This is part of a guide to setting up Ubuntu Server Edition 11.04 for a small/medium business. The server will provide DHCP, DNS, NTP, LDAP, Kerberos and NFS services such that users can login to any machine on the network and all their files and settings will be the same across the entire network.
It’s time to install and configure Kerberos.
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This is part of a guide to setting up Ubuntu Server Edition 11.04 for a small/medium business. The server will provide DHCP, DNS, NTP, LDAP, Kerberos and NFS services such that users can login to any machine on the network and all their files and settings will be the same across the entire network.
OpenLDAP is a directory service. Think of it as a database for storing all your users, their groups and other information. In time you can use it to store much more, but initially we’re going to use it as a centralised authorisation system. Clients will check usernames and permissions against those stored in the directory on the server. Though it is also possible to store passwords in LDAP and use it for authentication, we’ll be using Kerberos for this purpose.
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This is part of a guide to setting up Ubuntu Server Edition 11.04 for a small/medium business. The server will provide DHCP, DNS, NTP, LDAP, Kerberos and NFS services such that users can login to any machine on the network and all their files and settings will be the same across the entire network.
Your server will automatically request the time from the Ubuntu NTP servers on every boot… but hopefully you’re not going to reboot it very often. It is useful for the server time to be correct when debugging and it is ESSENTIAL for the server and all the clients on the network to have the same time (±5mins by default) for Kerberos to work.
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This is part of a guide to setting up Ubuntu Server Edition 11.04 for a small/medium business. The server will provide DHCP, DNS, NTP, LDAP, Kerberos and NFS services such that users can login to any machine on the network and all their files and settings will be the same across the entire network.
The first thing to get your server to do is act as a DHCP and DNS server. This will allow you to map hostnames to IP addresses (and vice versa!) automatically. This means all network clients will know that neo.danbishop.org and 192.168.0.2 are one and the same. This is ESSENTIAL if you plan to use Kerberos later on.
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THIS SECTION IS A WORK IN PROGRESS! A DESCRIPTION OF WHAT WILL BE ACHIEVED FOLLOWS:
By their very nature, laptops tend to have unreliable network connections. Sometimes they’ll be connected to wifi at work, wired at home, 3G/mobile networks out and about… sometimes no connection at all.
The aim of this part of the guide is to make the laptop function as much like a desktop client as possible, but taking into account the network connection issues.
The first time a user logs in to the laptop, their home directory will be copied to the laptop and their login credentials cached. The home directory will continue to be synchronised in the background whilst the user works, this will avoid the need to resync at logoff causing a long delay at a potentially very inconvenient time for the user.
The next time the user logs into the laptop, their credentials will again be checked against the Kerberos server… but if this is unavailable, the cached credentials will be used. Should a network connection become available once the user has logged in, synchronisation will begin in the background. If not, the sync will simply happen the next time the user does have a network connection.
Synchronisation will be handled by Unison using SSH. Whilst the use of Kerberised SSH is a possibility, it would required the user being prompted for their password when a network connection becomes available post-login so as to obtain a ticket. To avoid this, SSH keys will be used instead.
Before we begin, it is necessary to install unison on the server like so:
sudo apt-get install unison
Follow the regular client guide but DO NOT setup AUTOFS – relevant parts will be copy and pasted here soon. Then:
sudo apt-get install auth-client-config nss-updatedb libnss-db libpam-cracklib libpam-ccreds
sudo nano /etc/auth-client-config/profile.d/krb-auth-config
[krb5ldap]
nss_passwd=passwd: files ldap
nss_group=group: files ldap
nss_shadow=shadow: files ldap
nss_netgroup=netgroup: files ldap
pam_auth=auth sufficient pam_krb5.so
auth required pam_unix.so nullok_secure use_first_pass
pam_account=account sufficient pam_krb5.so
account required pam_unix.so
pam_password=password sufficient pam_krb5.so
password required pam_unix.so nullok obscure min=4 max=8 md5
pam_session=session required pam_unix.so
session required pam_mkhomedir.so skel=/etc/skel/
session optional pam_krb5.so
session optional pam_foreground.so
session optional pam_exec.so /bin/sh /usr/share/episync/epi-home-prep
[krb5ldap.cached]
nss_passwd=passwd: files ldap [NOTFOUND=return] db
nss_group=group: files ldap [NOTFOUND=return] db
nss_shadow=shadow: files ldap
nss_netgroup=netgroup: files ldap
pam_auth=auth required pam_env.so
auth sufficient pam_unix.so likeauth nullok
auth [default=ignore success=1 service_err=reset] pam_krb5.so use_first_pass
auth [default=die success=done] pam_ccreds.so action=validate use_first_pass
auth sufficient pam_ccreds.so action=store use_first_pass
auth required pam_deny.so
pam_account=account sufficient pam_krb5.so
account required pam_unix.so
pam_password=password sufficient pam_krb5.so
