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        <channel>
                <title>Petter Reinholdtsen</title>
                <description></description>
                <link>http://people.skolelinux.org/pere/blog/</link>
                <atom:link href="http://people.skolelinux.org/pere/blog/index.rss" rel="self" type="application/rss+xml" />
        
        <item>
                <title>Broken hard link handling with sshfs</title>
                <link>http://people.skolelinux.org/pere/blog/Broken_hard_link_handling_with_sshfs.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Broken_hard_link_handling_with_sshfs.html</guid>
                <pubDate>Mon, 30 Aug 2010 19:30:00 +0200</pubDate>
                <description>
&lt;p&gt;Just got an email from Tobias Gruetzmacher as a followup on my
&lt;a href=&quot;http://people.skolelinux.org/pere/blog/Broken_umask_handling_with_sshfs.html&quot;&gt;previous
post about sshfs&lt;/a&gt;.  He reported another problem with sshfs.  It
fail to handle hard links properly.  A simple way to spot this is to
look at the . and .. entries in the directory tree.  These should have
a link count &gt;1, but on sshfs the count is 1.  I just tested to see
what happen when trying to hardlink, and this fail as well:&lt;/p&gt;

&lt;pre&gt;
% ln foo bar
ln: creating hard link `bar&#39; =&gt; `foo&#39;: Function not implemented
%
&lt;/pre&gt;

&lt;p&gt;I have not yet found time to implement a test for this in my file
system test code, but believe having working hard links is useful to
avoid surprised unix programs.  Not as useful as working file locking
and symlinks, which are required to get a working desktop, but useful
nevertheless. :)&lt;/p&gt;

&lt;p&gt;The latest version of the file system test code is available via
git from
&lt;a href=&quot;http://github.com/gebi/fs-test&quot;&gt;http://github.com/gebi/fs-test&lt;/a&gt;&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>Sikkerhetsteateret på flyplassene fortsetter</title>
                <link>http://people.skolelinux.org/pere/blog/Sikkerhetsteateret_p___flyplassene_fortsetter.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Sikkerhetsteateret_p___flyplassene_fortsetter.html</guid>
                <pubDate>Sat, 28 Aug 2010 10:40:00 +0200</pubDate>
                <description>
&lt;p&gt;Jeg skrev for et halvt år siden hvordan
&lt;a href=&quot;http://people.skolelinux.org/pere/blog/Sikkerhet__teater__og_hvordan_gj__re_verden_sikrere.html&quot;&gt;samfunnet
kaster bort ressurser på sikkerhetstiltak som ikke fungerer&lt;/a&gt;.  Kom
nettopp over en
&lt;a href=&quot;http://www.askthepilot.com/essays-and-stories/terrorism-tweezers-and-terminal-madness-an-essay-on-security/&quot;&gt;historie
fra en pilot fra USA&lt;/a&gt; som kommenterer det samme.  Jeg mistenker det
kun er uvitenhet og autoritetstro som gjør at så få protesterer.  Har
veldig sans for piloten omtalt i &lt;a
href=&quot;http://www.aftenposten.no/nyheter/iriks/article2057501.ece&quot;&gt;Aftenposten&lt;/a&gt; 2007-10-23,
og skulle ønske flere rettet oppmerksomhet mot problemet.  Det gir
ikke meg trygghetsfølelse på flyplassene når jeg ser at
flyplassadministrasjonen kaster bort folk, penger og tid på tull i
stedet for ting som bidrar til reell økning av sikkerheten.  Det
forteller meg jo at vurderingsevnen til de som burde bidra til økt
sikkerhet er svært sviktende, noe som ikke taler godt for de andre
tiltakene.&lt;/p&gt;

&lt;p&gt;Mon tro hva som skjer hvis det fantes en enkel brosjyre å skrive ut
fra Internet som forklarte hva som er galt med sikkerhetsopplegget på
flyplassene, og folk skrev ut og la en bunke på flyplassene når de
passerte.  Kanskje det ville fått flere til å få øynene opp for
problemet.&lt;/p&gt;

