Technology Tales

Reloading .bashrc within a BASH terminal session

BASH is a command-line interpreter that is commonly used by Linux and UNIX operating systems. Chances are that you will 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.

Batch conversion of DNG files to other file types with the Linux command line

At the time of writing, Google Drive is unable to accept DNG files, the Adobe file type for RAW images from digital cameras. While the uploads themselves work fine, the additional processing at the end that, I believe, is needed for Google Photos appears to be failing. Because of this, I thought of other possibilities like uploading them to Dropbox or enclosing them in ZIP archives instead; of these, it is the first that I have been doing and with nothing but success so far. Another idea is to convert the files into an image format that Google Drive can handle, and TIFF came to mind because it keeps all the detail from the original image. In contrast, JPEG files lose some information because of the nature of the compression.

Handily, a one line command does the conversion for all files in a directory once you have all the required software installed:

find -type f | grep -i "DNG" | parallel mogrify -format tiff {}

The find and grep commands are standard, with the first getting you a list of all the files in the current directory and sending (piping) these to the grep command, so the list only retains the names of all DNG files. The last part uses two commands for which I found installation was needed on my Linux Mint machine. The parallel package is the first of these and distributes the heavy workload across all the cores in your processor, and this command will add it to your system:

sudo apt-get install parallel

The mogrify command is part of the ImageMagick suite along with others like convert and this is how you add that to your system:

sudo apt-get install imagemagick

In the command at the top, the parallel command works through all the files in the list provided to it and feeds them to mogrify for conversion. Without the use of parallel, the basic command is like this:

mogrify -format tiff *.DNG

In both cases, the -format switch specifies the output file type, with the tiff portion triggering the creation of TIFF files. The *.DNG portion itself captures all DNG files in a directory, but {} does this in the main command at the top of this post. If you wanted JPEG ones, you would replace tiff with jpg. Should you ever need them, a full list of what file types are supported is produced using the identify command (also part of ImageMagick) as follows:

identify -list format

Overriding replacement of double or triple hyphenation in WordPress

On here, I have posts with example commands that include double hyphens, and they have been displayed merged together, something that has resulted in a comment posted by a visitor to this part of the web. All the while, I have been blaming the fonts that I have been using, only for it to be the fault of WordPress itself.

Changing multiple dashes to something else has been a feature of Word autocorrect, but I never expected to see WordPress aping that behaviour, and it has been doing so for a few years now. The culprit is wptexturize and that cannot be disabled, for it does many other useful things.

What happens is that the wptexturize filter changes '--' (double hyphens) to '–' (– in web entity encoding) and '---' (triple hyphens) to '—' (— in web entity encoding). The solution is to add another filter to the content that changes these back to the way they were, and the following code does this:

add_filter( 'the_content' , 'mh_un_en_dash' , 50 );
function mh_un_en_dash( $content ) {
$content = str_replace( '–' , '--' , $content );
$content = str_replace( '—' , '---' , $content );
return $content;
}

The first line of the segment adds in the new filter that uses the function defined below it. The third and fourth lines above do the required substitution before the function returns the post content for display in the web page. The whole code block can be used to create a plugin or placed in the theme's functions.php file. Either way, things appear without the substitution, confusing your readers. It makes me wonder if a bug report has been created for this because the behaviour looks odd to me.

Compressing a VirtualBox VDI file for a Linux guest

In a previous posting, I talked about compressing a virtual hard disk for a Windows guest system running in VirtualBox on a Linux system. Since then, I have needed to do the same for a Linux guest following some housekeeping. Because the Linux distribution used is Debian, the instructions are relevant to that and maybe its derivatives such as Ubuntu, Linux Mint and their like.

