Ubuntu 10.10 SBS (Small Business Server) Setup: Part 9 – Connecting Portable Clients (Laptops) to Your Ubuntu Server with Kerberos, LDAP and Synchronised Home Directories

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.

Changes to the Server

Before we begin, it is necessary to install unison on the server like so:

sudo apt-get install unison

The Laptop

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.so
sudo 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: $PROFILE
 sudo 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
fi
sudo chmod +x /usr/share/episync/*