Adventures & experiences in contemporary technology
My usual way for sending the output of one command to another is to be place one command after another, separated by the pipe (|) operator and adjusting the second command as needed. However, I recently found that this approach does not work well for docker pull commands and I then uncovered another option.
That is to enclose the input command in $( ) within the output command. Within the parentheses, any kind of command can be declared and includes anything with piping as part of it. As long as text is being printed to the terminal, it can be fed to the second command and used as required. Thus, you can have something like the following:
docker pull $([command outputting name of image to download])
This approach has helped with other kinds of automation of docker image and container use and deployment because it is so general. There may be other uses found for the approach yet.
Since I often use the tail command to look at the end of a log file and occasionally in combination with the watch command for constant updates, I got to wondering if the number of lines issued by the tail command could be changed. That is a simple thing to do with the -n switch. All you need is something like the following:
tail -n 20 logfile.log
Here the value of 20 is the number of lines produced when it would be 10 by default, and logfile.log gets replaced by the path and name of what you are examining. One thing to watch is that your terminal emulator can show all the lines being displayed. If you find that you are not seeing all the lines that you expect, then that might be the cause.
While you could find this by looking through the documentation, things do not always register with you during dry reading of something laden with lists of parameters or switches. That is an affliction with tools that do a lot and/or allow a lot of customisation.
With Windows 10 support to end in October 2025 and VirtualBox now offering full support for Windows 11, I have moved onto Windows 11 for personal use while retaining Windows 10 for professional work, at least for now. Of course, a lot could happen before 2025 with rumours of a new Windows version, the moniker Windows 12 has been mooted, but all that is speculation for now.
As part of the changeover, I moved the Adobe apps that I have in an ongoing subscription, Lightroom Classic and Photoshop are the main ones for me, to the new virtual machine. That meant that some settings from the previous one were lost and needed reinstating.
One of those was the persistence of Library Filters, so I had to find out how to get that sorted. If my memory is not fooling me, this seemed to be a default action in the past and that meant that I was surprised by the change in behaviour.
Nevertheless, I had to go to the File menu, select Library Filters (it is near the bottom of the menu in the current version at the time of writing) and switch on Lock Filters by clicking on it to get a tick mark preceding the text. There is another setting called Remember Each Source’s Filters Separately in the same place that can be set in the same manner if so desired, and I am experimenting with that at the moment, even though I have not bothered with this in the past.
Recently, I wanted to extract some text from the Linux command by word number only for multiple spaces to make things less predictable. The solution was to remove the duplicate spaces. This can be done using sed but you add the complexity of regular expressions if you opt for that solution. Instead, the tr command offers a neater approach. For removing duplicate spaces, the command takes the following form:
echo "test test" | tr -s " "
Since I was piping some text to the command, that is what I have above. The tr command is intended to replace or delete characters and the -s switch is a shorthand for --squeeze-repeats. The actual character to be deduplicated is passed in quotes at the end; here, it is a space but it could be anything that is duplicated. The resulting text in this example becomes:
test test
After the processing, there is now only one space separating the two words, which is the solution that I sought. It certainly cut out any variability that I was encountering in my usage.
In recent days, I have been trying to get Windows 11 to run smoothly within a VirtualBox virtual machine, and there has been a lot of experimentation along the way. This was to eradicate intermittent freezes that escalated CPU usage and necessitated hard restarts. If I was to use Windows 11 as a long-term replacement for Windows 10, these needed to go.
An internet search showed that others faced the same predicament but a range of proposed solutions did nothing for me. The suggestion of enabling 3D graphics capability did nothing but produce a black screen at startup time so that was not a runner. It might have been the combination of underlying graphics hardware and the drivers on my Linux Mint machine that hindered me when it helped others.
In the end, a look at the bug tracker for Windows guest operating systems running on VirtualBox sent me in another direction. The Paravirtualisation interface also may have caused issues with Windows 10 virtual machines since these were all set to KVM. Doing the same for Windows 11 seems to have stopped the freezing behaviour so far. It meant going to the virtual machine settings, navigating to System > Acceleration and changing the dropdown menu value from Default to KVM before clicking on the OK button.
