TOPIC: CROSS-PLATFORM SOFTWARE
Controlling display of users on the logon screen in Linux Mint 20.3
15th February 2022Recently, 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 username. 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.
Something to watch with the SYSODSESCAPECHAR automatic SAS macro variable
10th October 2021Recently, a client of mine updated one of their systems from SAS 9.4 M5 to SAS 9.4 M7. Despite performing due diligence regarding changes between the maintenance release, a change in behaviour of the SYSODSESCAPECHAR automatic macro variable surprised them. The macro variable captures the assignment of the ODS escape character used to prefix RTF codes for page numbering and other things. That setting is made using an ODS ESCAPECHAR statement like the following:
ods escapechar="~";
In the M5 release, the tilde character in this example was output by the automatic macro variable, but that changed in the M7 release to 7E, the hexadecimal code for the same and this tripped up one of their validated macro programs used in output production. The adopted solution was to use the escape sequence (ESC) that gave the same outcome that was there before the change. That was less verbose than alternative code changing the hexadecimal code into the expected ASCII character that follows.
data _null_;
call symput("new",byte(input("&sysodsescapechar.",hex.)));
run;The above supplies a hexadecimal code to the BYTE function for correct rendering, with the SYMPUT routine assigning the resulting value to a macro variable named new. Just using the escape sequence is far more succinct, though there is now an added validation need once user pilot testing has completed. In my line of business, the updating of code is the quickest part of many such changes; documentation and testing always take longer.
Using multi-line commenting in Perl to inactivate blocks of code during testing
26th December 2019Recently, I needed to inactivate blocks of code in a Perl script while doing some testing. Since this is something that I often do in other computing languages, I sought the same in Perl. To accomplish that, I need to use the POD methodology. This meant enclosing the code as follows.
=start
<< Code to be inactivated by inclusion in a comment >>
=cut
While the =start line could use any word after the equality sign, it seems that =cut is required to close the multi-line comment. If this was actual programming documentation, then the comment block should include some meaningful text for use with perldoc. However, that was not a concern here because the commenting statements would be removed afterwards anyway. It also is good practice not to leave commented code in a production script or program to avoid any later confusion.
In my case, this facility allowed me to isolate the code that I had to alter and test before putting everything back as needed. It also saved time since I did not need to individually comment out every executable line because multiple lines could be inactivated at a time.
Getting Eclipse to start without incompatibility errors on Linux Mint 19.1
12th June 2019Recent curiosity about Java programming and Groovy scripting got me trying to start up the Eclipse IDE that I had installed on my main machine. What I got instead of a successful application startup was a message that included the following:
!MESSAGE Exception launching the Eclipse Platform:
!STACK
java.lang.ClassNotFoundException: org.eclipse.core.runtime.adaptor.EclipseStarter
at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:466)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:566)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:626)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
at org.eclipse.equinox.launcher.Main.run(Main.java:1438)
at org.eclipse.equinox.launcher.Main.main(Main.java:1414)
The cause was a mismatch between Eclipse and the installed version of Java that it needed to run. After all, the software itself is written in the Java language and the installed version from the usual software repositories was too old for Java 11. The solution turned out to be installing a newer version as a Snap (Ubuntu's answer to Flatpak). The following command did the needful since snapd already was running on my machine:
sudo snap install eclipse --classic
The only part of the command that warrants extra comment is the --classic switch, since that is needed for a tool like Eclipse that needs to access a host file system. On executing, the software was downloaded from Snapcraft and then installed within its own bundle of dependencies. The latter adds a certain detachment from the underlying Linux installation and ensures that no messages appear because of incompatibilities like the one near the start of this post.
Moving a website from shared hosting to a virtual private server
24th November 2018This year has seen some optimisation being applied to my web presences, guided by the results of GTMetrix scans. It 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. Usage of Matomo also was curtailed in favour of Google Analytics, while HTML, CSS and JS minification followed. Something that had yet to happen was a search for a faster server. Now, 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 than 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 using SSH helps too and should mean that I have fewer 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 yielded enough success for me to change the IP address in my Cloudflare dashboard so it pointed 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 to 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 than what was there before, so the effort has been rewarded already.
Updating Piwik using the Linux Command Line
28th November 2016Because updating Piwik using its web interface has proved tempestuous, I have decided to update the self-hosted analytics application on an SSH session. The production web servers that I use are hosted on Linux systems, so that is why any commands apply to the Linux or UNIX command line only. What is needed for Windows servers may differ.
The first step is to down the required ZIP file with this command:
wget https://builds.piwik.org/piwik.zip
Once the download is complete, the contents of the ZIP archive are extracted into a new subfolder. This is a process that I carry out in a separate folder to that where the website files are kept before copying everything from the extraction folder in there. Here is the unzip command, and the -o switch turns on overwriting of any previously existing files:
unzip -o piwik.zip
Without the required folder in the web server area to be updated, the next step is to do the actual system update that includes any updates to the Piwik database that you are using. There are two commands that you can use once you have specified the location of your Piwik installation. The second is needed when the first option cannot find where the PHP executable is stored. My systems had something more specific than these because both PHP 5.6 and PHP 7.0 are installed. Looking in /usr/bin was enough to find what I needed to execute in place of PHP below. Otherwise, the command was the same.
./[path to piwik]/console core:update
php [path to piwik]/console core:update
While the upgrade is ongoing, it prompts you to permit it to continue before it goes and modifies the database. This did not take long on my systems, but that depends on how much data there is. Once, the process has completed, you can delete any extraneous files using the rm command.
