During 14.04->16.04 upgrade, tmux is unable to re-attach

[eloquence]

An organization performing a Xenial upgrade reported that they were unable to re-attach to the Application Server after the sshd restart. They attributed this to the fact that tmux itself was upgraded before then. They were able to manually re-attach by finding the old process ID via pgrep and re-attaching via /proc/$pid/exe.

They did not experience the same issue upgrading the Monitor Server.

We should attempt to understand the root cause and, if warranted, add an update to the documentation to help users work around this issue.

[rmol]

I've reproduced this. Happened exactly as described -- only on the app server, where attaching via the old executable under /proc worked. I've got a fix -- basically incorporating their workaround by adding to /etc/profile.d/bashrc_securedrop_additions an attempt to attach via the /proc copy of the old executable if attaching fails but a session is found -- but want to go through another test cycle or two to validate it.

[eloquence]

Thanks for the repro! This seems like a good candidate for the point release, so tentatively added to the milestone. That said, if we're certain this will impact prod upgrades, we should update the docs with the workaround before then.

[kushaldas]

Is this over tor or direct ssh also? Asking because I never had this trouble in direct ssh connections.

[rmol]

The problem did not occur with direct SSH connections to the servers.