&lt;p&gt;Personlig synes jeg flyopplevelsen er blitt så avskyelig at jeg
forsøker å klare meg med tog, bil og båt for å slippe ubehaget.  Det
er dog noe vanskelig i det langstrakte Norge og for å kunne besøke de
delene av verden jeg ønsker å nå.  Mistenker at flere har det slik, og
at dette går ut over inntjeningen til flyselskapene.  Det er antagelig
en god ting sett fra et miljøperspektiv, men det er en annen sak.&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>Skolelinux i Osloskolen</title>
                <link>http://people.skolelinux.org/pere/blog/Skolelinux_i_Osloskolen.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Skolelinux_i_Osloskolen.html</guid>
                <pubDate>Thu, 26 Aug 2010 22:25:00 +0200</pubDate>
                <description>
&lt;p&gt;Denne høsten skal endelig alle Osloskolene få mulighet til å bruke
&lt;a href=&quot;http://www.skolelinux.org/&quot;&gt;Skolelinux&lt;/a&gt;.  Ny IT-løsning
har vært rullet ut i noen måneder nå, og så vidt jeg fikk vite før
sommeren skulle alle skoler ha nytt opplegg på plass før oppstart nå i
høst.  På alle skolene skal en kunne velge ved installasjon om en skal
ha Windows eller Skolelinux på maskinene, og en kan i tillegg
PXE-boote maskinene over nett som tynne klienter eller diskløse
arbeidsstasjoner. Jeg er spent på hvor mange skoler som velger å ta i
bruk Skolelinux, og gleder meg til å se hvordan dette utvikler seg.
Løsningen leveres av
&lt;a href=&quot;http://www.logica.no/&quot;&gt;Logica&lt;/a&gt; med
&lt;a href=&quot;http://www.slxdrift.no/&quot;&gt;Skolelinux Drift AS&lt;/a&gt; som
underleverandør, og jeg har vært involvert i utviklingen av løsningen
via Skolelinux Drift AS siden prosjektet starter.  Jeg synes det er
fantastisk at Skolelinux er kommet så langt siden vi startet i 2001 at
alle elevene i Osloskolene nå skal få mulighet til å bruke
løsningen.  Jeg håper de vil sette pris på alle de
&lt;a href=&quot;http://www.skolelinux.no/linux-signpost/&quot;&gt;fantastiske
brukerprogrammene&lt;/a&gt; som er tilgjengelig i Skolelinux.&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>Broken umask handling with sshfs</title>
                <link>http://people.skolelinux.org/pere/blog/Broken_umask_handling_with_sshfs.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Broken_umask_handling_with_sshfs.html</guid>
                <pubDate>Thu, 26 Aug 2010 13:30:00 +0200</pubDate>
                <description>
&lt;p&gt;My file system sematics program
&lt;a href=&quot;http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html&quot;&gt;presented
a few days ago&lt;/a&gt; is very useful to verify that a file system can
work as a unix home directory,and today I had to extend it a bit.  I&#39;m
looking into alternatives for home directory access here at the
University of Oslo, and one of the options is sshfs.  My friend
Finn-Arne mentioned a while back that they had used sshfs with Debian
Edu, but stopped because of problems.  I asked today what the problems
where, and he mentioned that sshfs failed to handle umask properly.
Trying to detect the problem I wrote this addition to my fs testing
script:&lt;/p&gt;

&lt;pre&gt;
mode_t touch_get_mode(const char *name, mode_t mode) {
  mode_t retval = 0;
  int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, mode);
  if (-1 != fd) {
    unlink(name);
    struct stat statbuf;
    if (-1 != fstat(fd, &amp;statbuf)) {
      retval = statbuf.st_mode &amp; 0x1ff;
    }
    close(fd);
  }
  return retval;
}

/* Try to detect problem discovered using sshfs */
int test_umask(void) {
  printf(&quot;info: testing umask effect on file creation\n&quot;);

  mode_t orig_umask = umask(000);
  mode_t newmode;
  if (0666 != (newmode = touch_get_mode(&quot;foobar&quot;, 0666))) {
    printf(&quot;  error: Wrong file mode %o when creating using mode 666 and umask 000\n&quot;,
           newmode);
  }
  umask(007);
  if (0660 != (newmode = touch_get_mode(&quot;foobar&quot;, 0666))) {
    printf(&quot;  error: Wrong file mode %o when creating using mode 666 and umask 007\n&quot;,
           newmode);
  }

  umask (orig_umask);
  return 0;
}

int main(int argc, char **argv) {
  [...]
  test_umask();
  return 0;
}
&lt;/pre&gt;

&lt;p&gt;Sure enough.  On NFS to a netapp, I get this result:&lt;/p&gt;

&lt;pre&gt;
Testing POSIX/Unix sematics on file system
info: testing symlink creation
info: testing subdirectory creation
info: testing fcntl locking
  Read-locking 1 byte from 1073741824
  Read-locking 510 byte from 1073741826
  Unlocking 1 byte from 1073741824
  Write-locking 1 byte from 1073741824
  Write-locking 510 byte from 1073741826
  Unlocking 2 byte from 1073741824
info: testing umask effect on file creation
&lt;/pre&gt;

