Petter Reinholdtsen

For a while now, I have wanted to find a way to change the DNS and DHCP services in Debian Edu to use the same LDAP objects for a given computer, to avoid the possibility of having a inconsistent state for a computer in LDAP (as in DHCP but no DNS entry or the other way around) and make it easier to add computers to LDAP.

I've looked at how powerdns and dhcpd is using LDAP, and using this information finally found a solution that seem to work.

The old setup required three LDAP objects for a given computer. One forward DNS entry, one reverse DNS entry and one DHCP entry. If we switch powerdns to use its strict LDAP method (ldap-method=strict in pdns-debian-edu.conf), the forward and reverse DNS entries are merged into one while making it impossible to transfer the reverse map to a slave DNS server.

If we also replace the object class used to get the DNS related attributes to one allowing these attributes to be combined with the dhcphost object class, we can merge the DNS and DHCP entries into one. I've written such object class in the dnsdomainaux.schema file (need proper OIDs, but that is a minor issue), and tested the setup. It seem to work.

With this test setup in place, we can get away with one LDAP object for both DNS and DHCP, and even the LTSP configuration I suggested in an earlier email. The combined LDAP object will look something like this:

  dn: cn=hostname,cn=group1,cn=THINCLIENTS,cn=DHCP Config,dc=skole,dc=skolelinux,dc=no
  cn: hostname
  objectClass: dhcphost
  objectclass: domainrelatedobject
  objectclass: dnsdomainaux
  associateddomain: hostname.intern
  arecord: 10.11.12.13
  dhcphwaddress: ethernet 00:00:00:00:00:00
  dhcpstatements: fixed-address hostname
  ldapconfigsound: Y

The DNS server uses the associateddomain and arecord entries, while the DHCP server uses the dhcphwaddress and dhcpstatements entries before asking DNS to resolve the fixed-adddress. LTSP will use dhcphwaddress or associateddomain and the ldapconfig* attributes.

I am not yet sure if I can get the DHCP server to look for its dhcphost in a different location, to allow us to put the objects outside the "DHCP Config" subtree, but hope to figure out a way to do that. If I can't figure out a way to do that, we can still get rid of the hosts subtree and move all its content into the DHCP Config tree (which probably should be renamed to be more related to the new content. I suspect cn=dnsdhcp,ou=services or something like that might be a good place to put it.

If you want to help out with implementing this for Debian Edu, please contact us on debian-edu@lists.debian.org.

Vagrant mentioned on IRC today that ltsp_config now support sourcing files from /usr/share/ltsp/ltsp_config.d/ on the thin clients, and that this can be used to fetch configuration from LDAP if Debian Edu choose to store configuration there.

Armed with this information, I got inspired and wrote a test module to get configuration from LDAP. The idea is to look up the MAC address of the client in LDAP, and look for attributes on the form ltspconfigsetting=value, and use this to export SETTING=value to the LTSP clients.

The goal is to be able to store the LTSP configuration attributes in a "computer" LDAP object used by both DNS and DHCP, and thus allowing us to store all information about a computer in one place.

This is a untested draft implementation, and I welcome feedback on this approach. A real LDAP schema for the ltspClientAux objectclass need to be written. Comments, suggestions, etc?

# Store in /opt/ltsp/$arch/usr/share/ltsp/ltsp_config.d/ldap-config
#
# Fetch LTSP client settings from LDAP based on MAC address
#
# Uses ethernet address as stored in the dhcpHost objectclass using
# the dhcpHWAddress attribute or ethernet address stored in the
# ieee802Device objectclass with the macAddress attribute.
#
# This module is written to be schema agnostic, and only depend on the
# existence of attribute names.
#
# The LTSP configuration variables are saved directly using a
# ltspConfig prefix and uppercasing the rest of the attribute name.
# To set the SERVER variable, set the ltspConfigServer attribute.
#
# Some LDAP schema should be created with all the relevant
# configuration settings.  Something like this should work:
# 
# objectclass ( 1.1.2.2 NAME 'ltspClientAux'
#     SUP top
#     AUXILIARY
#     MAY ( ltspConfigServer $ ltsConfigSound $ ... )

