** EDITED (update) at the end of the post**
I finally gave up on Mint 18 KDE after trying everything I could to get the latest release working. Then a few days ago I found that Kubuntu 17.10 had been released, so I installed it. But it was still suffering from some problems even after updating everything. Always looking for possible fixes, I installed Plasma 5.11 from the repositories.
For a day it ran nicely. Everything was fairly smooth, although rather slow compared to Mint 17.3 with KDE 4.x and I was optimistic.
I thought I 'might' have the whole mess sorted at last. The post below was written after another round of frustration with the file indexing systems in Kubuntu 17 (and probably still in Mint 18).
Then I noticed an old problem back again. On my quad core system the cores were alternating loads, often with two around 100% and two between 15 and 24%.
The main culprits were akonadi (which indexes files), update-apt-xapi, (which indexes files), and baloo_file_extractor (which indexes files).
So there I was with the whole system coming to a grinding halt frequently. Not even web pages would scroll, desktops or activities would not switch, programs would not start, the whole system was just stop-start.
I managed to shut down the various processes and went into settings to tell Kubuntu NOT to index files and folders. But eventually I gave up. I'm writing this on good old Mint 17.3 and KDE 4 point whatever, and I'll boot Kubuntu occasionally and update it once in a while in the hope that eventually someone fixes it.
I'm not the only person who has this problem. A little googling shows there is a whole big mob of people out there who can;t find a permanent way to make Plasma 5.x work usefully for any real length of time. And of course, there are many others who wonder what the fuss is, because their system works perfectly.
For the xapian index ('update-apt-xapi' hogging a CPU core at 100% for extended periods of time, someone found that if you edit
/etc/cron.weekly/apt-xapian-index and replace it with this code
#!/bin/sh
CMD=/usr/sbin/update-apt-xapian-index
IONICE=/usr/bin/ionice
# Rebuild the index
if [ -x $CMD ]
then
if [ -x $IONICE ]
then
nice -n 19 $IONICE -c 3 $CMD --update --quiet
else
nice -n 19 $CMD --update --quiet
fi
fi
(back up the original file first), you can more or less sort that on out. One down - two to go.
Akonadi is the next villain. Akonadi is used to index your kmail database, iincluding Personal Information Manager, Calendar, Korganizer, Kalarms and contact lists etc. But even if you don't have Kmail installed, it is started by some KDE programs and also Plasma widgets and the digital clock in the KDE Panel.
You can make sure Akonadi doesn't start by not having certain KDE programs in the Auto Start settings, and also by making sure PIM Events Plugin is unchecked in the Digital Clock settings.
Number 3 in our bad guys list is baloo_file_extractor. Baloo is apparently another part of Akonadi, and it seems to index pretty well ALL files on the system eventually. And it also tends to run 100% of one CPU core at a time.
To turn it off, open Settings > System Settings then in the search tab uncheck the Index Files check box.
***********
Now, after doing all those things, Kubuntu 17.10 with Plasma 5.11 runs really smoothly and fast again. For a while! Then eventually it starts bogging down again. Eventually after Kubuntu has been running perfectly for as while, scrolling the mousewheel on the desktop or the pager does nothing for 20 seconds or sometimes longer, then suddenly does what it should.
Something similar happens when trying to change tabs in Chromium or Firefox, and opening a new program - well, that's a good opportunity to make a cup of coffee or maybe write a short novel. but not using the computer, unless you are happy typing a few words, then waiting patiently for them to suddenly appear on the screen.
The one thing I am convinced of is that some aspects of Linux with the KDE desktop have finally gone backwards to the point where Windows was back in about the year 2000.
Fortunately, I still have Mint 17.3 KDE4 on another root partition and it works perfectly. The only reason for bothering to mess with distros using Plasma 5 is that KDE4 is going to be a thing of the past soon.
EDIT
There are also problems with Mint 18 and Kubntu 17 slowing down and locking for a while, which seem to be a memory issue with Plasma 5.x.
It has been an on-going issue for some time according to google searches. I only have 8GB of RAM on my Quad Core system. And I notice that initially RAM usage is a bit over 1GB, then it climbs rapidly to about 1.7GB after opening a browser and doing a few things. Soon after that it is over 2GB, and even after I close various program windows, it stays high. Eventually it will be up around 6.8GB or 7.2GB of RAM being used, even if most windows are closed again. With the same system using KDE with Plasma 4.x, the maximum RAM used is fairly consistently less than 2GB. It does increase a bit if I load the OS with open programs, but as I clse them it decreases again.
When Plasma 4 was doing this some years ago I wrote a script that would reboot PLASMA, without rebooting the computer. It will not work with Plasma 4, so I rewrote it to work with Plasma 5. While it will not solve the problem, i use it to reset the RAM used for a while so I can get on with whatever I was doing - then save stuff and reboot into KDE 17 so I can work normally.
The script is:
!#/bin/bash
kquitapp5 plasmashell && kstart plasmashell
Type it into a plain text file, then save it and set it as executable (right click the file and choose 'properties', then check the 'executable' box). Then drag it and drop it onto the Panel in Plasma 5.
Clicking on the icon should blank the screen while Plasma restarts. If you are watching the system monitor, you should see the amount of RAM being used, reset to whatever your default is.