&lt;p&gt;When mounting the same directory using sshfs, I get this
result:&lt;/p&gt;

&lt;pre&gt;
Testing POSIX/Unix sematics on file system
info: testing symlink creation
info: testing subdirectory creation
info: testing fcntl locking
  Read-locking 1 byte from 1073741824
  Read-locking 510 byte from 1073741826
  Unlocking 1 byte from 1073741824
  Write-locking 1 byte from 1073741824
  Write-locking 510 byte from 1073741826
  Unlocking 2 byte from 1073741824
info: testing umask effect on file creation
  error: Wrong file mode 644 when creating using mode 666 and umask 000
  error: Wrong file mode 640 when creating using mode 666 and umask 007
&lt;/pre&gt;

&lt;p&gt;So, I can conclude that sshfs is better than smb to a Netapp or a
Windows server, but not good enough to be used as a home
directory.&lt;/p&gt;

&lt;p&gt;Update 2010-08-26: Reported the issue in
&lt;a href=&quot;http://bugs.debian.org/594498&quot;&gt;BTS report #594498&lt;/a&gt;&lt;/p&gt;

&lt;p&gt;Update 2010-08-27: Michael Gebetsroither report that he found the
script so useful that he created a GIT repository and stored it in
&lt;a href=&quot;http://github.com/gebi/fs-test&quot;&gt;http://github.com/gebi/fs-test&lt;/a&gt;.&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>Elektronisk stemmegiving er ikke til å stole på - heller ikke i Norge</title>
                <link>http://people.skolelinux.org/pere/blog/Elektronisk_stemmegiving_er_ikke_til____stole_p_____heller_ikke_i_Norge.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Elektronisk_stemmegiving_er_ikke_til____stole_p_____heller_ikke_i_Norge.html</guid>
                <pubDate>Mon, 23 Aug 2010 19:30:00 +0200</pubDate>
                <description>
&lt;p&gt;I Norge pågår en prosess for å
&lt;a href=&quot;http://www.e-valg.dep.no/&quot;&gt;innføre elektronisk
stemmegiving&lt;/a&gt; ved kommune- og stortingsvalg.  Dette skal
introduseres i 2011.  Det er all grunn til å tro at valg i Norge ikke
vil være til å stole på hvis dette blir gjennomført.  Da det hele var
oppe til høring i 2006 forfattet jeg
&lt;a href=&quot;http://www.nuug.no/dokumenter/valg-horing-2006-09.pdf&quot;&gt;en
høringsuttalelse fra NUUG&lt;/a&gt; (og EFN som hengte seg på) som skisserte
hvilke punkter som må oppfylles for at en skal kunne stole på et valg,
og elektronisk stemmegiving mangler flere av disse.  Elektronisk
stemmegiving er for alle praktiske formål å putte ens stemme i en sort
boks under andres kontroll, og satse på at de som har kontroll med
boksen er til å stole på - uten at en har mulighet til å verifisere
dette selv.  Det er ikke slik en gjennomfører demokratiske valg.&lt;/p&gt;

&lt;p&gt;Da problemet er fundamentalt med hvordan elektronisk stemmegiving
må fungere for at også ikke-krypografer skal kunne delta, har det vært
mange rapporter om hvordan elektronisk stemmegiving har sviktet i land
etter land.  En
&lt;a href=&quot;http://wiki.nuug.no/uttalelser/2006-elektronisk-stemmegiving&quot;&gt;liten
samling referanser&lt;/a&gt; finnes på NUUGs wiki.  Den siste er fra India,
der valgkomisjonen har valgt
&lt;a href=&quot;http://www.freedom-to-tinker.com/blog/jhalderm/electronic-voting-researcher-arrested-over-anonymous-source&quot;&gt;å
pusse politiet på en forsker&lt;/a&gt; som har dokumentert svakheter i
valgsystemet.&lt;/p&gt;

&lt;p&gt;Her i Norge har en valgt en annen tilnærming, der en forsøker seg
med teknobabbel for å få befolkningen til å tro at dette skal bli
sikkert.  Husk, elektronisk stemmegiving underminerer de demokratiske
valgene i Norge, og bør ikke innføres.&lt;/p&gt;

