Bug#1092123: debian-edu-config: DNS stops working on LTSP clients after unusual mksquashfs process terminates

Package: debian-edu-config
Version: 2.12.44~deb12u1
Severity: important

Dear Maintainer,

I made a default debian-edu bookworm install on single server with two 
network interfaces.
Roles: main server, ltsp server, workstation
Desktop: Default/xfce
Network settings: installer defaults
Configured single 'student' user jdoe in addition to main/first user.

Proceeded to test LTSP network booting on multiple clients.

LTSP boot proceeds normally, but after login a mksquashfs process using
nearly all CPU capacity starts after about 1 minute.
Sections of the rootfs are mounted under /tmp/randomnamexx.
Client remains usable if slower, with 2G RAM usage.
A squashfs image is being created in /srv/ltsp/images/x86_64.img.tmp

This process eventually creates a 5.5GB file, /srv/ltsp/images/x86_64.img
and then terminates.
At this point, DNS name resolution stops working. 
/etc/resolv.conf becomes empty (checked using 'watch /etc/resolv.conf)
Web browsing no longer works as a result, and the LDAP server can't be
accessed, so if I do a 'logout' without reboot, further login attempts fail.
The resolvconf.service is still running but can't be restarted due to
lack of privileged access.

I could not understand the purpose of creating the squashfs image on the 
client.

So I decided to re-create the ltsp image on the server, with:

sudo debian-edu-ltsp-install --diskless_workstation yes

After the image is regenerated and client rebooted, the mysterious 
mksquashfs process no longer runs after LTSP client logon, and DNS etc
function normally.

I am guessing there is an issue with the LTSP image creation in the original installer. Checked by reinstall from scratch, problem reappears.
As I  am new to the rather complex setup of debian-edu, I can't be more specific than that, sorry.

Chris Billington

-- System Information:
Debian Release: 12.8
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.1.0-28-amd64 (SMP w/8 CPU threads; PREEMPT)
Kernel taint flags: TAINT_FIRMWARE_WORKAROUND
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB.UTF-8
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages debian-edu-config depends on:
ii  adduser                                    3.134
ii  bind9-host                                 1:9.18.28-1~deb12u2
ii  cfengine3                                  3.21.0-2
ii  dconf-gsettings-backend [gsettings-backen  0.40.0-4
    d]
ii  debconf [debconf-2.0]                      1.5.82
ii  debconf-utils                              1.5.82
ii  debian-edu-artwork                         2.12.4-1~deb12u1
ii  e2fsprogs                                  1.47.0-2
ii  education-tasks                            2.12.15
ii  fping                                      5.1-1
ii  gnutls-bin                                 3.7.9-2+deb12u3
ii  iptables                                   1.8.9-2
ii  isenkram-cli                               0.51
ii  ldap-utils                                 2.5.13+dfsg-5
ii  libconfig-inifiles-perl                    3.000003-2
ii  libfilesys-df-perl                         0.92-7+b1
ii  libglib2.0-bin                             2.74.6-2+deb12u4
ii  libhtml-fromtext-perl                      2.07-3
ii  libio-socket-ssl-perl                      2.081-2
ii  libnet-ldap-perl                           1:0.6800+dfsg-1
ii  libnet-netmask-perl                        2.0002-2
ii  libnss3-tools                              2:3.87.1-1+deb12u1
ii  libpacparser1                              1.3.6-1.4
ii  libpam-python                              1.1.0~git20220701.1d4e111-0.3+b1
ii  libproxy1-plugin-kconfig                   0.4.18-1.2
ii  libproxy1-plugin-networkmanager            0.4.18-1.2
ii  libproxy1-plugin-webkit                    0.4.18-1.2
ii  libsitesummary-perl                        0.1.56~deb12u2
ii  libterm-readkey-perl                       2.38-2+b1
ii  libtext-unaccent-perl                      1.08-1.3+b7
ii  lockfile-progs                             0.1.19
ii  lsb-release                                12.0-1
ii  media-types                                10.0.0
ii  net-tools                                  2.10-0.1
ii  ng-utils                                   1.1-1
ii  openssl                                    3.0.15-1~deb12u1
ii  patch                                      2.7.6-7
ii  python3                                    3.11.2-1+b1
ii  python3-notify2                            0.3-5
ii  ssl-cert                                   1.1.2
ii  swaks                                      20201014.0-2
ii  tftp-hpa                                   5.2+20150808-1.4
ii  uuid                                       1.6.2-1.5+b11
ii  wget                                       1.21.3-1+b2

Versions of packages debian-edu-config recommends:
ii  binutils       2.40-2
ii  libnotify-bin  0.8.1-1
ii  lsof           4.95.0-1
ii  memtest86+     6.10-4
ii  resolvconf     1.91+nmu1
ii  syslinux       3:6.04~git20190206.bf6db5b4+dfsg1-3+b1

debian-edu-config suggests no packages.

-- Configuration Files:
/etc/bind/db.0.168.192.in-addr.arpa. [Errno 13] Permission denied: '/etc/bind/db.0.168.192.in-addr.arpa.'
/etc/bind/db.1.168.192.in-addr.arpa. [Errno 13] Permission denied: '/etc/bind/db.1.168.192.in-addr.arpa.'
/etc/bind/db.10.in-addr.arpa. [Errno 13] Permission denied: '/etc/bind/db.10.in-addr.arpa.'
/etc/bind/db.intern [Errno 13] Permission denied: '/etc/bind/db.intern'
/etc/bind/db.subnet00.intern [Errno 13] Permission denied: '/etc/bind/db.subnet00.intern'
/etc/bind/db.subnet01.intern [Errno 13] Permission denied: '/etc/bind/db.subnet01.intern'
/etc/sssd/sssd-debian-edu.conf [Errno 13] Permission denied: '/etc/sssd/sssd-debian-edu.conf'

-- debconf information:
  debian-edu-config/kdc-password-empty:
* debian-edu-config/first-user-name: chris
  debian-edu-config/ldap-password-mismatch:
  debian-edu-config/ldap-password-empty:
  debian-edu-config/kdc-password-mismatch:
* debian-edu-config/first-user-fullname: Chris Billington
* debian-edu-config/update-hostname: false
* debian-edu-config/enable-nat: true