The behavior you're observing is likely due to how Android's package manager (pm) and the adb uninstall command interact with the /data/data/<package> directory. Here's why /data/data/com.termux_bak/ might be deleted when running adb uninstall com.termux:

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Why This Happens

1. Android's Package Manager Behavior: When you run adb uninstall com.termux, the Android package manager (pm) removes:

   • The APK file associated with com.termux.
   • The entire /data/data/com.termux/ directory, including all its contents (files, subdirectories, etc.).

2. Symbolic Links or Bind Mounts:

   • If /data/data/com.termux_bak/ was not a true copy but instead a symbolic link or bind mount pointing to /data/data/com.termux/, then moving the directory with mv would not create an independent copy. Instead, it would just create a new reference to the same data.
   • When adb uninstall runs, it removes the original /data/data/com.termux/ directory, which would also delete the data referenced by /data/data/com.termux_bak/ if it was a link or bind mount.

3. Filesystem-Level Behavior:

   • On some Android devices (especially those with FUSE-based storage or dm-verity), the /data partition may use copy-on-write (CoW) or union filesystems. In such cases, moving a directory might not create a true independent copy, and the uninstallation could still affect the "moved" directory.

4. Termux-Specific Behavior:

   • Termux's data directory (/data/data/com.termux/) might have special permissions or SELinux contexts that cause the entire directory tree to be treated as a single unit during uninstallation.

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How to Properly Back Up /data/data/com.termux/

If you want to safely back up Termux's data before uninstalling, use one of these methods:

Method 1: Use tar to Create a True Copy

bash
Copy
adb shell "tar -czf /sdcard/termux_backup.tar.gz -C /data/data/ com.termux"
adb pull /sdcard/termux_backup.tar.gz
adb shell rm /sdcard/termux_backup.tar.gz

• This creates a compressed archive of the directory, ensuring no links or mounts are preserved.

Method 2: Copy to External Storage

bash
Copy
adb shell cp -r /data/data/com.termux /sdcard/com.termux_bak

• This ensures the data is copied to a separate filesystem (e.g., /sdcard), which is not affected by adb uninstall.

Method 3: Use rsync (if available)

bash
Copy
adb shell rsync -a /data/data/com.termux/ /sdcard/com.termux_bak/

• This creates a recursive, independent copy of the directory.

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Why mv Didn’t Work as Expected

• mv on Android (especially in /data) might not behave like a traditional Unix mv. If the filesystem is FUSE-based or uses bind mounts, the move operation might not create a true independent copy.
• The adb uninstall command forcefully removes the package's data directory, regardless of whether it was moved or linked.

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Key Takeaway

Always copy (not move) data before uninstalling an app if you want to preserve it. Use tar, cp -r, or rsync to ensure a true backup. The mv command in /data may not work as expected due to Android's filesystem quirks.