&lt;p&gt;Den offentlige diskusjonen blir litt vanskelig av at media har
valgt å kalle dette &quot;evalg&quot;, som kan sies å både gjelde elektronisk
opptelling av valget som Norge har gjort siden 60-tallet og som er en
svært god ide, og elektronisk opptelling som er en svært dårlig ide.
Diskusjonen gir ikke mening hvis en skal diskutere om en er for eller
mot &quot;evalg&quot;, og jeg forsøker derfor å være klar på at jeg snakker om
elektronisk stemmegiving og unngå begrepet &quot;evalg&quot;.&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>Robot, reis deg...</title>
                <link>http://people.skolelinux.org/pere/blog/Robot__reis_deg___.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Robot__reis_deg___.html</guid>
                <pubDate>Sat, 21 Aug 2010 22:10:00 +0200</pubDate>
                <description>
&lt;p&gt;I dag fikk jeg endelig tittet litt på mine nyinnkjøpte roboter, og
har brukt noen timer til å google etter interessante referanser og
aktuell kildekode for bruk på Linux.  Det mest lovende så langt er
&lt;a href=&quot;http://ispykee.toyz.org/&quot;&gt;ispykee&lt;/a&gt;, som har en
BSD-lisensiert linux-daemon som står som mellomledd mellom roboter på
lokalnettet og en sentral tjeneste der en iPhone kan koble seg opp for
å fjernstyre roboten.  Linux-daemonen implementerer deler av
protokollen som roboten forstår.  Etter å ha knotet litt med å oppnå
kontakt med roboten (den oppretter et eget ad-hoc wifi-nett, så jeg
måtte gå av mitt vanlige nett for å få kontakt), og kommet frem til at
den lytter på IP-port 9000 og 9001, gikk jeg i gang med å finne ut
hvordan jeg kunne snakke med roboten vha. disse portene.  Robotbiten
av protokollen er publisert av produsenten med GPL-lisens, slik at det
er mulig å se hvordan protokollen fungerer.  Det finnes en java-klient
for Android som så ganske snasen ut, men fant ingen kildekode for
denne.  Derimot hadde iphone-løsningen kildekode, så jeg tok
utgangspunkt i den.&lt;/p&gt;

&lt;p&gt;Daemonen ville i utgangspunktet forsøke å kontakte den sentrale
tjenesten som iphone-programmet kobler seg til.  Jeg skrev dette om
til i stedet å sette opp en nettverkstjeneste på min lokale maskin,
som jeg kan koble meg opp til med telnet og gi kommandoer til roboten
(act, forward, right, left, etc).  Det involverte i praksis å bytte ut
socket()/connect() med socket()/bind()/listen()/accept() for å gjøre
klienten om til en tjener.&lt;/p&gt;

&lt;p&gt;Mens jeg har forsøkt å få roboten til å bevege seg har min samboer
skrudd sammen resten av roboten for å få montert kamera og plastpynten
(armer, plastfiber for lys).  Nå er det hele montert, og roboten er
klar til bruk.  Må få flyttet den over til mitt vanlige trådløsnett
før det blir praktisk, men de bitene av protokollen er ikke
implementert i ispykee-daemonen, så der må jeg enten få tak i en mac
eller en windows-maskin, eller implementere det selv.&lt;/p&gt;

&lt;p&gt;Vi var tre som kjøpte slike roboter, og vi har blitt enige om å
samle notater og referanser på &lt;a
href=&quot;http://wiki.nuug.no/grupper/robot/&quot;&gt;NUUGs wiki&lt;/a&gt;.  Ta en titt
der hvis du er nysgjerrig.&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>2 Spykee-roboter i hus, nå skal det lekes</title>
                <link>http://people.skolelinux.org/pere/blog/2_Spykee_roboter_i_hus__n___skal_det_lekes.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/2_Spykee_roboter_i_hus__n___skal_det_lekes.html</guid>
                <pubDate>Wed, 18 Aug 2010 13:30:00 +0200</pubDate>
                <description>
&lt;p&gt;Jeg kjøpte nettopp to
&lt;a href=&quot;http://www.spykee-robot.com/&quot;&gt;Spykee&lt;/a&gt;-roboter, for test og
leking.  Kjøpte to da det var så billige, og gir meg mulighet til å
eksperimentere uten å være veldig redd for å ødelegge alt ved å bytte
ut firmware og slikt.  Oppdaget at lekebutikken på Bryn senter hadde
en liten stabel på lager som de ikke hadde klart å selge ut etter
fjorårets juleinnkjøp, og var villig til å selge for en femtedel av
vanlig pris.  Jeg, Ronny og Jarle har skaffet oss restbeholdningen, og
det blir morsomt å se hva vi får ut av dette.&lt;/p&gt;