LDAPSERVER=$(debian-edu-ldapserver)
if [ "$LDAPSERVER" ] ; then
    LDAPBASE=$(debian-edu-ldapserver -b)
    for MAC in $(LANG=C ifconfig |grep -i hwaddr| awk '{print $5}'|sort -u) ; do
	filter="(|(dhcpHWAddress=ethernet $MAC)(macAddress=$MAC))"
	ldapsearch -h "$LDAPSERVER" -b "$LDAPBASE" -v -x "$filter" | \
	    grep '^ltspConfig' | while read attr value ; do
	    # Remove prefix and convert to upper case
	    attr=$(echo $attr | sed 's/^ltspConfig//i' | tr a-z A-Z)
	    # bass value on to clients
	    eval "$attr=$value; export $attr"
	done
    done
fi

I'm not sure this shell construction will work, because I suspect the while block might end up in a subshell causing the variables set there to not show up in ltsp-config, but if that is the case I am sure the code can be restructured to make sure the variables are passed on. I expect that can be solved with some testing. :)

If you want to help out with implementing this for Debian Edu, please contact us on debian-edu@lists.debian.org.

Since my last post about available LDAP tools in Debian, I was told about a LDAP GUI that is even better than luma. The java application jXplorer is claimed to be capable of moving LDAP objects and subtrees using drag-and-drop, and can authenticate using Kerberos. I have only tested the Kerberos authentication, but do not have a LDAP setup allowing me to rewrite LDAP with my test user yet. It is available in Debian testing and unstable at the moment. The only problem I have with it is how it handle errors. If something go wrong, its non-intuitive behaviour require me to go through some query work list and remove the failing query. Nothing big, but very annoying.

De siste dagene har Aftenposten fortalt hvordan politet har brukt skriveverktøy som ikke håndterer arabisk tekst og tekst som skal skrives fra høyre mot venstre når de har laget løpeseddel for å be om informasjon fra publikum. Resultatet har vært en uleselig arabisk-bit på løpeseddelen. Feilen har oppstått når teksten har blitt "kopiert inn i programvare som ikke har støtte for språk som skrives fra høyre mot venstre", og jeg er ganske sikker på at det er snakk om Microsoft Office i dette tilfellet. Er det slik at MS Office i norsk språkdrakt ikke har støtte for tekst som skal skrives fra høyre mot venstre? Jeg tror alle utgaver av OpenOffice.org har slik støtte, og det er jo ikke veldig vanskelig å la slik støtte finnes i alle utgaver av et program hvis støtten først er utviklet. Aftenpostens melding får meg til å undre om problemet ville vært unngått hvis politiet brukte OpenOffice.org i stedet for MS Office.

Mon tro om det er flere eksempler på at MS Office har ødelagt for offentlig myndighet?

Here is a short update on my my Debian Lenny->Squeeze upgrade testing. Here is a summary of the difference for Gnome when it is upgraded by apt-get and aptitude. I'm not reporting the status for KDE, because the upgrade crashes when aptitude try because of missing conflicts (#584861 and #585716).

At the end of the upgrade test script, dpkg -l is executed to get a complete list of the installed packages. Based on this I see these differences when I did a test run today. As usual, I do not really know what the correct set of packages would be, but thought it best to publish the difference.

