Reproducible Live images

This page tracks the progress on creating reproducible live images, using live-build from DebianLive

Contents

Reproducible Live images

Configuration

The computer that is used for generating live images:

Debian/sid
apt-cacher-ng running on http://localhost:3142
The most recent checkout of the git repository of live-build (https://salsa.debian.org/live-team/live-build)
An additional line in /etc/apt-cacher-ng/acnf.conf: VfilePatternEx: /project/trace/ftp-master\.debian\.org$

Snapshot

In order to get a more reproducible image, a snapshot is used. At the time of focusing on Bullseye, the timestamp 20210101T083123Z (1609489883) was chosen.

Considerations

Building an image must be fast, because a lot of rebuilds will be required -> use /dev/shm
Reduce network traffic, don't download the same files over-and-over -> use apt-cacher-ng
While looking for (non-)reproducibility, the command line option --parent-mirror-binary is used. Official live images should not use this command line option (and will therefore use deb.debian.org in /var/lib/apt/lists)

Preparing the build environment

All command lines must be executed as root.

export LIVE_BUILD=/home/roland/git/live-build
export SOURCE_DATE_EPOCH=1609489883
cd /dev/shm
mount /dev/shm -odev,exec,remount
mkdir live
cd live

Building images for Debian Buster

Timestamp: 20210210T031935Z

export LIVE_BUILD=/home/roland/git/live-build
export SOURCE_DATE_EPOCH=1612927175
cd /dev/shm
mount /dev/shm -odev,exec,remount
mkdir live
cd live

Mini, with live installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210210T031935Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/202102101031935Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution buster --debian-installer live --cache-packages false

Building images for Debian Bullseye

Image	Installer	Reproducible	Notes
mini	none	yes
mini	live/text	yes	1
mini	live/gui	yes	1
mini	daily	yes	2
standard	none	yes	3, 4
standard	live	yes	1, 3, 4
GNOME	none	yes	3, 4, 5
GNOME	live	yes	1, 3, 4, 5
KDE	live	yes	1, 3, 4, 5

Note 1: The installer fails, because the installer uses an older kernel. Use the daily installer instead, until the installer is updated
Note 2: Reproducibility tested by setting SOURCE_DATE_EPOCH during the first lb build and running the second build a few minutes after finishing the first build
Note 3: fontconfig uses random GUIDs, which can be circumvented. Hooks 1000 and 1001 implement a work around
Note 4: mdadm adds a timestamp to the configuration file, which can be circumvented. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982607. Until mdadm is updated, hook 1002 implements a work around
Note 5: During update-initramfs, the hook of plymouth adds fonts to the initrds. Hooks 1000 and 1003 implement a work around

Command lines

Mini, without installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer none --cache-packages false

Mini, with live/text-only installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer live --cache-packages false --debian-installer-gui false

Mini, with latest installer

unset SOURCE_DATE_EPOCH
lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/deb.debian.org/debian --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --distribution bullseye --debian-installer live --cache-packages false --debian-installer-gui false --parent-debian-installer-distribution daily
# When doing comparisons, use the following line for the first run:
#   export SOURCE_DATE_EPOCH=`date +%s`; lb build

Mini, with live installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer live --cache-packages false

Standard, without installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer none --cache-packages false
echo "live-task-standard" > config/package-lists/desktop.list.chroot

Standard, with live installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer live --cache-packages false
echo "live-task-standard" > config/package-lists/desktop.list.chroot

GNOME desktop, without installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer none --cache-packages false
echo "live-task-gnome" > config/package-lists/desktop.list.chroot

GNOME desktop, with live installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer live --cache-packages false
echo "live-task-gnome" > config/package-lists/desktop.list.chroot

KDE desktop, with live installer

lb config --apt-http-proxy http://localhost:3142 --parent-mirror-bootstrap http://localhost:3142/snapshot.debian.org/archive/debian/20210101T083123Z --parent-mirror-binary http://snapshot.debian.org/archive/debian/20210101T083123Z --security false --updates false --apt-options "--yes -o Acquire::Check-Valid-Until=false" --distribution bullseye --debian-installer live --cache-packages false
echo "live-task-kde" > config/package-lists/desktop.list.chroot

The hook scripts that should be applied after any of the command lines above, to fix non-reproducible packages

cat > config/hooks/normal/1000-reproducible-function-uuid_generate_random.hook.chroot << EOF
#!/bin/sh
set -e

# util-linux creates random UUIDs when uuid_generate_random is called
# Use LD_PRELOAD to replace uuid_generate_random with a less random version

# Don't run if gcc is not installed
if [ ! -e /usr/bin/cc ];
then
  exit 0
fi

cat > unrandomize_uuid_generate_random.c << END_OF_SOURCE
#include <stdlib.h>
#include <stdio.h>

#define SEQUENCE_FILENAME "/var/cache/unrandomize_uuid_generate_random.sequence_number"

/* https://tools.ietf.org/html/rfc4122 */
typedef unsigned char uuid_t[16];

/* Our pseudo-random version */
void uuid_generate_random(uuid_t out)
{
  /* Nil UUID */
  for (int i=0;i<16;i++) {
    out[i] = 0x00;
  }
  out[6]=0x40; /* UUID version 4 means randomly generated */
  out[8]=0x80; /* bit7=1,bit6=0 */

