to report when I come home: from here it'll take ages, and lots of money on the hotel internet connection, and some are Ubuntu-specific so I'd need to do everything online with Malone.

As usual, teaching is one of the best ways to find bugs.

I propose an Etch training session a month before release.

Other things to do:

Update: Matt Zimmerman writes:

I read your blog entry at http://www.enricozini.org/blog/eng/second-day-in-addis and wanted to respond as follows:

  • localeconf is not the standard way to configure locales in Ubuntu; what documentation told you that? It's an unsupported package from Progeny. If what you wanted was to set the system default locale from the command line, editing /etc/environment is probably the best way.

  • I suggest filing a bug report at https://launchpad.net/products/ubuntu-website about the HTTPS issue; I don't think it's necessary for the entire wiki to be HTTPS, only authentication.

  • Synaptic may be able to use the GNOME proxy settings without introducing undesirable dependencies; please file a wishlist bug

  • dict, squid and other packages from main are not on the Ubuntu CDs because there is no space. The DVD contains these packages.

  • The cupsys documentation bug was quite likely inherited from Debian and should be reported there

  • You can file bugs in Malone via email; this has been possible for a long time now. Please don't reinforce this misconception.



debian eng etiopia pdo ubuntu
2009-06-06 00:57:39+02:00

First day in Addis

First day in Addis Ababa, after the introductory session for this 10 days Linux training.

Interesting new quotes I picked up from the excellent presentation of Dr. Dawit:

Much that I bound I could not free Much that I freed returned to me

(I didn't manage to transcribe the attribution)

And this one for Bubulle, about translation:

When you speak to me in my language you speak to my heart when you speak to me in English you speak to my head


Incomplete list of questions I've been asked, in bogosort -n order:

I'm happy to find that we've been successful in building more and more good answers for these questions.

eng etiopia pdo
2009-06-06 00:57:39+02:00


Da una canzone in amarico:

"Il tuo amore รจ diventato vecchio

come gli edifici costruiti dagli italiani"

etiopia ita life
2009-06-06 00:57:39+02:00

Fourth day in Addis

Unix file permissions:

    drwxr-xr-x   2 root root    38 2006-07-14
    +- Is a directory

    drwxr-xr-x   2 root root    38 2006-07-14
      +- User permissions (u)

    drwxr-xr-x   2 root root    38 2006-07-14
         +- Group permissions (g)

    drwxr-xr-x   2 root root    38 2006-07-14
            +- Permissions for others (o)

    drwxr-xr-x   2 root root    38 2006-07-14
                    +- Owner user

    drwxr-xr-x   2 root root    38 2006-07-14
            Owner group -+

Other bits:

The executable bit for directories means "can access the files in the directory".

If a directory is readable but not executable, then I can see the list of files (with ls) but I cannot access the files.

To access a file, all the directories of its path up to / need to be executable.

Commands to manipulate permissions:

Example setup for a website for students:

    # Create the group 'students'
    mkdir /var/www/students
    chgrp students /var/www/students
    chmod 2775 /var/www/students

    # If you don't want other users to read the files of the students:

    chmod 2770 /var/www/students
    adduser www-data students
     (this way the web server can read the

    # when you add a user to a group, it does not affect running processes:

     - users need to log out and in again
     - servers need to be restarted


in /etc/apache/apache2.conf (set it to your IP address)

Apache troubleshooting:

This it is always a good thing to do before restarting or reloading apache.

To install PHP

To install MySQL

To use MySQL from PHP:

    apt-get install php5-mysqli php5-mysql

Problems found today:

eng etiopia pdo tips
2009-06-06 00:57:39+02:00

Third day in Addis

Believe it or not, a network that fails often is the best thing to have when you are teaching network troubleshooting.

Various tools useful for networking:


    # Look at what machines are active in the local network:
    nmap -sP

    # Look at what ports are open in a machine:

It can be used to see if there is traffic, and to detect traffic that shouldn't be there.

Useful tip:

    # Convert a unix timestamp to a readable date
    date -d @1152841341

What happens when you browse a web page:

  1. type the address www.google.com in the browser
  2. the browser needs the IP address of the web server:

  3. look for the DNS address in /etc/resolv.conf (/etc/resolv.conf is created automatically by the DHCP client)

  4. try all the DNS servers in /etc/resolv.conf until one gives you the IP address of www.google.com
  5. take the first address that comes from the DNS (in our case was

  6. figure out how to connect to

  7. consult the routing table to see if it's in the local network:

    1. if it's in the local network, then look for the MAC address (using ARP
      • Address Resolution Protocol)
    2. if it'd not in the local network, then send through the gateway (again using ARP to find the MAC address of the gateway)
  8. Send out the HTTP request to the local web server or through the gateway, using the Ethernet physical protocol, and the MAC address to refer to the other machine.

