Adventures & experiences in contemporary technology
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.
In the world of UNIX and Linux, symbolic links are shortcuts but they do not work like normal Windows shortcuts because you do not jump from one location to another with the file manager’s address bar changing what it shows. Instead, it is as if you see the contents of the directory at another quicker to access location in the file system and the same sort of thinking applies to files too. In some ways, it is like giving files and directories alternative aliases. There are soft links that point to the name of a given directory or file and hard links that point to actual files or directories.
For a long time, I was under the mistaken impression that such things did not exist in Windows until I came across the mklink command, which came with the launch of Windows Vista at the start of 2007. While the then new feature may not be an obvious to most of us, it does does that Windows did incorporate a feature from UNIX and Linux well before the advent of virtual desktops on Windows 10.
By default, the aforementioned command sets up symbolic links to files and the /D switch allows the same to be done for directories too. The /H switch makes a hard link instead of a soft link so we get much of the functionality of the ln command in UNIX and Linux. Here is an example that creates a soft symbolic link for a directory:
mklink /D shortcut target_directory
Above, shortcut is the name of the symbolic link file and target_directory is the destination to which it links. In my experience, it works best for destinations beyond your home folder and, from what I have read, hard links may not be possible across different disks either.
On Friday, I was working on a system where a session is instantiated from a stored virtual machine that produces a fresh session every time so all previous changes get lost. What I have is a batch script that I run to reinstate what I need and I encountered another task that I wanted it to do.
Part of my work involves the creation of plain text files with the extension lst and this is getting associated with SAS instead of Notepad. While you can reassign such associations using the GUI, it would be nice to do it via the command line too so the assoc and ftype commands caught my interest. The first of these associates a file with a given extension with a desired file type while the second shows the available file types together with the associated applications that open them. The assoc command also show all the associations that are in place when it is executed with no parameters and the ftype command does the same for file types.
Once you have picked out a file type with the ftype command, then the assoc can be used like the following:
assoc .lst=txtfile
The above associates an extension with a file type. In the this, .lst files are going to get opened by Notepad because of the txtfile association. Though it did not do what I wanted on Friday due to system lockdown, it is good to know that this is possible and that even the Windows command line supports goodies like these.
It seems that the Rename-Item commandlet in Powershell is a very useful tool when it comes to smarter renaming of files. Even text substitution is a possibility and what follows is an example that takes the output of the Dir command for listing the files in a directory and replaces hyphens with underscores in each one.
Dir | Rename-Item –NewName { $_.name –replace “-“,”_” }
The result is that something like the-file.txt becomes the_file.txt. This behaviour is reminiscent of the rename command found on Linux and UNIX systems, where regular expressions can be used like in the following example that has the same result as the above:
rename ‘s/-/_/g’ *
In both cases, you do need to be careful as to what files are in a directory for this though the wildcard syntax on Linux or UNIX will be more familiar who has worked with files via almost any command line. Another thing to watch in the UNIX world is that ** parses the whole directory structure and that could be something that is not wanted for much of the time.
All of this is a far cry from the capabilities of the ren or rename command used in the days of MS-DOS and what has become the legacy Windows command line. Apart from simple renaming, any attempt at tweaking a filename through substitution ended up with the extra string getting appended to filenames when I tried it. Thus, the Powershell option looks better in comparison.
Recently, a timestamp got changed on an otherwise unaltered file on me and I needed to change it back. Luckily, I found an answer on the web that used PowerShell to do what I needed and I am recording it here for future reference. The possible commands are below:
$(Get-Item temp.txt).creationtime=$(Get-Date "27/10/2014 04:20 pm")
$(Get-Item temp.txt).lastwritetime=$(Get-Date "27/10/2014 04:20 pm")
$(Get-Item temp.txt).lastaccesstime=$(Get-Date "27/10/2014 04:20 pm")
The first of these did not interest me since I wanted to leave the file creation date as it was. The last write and access times were another matter because these needed altering. The Get-Item commandlet brings up the file, so its properties can be set. Here, these include creationtime, lastwritetime and lastaccesstime. The Get-Date commandlet reads in the provided date and time for use in the timestamp assignment. While PowerShell itself is case-insensitive, I have opted to show the camel case that is produced when you are tabbing through command options for the sake of clarity.