While there are other alternatives like dd, I am going to stick with a utility named zerofree to overwrite the newly freed up disk space with zeroes to aid compression later on in the process for this and the first step is to install it using the following command:

apt-get install zerofree

Once that has been completed, the next step is to unmount the relevant disk partition. Luckily for me, what I needed to compress was an area that I reserved for synchronisation with Dropbox. If it was the root area where the operating system files are kept, a live distro would be needed instead. In any event, the required command takes the following form, with the mount point being whatever it is on your system (/home, for instance):

sudo umount [mount point]

With the disk partition unmounted, zerofree can be run by issuing a command that looks like this:

zerofree -v /dev/sdxN

Above, the -v switch tells zerofree to display its progress and a continually updating percentage count tells you how it is going. The /dev/sdxN piece is generic with the x corresponding to the letter assigned to the disk on which the partition resides (a, b, c or whatever) and the N is the partition number (1, 2, 3 or whatever; before GPT, the maximum was 4). Putting all this together, we get an example like /dev/sdb2.

Once, that had completed, the next step is to shut down the VM and execute a command like the following on the host Linux system ([file location/file name] needs to be replaced with whatever applies on your system):

VBoxManage modifyhd [file location/file name].vdi --compact

With the zero filling in place, there was a lot of space released when I tried this. While it would be nice for dynamic virtual disks to reduce in size automatically, I accept that there may be data integrity risks with those, so the manual process will suffice for now. It has not been needed that often anyway.

Getting rid of Windows 10 notifications about disabling start-up applications

On several Windows 10 machines, I have been seeing messages appearing in its Action Centre pane with the heading Disable apps to help improve performance. It appeared again recently, so I decided to look further into the matter.

What I found was that the solution first involves opening up the Control Panel, which takes a little finding in Windows 10. You could use Cortana to get to it or right-clicking on the Start Menu and left-clicking on the Control Panel menu. Using the Windows key + X will produce the same menu, and choosing the same entry will have the same effect.

Once the Control Panel is open, it makes life a little easier if you change to the Large icons view using the drop-down menu under the Search Control Panel box on the right-hand side. Then, what you need to do is click on the Security and Maintenance icon.

Once in that Security and Maintenance section, you are presented with two subheadings, one for Security and one for Maintenance. So long as you have not dismissed the message in the action centre, you will see a corresponding entry under the Maintenance section. At the bottom of that entry, there will be a link that turns off these messages permanently, and clicking on this will have the desired effect.

Turning off push notifications in Firefox 46

Firefox 44 introduced a feature I only recently noticed when Yahoo Mail offered browser notifications for new emails; I did not need this and could not switch it off permanently for that site. This meant I was bothered each time I checked that email address, an unnecessary irritation. Other websites offered similar push notifications but allowed permanent deactivation, making this a site-specific function unless you take an alternative approach.

Open a new browser tab and enter about:config in the address bar, then press return. If this is your first time, a warning message will appear, which you can dismiss permanently. This reveals a searchable list of options. Find dom.webnotifications.enabled and dom.webnotifications.serviceworker.enabled. By default, these values are set to 'true'. Double-click each one to change them to 'false'. This will prevent push notification offers from web services like Yahoo Mail, reducing intrusions during your browsing.

Compressing a VirtualBox VDI file for a Windows guest running on a Linux Host

Recently, I had a situation where my the VDI files for my Windows 10 virtual machine expanded in size all of a sudden and I needed to reduce them. My downloading maps for use with RouteBuddy may have been the cause, so I moved the ISO installation files onto the underlying Linux Mint drives. With that space, I then set to uncovering how to compact the virtual disk file, and the Sysinternals sdelete tool was recommended for clearing unused space. After downloading, I set it to work in a PowerShell session running on the guest operating system from its directory using the following command:

.\sdelete -z [drive letter designation; E: is an example]

From the command prompt, the following should do:

sdelete -z [drive letter designation; E: is an example]

Once, that had completed, I shut down the VM and executed a command like the following from a bash terminal session:

VBoxManage modifyhd [file location/file name].vdi --compact

Where there was space to release, VDI files were reduced in size to return more disk space. More could be done, so I will look into the Windows 10 drives to see what else needs to be moved out of them.

Killing Windows processes from the command line

During my days at work, I often hear about the need to restart a server because something has gone awry with it. This makes me wonder if you can kill processes from the command line, like you do in Linux and UNIX. A recent need to reset Windows Update on a Windows 10 machine gave me enough reason to answer the question.