  /* The file doesn't need to exist yet */
  FILE *f = fopen(SEQUENCE_FILENAME, "rb");
  if (f) {
    fread(out+12, 4, 1, f);
    fclose(f);
  }
  /* Use the next number. Endianness is not important */
  (*(unsigned long*)(out+12))++;

  unsigned long long epoch;
  /* Use SOURCE_DATE_EPOCH when provided */
  char *date = getenv("SOURCE_DATE_EPOCH");
  if (date) {
    epoch = strtoll(date, NULL, 10);
  } else {
    epoch = 0ll;
  }
  out[0] = (epoch & 0xFF000000) >> 24;
  out[1] = (epoch & 0x00FF0000) >> 16;
  out[2] = (epoch & 0x0000FF00) >>  8;
  out[3] = (epoch & 0x000000FF);

  /* Write the sequence number */
  f = fopen(SEQUENCE_FILENAME, "wb");
  if (f) {
    fwrite(out+12, 4, 1, f);
    fclose(f);
  }
}
END_OF_SOURCE
/usr/bin/cc -shared -fPIC unrandomize_uuid_generate_random.c -Wall --pedantic -o /usr/lib/unrandomize_uuid_generate_random.so
rm -f unrandomize_uuid_generate_random.c
EOF
cat > config/hooks/normal/1001-reproducible-fontconfig.hook.chroot << EOF
#!/bin/sh
set -e

# fontconfig creates non-reproducible files with UUIDs
# See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=864082
#
# Because the UUIDs should not be deleted, the proposed work-around is:
# * Use LD_PRELOAD to replace uuid_generate_random with a less random version

# Don't run if fontconfig is not installed
if [ ! -e /usr/bin/fc-cache ];
then
  exit 0
fi

# Don't run if the LD_PRELOAD module is not compiled
if [ ! -e /usr/lib/unrandomize_uuid_generate_random.so ];
then
  exit 0
fi

LD_PRELOAD=/usr/lib/unrandomize_uuid_generate_random.so /usr/bin/fc-cache --force --really-force --system-only --verbose
EOF
cat > config/hooks/normal/1002-reproducible-mdadm.hook.chroot << EOF
#!/bin/sh
set -e

# mkconf of mdadm creates a file with a timestamp
# A bug report with patch is available at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982607
# This script duplicates that patch

# Don't run if mdadm is not installed
if [ ! -e /usr/share/mdadm/mkconf ];
then
  exit 0
fi

# If mkconf already contains references to SOURCE_DATE_EPOCH, there is no need to patch the file
if grep -q SOURCE_DATE_EPOCH /usr/share/mdadm/mkconf;
then
  exit 0
fi
sed -i -e '/# This configuration was auto-generated on/cif [ -z \$SOURCE_DATE_EPOCH ]; then\n  echo "# This configuration was auto-generated on \$(date -R) by mkconf"\nelse\n  echo "# This configuration was auto-generated on \$(date -R --utc -d@\$SOURCE_DATE_EPOCH) by mkconf"\nfi' /usr/share/mdadm/mkconf
EOF
cat > config/hooks/normal/1003-reproducible-plymouth.hook.chroot << EOF
#!/bin/sh
set -e

# The hook of plymouth in update-initramfs calls fc-cache

# Don't run if plymouth is not installed
if [ ! -e /usr/share/initramfs-tools/hooks/plymouth ];
then
  exit 0
fi

# Don't patch if the LD_PRELOAD module is not compiled
if [ ! -e /usr/lib/unrandomize_uuid_generate_random.so ];
then
  exit 0
fi

# If the hook already contains references to LD_PRELOAD, there is no need to patch the file
if grep -q LD_PRELOAD /usr/share/initramfs-tools/hooks/plymouth;
then
  exit 0
fi
sed -i -e 's|fc-cache -s|LD_PRELOAD=/usr/lib/unrandomize_uuid_generate_random.so fc-cache|' /usr/share/initramfs-tools/hooks/plymouth
EOF

Checking reproducibility

Ideally reprotest will be used to check reproducibility. For now, 2 images are built and then compared with diffoscope.

Using diffoscope

# 1) Prepare the build environment
# 2) Run the command line to create the configuration (see above)
lb build
mv live-image-amd64.hybrid.iso run01.iso
lb clean --purge
lb config
lb build
mv live-image-amd64.hybrid.iso run02.iso
diffoscope run01.iso run02.iso --html-dir html_run01_02

Using reprotest

reprotest requires full access on /tmp, so it must be remounted (when applicable)

# 1) Prepare the build environment
# 2) Run the command line to create the configuration (see above)
mount /tmp -odev,exec,suid,remount
reprotest  --variations=-all,+environment,+build_path,-kernel,+aslr,+num_cpus,+time,-user_group,-fileordering,-domain_host,+home,+locales,+exec_path,+timezone,-umask  "lb clean --purge&&lb config&&lb build" "*.iso"
# Disabled tests:
#  kernel        The variant with kernel 2.6 is too old for debootstrap
#  user_group    Live build only works for root, the variation needs a list
#  fileordering  Disorderfs needs to be mounted with dev,exec,suid
#  domain_host   Needs additional rights during debootstrap
#  umask         Some files get a different umask, further investigation is required

ReproducibleInstalls
LiveImages

Reproducible Live images

Configuration

Snapshot

Considerations

Preparing the build environment

Building images for Debian Buster

Building images for Debian Bullseye

Command lines

Checking reproducibility

Using diffoscope

Using reprotest

See also

ReproducibleInstallsLiveImages

Reproducible Live images

Configuration

Snapshot

Considerations

Preparing the build environment

Building images for Debian Buster

Building images for Debian Bullseye

Command lines

Checking reproducibility

Using diffoscope

Using reprotest

See also

ReproducibleInstalls
LiveImages