Enrico's pages/ tags/ etiopia

Pages related to my visit in Addis Ababa for a Linux training course.

Addis course Tasks & Skills questions

Addis course Tasks & Skills questions

Posted Fri 04 Aug 2006 17:56:33 CEST Tags: etiopia
Seventh day in Addis

Seventh day in Addis

Setting up a mail server

Background

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.

Cheers,

Enrico

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
DATA
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
QUIT
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
DATA
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
  from 10.4.15.158


Hi Richard,


Addis is a wonderful city, even if
it rains a lot.


Bye,  Enrico
.
200 OK Message accepted
QUIT
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.

postfix

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
HELO me
MAIL FROM: <a@b.c>
RCPT TO: <mail@of.a.local.user>
DATA

hi
.
QUIT

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.

Example::

    mailq

postqueue - Postfix queue control

Examples::

    # 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

Examples::

    # 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::

/var/log/mail.log
/var/log/mail.err
/var/log/mail.info
/var/log/mail.warn

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

Installation:

apt-get install dovecot

Configuration is in::

/etc/dovecot/dovecot.conf

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,
                                     permit_sasl_authenticated,
                                     reject_unauth_destination
      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
Posted Fri 28 Jul 2006 16:45:39 CEST Tags: etiopia
Fifth day in Addis

Fifth day in Addis

Samba

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

Documentation:

    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:

    [web]
       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:

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

Print server (CUPS)

Installation:

    apt-get install cupsys

Configuration:

Example IPP URIs:

    ipp://server[:port]/printers/queue
    http://server:631/printers/queue
    ipp://server[:port]/...

For example:

    ipp://server/printers/laserjet

"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

Installation:

    apt-get install ldap-utils slapd

The configuration is in /etc/ldap.

To access a ldap server:

    apt-get install gq

Various LDAP HOWTOs:

GRUB

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

Firewall

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:

Squid

Installation:

    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 10.4.15.0/24
    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.

Posted Fri 28 Jul 2006 16:42:51 CEST Tags: etiopia
Third day in Addis

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:

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:

    1. look for the DNS address in /etc/resolv.conf (/etc/resolv.conf is created automatically by the DHCP client)
    2. try all the DNS servers in /etc/resolv.conf until one gives you the IP address of www.google.com
    3. take the first address that comes from the DNS (in our case was 64.233.167.104)

  3. figure out how to connect to 64.233.167.104:

    1. 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
      2. Address Resolution Protocol)
      3. if it'd not in the local network, then send through the gateway (again using ARP to find the MAC address of the gateway)

  4. 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:

    1. 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

  2. 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]

  3. See if the local physical network works:

    1. 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.
    2. Try arping or ping -n on a machine in the local network (like the gateway) to see if the local network works.

  4. See if the DNS works:

    1. Find out the DNS address:

      cat /etc/resolv.conf

    2. If it's local, arping it

    3. If it's not local, ping -n it

    4. Try to resolve a famous name using that DNS:

      $ host [name] [IP address of the DNS]

    5. 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.

  5. 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.

  6. 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

dnsmasq:

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:

    dhcp-range=192.168.0.50,192.168.0.150,12h

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
    dhcp-option=1,255.255.255.0
    dhcp-option=3,192.168.0.1
    dhcp-option=6,192.168.0.1
    dhcp-option=28,192.168.0.255

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 10.5.15.123 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 10.5.15.0/24 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.html

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.

Posted Fri 28 Jul 2006 16:38:11 CEST Tags: etiopia
First pratical lesson

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:

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.html 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 ; 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.

    https://help.launchpad.net/UsingMaloneEmail

Update:

Posted Fri 28 Jul 2006 16:23:06 CEST Tags: etiopia
Ninth day in Addis

Ninth day in Addis

SSH

To enable remote logins with ssh

apt-get install openssh-server

Then you can login with:

$ ssh efossnet@proxy.dream.edu.et

To verify the host key fingerprint of a machine:

$ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key.pub

Note: you need to verify it before logging in!

More information at http://www.securityfocus.com/infocus/1806

Example ssh usages

To log in:

    $ ssh efossnet@proxy

To run a command in the remote computer:

    $ ssh efossnet@proxy "cat /etc/hosts"

To copy a file to the remote computer:

    $ scp Desktop/july-18.tar.gz efossnet@proxy:

To copy a file from the remote computer:

    $ scp efossnet@proxy:july-18.tar.gz /tmp/

Beware of brute-force login attempts

Warning about SSH: there are people who run automated scans for ssh servers and try to login using commonly used easy passwords.

If you have an SSH server on the network, use strong passwords, or if you can it's even better to disable password authentication: in /etc/ssh/sshd_config, add:

    PasswordAuthentication no

To log in using public/private keys:

  1. Create your key:

    ssh-keygen -t rsa

  2. Copy your public key to the machine where you want to log in:

    ssh-copy-id -i .ssh/id_rsa.pub efossnet@proxy

  3. Now you can ssh using your RSA key

If you use ssh often, read these:

proxy

Problems we had today with the proxy:

ssl does not work

Reason: squid tries to directly connect to the ssl server, but the AAU network wants us to go through their proxy.

Ideal solution: none. There is no way to tell squid to use a parent proxy for SSL connections.

Solution: update the documentation for the Dream university users telling to setup a different proxy for SSL connections.

Longer term solution: get the AAU network admins to enable outgoing SSL connections from the Dream university proxy.

Other things that can be done:

Browsing normal pages returns an error of 'Connection refused'.

