X-Server | Dirk Mittler's Blog

Successful X-server Update Today

Today the Debian / Jessie package maintainers pushed through an update to my X-server, bringing that up to version ‘2:1.16.4-1+deb8u1‘. In a case like this, it’s better to restart the session, just to load the new X-server version, but also, to make sure that any problems in running the X-server do not take us by surprise, during some later reboot.

As it happens, the computer this took place on, which I name ‘Phoenix‘, is also my Web-server. And so it’s desirable to perform the restart of the session, without doing a full reboot of the computer. Under Linux, with the ‘KDE’ desktop manager, we can do this by just Logging Out, and then Logging back In. Doing so also causes an X-server restart.

Not doing a full reboot of my computer, also meant that my Apache Web-server continued running, without causing any disruption to the visibility of my Web-site, or of this blog.

Yet, there was a glitch. As I told my user-session to log out, the display hanged, with the mouse-pointer still visible, but with the rest of my display black, and with no further activity on the hard-drive. In this situation I can help myself, by using the KDE, <Ctrl>+<Alt>+Backspace key-combination, to force an X-server restart. Doing so successfully ended my user-session. Then, the X-server restarted, and I got to log back in.

What this means is that the preparatory work I did according to this earlier posting, has paid off.

I count this as a successful update.

Dirk

User-Session Restart Today

When most of us want to make sure that our laptops are stable, and have saved their user-data, and have a fresh slate of available memory again, we just perform a reboot. However, on a tower computer which is also acting as a Web-server, this may not be such a viable option, because a true reboot would also cause said Web-server to go offline briefly. But as an alternative, we can log out the current user without shutting down the system, and then log back in again. On most Linux systems that have real desktop managers, this also restarts the X-server, and frees some additional graphics memory.

I just performed such a User-Session Restart, on the computer I name ‘‘. When I do this, it actually empties out the large amount of data which my system has swapped out. What tends to happen on this machine, which only possesses 4GB of RAM, is that its heavy KDE Desktop Manager has resource leaks, which continuously cause memory to be allocated but not used. The unused memory gets paged to the swap partition. But because it is also a 64-bit machine, there is no real risk that the system would run out of 64-bit virtual addresses, corresponding to this leaked resource. Only, the used portion of the swap partition becomes embarrassingly large. A log-out followed by a log-in, forces the desktop environment to save all its data, and in so doing, also forces all the data which has been swapped out, to be swapped back in, simultaneously.

I believe that this is reason, why actual restarts on this one machine are really so slow. It takes several minutes just for the wallpaper to disappear, and then the mouse-cursor, and then for an actual X-server-restart to take place.

At the same time, this exercise has confirmed what I already thought, which was that a ‘gstreamer’ update weeks ago, did not affect my sound server adversely. I still have sound.

Also, in the province of Quebec, Daylight Savings Time started several weeks ago, and whenever this happens, my Desktop Notification Icon, ‘‘, starts to fire off user-notifications for scheduled events at an illogical time but persistently, around 23h00 or so, until 24h00. The only way to stop that in the short term, is actually to disable these alarms, until the desktop is given a new session. Then, as experience on my laptop ‘‘ already confirmed, can be re-enabled, and those illogical, wrongly-scheduled alarms stop happening.

Finally, when and if there finally is another power failure, the risk of data-loss becomes lower.

None of this should have affected system services, nor the Web-server, and therefore not my site either.

Dirk

Recent Update to libevent

Sometimes updates come through the package manager, which I do not blog about immediately. One such update took place in recent days, to the package ‘libevent-2.0-5‘.

After the update, I assumed that most of the programs which depended on this library were user-space applications. So I logged out my session and logged back in, without affecting system services such as the Web-server or ‘memcached‘. This maintenance-action of mine went by uneventfully – no pun intended. And doing so also restarted my X-server.

But then I decided to inquire, which services exactly depended on this library. And it turns out that ‘memcached‘ was the single process which remained, that did, and which therefore also deserved a restart. So I restarted this daemon tonight, thus flushing the cache. Therefore, response to readers of this blog might seem a little slow in the next few days.

Aside from that, I have a quiet feeling that by updating this library, the Debian Team may have fixed my spring.

Dirk

NoMachine NX

When people connect to their VPN, this could simply allow them to access shared files. But alternatively, this could also mean that they wish to create a virtual session, on the remote desktop of one of their servers. The latter exists under the terms VNC, RDP, XRDP, and several others.

On my main Linux server named ‘Phoenix’, I have the XRDP service installed, which is the Linux equivalent of RDP. But one main drawback of this method, of remotely accessing a desktop, is the fact that XRDP does not allow file-sharing, specifically in the version of this protocol that runs out-of-the-box from the package manager. I have read that certain custom-compiled versions support this, but do recall that this service is a mess to custom-compile, and to set up in such a way that it runs reliably. So I stick to the packaged version for now, and do not obtain file-sharing.

There exists a closed-source application named , which we could use to bridge this gap. But while their paid software subscriptions are very expensive (from my perspective), their Free software version has some big disadvantages.

First of all, even their Free version can be run in client or in server mode. I think that this is terrific. But in server mode – which affords access to the local machine desktop from elsewhere – there is no built-in support for SSH protocol. There is only the unencrypted NX protocol, for which their service listens.

Secondly, not every computer is strong enough to run in server mode. On the computer ‘Phoenix’ I have a fragile X-server, and this service has actually crashed my X-server. Not only that, but allowing this service to run on reboot, consistently prevents my X-server from starting. It gets its hooks into the session so early on boot, that the X-server crashes, before the user is even asked for a graphical log-in.

On the plus side, there are ways of solving both problems.

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