Installed using apt-get, missing with aptitude

at-spi cpp-4.3 finger gnome-spell gstreamer0.10-gnomevfs libatspi1.0-0 libcupsys2 libeel2-data libgail-common libgdl-1-common libgnomeprint2.2-data libgnomeprintui2.2-common libgnomevfs2-bin libgtksourceview-common libpt-1.10.10-plugins-alsa libpt-1.10.10-plugins-v4l libservlet2.4-java libxalan2-java libxerces2-java openoffice.org-writer2latex openssl-blacklist p7zip python-4suite-xml python-eggtrayicon python-gtkhtml2 python-gtkmozembed svgalibg1 xserver-xephyr zip

Installed using apt-get, removed with aptitude

bluez-utils dhcdbd djvulibre-desktop epiphany-gecko gnome-app-install gnome-mount gnome-vfs-obexftp gnome-volume-manager libao2 libavahi-compat-libdnssd1 libavahi-core5 libbind9-50 libbluetooth2 libcamel1.2-11 libcdio7 libcucul0 libcurl3 libdirectfb-1.0-0 libdvdread3 libedata-cal1.2-6 libedataserver1.2-9 libeel2-2.20 libepc-1.0-1 libepc-ui-1.0-1 libexchange-storage1.2-3 libfaad0 libgd2-noxpm libgda3-3 libgda3-common libggz2 libggzcore9 libggzmod4 libgksu1.2-0 libgksuui1.0-1 libgmyth0 libgnome-desktop-2 libgnome-pilot2 libgnomecups1.0-1 libgnomeprint2.2-0 libgnomeprintui2.2-0 libgpod3 libgraphviz4 libgtkhtml2-0 libgtksourceview1.0-0 libgucharmap6 libhesiod0 libicu38 libisccc50 libisccfg50 libiw29 libkpathsea4 libltdl3 liblwres50 libmagick++10 libmagick10 libmalaga7 libmtp7 libmysqlclient15off libnautilus-burn4 libneon27 libnm-glib0 libnm-util0 libopal-2.2 libosp5 libparted1.8-10 libpisock9 libpisync1 libpoppler-glib3 libpoppler3 libpt-1.10.10 libraw1394-8 libsensors3 libsmbios2 libsoup2.2-8 libssh2-1 libsuitesparse-3.1.0 libswfdec-0.6-90 libtalloc1 libtotem-plparser10 libtrackerclient0 libvoikko1 libxalan2-java-gcj libxerces2-java-gcj libxklavier12 libxtrap6 libxxf86misc1 libzephyr3 mysql-common swfdec-gnome totem-gstreamer wodim

Installed using aptitude, missing with apt-get

gnome gnome-desktop-environment hamster-applet python-gnomeapplet python-gnomekeyring python-wnck rhythmbox-plugins xorg xserver-xorg-input-all xserver-xorg-input-evdev xserver-xorg-input-kbd xserver-xorg-input-mouse xserver-xorg-input-synaptics xserver-xorg-video-all xserver-xorg-video-apm xserver-xorg-video-ark xserver-xorg-video-ati xserver-xorg-video-chips xserver-xorg-video-cirrus xserver-xorg-video-dummy xserver-xorg-video-fbdev xserver-xorg-video-glint xserver-xorg-video-i128 xserver-xorg-video-i740 xserver-xorg-video-mach64 xserver-xorg-video-mga xserver-xorg-video-neomagic xserver-xorg-video-nouveau xserver-xorg-video-nv xserver-xorg-video-r128 xserver-xorg-video-radeon xserver-xorg-video-radeonhd xserver-xorg-video-rendition xserver-xorg-video-s3 xserver-xorg-video-s3virge xserver-xorg-video-savage xserver-xorg-video-siliconmotion xserver-xorg-video-sis xserver-xorg-video-sisusb xserver-xorg-video-tdfx xserver-xorg-video-tga xserver-xorg-video-trident xserver-xorg-video-tseng xserver-xorg-video-vesa xserver-xorg-video-vmware xserver-xorg-video-voodoo

Installed using aptitude, removed with apt-get

deskbar-applet xserver-xorg xserver-xorg-core xserver-xorg-input-wacom xserver-xorg-video-intel xserver-xorg-video-openchrome

I was told on IRC that the xorg-xserver package was changed in git today to try to get apt-get to not remove xorg completely. No idea when it hits Squeeze, but when it does I hope it will reduce the difference somewhat.