&lt;p&gt;Roboten har belter styrt av to motorer, kamera, høytaler, mikrofon
og wifi-tilkobling.  Det hele styrt av en GPL-lisensiert databoks som
jeg mistenker kjører linux.  Firmware-kildekoden ble visst publisert i
mai.  Eneste utfordringen er at kontroller-programvaren kun finnes til
Windows, men det må en kunne jobbe seg rundt når vi har kildekoden til
firmwaren. :)&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;&lt;a href=&quot;http://en.wikipedia.org/wiki/Spykee&quot;&gt;Wikipedia-oppføring&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=http://www.spykeeworld.com/spykee/US/freeSoftware.html&quot;&gt;Nedlasting av firmware-kilden&lt;/a&gt;&lt;/li&gt;
&lt;li&gt;&lt;a href=&quot;http://wiki.nuug.no/grupper/robot&quot;&gt;prosjektwiki hos NUUG&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;
</description>
        </item>
        
        <item>
                <title>Rob Weir: How to Crush Dissent</title>
                <link>http://people.skolelinux.org/pere/blog/Rob_Weir__How_to_Crush_Dissent.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Rob_Weir__How_to_Crush_Dissent.html</guid>
                <pubDate>Sun, 15 Aug 2010 22:20:00 +0200</pubDate>
                <description>
&lt;p&gt;I found the notes from Rob Weir on
&lt;a href=&quot;http://feedproxy.google.com/~r/robweir/antic-atom/~3/VGb23-kta8c/how-to-crush-dissent.html&quot;&gt;how
to crush dissent&lt;/a&gt; matching my own thoughts on the matter quite
well.  Highly recommended for those wondering which road our society
should go down.  In my view we have been heading the wrong way for a
long time.&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>No hardcoded config on Debian Edu clients</title>
                <link>http://people.skolelinux.org/pere/blog/No_hardcoded_config_on_Debian_Edu_clients.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/No_hardcoded_config_on_Debian_Edu_clients.html</guid>
                <pubDate>Mon, 9 Aug 2010 20:15:00 +0200</pubDate>
                <description>
&lt;p&gt;As reported earlier, the last few days I have looked at how Debian
Edu clients are configured, and tried to get rid of all hardcoded
configuration settings on the clients.  I believe the work to be
mostly done, and the clients seem to work just fine with dynamically
generated configuration.&lt;/p&gt;

&lt;p&gt;What is the point, you might ask?  The point is to allow a Debian
Edu desktop to integrate into an existing network infrastructure
without any manual configuration.&lt;/p&gt;

&lt;p&gt;This is what happens when installing a Debian Edu client here at
the University of Oslo using PXE.  With the PXE installation, I am
asked for language (Norwegian Bokmål), locality (Norway) and keyboard
layout (no-latin1), Debian Edu profile (Roaming Workstation), if I
accept to reformat the hard drive (yes), if I want to submit info to
popcon.debian.org (no) and root password (secret).  After answering
these questions, the installer goes ahead and does its thing, and
after around 50 minutes it is done.  I press enter to finish the
installation, and the machine reboots into KDE.  When the machine is
ready and kdm asks for login information, I enter my university
username and password, am told by kdm that a local home directory has
been created and that I must log in again, and finally log in with the
same username and password to the KDE 4.4 desktop.  At no point during
this process did it ask for university specific settings, and all the
required configuration was dynamically detected using information
fetched via DHCP and DNS.  The roaming workstation is now ready for
use.&lt;/p&gt;

&lt;p&gt;How was this done, you might wonder?  First of all, here is the
list of things that need to be configured on the client to get it
working properly out of the box:&lt;/p&gt;

&lt;ul&gt;
&lt;li&gt;IP address/netmask and DNS server.&lt;/li&gt;
&lt;li&gt;Web proxy URL.&lt;/li&gt;
&lt;li&gt;LDAP server for NSS directory information (user, group, etc).&lt;/li&gt;
&lt;li&gt;Kerberos server for PAM password checking.&lt;/li&gt;
&lt;li&gt;SMB mount point to access the network home directory. (*)&lt;/li&gt;
&lt;li&gt;Central syslog server to send syslog messages to. (*)&lt;/li&gt;
&lt;li&gt;Sitesummary collector URL to submit info to central server. (*)&lt;/li&gt;
&lt;/ul&gt;

&lt;p&gt;(Hm, did I forget anything?  Let me knew if I did.)&lt;/p&gt;

&lt;p&gt;The points marked (*) are not required to be able to use the
machine, but needed to provide central storage and allowing system
administrators to track their machines.  Since yesterday, everything
but the sitesummary collector URL is dynamically discovered at boot
and installation time in the svn version of Debian Edu.&lt;/p&gt;

