How does freezing an app work technically?

Question

Apps like Link2SD and Titanium Backup are able to "freeze" other apps, that is disable them without removing them. What do these apps do to achieve this?

Answer 1

Titanium Backup etc just use in-built Package Manager (pm) to freeze an app. pm has a feature to prevent apps from running & from appearing in Launcher. To use it, Titanium Backup etc execute following command:

pm disable {package_name}

You can freeze apps by yourself without using a dedicated freezer app. Just use the above command in Terminal Emulator or ADB Shell.

For example, if you want to freeze Stock Web Browser, open Terminal Emulator & switch to root using su command. Then, execute # pm disable com.android.browser.
It'll return #Package com.android.browser new state: disabled. Done!
Restart your Launcher (some devices may require reboot) to see the app icon gone.

To defrost the app, just replace disable with enable in the command.

Answer 2

I found how pm disable works:

If you run cat /system/bin/pm, it gives:

# Script to start "pm" on the device, which has a very rudimentary
# shell.
#
base=/system
export CLASSPATH=$base/framework/pm.jar
exec app_process $base/bin com.android.commands.pm.Pm "$@"

So apparently it is the same as the PackageManager we use from Java, it is calling it - just in a root context that no user app can directly access.

You CAN check if something is frozen, using

getPackageManager().getApplicationEnabledSetting( the package name ) ==
        getPackageManager().COMPONENT_ENABLED_STATE_DISABLED)

Answer 3

pm disable can be bypassed by the app re-enabling the component. A better way to do this is to use the undocumented feature of Intent Firewall as such: https://github.com/lihenggui/blocker

Answer 4

In Unix systems, files have 3 authorizations: read, write, and execute.

(For 3 categories of people: the owner of the file [usually its creator], a group of people, and everyone else, but it is out of the subject).

If you remove the execute authorization of the file, it cannot be launched (executed) anymore.