For a laptop, centralized user directories and password checking is a bit troubling. Laptops are typically used also when not connected to the network, and it is vital for a user to be able to log in or unlock the screen saver also when a central server is unavailable. This is possible by caching passwords and directory information (user and group attributes) locally, and the packages to do so are available in Debian. Here follow two recipes to set this up in Debian/Squeeze. It is also possible to set up in Debian/Lenny, but require more manual setup there because pam-auth-update is missing in Lenny.

LDAP/Kerberos + nscd + libpam-ccreds + libpam-mklocaluser/pam_mkhomedir

This is the traditional method with a twist. The password caching is provided by libpam-ccreds (version 10-4 or later is needed on Squeeze), and the directory caching is done by nscd. The directory lookup and password checking is done using LDAP. If one want to use Kerberos for password checking the libpam-ldapd package can be replaced with libpam-krb5 or libpam-heimdal. If one is happy having a local home directory with the path listed in LDAP, one can use the pam_mkhomedir module from pam-modules to make this happen instead of using libpam-mklocaluser. A setup for pam-auth-update to enable pam_mkhomedir will have to be written until a fix for bug #568577 is in the archive. Because I believe it is a bad idea to have local home directories using misleading paths like /site/server/partition/, I prefer to create a local user with the home directory in /home/. This is done using the libpam-mklocaluser package.

These packages need to be installed and configured

libnss-ldapd libpam-ldapd nscd libpam-ccreds libpam-mklocaluser

The ldapd packages will ask for LDAP connection information, and one have to fill in the values that fits ones own site. Make sure the PAM part uses encrypted connections, to make sure the password is not sent in clear text to the LDAP server. I've been unable to get TLS certificate checking for a self signed certificate working, which make LDAP authentication unsafe for Debian Edu (nslcd is not checking if it is talking to the correct LDAP server), and very much welcome feedback on how to get this working.

Because nscd do not have a default configuration fit for offline caching until bug #485282 is fixed, this configuration should be used instead of the one currently in /etc/nscd.conf. The changes are in the fields reload-count and positive-time-to-live, and is based on the instructions I found in the LDAP for Mobile Laptops instructions by Flyn Computing.

	debug-level		0
	reload-count		unlimited
	paranoia		no

	enable-cache		passwd		yes
	positive-time-to-live	passwd		2592000
	negative-time-to-live	passwd		20
	suggested-size		passwd		211
	check-files		passwd		yes
	persistent		passwd		yes
	shared			passwd		yes
	max-db-size		passwd		33554432
	auto-propagate		passwd		yes

	enable-cache		group		yes
	positive-time-to-live	group		2592000
	negative-time-to-live	group		20
	suggested-size		group		211
	check-files		group		yes
	persistent		group		yes
	shared			group		yes
	max-db-size		group		33554432
	auto-propagate		group		yes

	enable-cache		hosts		no
	positive-time-to-live	hosts		2592000
	negative-time-to-live	hosts		20
	suggested-size		hosts		211
	check-files		hosts		yes
	persistent		hosts		yes
	shared			hosts		yes
	max-db-size		hosts		33554432

	enable-cache		services	yes
	positive-time-to-live	services	2592000
	negative-time-to-live	services	20
	suggested-size		services	211
	check-files		services	yes
	persistent		services	yes
	shared			services	yes
	max-db-size		services	33554432

While we wait for a mechanism to update /etc/nsswitch.conf automatically like the one provided in bug #496915, the file content need to be manually replaced to ensure LDAP is used as the directory service on the machine. /etc/nsswitch.conf should normally look like this:

passwd:         files ldap
group:          files ldap
shadow:         files ldap
hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4
networks:       files
protocols:      files
services:       files
ethers:         files
rpc:            files
netgroup:       files ldap

The important parts are that ldap is listed last for passwd, group, shadow and netgroup.

With these changes in place, any user in LDAP will be able to log in locally on the machine using for example kdm, get a local home directory created and have the password as well as user and group attributes cached.