Troubleshooting network problems:

  1. See if the network driver works:

  2. With ifconfig, see if you see the HWaddr:. If you do not see it, then the linux driver for the network card is not working. Unfortunately there's no exact way to say that it works perfectly

  3. See if you have an IP address with ifconfig. If you find out that you need to rerun DHCP (for example, if the network cable was disconnected when the system started), then you can do it either by deactivating/reactivating the Ethernet interface using System/Administration/Networking or, on a terminal, running:

    # ifdown eth0
    # ifup eth0

    If you don't get an IP, try to see if the DHCP server is reachable by running:

    $ arping -D [address of DHCP server]
  4. See if the local physical network works:

  5. With sudo mii-tool, see if the cable link is ok. If it's not, then it's a problem in the cable or the plugs, or simply the device at the other end of the cable is turned off.

  6. Try arping or ping -n on a machine in the local network (like the gateway) to see if the local network works.

  7. See if the DNS works:

  8. Find out the DNS address:

    cat /etc/resolv.conf
  9. If it's local, arping it

  10. If it's not local, ping -n it
  11. Try to resolve a famous name using that DNS:

    $ host [name] [IP address of the DNS]
  12. Try to resolve the name of the machine you're trying to connect. If you can resolve a famous name but not the name you need, then it's likely a problem with their DNS.

  13. If you use a proxy, see if the proxy is reachable: check if the proxy name resolves to an IP, if you can ping it, if you can telnet to the proxy address and port:

    $ telnet [proxy address] [proxy port]

    you quit telnet with ^]quit.

  14. If you can connect directly to the web server, try to see if it answers:

    $ telnet [address] 80

    If you are connected, you can confirm that it's a web server:

    GET / HTTP/1.0 (then Enter twice)

    If it's a web server, it should give you something like a webpage or an HTTP redirect.

When you try to setup a service and it doesn't work:

  1. check that it's running:

    $ ps aux | grep dnsmasq
  2. check that it's listening on the right port:

    $ sudo netstat -lp
  3. check that it's listening from the outside:

    $ nmap [hostname]
  4. check for messages in /var/log/daemon.log or /var/log/syslog

  5. check that the configuration is correct and reload or restart the server to make sure it's running with the right configuration:

    # /etc/init.d/dnsmasq restart


By default: works as a DNS server that serves the data in /etc/hosts.

By default: uses /etc/resolv.conf to find addresses of other DNS to use when a name is not found in /etc/hosts.

To enable the DHCP server, uncomment:


in /etc/dnsmasq.conf and set it to the range of addresses you want to serve. Pay attention to never put two DHCP servers on the same local network, or they will interfere with each others.

To test if the DHCP server is working, use dhcping (not installed by default on Ubuntu).

To communicate other information like DNS, gateway and netmask to the clients, use this piece of dnsmasq.conf:

    # For reference, the common options are:
    # subnet mask - 1
    # default router - 3
    # DNS server - 6
    # broadcast address - 28

Problems found today:

Quick start examples with tar:

    # Create an archive
    tar zcvf nmap.tar.gz *.deb

    # Extract an archive
    tar zxvf nmap.tar.gz

    # Look at the contents of an archive
    tar ztvf nmap.tar.gz

Quick & dirty way to send a file between two computers without web server, e-mail, shared disk space or any other infrastructure:

    # To send
    nc -l -p 12345 -q 1 < nmap.tar.gz

    # To receive
    nc 12345 > nmap.tar.gz

    # To repeat the send command 20 times
    for i in `seq 1 20`; do nc -l -p 12345 -q 1 < nmap.tar.gz ; done

Update: Javier Fernandez-Sanguino writes:

Your "XXX day in Addis" is certainly good reading, nice to see somebody reviewing common tools from a novice point of view. Some comments:

  • Regarding your comments on how to troubleshoot network connectivity problems I just wanted to point you to the network test script I wrote and submited to the debian-goodies package ages ago. It's available at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=307694 and should do automatically most of the stuff you commented on your blog.

  • Your example to test hosts alive in the network using nmap -sP is good. However, newer (v4) versions can do ARP ping in the local network which is much more efficient (some systems might block ICMP outbount), that's the -PR option and should be enabled (by default). See http://www.insecure.org/nmap/man/man-host-discovery.html Also, you might want to add a '-n' there so that nmap does not try to do DNS resolution of the hosts (which might take up some time if your DNS does not include local IPs)

  • tcpdump, it would be wiser to turn novice users to ethereal since it has a much better UI than tcpdump and it is able to dissect (interpret) protocols that tcpdump can't analyse.

  • you are missing arp as a tool in itself, it is useful to debug network issues since if the host is local and does not show up in arp output either a) it's down or b) you don't have proper network connectivity. (If you are missing an ARP entry for your default gateway your setup is broken)

Update: Marius Gedminas writes:

Re: http://www.enricozini.org/blog/eng/third-day-in-addis

In my experience if sudo cannot resolve the hostname (e.g. if you break /etc/hosts), you can still use sudo, but you have to wait something like 30 seconds until the DNS request times out.

I tried to break my /etc/hosts (while keeping a root shell so I can fix it if something goes wrong), but couldn't even get the timeout now. Sudo just said unable to lookup $hostname via gethostbyname() and gave me a root shell.

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