&lt;p&gt;The IP and DNS setup is fetched during boot using DHCP as usual.
When a DHCP update arrives, the proxy setup is updated by looking for
http://wpat/wpad.dat and using the content of this WPAD file to
configure the http and ftp proxy in /etc/environment and
/etc/apt/apt.conf.  I decided to update the proxy setup using a DHCP
hook to ensure that the client stops using the Debian Edu proxy when
it is moved outside the Debian Edu network, and instead uses any local
proxy present on the new network when it moves around.&lt;/p&gt;

&lt;p&gt;The DNS names of the LDAP, Kerberos and syslog server and related
configuration are generated using DNS information at boot.  First the
installer looks for a host named ldap in the current DNS domain.  If
not found, it looks for _ldap._tcp SRV records in DNS instead.  If an
LDAP server is found, its root DSE entry is requested and the
attributes namingContexts and defaultNamingContext are used to
determine which LDAP base to use for NSS.  If there are several
namingContexts attibutes and the defaultNamingContext is present, that
LDAP subtree is used as the base.  If defaultNamingContext is missing,
the subtrees listed as namingContexts are searched in sequence for any
object with class posixAccount or posixGroup, and the first one with
such an object is used as the LDAP base.  For Kerberos, a similar
search is done by first looking for a host named kerberos, and then
for the _kerberos._tcp SRV record.  I&#39;ve been unable to find a way to
look up the Kerberos realm, so for this the upper case string of the
current DNS domain is used.&lt;/p&gt;

&lt;p&gt;For the syslog server, the hosts syslog and loghost are searched
for, and the _syslog._udp SRV record is consulted if no such host is
found.  This algorithm works for both Debian Edu and the University of
Oslo.  A similar strategy would work for locating the sitesummary
server, but have not been implemented yet.  I decided to fetch and
save these settings during installation, to make sure moving to a
different network does not change the set of users being allowed to
log in nor the passwords required to log in.  Usernames and passwords
will be cached by sssd when the user logs in on the Debian Edu
network, and will not change as the laptop move around.  For a
non-roaming machine, there is no caching, but given that it is
supposed to stay in place it should not matter much.  Perhaps we
should switch those to use sssd too?&lt;/p&gt;

&lt;p&gt;The user&#39;s SMB mount point for the network home directory is
located when the user logs in for the first time.  The LDAP server is
consulted to look for the user&#39;s LDAP object and the sambaHomePath
attribute is used if found.  If it isn&#39;t found, the home directory
path fetched from NSS is used instead.  Assuming the path is of the
form /site/server/directory/username, the second part is looked up in
DNS and used to generate a SMB URL of the form
smb://server.domain/username.  This algorithm works for both Debian
edu and the University of Oslo.  Perhaps there are better attributes
to use or a better algorithm that works for more sites, but this will
do for now. :)&lt;/p&gt;

&lt;p&gt;This work should make it easier to integrate the Debian Edu clients
into any LDAP/Kerberos infrastructure, and make the current setup even
more flexible than before.  I suspect it will also work for thin
client servers, allowing one to easily set up LTSP and hook it into a
existing network infrastructure, but I have not had time to test this
yet.&lt;/p&gt;

&lt;p&gt;If you want to help out with implementing these things for Debian
Edu, please contact us on debian-edu@lists.debian.org.&lt;/p&gt;

&lt;p&gt;Update 2010-08-09: Simon Farnsworth gave me a heads-up on how to
detect Kerberos realm from DNS, by looking for _kerberos TXT entries
before falling back to the upper case DNS domain name.  Will have to
implement it for Debian Edu. :)&lt;/p&gt;
</description>
        </item>
        
        <item>
                <title>Testing if a file system can be used for home directories...</title>
                <link>http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html</link>
                <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Testing_if_a_file_system_can_be_used_for_home_directories___.html</guid>
                <pubDate>Sun, 8 Aug 2010 21:20:00 +0200</pubDate>
                <description>
&lt;p&gt;A few years ago, I was involved in a project planning to use
Windows file servers as home directory servers for Debian
Edu/Skolelinux machines.  This was thought to be no problem, as the
access would be through the SMB network file system protocol, and we
knew other sites used SMB with unix and samba as the file server to
mount home directories without any problems.  But, after months of
struggling, we had to conclude that our goal was impossible.&lt;/p&gt;

&lt;p&gt;The reason is simply that while SMB can be used for home
directories when the file server is Samba running on Unix, this only
work because of Samba have some extensions and the fact that the
underlying file system is a unix file system.  When using a Windows
file server, the underlying file system do not have POSIX semantics,
and several programs will fail if the users home directory where they
want to store their configuration lack POSIX semantics.&lt;/p&gt;