The Get-Item and Get-Date have aliases of gi and gd, respectively and the Get-Alias commandlet will show you a full list while Get-Command (gcm) gives you a list of commandlets. Issuing the following gets you a formatted list that is sent to a text file:
gcm | Format-List > temp2.txt
There is some online help but it is not quite as helpful as it ought to be so I have popped over to Microsoft Learn whenever I needed extra enlightenment. Here is a command that pops the full thing into a text file:
Get-Help Format-List -full > temp3.txt
In fact, getting a book might be the best way to find your way around PowerShell because of all its commandlets and available objects.
For now, other commands that I have found useful include the following:
Get-Service | Format-List
New-Item -Name test.txt -ItemType "file"
The first of these gets you a list of services while the second creates a new blank text file for you and it can create new folders for you too. Other useful commandlets are below:
Get-Location (gl)
Set-Location (sl)
Copy-Item
Remove-Item
Move-Item
Rename-Item
The first of the above is like the cwd or pwd commands that you may have seen elsewhere in that the current directory location is given. Then, the second will change your directory location for you. After that, there are commandlets for copying, deleting, moving and renaming files. These also have aliases so users of the legacy Windows command line or a UNIX or Linux shell can use something that is familiar to them.
Little fixes like the one with which I started this piece are all very good to know but it is in scripting that PowerShell really is said to show its uses. Having seen the usefulness of such things in the world on Linux and UNIX, I cannot disagree with that and PowerShell has its own IDE too. That may be just as well given how much there is to learn. That especially is the case when you might need to issue the following command in a PowerShell session opened using the Run as Administrator option just to get the execution as you need it:
Set-ExecutionPolicy RemoteSigned
Issuing Get-ExecutionPolicy will show you if this is needed when the response is: Restricted. A response of RemoteSigned shows you that all is in order, though you need to check that any script you then run has no nasty payload in there, which is why execution is restrictive in the first place. This sort of thing is yet another lesson to be learnt with PowerShell.
With the release of Windows 8 around this time last year, I thought that the full retail version that some of us got for fresh installations on PC’s, real or virtual, had become a thing of the past. In fact, it did seem that every respecting technology news website and magazine was saying just that. The release that you would buy from Microsft or from mainstream computer stores was labelled as an upgrade. That made it look as if you needed the OEM or System Builder edition for those PC’s that needed a new Windows installation and that the licence that you bought was then attached to the machine from when it got installed on there.
As is usual with Microsoft, the situation is less clear cut than that. For instance, there was some back-pedalling to allow OEM editions of Windows to be licensed for personal use on real or virtual PC’s. With Windows & and its predecessors, it even was possible to be able to install afresh on a PC without Windows by first installing on inactivated copy on there and then upgrading that as if it was a previous version of Windows. Of course, an actual licence was of the previous version of Windows was needed for full compliance if not the actual installation. At times, Microsoft muddies waters so as to keep its support costs down.
Even with Microsoft’s track record in mind, it still did surprise me when I noticed that Amazon was selling what appeared to be full versions of both Windows 8.1 and Windows 8.1 Pro. Having set up a 64-bit VirtualBox virtual machine for Windows 8.1, I got to discovering the same for software purchased from the Microsoft web site. However, unlike the DVD versions, you do need an active Windows installation if you fancy a same day installation of the downloaded software. For those without Windows on a machine, this can be as simple as downloading either the 32-bit or the 64-bit 90 day evaluation editions of Windows 8.1 Enterprise and using that as a springboard for the next steps. This not only be an actual in-situ installation but there options to create an ISO or USB image of the installation disk for later installation.
In my case, I created a 64-bit ISO image and used that to reboot the virtual machine that had Windows 8.1 Enterprise on there before continuing with the installation. By all appearances, there seemed to be little need for a pre-existing Windows instance for it to work so it looks as if upgrades have fallen by the wayside and only full editions of Windows 8.1 are available now. The OEM version saves money so long as you are happy to stick with just one machine and most users probably will do that. As for the portability of the full retail version, that is not something that I have tested and I am unsure that I will go beyond what I have done already.
My main machine has seen a change of motherboard, CPU and memory so it could have de-activated a pre-existing Windows licence. However, I run Linux as my main operating system and, apart possibly from one surmountable hiccup, this proves surprisingly resilient in the face of such major system changes. For running Windows, I turn to virtual machines and there were no messages about licence activation during the changeover either. Microsoft is anything but confiding when it comes to declaring what hardware changes inactivate a licence. Changing a virtual machine from VirtualBox to VMware or vice versa definitely so does it so I tend to avoid doing that. One item that is fundamental to either a virtual or a real PC is the mainboard and I have seen suggestions that this is the critical component for Windows licence activation and it would make sense if that was the case.
