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Error: write to TUN/TAP : Input/output error (code=5)

OpenVPN may display the error message "write to TUN/TAP : Input/output error (code=5)" if it cannot send network packets through the VPN's network interface. This is usually due to the network interface not being ready yet, and hence it's not uncommon for several of the errors to appear while the network interface is still being setup.

However if these error messages do not stop, and you are unable to access anything on the VPN network, it's likely the network interface hasn't been assigned an IP address. This is common for TAP based connections where the IP address is assigned using a DHCP server. In this instance you should enable Viscosity's DHCP support like so:

  1. Open Viscosity's Preferences window
  2. Select your connection and click the Edit button
  3. Tick the "Enable DHCP" option
  4. Click the Save button
  5. Try reconnecting

The DHCP option should only be enabled if the IP address should be assigned by a DHCP server. Enabled the DHCP option when it's not necessary can result in the VPN network interface having multiple IP addresses assigned which can cause routing problems.