When working with Debian-based systems, APT (Advanced Package Tool) maintains metadata about package installation states. Each package is marked as either:

• Automatically installed: Installed as a dependency of another package
• Manually installed: Explicitly requested by the user

# Example output showing installation status
$ apt-mark showmanual | grep zlib1g-dev
zlib1g-dev

During development, you might explicitly install a package that was previously auto-installed as a dependency. After completing your task, you want to revert this status change to maintain system cleanliness.

The correct way to change the status is using the apt-mark command:

# Mark package as automatically installed
$ sudo apt-mark auto zlib1g-dev

# Verify the change
$ apt-mark showmanual | grep zlib1g-dev
[No output means success]

If you prefer aptitude's interactive interface:

$ sudo aptitude
> Search for zlib1g-dev
> Press 'M' to toggle manual/auto status
> 'q' to quit

These commands modify /var/lib/apt/extended_states, which stores the auto-installed status. While you could edit this file directly:

Package: zlib1g-dev
Auto-Installed: 1

It's better to use the official tools to ensure proper database consistency.

Properly marked packages allow efficient system cleanup:

# Safely remove unneeded dependencies
$ sudo apt-get autoremove

This helps keep your development environment clean and avoids accumulating unnecessary packages.

Here's a complete example for a typical development scenario:

# 1. Check initial status
$ apt-mark showauto zlib1g-dev
[No output means manual]

# 2. Compile your project
$ make

# 3. Mark the dependency as auto when done
$ sudo apt-mark auto zlib1g-dev

# 4. Later cleanup
$ sudo apt-get autoremove

When you explicitly install a package that was previously auto-installed as a dependency, APT changes its status to "manually installed". This prevents apt-get autoremove from cleaning it up later, even when no other packages depend on it.

# Original state (auto-installed as dependency)
$ apt-get install zlib1g-dev
zlib1g-dev is already the newest version.
zlib1g-dev set to manually installed.

Instead of manually editing /var/lib/apt/extended_states, use the official tool:

# Mark as auto-installed
sudo apt-mark auto zlib1g-dev

# Verify the change
apt-mark showauto zlib1g-dev

APT maintains two lists of packages:

• Manual: apt-mark showmanual
• Auto: apt-mark showauto

You can check all dependencies that pulled in your package:

apt-cache rdepends --installed zlib1g-dev

Here's how I handle temporary build dependencies:

# 1. Check current status
apt-mark showmanual | grep zlib1g-dev

# 2. Temporarily install for compilation
sudo apt-get install zlib1g-dev

# 3. After build completes, reset to auto
sudo apt-mark auto zlib1g-dev

# 4. Later cleanup when safe
sudo apt-get autoremove

For multiple packages, use xargs:

# Reset all dev packages to auto
dpkg -l | grep '\-dev' | awk '{print $2}' | xargs sudo apt-mark auto

While editing /var/lib/apt/extended_states works, it's risky because:

• APT may overwrite your changes during operations
• No validation of package names
• Requires manual cache updates

The proper sequence if you must edit manually:

sudo nano /var/lib/apt/extended_states
sudo apt-get update