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It's complicated!
I used a different program and uninstalled it, but with Tunnelblick all I can see are my old configurations!
How can you tell if OpenVPN connected to a server?
If OpenVPN is not connected to the server
OpenVPN Connects, but you can't surf the Internet
A connection is established, but drops out or is restarted after a few seconds or minutes, or DNS stops working after a few minutes
An error messages says to see details in the Console Log
An error message says 'write to TUN/TAP : Input/output error (code=5)'
An error message says 'You have tried to connect using a configuration file that is the same as the sample configuration file installed by Tunnelblick'
An OpenVPN log entry says 'potential route subnet conflict'
An OpenVPN log entry says 'Cannot allocate TUN/TAP dev dynamically'
An error message says 'Tunnelblick was not able to load a device driver (kext) that is needed to connect...'
An OpenVPN log entry says 'Tunnelblick: openvpnstart status #247: Error: Unable to load tun and tap kexts. Status = 71'
An OpenVPN log entry says 'Tunnelblick: openvpnstart status #247: Error: Unable to load net.tunnelblick.tun and/or net.tunnelblick.tap kexts in 5 tries. Status = 71'
An OpenVPN log entry says 'Note: unable to redirect default gateway -- Cannot read current default gateway from system'
An OpenVPN log entry says 'Cannot load certificate file XXX.crt: error: 02001002:system library:fopen:No such file or directory: error: 20074002:BIO routines:FILE_CTRL:system lib: error:140AD002:SSL routines'
An OpenVPN log entry says 'TLS Error: Auth Username/Password was not provided by peer'
An OpenVPN log entry says 'script failed: could not execute external program'
Cannot Empty the Trash
I am repeatedly asked for my password or token value (Tunnelblick 3.6.9beta02 or higher)

It's complicated!

Tunnelblick is an interface for OpenVPN. Most problems people think they have with Tunnelblick are really problems they are having with OpenVPN, so what follows is a mix of information about Tunnelblick and OpenVPN.

OpenVPN is such a powerful tool with so many options, and computer configurations are so varied, that it is difficult to have an exhaustive guide to troubleshooting problems. Tunnelblick is designed to deal easily with the most common setups, so if it doesn't apply to your situation, or doesn't help, ask the Tunnelblick Discussion Group or the OpenVPN users mailing list for help.

I used a different program and uninstalled it, but with Tunnelblick all I can see are my old configurations!

The different program (for example, Urban Shield) uses a customized version of Tunnelblick that makes backups of their configurations and restores them when Tunnelblick starts up, and also hides all other configurations. To solve this problem:

1. Rename the /Library/Application Support/Tunnelblick folder to be named Tunnelblick.old. (This will hide the backup, so Tunnelblick doesn't see it and doesn't restore it.)
2. Reinstall Tunnelblick from the .dmg (disk image)

How can you tell if OpenVPN connected to a server?

1. Click on the Tunnelblick icon at the top of the display.
2. See what appears in the drop-down list for the configuration you are trying to troubleshoot:
   • If the entry shows Connect xyz, configuration xyz is not connected and Tunnelblick is not trying to connect
   • If the entry shows √ Disconnect xyz, configuration xyz is connected
   • If the entry shows - Connect xyz, Tunnelblick is trying to connect configuration xyz

If OpenVPN is not connected to the server

If OpenVPN can't connect to the server and Tunnelblick hasn't popped up a window explaining why, there should be one or more error messages in the OpenVPN log to indicate what the problem is. To see the OpenVPN log, click on the Tunnelblick icon, click on 'VPN Details', click on the large 'Configurations' button at the top of the window, click on the name of the configuration you are troubleshooting on the left side of the window, and then click on the 'Log' tab on the right side. The OpenVPN log is the large area of black text on a white background. (It contains messages from Tunnelblick in addition to the messages from OpenVPN.)

Look at lines near the end of the log for an error message.

OpenVPN Connects, but you can't surf the Internet

See Connects OK, But....

A connection is established, but drops out or is restarted after a few seconds or minutes, or DNS stops working after a few minutes

This can have several causes:

• Another computer on your network is attempting to connect to the VPN using the same credentials.
• You don't have 'Monitor connection' checked. When DHCP is renewed, the change is ignored (because 'Monitor connection' isn't checked) and the VPN-supplied DNS server is replaced with the DHCP-supplied server. Often a DHCP-supplied server will only respond to queries which originate within that network. Since the DNS queries originate from the VPN, which is outside of that network, the queries will not be answered. Put a check next to 'Monitor network'.

An error messages says to see details in the Console Log

See The Console Log for instructions on viewing the Console Log.

An error message says 'write to TUN/TAP : Input/output error (code=5)'

OpenVPN may display a series of these messages when using a TAP connection. Although a few such messages are normal, if they continue to be displayed for more than a few seconds and the connection is never established, try to connect with DNS/WINS set to 'Set nameserver (alternate 1)'.

An error message says 'You have tried to connect using a configuration file that is the same as the sample configuration file installed by Tunnelblick'

This means that you have tried to connect to a VPN without setting up a configuration file. Consult your network administrator or your VPN service provider to obtain configuration and other files or the information you need to modify the sample file. For more information, see Getting VPN Service.

