Debian has multiple releases at different maturity levels: Stable, Testing, and Unstable.

• Stable (current): thoroughly tested, conservative updates, security fixes for ~5 years
• Testing (next): receives new package versions daily, tested less, becomes stable every 2 years
• Unstable/Sid: bleeding-edge, permanent, breaks frequently, for developers only
• Old Stable: previous stable release, gets security updates for ~1 year after new stable

Current (as of 2024):

• Stable: Bookworm (12)
• Testing: Trixie (13)
• Unstable: Sid (permanent)

cat /etc/os-release
cat /etc/debian_version
lsb_release -a

To upgrade from Stable to Testing:

sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
sudo sed -i 's/bookworm/trixie/g' /etc/apt/sources.list
sudo apt update
sudo apt full-upgrade

Then reboot:

sudo reboot

• Stable → Testing: possible, expect breakage
• Testing → Unstable: possible, expect major breakage
• Never downgrade: once upgraded, can only upgrade further

Major releases every ~2 years. Typical cycle:

1. Testing — development, ~1 year
2. Freeze — bug fixes only, feature freeze
3. Release — becomes new Stable

• Stable: Long-term support, frequent security updates
• Testing: Less frequent security updates
• Unstable: No guarantees, for developers

Production servers should run Stable. Never Unstable.

See Debian release info:

https://wiki.debian.org/DebianReleases

Release dates are announced well in advance but are “when ready,” not fixed.

Old to new:

• Wheezy (7, EOL)
• Jessie (8, EOL)
• Stretch (9, EOL)
• Buster (10, old-stable)
• Bullseye (11, old-stable)
• Bookworm (12, stable)
• Trixie (13, testing)
• Sid (unstable)

• Use Stable for production
• Use Testing only if you need newer packages
• Use Unstable only for development
• Run apt full-upgrade before critical work (never during)
• Backup before major upgrades
• Read release notes before upgrading