Technology Tales

When CRON is stalled by incorrect file and folder permissions

During the past week, I rebooted my system only to find that a number of things no longer worked and my Pi-hole DNS server was among them. Having exhausted other possibilities by testing out things on another machine, I did a status check when I spotted a line like the following in my system logs and went investigating further:

cron[322]: (root) INSECURE MODE (mode 0600 expected) (crontabs/root)

It turned out to be more significant than I had expected because this was why every CRON job was failing and that included the network set up needed by Pi-hole; a script is executed using the @reboot directive to accomplish this and I got Pi-hole working again by manually executing it. The evening before, I did make some changes to file permissions under /var/www but I was not expecting it to affect other parts of /var though that may have something to do with some forgotten heavy-handedness. The cure was to issue a command like the following for execution in a terminal session:

sudo chmod -R 600 /var/spool/cron/crontabs/

Then, CRON itself needed starting since it had not not running at all and executing this command did the needful without restarting the system:

sudo systemctl start cron

That outcome was proved by executing the following command to issue some terminal output that include the welcome text “active (running)” highlighted in green:

sudo systemctl status cron

There was newly updated output from a frequently executing job that checked on web servers for me but this was added confirmation. It was a simple solution to a perplexing situation that led up all sorts of blind alleys before I alighted on the right solution to the problem.

When a hard drive is unrecognised by the Linux hddtemp command

One should not do a new PC build in the middle of a heatwave if you do not want to be concerned about how fast fans are spinning and how hot things are getting. Yet, that is what I did last month after delaying the act for numerous months.

My efforts mean that I have a system built around an AMD Ryzen 9 5950X CPU and a Gigabyte X570 Aorus Pro with 64 GB of memory and things are settling down after the initial upheaval. That also meant some adjustments to the CPU fan profile in the BIOS for quieter running while the the use of Be Quiet! Dark Rock 4 cooler also helps as does a Be Quiet! Silent Wings 3 case fan. All are components from trusted brands though I wonder how much abuse they got during their installation and subsequent running in.

Fan noise is a non-quantitative indicator of heat levels as much as touch so more quantitative means are in order. Aside from using a thermocouple device, there are in-built sensors too. My using Linux Mint means that I have the sensors command from the lm-sensors package for checking on CPU and other temperatures though hddtemp is what you need for checking on the same for hard drives. The latter can be used as follows:

sudo hddtemp /dev/sda /dev/sdb

This has to happen using administrator access and a list of drives needs to be provided because it cannot find them by itself. In my case, I have no mechanical hard drives installed in non-NAS systems and I even got to replacing a 6 TB Western Digital Green disk with an 8 TB SSD but I got the following when I tried checking on things with hddtemp:

WARNING: Drive /dev/sda doesn't seem to have a temperature sensor.
WARNING: This doesn't mean it hasn't got one.
WARNING: If you are sure it has one, please contact me ([email protected]).
WARNING: See --help, --debug and --drivebase options.
/dev/sda: Samsung SSD 870 QVO 8TB: no sensor

The cause of the message for me was that there is no entry for Samsung SSD 870 QVO 8TB in /etc/hddtemp.db so that needed to be added there. Before that could be rectified, I needed to get some additional information using smartmontools and these needed to be installed using the following command:

sudo apt-get install smartmontools

What I needed to do was check the drive’s SMART data output for extra information and that was achieved using the following command:

sudo smartctl /dev/sda -a | grep -i Temp

What this does is to look for the temperature information from smartctl output using the grep command with output from the first being passed to the second through a pipe. This yielded the following:

190 Airflow_Temperature_Cel 0x0032 072 050 000 Old_age Always - 28

The first number in the above (190) is the thermal sensor’s attribute identifier and that was needed in what got added to /etc/hddtemp.db. The following command added the necessary data to the aforementioned file:

echo \"Samsung SSD 870 QVO 8TB\" 190 C \"Samsung SSD 870 QVO 8TB\" | sudo tee -a /etc/hddtemp.db

Here, the output of the echo command was passed to the tee command for adding to the end of the file. In the echo command output, the first part is the name of the drive, the second is the heat sensor identifier, the third is the temperature scale (C for Celsius or F for Fahrenheit) and the last part is the label (it can be anything that you like but I kept it the same as the name). On re-running the hddtemp command, I got output like the following so all was as I needed it to be.