&lt;p&gt;As part of this work, I wrote a small C program I want to share
with you all, to replicate a few of the problematic applications (like
OpenOffice.org and GCompris) and see if the file system was working as
it should.  If you find yourself in spooky file system land, it might
help you find your way out again.  This is the fs-test.c source:&lt;/p&gt;

&lt;pre&gt;
/*
 * Some tests to check the file system sematics.  Used to verify that
 * CIFS from a windows server do not work properly as a linux home
 * directory.
 * License: GPL v2 or later
 * 
 * needs libsqlite3-dev and build-essential installed
 * compile with: gcc -Wall -lsqlite3 -DTEST_SQLITE fs-test.c -o fs-test
*/

#define _FILE_OFFSET_BITS 64
#define _LARGEFILE_SOURCE 1
#define _LARGEFILE64_SOURCE 1

#define _GNU_SOURCE /* for asprintf() */

#include &amp;lt;errno.h&gt;
#include &amp;lt;fcntl.h&gt;
#include &amp;lt;stdio.h&gt;
#include &amp;lt;string.h&gt;
#include &amp;lt;stdlib.h&gt;
#include &amp;lt;sys/file.h&gt;
#include &amp;lt;sys/stat.h&gt;
#include &amp;lt;sys/types.h&gt;
#include &amp;lt;unistd.h&gt;

#ifdef TEST_SQLITE
/*
 * Test sqlite open, as done by gcompris require the libsqlite3-dev
 * package and linking with -lsqlite3.  A more low level test is
 * below.
 * See also &amp;lt;URL: http://www.sqlite.org./faq.html#q5 &gt;.
 */
#include &amp;lt;sqlite3.h&gt;
#define CREATE_TABLE_USERS                                              \
  &quot;CREATE TABLE users (user_id INT UNIQUE, login TEXT, lastname TEXT, firstname TEXT, birthdate TEXT, class_id INT ); &quot;
int test_sqlite_open(void) {
  char *zErrMsg;
  char *name = &quot;testsqlite.db&quot;;
  sqlite3 *db=NULL;
  unlink(name);
  int rc = sqlite3_open(name, &amp;db);
  if( rc ){
    printf(&quot;error: sqlite open of %s failed: %s\n&quot;, name, sqlite3_errmsg(db));
    sqlite3_close(db);
    return -1;
  }

  /* create tables */
  rc = sqlite3_exec(db,CREATE_TABLE_USERS, NULL,  0, &amp;zErrMsg);
  if( rc != SQLITE_OK ){
    printf(&quot;error: sqlite table create failed: %s\n&quot;, zErrMsg);
    sqlite3_close(db);
    return -1;
  }
  printf(&quot;info: sqlite worked\n&quot;);
  sqlite3_close(db);
  return 0;
}
#endif /* TEST_SQLITE */

/*
 * Demonstrate locking issue found in gcompris using sqlite3.  This
 * work with ext3, but not with cifs server on Windows 2003.  This is
 * done in the sqlite3 library.
 * See also
 * &amp;lt;URL:http://www.cygwin.com/ml/cygwin/2001-08/msg00854.html&gt; and the
 * POSIX specification
 * &amp;lt;URL:http://www.opengroup.org/onlinepubs/009695399/functions/fcntl.html&gt;.
 */
int test_gcompris_locking(void) {
  struct flock fl;
  char *name = &quot;testsqlite.db&quot;;
  unlink(name);
  int fd = open(name, O_RDWR|O_CREAT|O_LARGEFILE, 0644);
  printf(&quot;info: testing fcntl locking\n&quot;);

  fl.l_whence = SEEK_SET;
  fl.l_pid    = getpid();
  printf(&quot;  Read-locking 1 byte from 1073741824&quot;);
  fl.l_start  = 1073741824;
  fl.l_len    = 1;
  fl.l_type   = F_RDLCK;
  if (0 != fcntl(fd, F_SETLK, &amp;fl) ) printf(&quot; - error!\n&quot;); else printf(&quot;\n&quot;);

  printf(&quot;  Read-locking 510 byte from 1073741826&quot;);
  fl.l_start  = 1073741826;
  fl.l_len    = 510;
  fl.l_type   = F_RDLCK;
  if (0 != fcntl(fd, F_SETLK, &amp;fl) ) printf(&quot; - error!\n&quot;); else printf(&quot;\n&quot;);

