On LineageOS (and most modern Android versions), the run-as command enforces SELinux and app sandboxing restrictions, even for the root user. The error run-as: package not debuggable: com.termux means that Termux is not marked as a debuggable app in its manifest, so run-as refuses to switch to its user context—even with root privileges.

Workarounds to Run Commands as com.termux User

1. Temporarily Make Termux Debuggable

• Requires: Root access and a way to modify app manifests (e.g., apktool or smali patching).
• Steps:
  1. Extract Termux’s APK:
     bash

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     apktool d /data/app/com.termux-*/base.apk -o termux_mod

  2. Edit AndroidManifest.xml to add android:debuggable="true" to the <application> tag.
  3. Rebuild and reinstall the APK:
     bash

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     apktool b termux_mod -o termux_debug.apk
     adb install -r termux_debug.apk

  4. Now run-as com.termux should work.
• Downside: Requires rebuilding the APK, and updates may revert the change.

2. Use su to Switch to Termux’s UID

• If Termux’s UID is known (e.g., u0_a123), you can use su to switch to it:
  bash

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  su -c "su u0_a123 -c 'export PATH=/data/data/com.termux/files/usr/bin:\$PATH; bash -i'"

• Find Termux’s UID:
  bash

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  grep termux /data/system/packages.list

  or
  bash

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  ls -n /data/data | grep com.termux

• Note: This may still fail if SELinux denies the transition.

3. Directly Access Termux’s Files as Root

• If your goal is to run scripts or access files in Termux’s directory, you can do so directly as root:
  bash

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  cd /data/data/com.termux/files/usr/bin
  ./bash -lic 'export PATH=/data/data/com.termux/files/usr/bin:$PATH; bash -i'

• Limitation: Some Termux-specific environment variables (e.g., $PREFIX) may not be set.

4. Use nsenter to Join Termux’s Namespace

• If Termux is running, you can find its PID and join its namespace:
  bash

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  pid=$(pgrep -u u0_a123 bash)  # Replace u0_a123 with Termux's UID
  nsenter -t $pid -m -u -i -n -p bash -c 'export PATH=/data/data/com.termux/files/usr/bin:$PATH; bash -i'

• Note: Requires nsenter support in your kernel and may not work on all devices.

5. Patch run-as or SELinux Policy (Advanced)

• For run-as: Some custom ROMs allow overriding the debuggable check by modifying the run-as binary.
• For SELinux: You can try setting it to permissive mode:
  bash

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  setenforce 0

  Then retry run-as com.termux. Warning: This weakens security.

Recommended Approach

• If you just need to run Termux commands, use Termux itself (e.g., via termux-exec or a Termux session).
• If you need to access Termux’s environment as root, use su + Termux’s UID (method 2).
• If you need full Termux user context, rebuild Termux as debuggable (method 1).