LDAP/Kerberos + nss-updatedb + libpam-ccreds + libpam-mklocaluser/pam_mkhomedir

Because nscd have had its share of problems, and seem to have problems doing proper caching, I've seen suggestions and recipes to use nss-updatedb to copy parts of the LDAP database locally when the LDAP database is available. I have not tested such setup, because I discovered sssd.

LDAP/Kerberos + sssd + libpam-mklocaluser

A more flexible and robust setup than the nscd combination mentioned earlier that has shown up recently, is the sssd package from Redhat. It is part of the FreeIPA project to provide a Active Directory like directory service for Linux machines. The sssd system combines the caching of passwords and user information into one package, and remove the need for nscd and libpam-ccreds. It support LDAP and Kerberos, but not NIS. Version 1.2 do not support netgroups, but it is said that it will support this in version 1.5 expected to show up later in 2010. Because the sssd package was missing in Debian, I ended up co-maintaining it with Werner, and version 1.2 is now in testing.

These packages need to be installed and configured to get the roaming setup I want

libpam-sss libnss-sss libpam-mklocaluser

The complete setup of sssd is done by editing/creating /etc/sssd/sssd.conf.

[sssd]
config_file_version = 2
reconnection_retries = 3
sbus_timeout = 30
services = nss, pam
domains = INTERN

[nss]
filter_groups = root
filter_users = root
reconnection_retries = 3

[pam]
reconnection_retries = 3

[domain/INTERN]
enumerate = false
cache_credentials = true

id_provider = ldap
auth_provider = ldap
chpass_provider = ldap

ldap_uri = ldap://ldap
ldap_search_base = dc=skole,dc=skolelinux,dc=no
ldap_tls_reqcert = never
ldap_tls_cacert = /etc/ssl/certs/ca-certificates.crt

I got the same problem here with certificate checking. Had to set "ldap_tls_reqcert = never" to get it working.

With the libnss-sss package in testing at the moment, the nsswitch.conf file is update automatically, so there is no need to modify it manually.

If you want to help out with implementing this for Debian Edu, please contact us on debian-edu@lists.debian.org.

The last few days I have been looking into the status of the LDAP directory in Debian Edu, and in the process I started to miss a GUI tool to browse the LDAP tree. The only one I was able to find in Debian/Squeeze and Lenny is LUMA, which has proved to be a great tool to get a overview of the current LDAP directory populated by default in Skolelinux. Thanks to it, I have been able to find empty and obsolete subtrees, misplaced objects and duplicate objects. It will be installed by default in Debian/Squeeze. If you are working with LDAP, give it a go. :)

I did notice one problem with it I have not had time to report to the BTS yet. There is no .desktop file in the package, so the tool do not show up in the Gnome and KDE menus, but only deep down in in the Debian submenu in KDE. I hope that can be fixed before Squeeze is released.

I have not yet been able to get it to modify the tree yet. I would like to move objects and remove subtrees directly in the GUI, but have not found a way to do that with LUMA yet. So in the mean time, I use ldapvi for that.

If you have tips on other GUI tools for LDAP that might be useful in Debian Edu, please contact us on debian-edu@lists.debian.org.

Update 2010-06-29: Ross Reedstrom tipped us about the gq package as a useful GUI alternative. It seem like a good tool, but is unmaintained in Debian and got a RC bug keeping it out of Squeeze. Unless that changes, it will not be an option for Debian Edu based on Squeeze.

A while back, I complained about the fact that it is not possible with the provided schemas for storing DNS and DHCP information in LDAP to combine the two sets of information into one LDAP object representing a computer.

In the mean time, I discovered that a simple fix would be to make the dhcpHost object class auxiliary, to allow it to be combined with the dNSDomain object class, and thus forming one object for one computer when storing both DHCP and DNS information in LDAP.

If I understand this correctly, it is not safe to do this change without also changing the assigned number for the object class, and I do not know enough about LDAP schema design to do that properly for Debian Edu.