An OpenVPN log entry says 'potential route subnet conflict'

This means that the remote network you are creating a VPN to has IP addresses that are also in your local LAN.

One way to fix this is to include a 'redirect gateway local' option in the OpenVPN configuration file and un-check Tunnelblick's 'Route all IPv4 traffic through the VPN'. (All traffic will still be routed through the VPN because of the 'redirect gateway' option.)

Another way to fix this is to change the addresses of your local LAN. You do this by changing your router's configuration. For some routers you specify the first three numbers of the LAN (e.g. 192.168.77); in other routers you specify the address of the router itself (e.g. 192.168.77.1).

After changing the LAN address, you should restart all computers (and other network devices including network printers), so they start using addresses in the new address range.

Example:
WARNING: potential route subnet conflict between local LAN [192.168.1.0/255.255.255.0] and remote VPN [192.168.1.0/255.255.255.0]

This means that both the remote network and your local network are using the 192.168.1.** range of IP addresses. So change your local network to use, for example, 192.168.5.**, or 192.168.23.*. If you get the same warning message, try another address range.

An OpenVPN log entry says 'Cannot allocate TUN/TAP dev dynamically'

This problem indicates a problem with the Tun and/or Tap system extensions.

• It can be caused by the following sequence in the configuration file:
  dev-type tun
  dev abcdefg
  and a workaround is to replace both lines with the single line
  dev tun
  (substitute 'tap' for 'tun' in the above if this is a Tap configuration.)
• It can be caused by extra Tun or Tap system extensions being loaded. See the following entry.

An error message says 'Tunnelblick was not able to load a device driver (kext) that is needed to connect...'

An OpenVPN log entry says 'Tunnelblick: openvpnstart status #247: Error: Unable to load tun and tap kexts. Status = 71'

An OpenVPN log entry says 'Tunnelblick: openvpnstart status #247: Error: Unable to load net.tunnelblick.tun and/or net.tunnelblick.tap kexts in 5 tries. Status = 71'

Please see Errors Loading System Extensions.

An OpenVPN log entry says 'Note: unable to redirect default gateway -- Cannot read current default gateway from system'

There is a problem (in macOS and/or OpenVPN) which causes OpenVPN to be unable to read the default gateway when you try to connect OpenVPN through an existing PPP connection; here is a workaround:

Create a ppp start-up script /etc/ppp/ip-up and add the following:

#!/bin/sh
PATH=/sbin:/usr/sbin/:/usr/bin:/bin
gw=`ifconfig ppp0|grep inet| awk '{ print $4 }'`
route change default $gw -ifscope ppp0


Save the script and make it executable running chmod a+x /etc/ppp/ip-up.

Please note that the above script was made for interface ppp0. If for any reason you have more/other, make the changes accordingly.

An OpenVPN log entry says 'Cannot load certificate file XXX.crt: error: 02001002:system library:fopen:No such file or directory: error: 20074002:BIO routines:FILE_CTRL:system lib: error:140AD002:SSL routines'

Your certificate file (XXX.crt) was not found. Usually the file should be in the same folder as the OpenVPN configuration file, not in a subfolder. For example, if the configuration file has a line such as
cert abcde.crt
or
ca abcde.crt
then the file abcde.crt should be in the same folder as the configuration. If the configuration file has a line such as
cert xyz/abcde.crt
or
ca xyz/abcde.crt
then the file abcde.crt should be in the xyz subfolder of the folder with the configuration.

An OpenVPN log entry says 'TLS Error: Auth Username/Password was not provided by peer'

Your client configuration file should include an 'auth-user-pass' option.

An OpenVPN log entry says 'script failed: could not execute external program'

An up or down script contains an error. Common causes:

• The use of a script file with Windows line breaks (CR-LF) instead of Unix/Mac line breaks (LF).
• The use of a script file that does not have execute permission for root.
• The use of a script file with syntax errors.

Cannot Empty the Trash

If you dragged an old copy of Tunnelblick to the Trash and now cannot empty the Trash and because Finder complains that something is 'in use' (probably something named Sparkle.framework), try the following:

Launch Terminal (in /Applications/Utilities).

Copy/paste the following into Terminal:

You will be asked for your password. Type it in (it will not show up as you type it) then press the 'enter/return' key on the keyboard.

Quit Terminal, then try to empty the Trash.

I am repeatedly asked for my password or token value (Tunnelblick 3.6.9beta02 or higher)

For some OpenVPN setups that use 'small block' ciphers and username/password authentication or two-factor authentication (2FA), this can be very annoying because the user will be asked to authenticate each time 64 MB has been transferred through the VPN.

There are several ways to avoid the problem:

• Use a cipher which is not a 'small block' cipher. (This must be done on both OpenVPN client and OpenVPN server.)
• Use OpenVPN 2.4 or higher and enable cipher negotiation. This must be done on both the server and client.
• For username/password authentication, have Tunnelblick save the username and password in the Keychain.
• For 2FA, do not use --auth-nocache, and use the --auth-token option in the client-connect and auth-user-pass-verify scripts on the server side to ask for 2FA once per session only.

More information is available at OpenVPN and SWEET32.