Upgrading from 25.10 to 26.04 LTS

lsb_release -a
# Should display Ubuntu 25.10
 
cat /etc/os-release

sudo apt update
sudo apt upgrade -y
sudo apt dist-upgrade -y
sudo apt autoremove -y

sudo apt install update-manager-core -y

cat /etc/update-manager/release-upgrades

# If it's normal, you can upgrade directly to the next version
# If it's lts, you need to change it to normal (since 25.10 is not an LTS)
sudo sed -i 's/^Prompt=.*/Prompt=normal/' /etc/update-manager/release-upgrades

# Back up personal data
rsync -avz /home/ /backup/home/
 
# Back up system configuration
sudo tar czf /backup/etc-backup.tar.gz /etc/
 
# Export installed package list
dpkg --get-selections > ~/packages-25.10.txt
 
# Record current kernel
uname -r > ~/kernel-25.10.txt

# List third-party sources
ls /etc/apt/sources.list.d/
 
# Interim version PPAs may not have packages for 26.04
# It is recommended to disable them in advance
for f in /etc/apt/sources.list.d/*.list; do
    sudo mv "$f" "$f.bak"
done
 
# For .sources format files
for f in /etc/apt/sources.list.d/*.sources; do
    [ -f "$f" ] && sudo mv "$f" "$f.bak"
done

# It is recommended to use screen to prevent connection interruption
screen -S upgrade
 
# Start the upgrade
sudo do-release-upgrade

# Allow the backup SSH port
sudo ufw allow 1022/tcp
 
# Run in screen/tmux
screen -S upgrade
sudo do-release-upgrade
 
# If disconnected, reconnect
screen -r upgrade
# Or connect via the backup port
ssh -p 1022 user@server-ip

# Use the -d parameter (development channel)
sudo do-release-upgrade -d
 
# Check network
curl -s https://changelogs.ubuntu.com/meta-release | grep -A5 "26.04"

lsb_release -a
# Distributor ID: Ubuntu
# Description:    Ubuntu 26.04 LTS
# Release:        26.04
# Codename:       resolute
 
uname -r
cat /etc/os-release

sudo sed -i 's/^Prompt=.*/Prompt=lts/' /etc/update-manager/release-upgrades
 
# Verify
grep Prompt /etc/update-manager/release-upgrades
# Should output: Prompt=lts

sudo apt update
sudo apt upgrade -y
sudo apt autoremove --purge -y
sudo apt clean

# Check for broken packages
sudo dpkg --audit
sudo apt --fix-broken install
 
# Check for failed services
systemctl --failed
 
# Check disk space
df -h
 
# Check logs for errors
sudo journalctl -p err --since "1 hour ago"

# View disabled sources
ls /etc/apt/sources.list.d/*.distUpgrade 2>/dev/null
ls /etc/apt/sources.list.d/*.bak 2>/dev/null
 
# After confirming third-party sources support 26.04, restore them one by one
# Note: The version codename may need to be updated from questing (25.10) to resolute (26.04)

# View installed kernels
dpkg --list | grep linux-image
 
# Remove old kernels
sudo apt autoremove --purge
 
# If you need to manually remove a specific old kernel
sudo apt remove --purge linux-image-x.x.x-xx-generic