However, this rule is not hard and fast either since there appears to be room for manoeuvre should your PC break. It might be worth calling Microsoft after a motherboard replacement to see if they can help you and I have seen that it is. All in all, Microsoft often makes what appear to be simple rules only to override them when faced with what happens in the real world. Is that why they can be unclear about some matters at times? Do they still hanker after how they want things to be even when they are impossible to keep like that?
Linux and UNIX have the touch command for changing the creation dates and times for files. However, it also will create empty text files for you as well. In fact, there are times when I feel the need to do this sort of thing on Windows too and the following command accomplishes the deed when run in a Command Prompt window:
type nul > command.bat
Essentially, null output is sent to a file that is created anew, command.bat in this case. Then, you can edit it in Notepad (or whatever is your choice of text editor) and add in what you need. This will not work in Powershell so you need another command for that:
New-Item command.bat -type file
This uses the New-Item command, which also can be used to create folders as well if you so desire. Then, the command becomes the following:
New-Item c:\commands -type directory
Note that file on the previous example has become directory and there is the -force option should you need to overwrite what already exists for some reason…
That other use of the UNIX/Linux touch command can be performed from the Command Prompt too and here is an example command:
copy /b file.txt +,,
The /b switch switches on binary behaviour for the copy command though that appears to be the default action anyway. The + operator triggers concatenation and ,, gets around not having a defined destination because you cannot copy a file over itself. If that were possible, then there would no need for special syntax for changing the date and time for a file.
For doing the same thing with Powershell, try the following:
(GetChildItem test.txt).LastWriteTime=Get-Date
The GetChildItem command has aliases of gci, dir and ls and the last two of these give away its essential purpose. Here, it is used to pick out the test.txt file so that its timestamp can be replaced with the current date and time returned by the Get-Date command. The syntax looks a little more complex even if it achieves the same end. Somehow, that touch command is easier to explain. Are Linux and UNIX that complicated after all?
Aside from permissions that can be set using the cacls command, Windows files have properties like read only, archive and hidden. Of course, these are not the same or as robust as access permissions but they may have a use in stopping accidental updates to files when you don’t have access to use of the cacls command. While you could set these attributes using the properties page of any file, executing the attrib command on the Windows command is more convenient. Here are some possible usage options:
Set the read only flag on a file:
attrib +r test.txt
Remove the read only flag from a file (found a use for this one recently):
attrib -r test.txt
Set the archive flag on a file:
attrib +a test.txt
Remove the archive flag from a file:
attrib -a test.txt
Set the hidden only flag on a file:
attrib +h test.txt
Remove the hidden flag from a file:
attrib -h test.txt
Using the /s option and wildcards processes a number of files at a time and /d applies the command to directories. They could come in handy when removing read only attributes (also called bits in places) from files copied from read only optical media such as CD’s and DVD’s.
2007-01-30 (next Tuesday) is given as the date for Windows Vista’s launch to the wider world. It’s an expensive beast so I think that I’ll wait for a while and take the plunge when all the hype has died down. When compared with retail prices, it seems that a TechNet Plus subscription would be a good move, particularly as it would be useful to have an awareness of up-and-coming Microsoft Technology for my work. However, what looks really tempting is the OEM option. There are caveats with this, especially since Microsoft changed the licensing arrangements so that OEM Windows should only be bought installed on a complete PC. This has always been the case with its server and office software, but buying a component such as a CPU or hard drive once was sufficient for OEM Windows. I suppose that I’ll keep waiting then…
I have a free subscription to Microsoft‘s Microsoft Learn but with the onset of Vista and the latest issue dangles a carrot in front of me: the idea of a Technet Plus subscription. Trouble is that it is £283 per annum in the UK, not cheap. Nevertheless, that does rather neatly compare to the price of Windows Vista and that comes as part of the package. I think that I’ll revisit the idea when upgrading time comes and that will be a while after the Vista launch date of 30/1/2007. Given the security changes in the latest Windows incarnation, I’ll wait to ensure that I will not be put out too much before making the jump.