The Problem
On Linux Mint 18 and similar distributions, TeamViewer may display an exclamation mark in the system tray with a “no internet connection” tooltip after system startup, even though the system has active network connectivity.
Solution
Restart the TeamViewer daemon service:
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sudo teamviewer --daemon restart
This restarts the TeamViewer background service and also launches the TeamViewer client, resolving the connectivity problem.
Why This Happens
The TeamViewer daemon may start before the network manager has fully established the network connection during boot. Restarting the daemon after the network is available forces TeamViewer to re-check connectivity.
Permanent Fix
If this issue occurs regularly, you can add the restart command to your session startup applications or create a systemd service that starts TeamViewer after the network is online.