Technology Tales

Adventures & experiences in contemporary technology

Controlling display of users on the logon screen in Linux Mint 20.3

15th February 2022

Recently, I tried using Commento with a static website that I was developing and this needed PostgreSQL rather than MySQL or MariaDB, which many content management tools use. That meant a learning curve that made me buy a book as well as the creation of a system account for administering PostgreSQL. These are not the kind of things that you want to be too visible so I wanted to hide them.

Since Linux Mint uses AccountsService, you cannot use lightdm to do this (the comments in /etc/lightdm/users.conf suggest as much). Instead, you need to go to /var/lib/AccountsService/users and look for a file called after the user name. If one exists, all that is needed is for you to add the following line under the [User] section:

SystemAccount=true

If there is no file present for the user in question, then you need to create one with the following lines in there:

[User]
SystemAccount=true

Once the configuration files are set up as needed, AccountsService needs to be restarted and the following command does that deed:

sudo systemctl restart accounts-daemon.service

Logging out should reveal that the user in question is not listed on the logon screen as required.

A quick look at the 7G Firewall

17th October 2021

There is a simple principal with the 7G Firewall from Perishable press: it is a set of mod_rewrite rules for the Apache web server that can be added to a .htaccess file and there also is a version for the Nginx web server as well. These check query strings, request Uniform Resource Identifiers (URI’s), user agents, remote hosts, HTTP referrers and request methods for any anomalies and blocks those that appear dubious.

Unfortunately, I found that the rules heavily slowed down a website with which I tried them so I am going have to wait until that is moved to a faster system before I really can give them a go. This can be a problem with security tools as I also found with adding a modsec jail to a Fail2Ban instance. As it happens, both sets of observations were made using the GTmetrix tool so it seems that there is a trade off between security and speed that needs to be assessed before adding anything to block unwanted web visitors.

Changing the UUID of a VirtualBox Virtual Disk Image in Linux

11th July 2021

Recent experimentation centring around getting my hands on a test version of Windows 11 had me duplicating virtual machines and virtual disk images though VirtualBox still is not ready for the next Windows version; it has no TPM capability at the moment. Nevertheless, I was able to get something after a fresh installation that removed whatever files were on the disk image. That meant that I needed to mount the old version to get at those files again.

Renaming partially helped with this but what I really needed to do was change the UUID so VirtualBox would not report a collision between two disk images with the same UUID. To avoid this, the UUID of one of the disk images had to be changed and a command like the following was used to accomplish this:

VBoxManage internalcommands sethduuid [Virtual Disk Image Name].vdi

Because I was doing this on Linux Mint, I could call VBoxManage without need to tell the system where it was as would be the case in Windows. Otherwise, it is the sethduuid portion that changes the UUID as required. Another way around this is to clone the VDI file using the following command but I had not realised that at the time:

VBoxManage clonevdi [old virtual disk image].vdi [new virtual disk image].vdi

It seems that there can be more than way to do things in VirtualBox at times so the second way will remain on reference for the future.

Using .htaccess to control hotlinking

10th October 2020

There are times when blogs cease to exist and the only place to find the content is on the Wayback Machine. Even then, it is in danger of being lost completely. One such example is the subject of this post.

Though this website makes use of the facilities of Cloudflare for various functions that include the blocking of image hotlinking, the same outcome can be achieved using .htaccess files on Apache web servers. It may work on Nginx to a point too but there are other configuration files that ought to be updated instead of using a .htaccess when some frown upon the approach. In any case, the lines that need adding to .htaccess are listed below though the web address needs to include your own domain in place of the dummy example provided:

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?yourdomain.com(/)?.*$ [NC]
RewriteRule .*\.(gif|jpe?g|png|bmp)$ [F,NC]

The first line turns on the mod_rewrite engine and you may have that done anyway. Of course, the module needs enabling in your Apache configuration for this to work and you have to be allowed to perform the required action as well. This means changing the Apache configuration files. The next pair of lines look at the HTTP referer strings and the third one only allows images to be served from your own web domain and not others. To add more, you need to copy the third line and change the web address accordingly. Any new lines need to precede the last line that defines the file extensions that are to be blocked to other web addresses.

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?yourdomain.com(/)?.*$ [NC]
RewriteRule \.(gif|jpe?g|png|bmp)$ /images/image.gif [L,NC]

Another variant of the previous code involves changing the last line to display a default image showing others what is happening. That may not reduce the bandwidth usage as much as complete blocking but it may be useful for telling others what is happening.

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

1st October 2019

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.

Moving a website from shared hosting to a virtual private server

24th November 2018

This year has seen some optimisation being applied to my web presences guided by the results of GTMetrix scans. It is was then that I realised how slow things were so server loads were reduced. Anything that slowed response times, such as WordPress plugins, got removed. Matomo usage also was curtailed in favour of Google Analytics while HTML, CSS and JS minification followed. What had not happened was a search for a faster server and another website has been moved onto a virtual private server (VPS) to see how that would go.