Before that, I have been blaming the newness of VirtualBox 7 (it is best not to expect too much of a fresh release bringing such major changes) and even the way that I installed Windows 11 using the streamlined installation or licensing issues. Now that things are going better, it may have been a lesson from Windows 10 that I had forgotten. The EFI, Secure Boot and TPM 2.0 requirements of Windows 11 also blindsided me, especially given the long wait for VirtualBox to add such compatibility, but that is behind me at this stage.
Windows 11 is not perfect but Start11 makes it usable and the October 2025 expiry for Windows 10 also focuses my mind. It is time to move over for sake of future-proofing if nothing else. In time, we may get a better operating system as Windows 11 matures and some minds surely are thinking of a “Windows 12”. However things go, it may be that we get to a point where something vintage in the nature of Windows XP, Windows 7 or Windows 10 appears. Those older versions of Windows became like old gold during their lives.
For reasons that I cannot recall now, I installed the Hugo static website generator on my Linux system and web servers using Homebrew. The only reason that I suggest is that it might have been a way to get the latest version at the time since Linux Mint only does major changes every two years, keeping it in line with long-term support editions of Ubuntu.
When Homebrew was installed, it changed the lookup path for command line executables by adding the following line to my .bashrc file:
eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"
This executed the following lines:
export HOMEBREW_PREFIX="/home/linuxbrew/.linuxbrew";
export HOMEBREW_CELLAR="/home/linuxbrew/.linuxbrew/Cellar";
export HOMEBREW_REPOSITORY="/home/linuxbrew/.linuxbrew/Homebrew";
export PATH="/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin${PATH+:$PATH}";
export MANPATH="/home/linuxbrew/.linuxbrew/share/man${MANPATH+:$MANPATH}:";
export INFOPATH="/home/linuxbrew/.linuxbrew/share/info:${INFOPATH:-}";
While the result suits Homebrew, it changed the setup of Python and its packages on my system. Eventually, this had undesirable consequences like messing up how Spyder started so I wanted to change this. There are other things that I have automated using Python and these were not working either.
One way that I have seen suggested is to execute the following command but I cannot vouch for this:
brew unlink python
What I did was to comment out the offending line in .bashrc and replace it with the following:
export PATH="$PATH:/home/linuxbrew/.linuxbrew/bin:/home/linuxbrew/.linuxbrew/sbin"
export HOMEBREW_PREFIX="/home/linuxbrew/.linuxbrew";
export HOMEBREW_CELLAR="/home/linuxbrew/.linuxbrew/Cellar";
export HOMEBREW_REPOSITORY="/home/linuxbrew/.linuxbrew/Homebrew";
export MANPATH="/home/linuxbrew/.linuxbrew/share/man${MANPATH+:$MANPATH}:";
export INFOPATH="${INFOPATH:-}/home/linuxbrew/.linuxbrew/share/info";
The first of these adds the Homebrew paths to the end of the PATH variable instead of the start of the same as was the case before. This means that system folders get searched for executable files before the Homebrew ones. It also means that Python packages are loaded from my user area and not the Homebrew one as was the case under its own terms. There are other things to remember with Python packages such as not having a version installed at the system level and another at the user one since these will conflict with one another.
So far, the result of the Homebrew changes is not unsatisfactory and I will watch for any rough edges that need addressing. If something comes up, then I will set things up in another way.
Recently, VirtualBox gained fuller support for Windows 11 and I successively set up a new Windows 11 virtual machine that I hope will supplant a Windows 10 counterpart in time. The setup itself was streamlined but I ran into such stability issues that I set the new VM aside until a new version of VirtualBox got released. That has happened with the appearance of version 7.0.2 but Windows 11 remains prone to freezing on my Linux Mint machine. Thankfully, that now is much less frequent but the need for added stability remains outstanding.