Anyway, for future reference, this is how I believe we could change the DHCP schema to solve at least part of the problem with the LDAP schemas available today from IETF.

--- dhcp.schema    (revision 65192)
+++ dhcp.schema    (working copy)
@@ -376,7 +376,7 @@
 objectclass ( 2.16.840.1.113719.1.203.6.6
        NAME 'dhcpHost'
        DESC 'This represents information about a particular client'
-       SUP top
+       SUP top AUXILIARY
        MUST cn
        MAY  (dhcpLeaseDN $ dhcpHWAddress $ dhcpOptionsDN $ dhcpStatements $ dhcpComments $ dhcpOption)
        X-NDS_CONTAINMENT ('dhcpService' 'dhcpSubnet' 'dhcpGroup') )

I very much welcome clues on how to do this properly for Debian Edu/Squeeze. We provide the DHCP schema in our debian-edu-config package, and should thus be free to rewrite it as we see fit.

If you want to help out with implementing this for Debian Edu, please contact us on debian-edu@lists.debian.org.

A few times I have had the need to simulate the way tasksel installs packages during the normal debian-installer run. Until now, I have ended up letting tasksel do the work, with the annoying problem of not getting any feedback at all when something fails (like a conffile question from dpkg or a download that fails), using code like this:

export DEBIAN_FRONTEND=noninteractive
tasksel --new-install

This would invoke tasksel, let its automatic task selection pick the tasks to install, and continue to install the requested tasks without any output what so ever. Recently I revisited this problem while working on the automatic package upgrade testing, because tasksel would some times hang without any useful feedback, and I want to see what is going on when it happen. Then it occured to me, I can parse the output from tasksel when asked to run in test mode, and use that aptitude command line printed by tasksel then to simulate the tasksel run. I ended up using code like this:

export DEBIAN_FRONTEND=noninteractive
cmd="$(in_target tasksel -t --new-install | sed 's/debconf-apt-progress -- //')"
$cmd

The content of $cmd is typically something like "aptitude -q --without-recommends -o APT::Install-Recommends=no -y install ~t^desktop$ ~t^gnome-desktop$ ~t^laptop$ ~pstandard ~prequired ~pimportant", which will install the gnome desktop task, the laptop task and all packages with priority standard , required and important, just like tasksel would have done it during installation.

A better approach is probably to extend tasksel to be able to install packages without using debconf-apt-progress, for use cases like this.

Dagbladet melder at Vinmonopolet med bakgrunn i vekterstreiken som pågår i Norge for tiden, har bestemt seg for med vitende og vilje å bryte sentralbanklovens paragraf 14 ved å nekte folk å betale med kontanter, og at flere butikker planlegger å følge deres eksempel. Jeg synes det er hårreisende hvis de slipper unna med et slikt soleklart lovbrudd, og lurer på hva slags muligheter jeg vil ha hvis jeg blir nektet å handle med kontanter. Jeg handler i hovedsak med kontanter selv, da jeg anser det som en borgerrett å kunne handle anonymt uten at det blir registrert. For meg er det et angrep på mitt personvern å nekte å ta imot kontant betaling.

Paragrafen i sentralbankloven lyder:

§ 14. Tvungent betalingsmiddel

Bankens sedler og mynter er tvungent betalingsmiddel i Norge. Ingen er pliktig til i én betaling å ta imot mer enn femogtyve mynter av hver enhet.

Sterkt skadde sedler og mynter er ikke tvungent betalingsmiddel. Banken gir nærmere forskrifter om erstatning for bortkomne, brente eller skadde sedler og mynter.

Selv om en avtale inneholder klausul om betaling av en pengeforpliktelse i gullverdi, kan skyldneren frigjøre seg med tvungne betalingsmidler uten hensyn til denne klausul.

Det er med bakgrunn i denne lovet ikke tillatt å nekte å ta imot kontakt betaling. Det er en lov jeg har sans for, og som jeg mener må håndheves strengt.