Few things are more frustrating than an interrupted system upgrade. When Ubuntu 8.10 was being upgraded to 9.04 on my machine, someone pulled the plug (literally). The result? A system that wouldn't boot properly - X errors, login screen issues, and general instability. While my /home data was safe, I needed to recover the system without a complete reinstall.

Before attempting any fixes, it's crucial to understand what state the package manager is in:

sudo dpkg --audit
sudo apt-get check

These commands will show you any broken or half-configured packages from the interrupted upgrade.

After several attempts, this sequence proved most effective for repairing the installation:

sudo dpkg --configure -a
sudo apt-get update
sudo dpkg --configure -a --abort-after=99999
sudo apt-get dist-upgrade
sudo apt-get -f install
sudo apt-get dist-upgrade

Let's break down what each command does:

• dpkg --configure -a: Attempts to configure all unpacked but unconfigured packages
• The --abort-after=99999 flag prevents premature termination during complex configurations
• apt-get -f install fixes broken dependencies

If the system remains unbootable, you can still extract important configuration data:

# List all installed packages
dpkg --get-selections > installed_packages.list

# Backup important configs
sudo tar -cvzf etc_backup.tar.gz /etc/
sudo tar -cvzf usr_share_backup.tar.gz /usr/share/

Some lessons learned:

1. Always use screen or tmux for long upgrade processes
2. Consider upgrading via the alternate installer rather than the GUI
3. Maintain regular backups with deja-dup or similar tools

If package repair fails, you can attempt an overinstall:

# Boot from 9.04 CD
# Choose "Install Ubuntu" but select "Manual" partitioning
# Mount existing partitions without formatting
# The installer should preserve your configs while fixing system files

Remember that while /home is preserved by default, system configurations in /etc might get overwritten during this process.

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When a distribution upgrade gets interrupted (especially between major versions like Ubuntu 8.10 to 9.04), you'll typically see:

• X server failing to start with cryptic errors
• Login screen appearing but rejecting credentials
• Broken package dependencies in the apt system

Boot into recovery mode (select it from GRUB) and run these essential commands:

sudo dpkg --configure -a
sudo apt-get update
sudo apt-get -f install
sudo apt-get dist-upgrade

The --abort-after flag can help with stuck configurations:

sudo dpkg --configure -a --abort-after=99999

For stubborn cases, manually verify package states:

sudo dpkg --audit
sudo dpkg --get-selections | grep -v deinstall
sudo apt-cache policy <problem-package>

After fixing packages, rebuild X configuration:

sudo dpkg-reconfigure xserver-xorg
sudo service gdm restart

For NVIDIA/ATI drivers:

sudo apt-get install --reinstall nvidia-current
sudo nvidia-xconfig

If all else fails, consider a fresh install while preserving:

/home
/etc (backup first!)
/var/lib/dpkg/status (contains installed package list)

To document installed packages before reinstall:

dpkg --get-selections > package_list.txt
sudo tar czf etc_backup.tar.gz /etc/

For production systems, consider using LTS releases or Debian stable with:

sudo apt-get install debian-goodies
sudo deborphan | xargs sudo apt-get -y purge