While I was thinking about trying our Virtualbox 7.0.0, I remembered a QEMU machine that I had running Windows 11. Though QEMU proved more limited than VirtualBox when it came to having easy availability of functionality like moving data in and out of the virtual machine or support for sound, there was no problem with TPM support or system stability. Since it did contain some useful data, I wondered about converting its virtual hard disk to VirtualBox format and it is easy to do. First, you need to install qemu-img and other utilities as follows:
sudo apt-get install qemu-utils
With that in place, executing a command like the following performs the required conversion. Here, the -O switch specifies the required file type of vdi in this case.
qemu-img convert -O vdi [virtual hard disk].qcow2 [virtual hard disk].vdi
While I have yet to mount it on the new Virtualbox Windows 11 virtual machine, it is good to have the old virtual hard disk available for doing so. The thought of using it as a boot drive in VirtualBox did enter my mind but the required change of drivers and other incompatibilities dissuaded me from doing so.
Recently, a message appear on some web servers that I have that exhorted me to upgrade to Ubuntu 22.04.1 using the do-release-upgrade command. In the interests of remaining current, I did just that to get another message, one like the following:
The upgrade needs a total of [amount of space with units] free space on disk `/boot`.
Please free at least an additional [amount of space with units] of disk space on `/boot`.
Empty your trash and remove temporary packages of former installations
using `sudo apt-get clean`.
Using sudo apt-get clean did not resolve the problem so the advice given was of no use. The actual problem was that there were too many old kernels cluttering up /boot and searching around the web provided that wisdom. What also came up was a single command for fixing the problem. However, removing the wrong kernel can trash a system so I took a more cautious approach. First, I listed the kernels to be removed and checked that they did not include the currently running one. This was done with the following command (broken up over several lines for clarity using the backslash character to denote continuation) and running uname -r found the details of the running kernel:
dpkg -l linux-{image,headers}-"[0-9]*" \
| awk '/ii/{print $2}' \
| grep -ve "$(uname -r \
| sed -r 's/-[a-z]+//')"
The dpkg command listed the installed kernels with awk, grep and sed filtering out unwanted sections of the text. The awk command takes the tabular output from dpkg and turns it into a list. The -v switch on the grep command gets the lines that do not match the search expression created by the sed command, while the -e switch makes grep look for patterns. The sed command removes all letters from the output of the uname command, where the -r switch produces the kernel release details, to leave on the release number of the current kernel. On being satisfied that nothing untoward would happen, the full command below (also broken up over several lines for clarity using the backslash character to denote continuation) could be executed.
sudo apt purge $(dpkg -l linux-{image,headers}-"[0-9]*" \
| awk '/ii/{print $2}' \
| grep -ve "$(uname -r \
| sed -r 's/-[a-z]+//')")
This apt to purge the unwanted kernels, thus freeing up enough space for the upgrade to continue. That happened without significant incident though there were some remediations needed on the PHP side to get the website working smoothly again.
This is the second post on Ansible following my main system’s upgrade to Linux Mint 21. Then, I manually ran some Ansible playbooks only to spot messages that I had not noticed before. Here, I discuss two messages issued because of an issue with an inventory file, which is where one defines lists of servers against which playbooks are executed. The default is called hosts and is located at /etc/ansible but the system upgrade had renamed the existing one so Ansible could not find it. The solution was to take a copy and put somewhere safer. Then, I needed to add the location of the new file to the affected ansible-playbook commands using the following construct:
ansible-playbook [playbook path] -i [inventory file path]
Before I did this, I was seeing messages including the text “Could not match supplied host pattern” or others with the following text:
[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided hosts list is empty, only localhost is available. Note that the implicit localhost does not match 'all'
The cause was the same in each case and attending to the inventory file got rid of the unwanted messages. The new file also should not be affected by system upgrades in the future.
My primary use for Ansible is doing system updates using the inbuilt apt module. Recently, I updated my main system to Linux Mint 21 and a few things like Ansible stopped working. Removing instances that I had added with pip3 sorted the problem but I then ran playbooks manually only for various warning messages to appear that I had not noticed before. What follows below is one of these.
[WARNING]: The value True (type bool) in a string field was converted to u'True' (type string). If this does not look like what you expect, quote the entire value to ensure it does not change.
The message is not so clear in some ways, not least because it had me looking for a boolean value of True when it should have been yes. A search on the web revealed something about the apt module that surprised me.: the value of the upgrade parameter is a string when others like it take boolean values of yes or no. Thus, I had passed a bareword of yes when it should have been declared in quotes as “yes”. To my mind, this is an inconsistency but I have changed things anyway to get rid of the message.