Three handy Linux commands, one each for navigation, system Information and upgrades
8th July 2015Here are some Linux commands that I encountered in a feature article in the current issue of Linux User & Developer that I had not met before:
cd -
This returns you to the previous directory where you were before with having to go back through the folder hierarchy to get there and is handy if you are jumping around a file system and any other means is far from speedy.
lsb_release -a
It can be useful to uncover what version of a distro you have from the command line and the above works for distros as diverse as Linux Mint, Debian, Fedora (it automatically installs in Fedora 22 if it is not installed already, a more advanced approach than showing you the command like in Linux Mint or Ubuntu), openSUSE and Manjaro. These days, the version may not change too often, but it still is good to uncover what you have.
yum install fedora-upgrade
This one can be run either with sudo or in a root session started with su and it is specific to Fedora. The command performs an upgrade of the Fedora distro itself, and I wonder if the functionality has been ported to the dnf command that has taken over from yum. My experiences with that in Fedora 22 so far suggest that it should be the case, though I need to check that further with the VirtualBox VM that I have created.
Setting the PHP version in .htaccess on Apache web servers
7th September 2014The default PHP version on my outdoors, travel and photography website is 5.2.17 and that is getting on a bit now since it is no longer supported by the PHP project and has not been thus since 2011. One obvious impact was Piwik, which I use for web analytics and needs at least 5.3.2. Since WordPress 4.0 will not work without having 5.2.24 or later, that upgrade became implausible. Therefore, I contacted Webfusion's support team, and they showed me how to get to at least 5.3.3 and even as far as 5.5.9. The trick is the addition of a line of code to the .htaccess file (near the top was my choice) like one of the following:
PHP 5.3.x
AddHandler application/x-httpd-php53 .php
PHP 5.5.x
AddHandler application/x-httpd-php55 .php
When I got one of these in place, things started to look promising, but for a locked database due to my not watching how big it had got. Replacing it with two additional databases addressed the problem of losing write-access, though there was a little upheaval caused by this. Using PHP 5.5.9 meant that I spotted messages regarding the deprecation of the mysql_connect function, so that needed fixing too. Prefixing it with @ might have been a temporary fix while I sought a more permanent one. Thus, I opted for piggybacking off what WordPress uses; make use of MySQLi or PDO_MySQL are other options. Sorting the database issue meant that I saw the upgrade message for WordPress as well as a mix of plugins and themes, so all looked better, leaving me to be less concerned about losing security updates. Also, I am up to the latest version of Piwik too, and that's an even better way to be.
Copying only updated new or updated files by command line in Linux or Windows
2nd August 2014With a growing collection of photographic images, I often find myself making backups of files using copy commands and the data volumes are such that I don't want to keep copying the same files over and over again, so incremental file transfers are what I need. So commands like the following often get issued from a Linux command line:
cp -pruv [source] [destination]
Because this is on Linux, it is the bash shell that I use, so the switches may not apply with others like ssh, fish or ksh. For my case, p preserves file properties such as its time and date and the cp command does not do this always, so it needs adding. The r switch is useful because the copy then in recursive, so only a directory needs to be specified as the source and the destination needs to be one level up from a folder with the same name there to avoid file duplication. It is the u switch that makes the file copy incremental, and the v one issues messages to the shell that show how the copying is going. Seeing a file name issued by the latter does tell you how much more needs to be copied and that the files are going where they should.
What inspired this post though is my need to do the same in a Windows session, and issuing xcopy commands will achieve the same end. Here are two that will do the needful:
xcopy [source] [destination] /d /s
xcopy [source] [destination] /d /e
In both cases, it is the d switch that ensures that the copy is incremental, and you can add a date too, with a colon between it and the /d, if you see fit. The s switch copies only directories that contain files, while the e one copies even empty directories. Using the d switch without either of those did not trigger any copying action when I tried, so I reckon that you cannot do without either of them. By default, both of these commands issue output to the command line so you can keep an eye on what is happening, and this especially is useful when ensuring that files are going to the right destination because the behaviour differs from that of the bash shell on Linux.
Removing advertisements from uTorrent
12th July 2014BitTorrent may have got some bad press due to its use for downloading copyrighted material such as music and movies, but it does have its legitimate uses too. In my case, many a Linux distro has been downloaded in this way, and it does take the weight off servers by distributing the load across users instead.
Speaking of Linux, my general choice of client has been Transmission and there are others. In the Windows world, there is a selection that includes BitTorrent, Inc. themselves. However, many favour uTorrent (or μTorrent) so that's the one that I tried and there are free and subscription-based options. To me, the latter feels like overkill when an eternal licence could be made available as an easy way to dispatch the advertisements on display in the free version.
As much as I appreciate the need for ads to provide revenue to a provider of otherwise free software, they do need to be tasteful and those in uTorrent often were for dating websites that had no scruples about exposing folk to images that were unsuitable for a work setting. Those for gaming websites were more tolerable in comparison. With the non-availability of an eternal licence option, I was left pondering alternatives like qBittorrent instead. That is Free Software too, so it does have that added advantage.
However, I uncovered an article on Lifehacker that sorted my problem with uTorrent. The trick is to go into Options > Preferences via the menus and then go to the Advanced section in the dialogue box that appears. In there, go looking for each of the following options and set each one to false in turn:
offers.left_rail_offer_enabled/left_rail_offergui.show_plus_upselloffers.sponsored_torrent_offer_enabled/sponsored_torrent_offer_enabledbt.enable_pulsegui.show_notorrents_nodeoffers.content_offer_autoexec
In practice, I found some of the above already set to false and another missing, though setting those that remained from true to false cleaned up the interface, so I hope never to glimpse those unsuitable ads again. The maker of uTorrent needs to look at the issue or revenue could get lost, and prospective users could see the operation as being cheapened by what is displayed. As for me, I am happy to have gained something in the way of control.