In the logs, the line is:

1153294204.912    887 192.168.0.200 TCP_MISS/503 1441 GET http://www.google.com.et/search? - NONE/- text/html

That "/503" is one of the HTTP error codes.

Explanation of the error codes:

Reason: the other proxy is refusing connections from our proxy.

Solution: none so far. Will need to get in touch with the admins of the other proxy to try to find out why it refuses connection to our proxy, and how we can fix the problem.

postfix on smtp.dream.edu.et

Basic information is at http://www.postfix.org/basic.html.

Difference between mail name and smarthost:

Quick way to send test mails:

apt-get install mailx
echo ciao | mail efossnet@localhost

To configure a workstation not to do any mail delivery locally and send all mail produced locally to smtp.dream.edu.et:

  1. install postfix choosing "Satellite system"
  2. put smtp.dream.edu.et as a smarthost.

To setup a webmail: apt-get install squirrelmail (on a working apache setup).

To setup mailing lists: apt-get install mailman, then follow the instructions in /usr/share/doc.

Mail server issues we encountered

When a mail is sent to efossnet@localhost, the system tries to send it to efossnet@yoseph.org

Investigation:

Cause: the user efossnet had forgotten that he or she had setup a .forward file in the home directory.

Solution:

 rm ~efossnet/.forward

Apache

To add a new website:

  1. cd /etc/apache2/sites-available
  2. sudo cp default course

  3. sudo vi course:

    1. Remove the first line
    2. Add a ServerName directive with the address of your server: ServerName course.dream.edu.et
    3. Customize the rest as needed: you at least want to remove the support for browsing /usr/share/doc and you want to use a different document root.

  4. sudo a2ensite course

  5. sudo /etc/init.d/apache2 reload

More VIM

Undo: u (in command mode)

Redo: ^R (in command mode)

You can undo and redo multiple times.

To recover a lost password for root or for the ubuntu admin user

Boot with a live CD, mount the system on the hard disk (the live CD usually does it automatically), then edit the file /etc/shadow, removing the password:

enrico:$1$3AJfasjJFHa234dfh230:13343:0:99999:7:::

becomes:

enrico::13343:0:99999:7:::

You can edit the file because, in the live CD system, you can always become root.

After you do this, reboot the system: you can log in without password, and set yourself a new password using the command passwd.

Installing packages not on the CDs

To get a package for installing when offline:

  1. apt-get --print-uris install dnsmasq
  2. Manually download the packages at the URLs that it gives you

Otherwise, apt-get --download-only install dnsmasq will download the package for you in /var/cache/apt/archives.

You can install various previously downloaded debian packages with:

dpkg -i *.deb

Backups

There are various ways:

Some data requires exporting before backing it up:

You can schedule these dumps to be made one hour before the time you make backups.

Scheduling tasks

As a user:

crontab -e

As root: add a file in one of the /etc/cron.* directories.

In cron.{hourly,daily,weekly,monthly} you put scripts.

In the other directories you put crontab files (man 5 crontab).

If the system is turned off during normal maintainance hours, you can do two things:

  1. Change /etc/crontab to use different maintanance hours
  2. Install anacron (it's installed by default in ubuntu)

For scheduling one-shot tasks, use at(1):

$ at 17:40
echo "Please tell Enrico that the lesson is finished" | mail efossnet@dream.edu.et
^D

When and how to automate

  1. First, you manage to do it yourself
  2. Then, you document it
  3. Then, you automate it

Start at step 1 and go to 2 or 3 if/when you actually need it.

(credits to sto@debian.org: he's the one from which I heard it for the first time, said so well).

Interesting programs to schedule during maintanance

Important keys to know in a Unix terminal

These are special keys that work on Unix terminals:

Therefore, if the terminal looks like it got stuck, try hitting ^Q.

Problems we had today with postfix

Problems found yesterday and today

Posted Fri 28 Jul 2006 14:35:17 CEST Tags: etiopia
Procedure to check if all the services of Dream University are up and running

Tenth day in Addis

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

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 192.168.0.1


# 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 10.4.15.6

  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:

Examples:

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
          address 192.168.0.201
          netmask 255.255.255.0
          gateway 192.168.0.3
    auto eth0:1

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

Links

squid documentation:

Shell programming:

Performance analysis:

Setting up mail services:

Posted Fri 28 Jul 2006 13:15:07 CEST Tags: etiopia
Etiopia

Etiopia

È interessante, bello e triste allo stesso tempo trovarsi a ridefinire il significato di "Abissinia". E maledire che per i primi 30 anni della tua vita, quella parola l'hai sentita soltanto quando uno stronzo cantava "Faccetta nera".

Posted Fri 28 Jul 2006 01:33:07 CEST Tags: etiopia
Eight day in Addis

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:

/etc/network/interfaces

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
dns-nameservers 192.168.0.1 192.168.0.2

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:

mtr 4.2.2.2

Basic NAT script:

OUT=eth2
IN=eth0

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
Trying 192.168.0.6...
Connected to proxy.dream.edu.et.
Escape character is '^]'.
GET http://www.google.com HTTP/1.0 [press enter twice]
Posted Fri 28 Jul 2006 01:33:07 CEST Tags: etiopia
Fourth day in Addis

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
      pages)

    # 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

Apache:

Apache troubleshooting:

To install PHP

To install MySQL

To use MySQL from PHP:

    apt-get install php5-mysqli php5-mysql

Problems found today:

Posted Fri 28 Jul 2006 01:33:07 CEST Tags: etiopia