/dev/sda: Samsung SSD 870 QVO 8TB: 28°C

Since then, temperatures may have cooled and the weather become more like what we usually get but I am still keeping an eye on things, especially when the system is put under load using Perl, R, Python or SAS. There may be further modifications such as changing the case or even adding water cooling, not least to have a cooler power supply unit, but nothing is being rushed as I monitor things to my satisfaction.

Getting rid of the Windows Resizing message from a Manjaro VirtualBox guest

Like Fedora, Manjaro also installs a package for VirtualBox Guest Additions when you install the Linux distro in a VirtualBox virtual machine. However, it does have certain expectations when doing this. On many systems and my own is one of these, Linux guests are forced to use the VMSVGA virtual graphics controller while Windows guests are allowed to use the VBoxSVGA one. It is the latter that Manjaro expects so you get a message like the following appearing when the desktop environment has loaded:

Windows Resizing
Set your VirtualBox Graphics Controller to enable windows resizing

After ensuring that gcc, make, perl and kernel headers are installed, I usually install VirtualBox Guest Additions myself from the included ISO image and so I did the same with Manjaro. Doing that and restarting the virtual machine got me extra functionality like screen resizing and being able to copy and paste between the VM and elsewhere after choosing the Bidirectional setting in the menus under Devices > Shared Clipboard.

That still left an unwanted message popping up on startup. To get rid of that, I just needed to remove /etc/xdg/autostart/mhwd-vmsvga-alert.desktop. It can be deleted but I just moved it somewhere else and a restart proved that the message was gone as needed. Now everything is working as I wanted.

Removing obsolete libraries from Flatpak

Along with various pieces of software, Flatpak also installs KDE and GNOME libraries needed to support them. However, it does not always remove obsolete versions of those libraries whenever software gets updated. One result is that messages regarding obsolete versions of GNOME may be issued and this has been known to cause confusion because there is the GNOME instance that is part of a Linux distro like Ubuntu and using Flatpak adds another one for its software packages to use. My use of Linux Mint may lesson the chances of misunderstanding.

Thankfully, executing a single command will remove any obsolete Flatpak libraries so the messages no longer appear and there then is no need to touch your actual Linux installation. This then is the command that sorted it for me:

flatpak uninstall --unused && sudo flatpak repair

The first part that removes any unused libraries is run as a normal user so there is no error in the above command. Administrative privileges are needed for the second section that does any repairs that are needed. It might be better if Flatpak did all this for you using the update command but that is not how the thing works. At least, there is a quick way to address this state of affairs and there might be some good reasons for having things work as they do.

Shrinking title bar search box in Microsoft Office 365 applications

It might be a new development but I only recently spotted the presence of a search box in the titles of both Microsoft Word and Microsoft Excel that I have as part of an Office 365 subscription. Though handy for searching file contents and checking on spelling and grammer, I also realised that the boxes take up quite a bit of space and decided to see if hiding them was possible.

In the event, I found that they could be shrunk from a box to an icon that expanded to pop up a box when you clicked on them. Since I did not need the box to be on view all the time, that outcome was sufficient for my designs though it may not satisfy others who want to hide this functionality completely.

To get it, it was a matter of going to File > Options and putting a tick in the box next to the Collapse the Microsoft Search box by default entry in the General tab before clicking on the OK button. Doing that freed up some title bar space as desired and searching is only a button press away.

Ensuring that Flatpak remains up to date on Linux Mint 19.2

The Flatpak concept offers a useful way of getting the latest version of software like LibreOffice or GIMP on Linux machines because repositories are managed conservatively when it comes to the versions of included software. Ubuntu has Snaps, which are similar in concept. Both options bundle dependencies with the packaged software so that its operation can use later versions of system libraries that what may be available with a particular distribution.

