A normal update of a bunch of things (including kernel)
on ubuntu 18.04 left me with boinccmd and boincmgr
not working:
boinccmd did nothing but return
Operation failed: authentication error

I finally did

boinccmd --project 'http://setiathome.berkeley.edu/' detach
boinccmd --project_attach 'http://setiathome.berkeley.edu/' projkey
where projkey is the project key you can find for the project
on your seti@home account or in
account_setiathome.berkeley.edu.xml in the BOINC data directory.

That restored boinccmd and boincmgr to working state.

Other ubuntu 18.04 and Linux Mint machines
running seti@home here have not had
this problem. Very odd.
I just though I would mention it in case it happens to someone else.

DavidA.

Well another machine, an Odroid-xu4, just got a kernel update and
that same problem of boincmgr getting 'authentication error'
and the detach command too fails with authentication error.
Arrrggggh.

In thread 84551 I described how I got setiathome reattached
on one machine.

Well, yesterday another kernel update (and lots else too)
this time on an odroid xu4, has, with any boinccmd

Operation failed: authentication error

boincmgr cannot see any project or task.

And so far none of the things that worked before to fix
this work.
I'm stumped for the moment.

Ok. Now this is working again.
IT turns out (maybe 'seems' is the better word
to be critical that the following file and symlink
exist:

sudo ls -l /var/lib/boinc-client/gui_rpc_auth.cfg /etc/boinc-client/gui_rpc_auth.cfg
-rw-r----- 1 root boinc 1 Aug 14 2017 /etc/boinc-client/gui_rpc_auth.cfg
lrwxrwxrwx 1 root root 34 Jun 28 2018 /var/lib/boinc-client/gui_rpc_auth.cfg -> /etc/boinc-client/gui_rpc_auth.cfg

Having these as identical files did not work (for me)! Symlink matters.
And no other gui_rpc_auth.cfg exists on the machine.

Sorry about all the noise on this, I'll repeat this message in the original thread
(84551) so it has a more complete analysis.

I wonder if the two 'identical' files had identical ownership and access permissions, too?

There's another crucial thing, just discovered today on
another machine when a bunch of updates done.

The only gui_rpc_auth.cfg on the machine should, apparently be

/etc/boinc-client/gui_rpc_auth.cfg

and there must also be a symlink:

/var/lib/boinc-client/gui_rpc_auth.cfg -> /etc/boinc-client/gui_rpc_auth.cfg

Having the second as a file (even identical to /etc/boinc-client/gui_rpc_auth.cfg)
did not work for me.

The kernel and other updates on the odroid xu4 did not involve any
choices asked of me...seti@home just was broken after the update till
I got the cfg files just right (which meant deleting a gui_rpc_auth.cfg
from my home directory...the update process created this one, it seems).

Why is this so tricky? Is it just me?

Anyway, it turns out it also crucial that
/etc/boinc-client/gui_rpc_auth.cfg
be an empty file. It works ok with a newline
or without, it seems, but no auth string should be there.
Why something *created* an auth string in there is
unknown to me.

With /etc/boinc-client/gui_rpc_auth.cfg
owned by boinc

and /var/lib/boinc-client/gui_rpc_auth.cfg (the symlink to the above file)
owned by root boinccmd things work. What ownerships will fail
is unknown to me.

Oh my.

I am running with a non-empty /etc/boinc-client/gui_rpc_auth.cfg file. In fact, it contains 8 letters, first letter p, last letter d, no newline - that's all I need when the permitted remote access is only from other machines within the secure perimeter of my home LAN.

That sets up the lock within the client, on the next and subsequent launches. Now, I need a key to open that lock.

I've modified the shortcut link on my local Linux Mint desktop to add "-p password" to the command line which launches the Manager. That works locally.

I've added the Linux machine to the list of computers monitored by BoincView (a Windows predecessor of BoincTasks). Usual port and password. That works remotely.

I've opened a "New BOINC Manager window..." on my Windows daily driver. I've filled in the Linux machine name and password. That works too.

I've never actually needed to use boinccmd under Linux yet, but I'm sure the same "-p password" command as I use for the Manager would work too. I do use terminal for sudo servicectl and chmod (if those are the right spellings - typing this from memory. Nice of terminal to remember the history of commands used for me), but that's all I need for some quite complicated testing.