  printf(&quot;  Unlocking 1 byte from 1073741824&quot;);
  fl.l_start  = 1073741824;
  fl.l_len    = 1;
  fl.l_type   = F_UNLCK;
  if (0 != fcntl(fd, F_SETLK, &amp;fl) ) printf(&quot; - error!\n&quot;); else printf(&quot;\n&quot;);

  printf(&quot;  Write-locking 1 byte from 1073741824&quot;);
  fl.l_start  = 1073741824;
  fl.l_len    = 1;
  fl.l_type   = F_WRLCK;
  if (0 != fcntl(fd, F_SETLK, &amp;fl) ) printf(&quot; - error!\n&quot;); else printf(&quot;\n&quot;);

  printf(&quot;  Write-locking 510 byte from 1073741826&quot;);
  fl.l_start  = 1073741826;
  fl.l_len    = 510;
  if (0 != fcntl(fd, F_SETLK, &amp;fl) ) printf(&quot; - error!\n&quot;); else printf(&quot;\n&quot;);

  printf(&quot;  Unlocking 2 byte from 1073741824&quot;);
  fl.l_start  = 1073741824;
  fl.l_len    = 2;
  fl.l_type   = F_UNLCK;
  if (0 != fcntl(fd, F_SETLK, &amp;fl) ) printf(&quot; - error!\n&quot;); else printf(&quot;\n&quot;);

  close(fd);
  return 0;
}

/*
 * Test if permissions of freshly created directories allow entries
 * below them.  This was a problem with OpenOffice.org and gcompris.
 * Mounting with option &#39;sync&#39; seem to solve this problem while
 * slowing down file operations.
 */
int test_subdirectory_creation(void) {
#define LEVELS 5
  char *path = strdup(&quot;test&quot;);
  char *dirs[LEVELS];
  int level;
  printf(&quot;info: testing subdirectory creation\n&quot;);
  for (level = 0; level &amp;lt; LEVELS; level++) {
    char *newpath = NULL;
    if (-1 == mkdir(path, 0777)) {
      printf(&quot;  error: Unable to create directory &#39;%s&#39;: %s\n&quot;,
             path, strerror(errno));
      break;
    }
    asprintf(&amp;newpath, &quot;%s/%s&quot;, path, &quot;test&quot;);
    free(path);
    path = newpath;
  }
  return 0;
}

/*
 * Test if symlinks can be created.  This was a problem detected with
 * KDE.
 */
int test_symlinks(void) {
  printf(&quot;info: testing symlink creation\n&quot;);
  unlink(&quot;symlink&quot;);
  if (-1 == symlink(&quot;file&quot;, &quot;symlink&quot;))
    printf(&quot;  error: Unable to create symlink\n&quot;);
  return 0;
}

int main(int argc, char **argv) {
  printf(&quot;Testing POSIX/Unix sematics on file system\n&quot;);
  test_symlinks();
  test_subdirectory_creation();
#ifdef TEST_SQLITE
  test_sqlite_open();
#endif /* TEST_SQLITE */
  test_gcompris_locking();
  return 0;
}
&lt;/pre&gt;

&lt;p&gt;When everything is working, it should print something like
this:&lt;/p&gt;

&lt;pre&gt;
Testing POSIX/Unix sematics on file system
info: testing symlink creation
info: testing subdirectory creation
info: sqlite worked
info: testing fcntl locking
  Read-locking 1 byte from 1073741824
  Read-locking 510 byte from 1073741826
  Unlocking 1 byte from 1073741824
  Write-locking 1 byte from 1073741824
  Write-locking 510 byte from 1073741826
  Unlocking 2 byte from 1073741824
&lt;/pre&gt;

&lt;p&gt;I do not remember the exact details of the problems we saw, but one
of them was with locking, where if I remember correctly, POSIX allow a
read-only lock to be upgraded to a read-write lock without unlocking
the read-only lock (while Windows do not).  Another was a bug in the
CIFS/SMB client implementation in the Linux kernel where directory
meta information would be wrong for a fraction of a second, making
OpenOffice.org fail to create its deep directory tree because it was
not allowed to create files in its freshly created directory.&lt;/p&gt;

&lt;p&gt;Anyway, here is a nice tool for your tool box, might you never need
it. :)&lt;/p&gt;

&lt;p&gt;Update 2010-08-27: Michael Gebetsroither report that he found the
script so useful that he created a GIT repository and stored it in
&lt;a href=&quot;http://github.com/gebi/fs-test&quot;&gt;http://github.com/gebi/fs-test&lt;/a&gt;.&lt;/p&gt;
</description>
        </item>
        
        </channel>
</rss>