"Could not install the security updates"
 

Hi
I recently installed Linux Mint 19.2 Xfce 64-bit.
When I launch the update manager, it shows me the available updates, but when I click on "install", I get the message "Could not install the security updates".
I can update on the terminal with apt-get upgrade.
Also when I click on "edit - software sources" nothing happens.
It may not have anything to do with this, but I can't launch Timeshift either.
In the log it says:

11.15@21:29 ++ Ready to launch synaptic
Error creating textual authentication agent: Error opening current controlling terminal for the process (`/dev/tty'): No such device or address
11.15@21:29 ++ Return code:127
11.15@21:29 ++ Install failed

Please can you help me?

probably the installation was not really successful. I would say you can try to reinstall, probably faster than find the reason.
But first a reboot, probably that helps. Or you can check the logs if there was something interesting.

This rings a faint bell.
There's been problems with authentication agents in the Debian world recently.

Try
in a terminal and show us what you get.

polkit-agent-helper-1: error response to PolicyKit daemon: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: No session for cookie
==== AUTHENTICATION FAILED ===
Error executing command as another user: Not authorized

This incident has been reported.

Please use code tags for this sort of stuff.

Strange.
I'm getting a similar error for e.g. However, it does not disturb me; I never use pkexec wittingly.

I put the error message in a search engine - some stuff to read through.

I found that, as someone else had done, I had unchecked the PolicyKit Authentication Agent. Now I can start Timeshift, access the software sources, and have successfully installed something with the Software Manager. I'll have to wait till there are new updates to see if I can install them with the Update Manager, but I reckon the problem is now solved.
Thanks a million ondoho!

Glad it helped!

Security updates
 

There are times when I have to reboot to get rid of some small quirks in Mint Mate 19.1. Other than that 19.1 works great.