password required pam_unix.so nullok obscure min=4 max=8 md5
pam_session=session required pam_unix.so
session required pam_mkhomedir.so skel=/etc/skel/
session optional pam_krb5.so
session optional pam_foreground.sosudo nss_updatedb ldap sudo auth-client-config -a -p krb5ldap.cached
sudo mkdir /usr/share/episync sudo nano /usr/share/episync/epi-home-prep
#!/bin/bash
USER=$PAM_USER
USERHOME=/home/$USER
PROFILE=$USERHOME/.profile
CONFIGURED_STAMP=~/.episync-configured-do-not-delete
SETUP_SCRIPT=/usr/share/episync/episync-user-setup
COMMENT="# Added by episync"
if ! grep -q "$COMMENT" $PROFILE
then
echo "\n$COMMENT" >> $PROFILE
# Execute episync setup unless it's already configured
# echo "[ -f $CONFIGURED_STAMP ] || $SETUP_SCRIPT" >> $PROFILE
# Always execute the roaming profile sync tool
echo "/usr/share/episync/episync-sync" >> $PROFILE
fi
# Set proper .profile ownership
chown $USER: $PROFILEsudo nano /usr/share/episync/episync-sync
#!/bin/bash
# If server address is not in the environment, read it
if [ -z "$SERVER" ]
then
SERVER=`grep ^host /etc/ldap.conf | cut -d' ' -f2 | cut -d: -f1`
fi
# Generate key pair if not already done
if ! [ -f ~/.ssh/id_rsa.pub ]
then
. /usr/share/episync/episync-generate-key
fi
# FIXME: This doesn't work, investigate why
IGNORE_LIST="-ignore 'Path .gvfs' -ignore 'Path .local/share/Trash' -ignore 'Regex .*(cache|Cache|te?mp|history|thumbnails).*'"
# Sync files with pulsating progress bar
(echo ; unison $HOME ssh://$USER@$SERVER//$HOME -batch) | zenity --title='EpiSync' --progress --auto-close --pulsate --text='Synchronising your files.'sudo nano /usr/share/episync/episync-generate-key
#!/bin/bash
# If server address is not in the environment, read it
if [ -z "$SERVER" ]
then
SERVER=`grep ^host /etc/ldap.conf | cut -d' ' -f2 | cut -d: -f1`
fi
TEXT="Welcome to EpiSync first login configuration.
You are seeing this because you have not logged onto this laptop before. After you close this dialog, you will be asked for your password. It is needed to copy your public key to the server so that your files can be synchronised. You will not have to do this again, just this time."
ssh-keygen -f $HOME/.ssh/id_rsa -N ''
zenity --text "$TEXT" --info
SSH_ASKPASS=ssh-askpass setsid ssh-copy-id $SERVER
if [ $? -eq 0 ]
then
zenity --text "Key copied successfully." --info
else
zenity --text "Copy public key to $SERVER failed." --error
fisudo chmod +x /usr/share/episync/*
It’s quite common to need to use SSH in scripts, particularly for backup purposes. Unfortunately, this would mean storing a password in the script, which would consequently appear in logs etc… A much better plan is to use SSH keypairs. Once you’ve created a passphrase-less keypair and copied it to both machines, you can login without a password.
Firstly SSH into the machine you want to be able to access without a password. In this case, username dan connecting to machine neo.
ssh neo -l dan
Now create the keypair with:
ssh-keygen -t rsa
When asked for a passphrase, simply hit enter for none.
Now quit the ssh session with “exit” and run the following on the machine you want to have password-less access:
ssh-copy-id -i ~/.ssh/id_rsa.pub dan@neo
All done 
You can now type “ssh neo” and it will log you straight in without asking for your password! 
If you notice your webcam is upside down on skype/flash but fine on everything else, there’s a good chance the following will solve your problem.
Simply run this command in a terminal, followed by the program you want to run. For example for skype:
export LD_PRELOAD=/usr/lib32/libv4l/v4l1-compat.so skype
Or
export LD_PRELOAD=/usr/lib32/libv4l/v4l1-compat.so chromium-browser
Note that the path contains lib32 as both flash and skype are 32bit programs. If you’re actually using a 32bit version of Ubuntu you can modify the path to read: /usr/lib/libv4l/v4l1-compat.so
If you’re using Ubuntu 11.04 (Natty) or above you need to use the following instead:
export LD_PRELOAD=/usr/lib32/libv4l/v4l1compat.so skype
Or
export LD_PRELOAD=/usr/lib32/libv4l/v4l1compat.so chromium-browser
Forgotten the admin password on your Mac? You can reset the welcome system that you usually get immediately after installing OS X (the welcome video followed by the lengthy, intrusive set of forms) to create a new admin account using the following steps:
mount -uw / rm /var/db/.AppleSetupDone reboot
After rebooting and following the welcome process, you will have a new admin account. Login as the new admin and reset the old admin’s password, you can then log in as the old admin and delete the new admin account.
If you have several Ubuntu machines on a network, you might like to mirror the Ubuntu repositories locally so that you’re not wasting bandwidth downloading the same packages from the internet for every single machine. If you’ve already got an Ubuntu server up and running for some other task (such as ldap+kerberos+nfs type server, or a local web server) it’s very easy to add mirroring repository functionality to it. All you need is a spare ten minutes and ~35GB of free space for main, universe and multiverse and ~70GB if you also want the source packages (deb-src).
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This is part of a guide to setting up an Ubuntu server for a small/medium business. The server will provide DHCP, DNS, LDAP, Kerberos and NFS services such that users can login to any machine on the network and all their files and settings will be the same across the entire network.
The clients are going to be configured so that they mount home directories from the server and verify usernames/password using ldap and kerberos.
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