Speed was not the only consideration since security was a factor too. After all, a VPS is more locked away from other users that a folder on a shared server. There also is the added sense of control so Let’s Encrypt SSL certificates can be added using the Electronic Frontier Foundation’s Certbot. That avoids the expense of using an SSL certificate provided through my shared hosting provider and a successful transition for my travel website may mean that this one undergoes the same move.

For the VPS, I chose Ubuntu 18.04 as its operating system and it came with the LAMP stack already in place. Have offload development websites, the mix of Apache, MySQL and PHP is more familiar to me than anything using Nginx or Python. It also means that .htaccess files become more useful than they were on my previous Nginx-based platform. Having full access to the operating system by means of SSH helps too and should mean that I have less calls on technical support since I can do more for myself. Any extra tinkering should not affect others either since this type of setup is well known to me and having an offline counterpart means that anything riskier is tried there beforehand.

Naturally, there were niggles to overcome with the move. The first to fix was to make the MySQL instance accept calls from outside the server so that I could migrate data there from elsewhere and I even got my shared hosting setup to start using the new database to see what performance boost it might give. To make all this happen, I first found the location of the relevant my.cnf configuration file using the following command:

find / -name my.cnf

Once I had the right file, I commented out the following line that it contained and restarted the database service afterwards using another command to stop the appearance of any error 111 messages:

bind-address 127.0.0.1
service mysql restart

After that, things worked as required and I moved onto another matter: uploading the requisite files. That meant installing an FTP server so I chose proftpd since I knew that well from previous tinkering. Once that was in place, file transfer commenced.

When that was done, I could do some testing to see if I had an active web server that loaded the website. Along the way, I also instated some Apache modules like mod-rewrite using the a2enmod command, restarting Apache each time I enabled another module.

Then, I discovered that Textpattern needed php-7.2-xml installed so the following command was executed to do this:

apt install php7.2-xml

Then, the following line was uncommented in the correct php.ini configuration file that I found using the same method as that described already for the my.cnf configuration and that was followed by yet another Apache restart:

extension=php_xmlrpc.dll

Addressing the above issues yield enough success for me to change the IP address in my Cloudflare dashboard so it point at the VPS and not the shared server. The changeover happened seamlessly without having to await DNS updates as once would have been the case. It had the added advantage of making both WordPress and Textpattern work fully.

With everything working to my satisfaction, I then followed the instructions on Certbot to set up my new Let’s Encrypt SSL certificate. Aside from a tweak to a configuration file and another Apache restart, the process was more automated than I had expected so I was ready to embark on some fine tuning to embed the new security arrangements. That meant updating .htaccess files and Textpattern has its own so the following addition was needed there:

RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

This complemented what was already in the main .htaccess file and WordPress allows you include http(s) in the address it uses so that was another task completed. The general .htaccess only needed the following lines to be added:

RewriteCond %{SERVER_PORT} 80
RewriteRule ^(.*)$ https://www.assortedexplorations.com/$1 [R,L]

What all these achieve is to redirect insecure connections to secure ones for every visitor to the website. After that, internal hyperlinks without https needed updating along with any forms so that a padlock sign could be shown for all pages.

With the main work completed, it was time to sort out a lingering niggle regarding the appearance of an FTP login page every time a WordPress installation or update was requested. The main solution was to make the web server account the owner of the files and directories but the following line was added to wp-config.php as part of the fix even if it probably is not necessary:

define('FS_METHOD', 'direct');

There also was the non-operation of WP Cron and that was addressed using WP-CLI and a script from Bjorn Johansen. To make double sure of its effectiveness, the following was added to wp-config.php to turn off the usual WP-Cron behaviour:

define('DISABLE_WP_CRON', true);

Intriguingly, WP-CLI offers a long list of possible commands that are worth investigating. A few have been examined but more await attention.

Before those, I still need to get my new VPS to send emails. So far, sendmail has been installed, the hostname changed from localhost and the server restarted. More investigations are needed but what I have not is faster that what was there before so the effort has been rewarded already.

Updating Flatpack applications on Linux Mint 19

10th August 2018

Since upgrading to Linux Mint 19, I have installed some software from Flatpack. The cause for my curiosity was that you could have the latest versions of applications like GIMP or Libreoffice without having to depend on a third-party PPA. Installation is straightforward given the support built into Linux Mint. You just need to download the relevant package from the Flatpack website and running the file through the GUI installer. Because the packages come with extras to ensure cross-compatibility, more disk space is used but there is no added system overhead beyond that from what I have seen. Updating should be as easy as running the following single command too:

flatpack update

However, I needed to do a little extra work before this was possible. The first step was to update the configuration file at ~/.local/share/flatpak/repo/config to add the following lines:

[remote "flathub"]
gpg-verify=true
gpg-verify-summary=true
url=https://flathub.org/repo/
xa.title=Flathub

Once that was completed, I ran the following commands to import the required GPG key:

wget https://flathub.org/repo/flathub.gpg
flatpak --user remote-modify --gpg-import=flathub.gpg flathub

With this complete, I was able to run the update process and update any applications as necessary. After that first run, it has been integrated in to my normal processes by adding the command to the relevant alias definition.