However, even Flatpak depends on what is available through the repositories for a distribution as I found when a software update needed a version of the tool. The solution was to add PPA using the following command and agreeing to the prompts that arise (answering Y, in other words):

sudo add-apt-repository ppa:alexlarsson/flatpak

With the new PPA instated, the usual apt commands were used to update the Flatpak package and continue with the required updates. Since then, all has gone smoothly as expected.

Shared folders not automounting on an Ubuntu 18.04 guest in a VirtualBox virtual machine

Over the weekend, I finally got to fixing a problem that has affected Ubuntu 18.04 virtual machine for quite a while. The usual checks on Guest Additions installation and vboxsf group access assignment were performed but were not causing the issue. Also, no other VM (Windows (7 & 10) and Linux Mint Debian Edition) on the same Linux Mint 19.2 machine was experiencing the same issue. The latter observation made the problem intrinsic to the Ubuntu VM itself.

Because I install the Guest Additions software from the included virtual CD, I executed the following command to open the relevant file for editing:

sudo systemctl edit --full vboxadd-service

If I had installed installed virtualbox-guest-dkms and virtualbox-guest-utils from the Ubuntu repositories instead, then this would have been the command that I needed to execute instead of the above.

sudo systemctl edit --full virtualbox-guest-utils

Whichever configuration gets opened, the line that needs attention is the one beginning with Conflicts (line 6 in the file on my system). The required edit removes systemd-timesync.service from the list following the equals sign. It is worth checking that file paths include the correct version number for the Guest Additions software that is installed in case this was not the case. The only change that was needed on my Ubuntu VM was to the Conflicts line and rebooting it got the Shared Folder automatically mounted under the /media directory as expected.

Creating a VirtualBox virtual disk image using the Linux command line

Much of the past weekend was spent getting a working Debian 10 installation up and running in a VirtualBox virtual machine. Because I chose the Cinnamon desktop environment, the process was not as smooth as I would have liked so a minimal installation was performed before I started to embellish as I liked. Along the way, I got to wondering if I could create virtual hard drives using the command line and I found that something like the following did what was needed:

VBoxManage createmedium disk --filename <full path including file name without extension> -size <size in MiB> --format VDI --variant Standard

Most of the options are self-explanatory part from the one named variant. This defines whether the VDI file expands to the maximum size specified using the size parameter or is reserved with the size defined in that parameter. Two VDI files were created in this way and I used these to replace their Debian 8 predecessors and even to save a bit of space too. If you want, you can find out more in the user documentation but this post hopefully gets you started anyway.

Enlarging a VirtualBox VDI virtual disk

It is amazing how the Windows folder manages to grow on your C drive and on in a Windows 7 installation was the cause of my needing to expand the VirtualBox virtual machine VDI disk on which it was installed. After trying various ways to cut down the size, an enlargement could not be avoided. In all of this, it was handy that I had a recent backup for restoration after any damage.

The same thing meant that I could resort to enlarging the VDI file with more peace of mind than otherwise might have been the case. This needed use of the command line once the VM was shut down. The form of the command that I used was the following:

VBoxManage modifyhd <filepath/filename>.vdi --resize 102400

It appears that this also would work on a Windows host but mine was Linux and it did what I needed. The next step was to attach it to an Ubuntu VM and use GParted to expand the main partition to fill the newly available space. That does not mean that it takes up 100 GiB on my system just yet because these things can be left to grow over time and there is a way to shrink them too if you ever need to do just that. As ever, having a backup made before any such operation may have its uses if anything goes awry.

Lightening of desktop background images on Linux Mint Debian Edition running in Virtualbox

After a recent upgrade to Linux Mint Debian Edition 3 in a VirtualBox virtual machine that I had running its predecessor, I began to notice that background images were being loaded with more washed out of faded colours. This happened at startup so selecting another background image worked as intended until the same thing happened to that after a system restart.

This problem is not new and has affected the Cinnamon desktop in the main Linux Mint variant (the one that is based on Ubuntu) and issuing the following command in a terminal session is a suggested solution:

gsettings set org.cinnamon.muffin background-transition fade-in

In my case, that solved the problem and desktop background image display is as it should be since I executed the above. All it took was a change to a system setting.