NOTE: is not an answer solving the root issue. Please provide a new answer if you think you can solve the root cause. You really have to read on why my solution is just an ugly hack.
Here's an explanation on what happens at boot time, identifying the culprit.
Using KDM (or LightDM) as log in manager, an X session is spawned for you upon logging in. The log in manager allows you to select an X session (e.g. GNOME, KDE Plasma, etc.) based on those available in your system. The directory /usr/share/xsessions
contains the files for each of those desktop environment installed and your user specific choice is saved in ~/.dmrc
.
While the desktop environment loads after logging in, it loads all scripts in /etc/X11/Xsession.d/
. On a Kubuntu 14.04 system I see /etc/X11/Xsession.d/90x11-common_ssh-agent
there by default, initialising an SSH agent. As expected. Great!
In practice however we see different things. Where does gnome-keyring-daemon
come from then and why is the regular ssh-agent
not started? Well, the GNOME keyring is started in two ways:
- XDG autostart, in
/etc/xdg/autostart/gnome-keyring-ssh.desktop
- As an Upstart session job in
/usr/share/upstart/sessions/gnome-keyring.conf
All scripts are first checking the environment values whether they will proceed. E.g.
[ -z "$SSH_AUTH_SOCK" ] || [ -z "$GPG_AGENT_INFO" ] || { stop; exit 0; }
This makes it a sort of race condition which SSH agent is actually started. First one wins. Brace for more nasty bits.
How come it works at one machine reliably and it doesn't reliably at another? The X session upstart jobs are only started when the DESKTOP_SESSION
environment variable is whitelisted for it in /etc/upstart-xsessions
, handled by /etc/X11/Xsession.d/00upstart
. KDM allows one to set a Desktop environment 'Default' (default
in ~/.dmrc
), effectively kde-plasma
, but not appearing kde-plasma
.
With Session=kde-plasma
:
⟫ echo $DESKTOP_SESSION
kde-plasma
With Session=default
in a KDE Plasma desktop:
⟫ echo $DESKTOP_SESSION
default
This is plain wrong. And you can guess now why it fails the whitelist check against /etc/upstart-xsessions
.
Quick fix for running terminal session
killall gnome-keyring-daemon && eval `ssh-agent`
Conclusion
It appears that one can hit a bug with all Upstart session jobs not being started at all. Another bug prevents proper interfacing with the GNOME keyring SSH agent (or ssh-add
should complain and fail). Oh I hate you, bugs.
Once I find time to do some research on what is exactly supposed to do what, I'll file the bug reports.
For now I decided to just 'use' the Upstart bug and prevent Upstart session jobs from running by setting Session=default
. I'm not sure how much this breaks, but so far I haven't seen anything falling apart.
The root cause is the appearance of GNOME keyring in the first place and which should not lie to me and keep offering wrong keys.
Best Answer
The ssh client will check all your keys until it finds one that matches.
This is how it works (this is very simplified, before this a quite complex dance has been made to encrypt all of this):
What files are keys depends on the client.
For the Openssh client (Ubuntu default client), according to its man page, the files that are supposed to be private keys are ./sshid_rsa, .ssh/id_dsa, .ssh/id_ecdsa, plus those given after the -i flag (it supports multiple files) and those declared in the config file.
You can give it the -v option to make it print a line when it tries to use any file as a key. This is an example from a non-key login:
As you can see, it prints all the keys it tries, it fails all. You can use this in your system to discover what files is ssh using in your own system.
Below you can see the output if some existing key is found and tried
user@xyz
is the information appended to the public key.If you're wondering how your ssh client finds your private keys, it's not magic. Under Gnome (xfce and KDE also) there is a special ssh-agent that automatically adds keys in
.ssh
directory that have a correspondending public key with the ending.pub
.If you not have such a comfortable ssh agent, you'll have to add your private keys with
ssh-add key
.