0

When I enter an SSH connection to a Linux host, the XAUTHORITY environment variable is unset. If I run sudo -b, the connection is dropped, unless I add a nohup command immediately after, in which case the operation fails, reporting X11 connection rejected because of wrong authentication.

As a workaround, I can manually set the value to $HOME/.Xauthority.

This variable is typically set automatically. What should I do to ensure that the variable is set in the preferred way (by the right process at the right time)?

Improve this question

1 Answer 1

Reset to default
1

If the Xauthority file is located at $HOME/.Xauthority, then you are not supposed to need the XAUTHORITY environment variable, since $HOME/.Xauthority is the default path: the X11 libraries should be checking it automatically.

If you then use sudo to switch to root, then it becomes more difficult to maintain the X11 session access through sudo, as it's no longer just a matter of preserving the DISPLAY and XAUTHORITY environment variables and letting the root user read the Xauthority from wherever it is: a suitable XAUTHORITY value will need to be set at some point to identify the actual location of the Xauthority file. It's not really important how it gets set, as long as it gets set before the process that will need it is started.

If sudo is already configured to preserve the XAUTHORITY variable, then you could work around this by explicitly setting XAUTHORITY in your login script (as your original user account before sudo) if DISPLAY is set, with something like this:

if [ "$DISPLAY" != "" ] && [ "$XAUTHORITY" = "" ]; then
    export XAUTHORITY=$HOME/.Xauthority
fi

Alternatively, if sudo does not preserve XAUTHORITY and/or you do not wish to configure sudo to preserve it, you could put the following snippet into the /etc/bash.bashrc or ~/.bashrc (or whatever script gets executed by the shell started by the sudo command).

if [ "$SUDO_USER" != "" ] && [ "$DISPLAY" != "" ]; then
    export XAUTHORITY=$(getent passwd "${SUDO_USER}" | cut -d : -f 6)/.Xauthority
fi
Improve this answer
2
  • There are two separate issues, apparently, setting the value on login versus carrying it into the environment created by sudo. It seems both are necessary, but you made a passing comment about sudo being "configured to preserve" XAUTHORITY. Would you please clarify? In my tests it is good enough for a value to be set in the environment inherited by sudo, but the man page says otherwise, that the entire environment comes from a root login, except for any variables preserved by command line switch. Commented Dec 12, 2021 at 13:46
  • In modern distributions, sudo typically has the env_reset setting in effect by default (see sudo -l). When using sudo without the -i option, it is possible to configure sudo to preserve (carry) some environment variables, by adding e.g. Defaults env_keep+=XAUTHORITY to /etc/sudoers or to any drop-in files in /etc/sudoers.d/. Some distributions preserve some variables by default, others don't. Depending on sudo configuration, you may or may not also be able to specify it as a command-line option: sudo --preserve-env=XAUTHORITY .... Commented Dec 12, 2021 at 14:11

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.