Sorting out sluggish start-up and shutdown times in Linux Mint 19

9th August 2018

The Linux Mint team never pushes anyone into upgrading to the latest version of their distribution but curiosity often is strong enough an impulse to make me do just that. When it brings me across some rough edges, then the wisdom of leaving things alone is evident. Nevertheless, doing so also brings its share of learning and that is what I am sharing in this post. It also also me to collect a number of titbits that may be of use to others.

Again, I went with the in-situ upgrade option though the addition of the Timeshift backup tool means that it is less frowned upon than once would have been the case. It worked well too part from slow start-up and shutdown times so I set about track down the causes on the two machines that I have running Linux Mint. As it happens, the cause was different on each machine.

On one PC, it was networking that holding up things. The cause was my specifying a fixed IP address in /etc/network/interfaces instead of using the Network Settings GUI tool. Resetting the configuration file back to its defaults and using the Cinnamon settings interface took away the delays. It was inspecting /var/log/boot.log that highlighted problem so that is worth checking if I ever encounter slow start times again.

As I mentioned earlier, the second PC had a very different problem though it also involved a configuration file. What had happened was that /etc/initramfs-tools/conf.d/resume contained the wrong UUID for my system’s swap drive so I was seeing messages like the following:

W: initramfs-tools configuration sets RESUME=UUID=<specified UUID for swap partition>
W: but no matching swap device is available.
I: The initramfs will attempt to resume from <specified file system location>
I: (UUID=<specified UUID for swap partition>)
I: Set the RESUME variable to override this.

Correcting the file and executing the following command fixed the issue by updating the affected initramfs image for all installed kernels and speeded up PC start-up times:

sudo update-initramfs -u -k all

Though it was not a cause of system sluggishness, I also sorted another message that I kept seeing during kernel updates and removals on both machines. This has been there for a while and causes warning messages about my system locale not being recognised. The problem has been described elsewhere as follows: /usr/share/initramfs-tools/hooks/root_locale is expecting to see individual locale directories in /usr/lib/locale but locale-gen is configured to generate an archive file by default.  Issuing the following command sorted that:

sudo locale-gen --purge --no-archive

Following these, my new Linux Mint 19 installations have stabilised with more speedy start-up and shutdown times. That allows me to look at what is on Flathub to see what applications and if they get updated to the latest version on an ongoing basis. That may be a topic for another entry on here but the applications that I have tried work well so far.

Reloading .bashrc within a BASH terminal session

3rd July 2016

BASH is a command-line interpretor that is commonly used by Linux and UNIX operating systems. Chances are that you will find find yourself in a BASH session if you start up a terminal emulator in many of these though there are others like KSH and SSH too.

BASH comes with its own configuration files and one of these is located in your own home directory, .bashrc. Among other things, it can become a place to store command shortcuts or aliases. Here is an example:

alias us=’sudo apt-get update && sudo apt-get upgrade’

Such a definition needs there to be no spaces around the equals sign and the actual command to be declared in single quotes. Doing anything other than this will not work as I have found. Also, there are times when you want to update or add one of these and use it without shutting down a terminal emulator and restarting it.

To reload the .bashrc file to use the updates contained in there, one of the following commands can be issued:

source ~/.bashrc

. ~/.bashrc

Both will read the file and execute its contents so you get those updates made available so you can continue what you are doing. There appears to be a tendency for this kind of thing in the world of Linux and UNIX because it also applies to remounting drives after a change to /etc/fstab and restarting system services like Apache, MySQL or Nginx. The command for the former is below:

sudo mount -a

Often, the means for applying the sorts of in-situ changes that you make are simple ones too and anything that avoids system reboots has to be good since you have less work interruptions.

Turning off Apport crash reporting on Ubuntu

6th April 2015

Last week, I kept getting a multitude of messages from Ubuntu’s crash reporting tool, Apport. So many would appear at once on reaching the desktop session during system start-up that I actually downloaded an installation ISO disk image with the intention of performing a fresh installation to rid myself of the problem. In the end, it never came to that because another remedy produced the result that I needed.

Emptying /etc/crash was a start but it did not do what I needed and I disabled Apport altogether. This meant editing its configuration file, which is named apport and is found in /etc/default/. The following command should open it up in Gedit on supplying your password:

gksudo gedit /etc/default/apport

With the file opened, look for the line with enabled=1 and change this to enabled=0. Once that is done, restart Apport as follows:

sudo restart apport

This will need your account password to be supplied before it will act and any messages should appear thereafter. Of course, I would not have done this if there was a real system problem but my Ubuntu GNOME installation was and is working smoothly so it is the remedy that I needed. The idea behind the tool is that Ubuntu developers get information on any application crashes but I find that it directs me to the Ubuntu Launchpad bug reporting website and that requires a user name and password for the information to be processed. For some reason, that is enough to stall me and I wonder if there could be a way of getting developers what they need without adding that extra manual step. Then, more information gets supplied and we get a more stable operating system in return.

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