Because I already knew the names of the services, I had no need to look at the Services tab in the Task Manager like you otherwise would. Then, it was a matter of opening up a command line session with Administrator privileges and issuing a command like the following (replacing [service name] with the name of the service):

sc queryex [service name]

From the output of the above command, you can find the process identifier, or PID. With that information, you can execute a command like the following in the same command line session (replacing [PID] with the actual numeric value of the PID):

taskkill /f /pid [PID]

After the above, the process no longer exists and the service can be restarted. With any system, you need to find the service that is stuck to kill it, but that would be the subject of another posting. What I have not got to testing is whether these work in PowerShell, since I used them with the legacy command line instead. Along with processes belonging to software applications (think Word, Excel, Firefox, etc.), that may be something else to try should the occasion arise.

WARNING: No bars were drawn. This could have been caused by ORDER= on the AXIS statement. You might wish to use the MIDPOINTS= option on the VBAR statement instead.

What you see above is an error issued by a SAS program, akin to what a colleague at work recently found. The following code will reproduce this, so let us walk through the steps to explain a possible cause for this.

The first stage is to create a test dataset containing variables y and x, for the vertical and midpoint axes, respectively, and populating these using a CARDS statement in a data step:

data a;
    input y x;
    cards;
    1 5
    3 9
    ;
run;

Now, we define an axis with tick marks for particular values that will be used as the definition for the midpoint or horizontal axis of the chart:

axis1 order=(1 3);

Then, we try creating the chart using the GCHART procedure that comes with SAS/GRAPH and this is what results in the error message being issued in the program log:

proc gchart data=a;
    vbar x / freq=y maxis=axis1;
    run;
quit;

The cause is that the midpoint axis tick marks are not included in the data, so changing these to the actual values of the x variable removes the message and allows the creation of the required chart. Thus, the AXIS1 statement needs to become the following:

axis1 order=(5 9);

Another solution is to remove the MAXIS option from the VBAR statement and let GCHART to be data-driven. However, if requirements do not allow this, create a shell dataset with all expected values for the midpoint axis with y set 0 since that is used for presenting frequencies as per the FREQ option in the VBAR statement.

Resolving Windows Update Error 0x80244019 on Windows 10

In Windows 10, the preferred place to look if you fancy prompting an update of the system is in the Update & Security section of the Settings application. At the top is the Windows Update, and the process usually is as simple as pressing the Check for updates button. For most of the time, that has been my experience, but it stopped working on my main Windows 10 virtual machine, so I needed to resolve the problem.

Initially, going into the Advanced Options section and deselecting the tick box for Give me updates for other Microsoft products when I update Windows helped. However, it seemed a non-ideal solution, so I looked further. When it was then that I found that manually resetting a system's Windows Updates components helped others, I tried that and restarted the system.

The first part of the process was to right-click on the Start Menu button and select the Windows PowerShell (Admin) entry from the menu that appeared. This may be replaced by Command Prompt (Admin) on your system on your machine, but the next steps in the process are the same. In fact, you could include any commands you see below in a script file and execute that if you prefer. Here, I will run through each group in succession.

From either PowerShell or the Command Prompt, you need to stop the Windows Update, Cryptographic, BITS (or Background Intelligent Transfer Service) and MSI Installer services. To accomplish this, execute the following commands at a command prompt:

net stop wuauserv
net stop cryptSvc
net stop bits
net stop msiserver

With the services stopped, it is then possible to rename the SoftwareDistribution and Catroot2 folders so you can refresh everything to remove them. To accomplish this, execute the following pair of commands using either PowerShell or the Command Prompt:

ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
ren C:\Windows\System32\catroot2 Catroot2.old

Once you have the folders renamed, then you can start the Windows Update, Cryptographic, BITS and MSI Installer services by executing the following commands in either PowerShell or the Command Prompt:

net start wuauserv
net start cryptSvc
net start bits
net start msiserver

Once these have completed, you may close the PowerShell or Command Prompt window that you were using and restart the machine. Going into the Update & Security section of the Settings tool afterwards and pressing the Check for updates button now builds new versions of the folders that you renamed, and this takes a little while longer than the usual update process. Otherwise, you could let your system rebuild things in its own time. As it happens, I opted for manual intervention and all has worked well since then.