Disable the “Other people are logged on to this computer” message on a Windows VM

If you’re logged on with Remote Desktop (and probably in several other cases) Windows will not respond appropriately to the power button being pressed. Instead of shutting down, it will display a message asking you if that’s what you really want to do, as if holding the same button for 5 seconds to force the damn thing to shut down isn’t your next move.

This solution may or may not be Windows XP specific, as that’s where I encountered the issue, but I’ve confirmed that setting the following registry key removes this message and shuts down when a simulated ACPI button is pressed:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Error Message Instrument]

How to use Invoke-WebRequest in PowerShell without having to first open Internet Explorer

So, you get this error message:

Invoke-WebRequest : The response content cannot be parsed because the Internet Explorer engine is not available, or Internet Explorer’s first-launch configuration is not complete. Specify the UseBasicParsing parameter and try again.

..and sure, you could use -UseBasicParsing but, depending on your use case, you might then have to write a lot of functionality yourself that’s already handled for you if you avoid basic parsing.

Luckily, the Internet Exporer First Run wizard can be disabled in the registry, and if your script runs as a privileged user, you can do this from PowerShell:

$keyPath = 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Internet Explorer\Main'
if (!(Test-Path $keyPath)) { New-Item $keyPath -Force | Out-Null }
Set-ItemProperty -Path $keyPath -Name "DisableFirstRunCustomize" -Value 1


It’s worth noting that if your computers are in a domain, there’s also an easy to use GPO for this, at Computer Configuration => Policies => Administrative Templates => Windows Components => Internet Explorer, called Prevent running First Run wizard.

More about that over here (local archive).

“Invalid provider type specified” CryptographicException when accessing the PrivateKey property of a certificate in C#/.Net

We recently encountered this in a production environment: A customer had installed a new certificate, and this exception began showing up in the logs. Luckily, the application was smart enough to at least fall back on using the previous (not yet expired) certificate, so no downtime occurred.

Turns out the customer had been provided with a certificate with the private key in CNG format. This is not compatible with several versions of .Net. The solution was to convert the key to a standard RSA key using the following commands on a machine with OpenSSL installed:

# You need to set these to match your environment
cert="CertificateFileNameHere.pfx" password="TopSecretCertificatePasswordHere"
# These should run as is - they use the variables provided above openssl pkcs12 -in "${cert}.pfx" -nokeys -out "${cert}.cer" -passin "pass:${password}" openssl pkcs12 -in "${cert}.pfx" -nocerts -out "${cert}.pem" -passin "pass:${password}" -passout "pass:${password}" openssl rsa -inform PEM -in "${cert}.pem" -out "${cert}.rsa" -passin "pass:${password}" -passout "pass:${password}" openssl pkcs12 -export -in "${cert}.cer" -inkey "${cert}.rsa" -out "converted.pfx" -passin "pass:${password}" -passout "pass:${password}"

Importing the converted certificate back into Windows’ Certificate Store, the .Net application was capable of loading it just fine.

The solution was mostly found here.

Docker starts slowly on Raspberry Pi / Raspbian

After installing the latest stable version of docker-ce (5:18.09.0~3-0~raspbian-stretch as of the time of writing), Docker would take ages to start after a reboot. Commands would even time out waiting for it.

/var/log/daemon.log shows a gap of almost 4 minutes between the attempt to start the Docker Application Container Engine and the first log line from dockerd.

Jul  5 10:10:37 RPi systemd[1]: Starting Docker Application Container Engine...
Jul 5 10:14:07 RPi dockerd[683]: time="2019-07-05T10:14:07.808215720+02:00" level=info msg="parsed scheme: \"unix\"" module=grpc

After installing a later version of docker-ce from the test branch in attempt to remedy this, I got an interesting message while the issue persisted:

Jul  5 10:42:18 RPi systemd[1]: Starting Docker Application Container Engine...
Jul 5 10:43:30 RPi dockerd[720]: crypto/rand: blocked for 60 seconds waiting to read random data from the kernel
Jul 5 10:47:27 RPi dockerd[720]: time="2019-07-05T10:47:27.245479521+02:00" level=info msg="Starting up"

Turns out it doesn’t have enough random entropy to start. We can help the Pi generate this by running haveged. A quick apt-get install haveged and a reboot later, the logs look much better, and Docker starts immediately.

# apt-get install haveged
# reboot

The result, after downgrading to the stable version of Docker again:

Jul  5 11:08:02 RPi systemd[1]: Starting Docker Application Container Engine...
Jul 5 11:08:06 RPi dockerd[707]: time="2019-07-05T11:08:06.793516408+02:00" level=info msg="parsed scheme: \"unix\"" module=grpc

From 4 minutes to 4 seconds is a rather significant improvement, I think 🙂

Reinstalling a used iMac (20-inch, Early 2008)

So, during spring cleaning, a used iMac was discovered at work. I figured it could be used for something, so I set it up on a table. It only booted to recovery mode, so I had to reinstall it. Simple, right? No, of course not! This is an Apple product.

Apple ID needed

So, booting into the recovery mode, there’s a built-in option to reinstall the operating system. Nice. However, it immediately asks for an Apple ID. So I go make one, in a browser on another machine. You can’t use the one you’re installing to. Then I connect the iMac to the WiFi and log in.


This Apple ID has not yet been used with the App Store

Apple wants all your information

So, I can’t reinstall without “using the Apple ID with the App Store”. How does one do that? A bit of Google action informed me that I needed to give them a credit card. What the heck?!

I’m not aware of any other manufacturer who requires you to provide your credit card details in order to reinstall their operating system.

So I grab my VISA card, put in the details on appleid.apple.com, and try to log in on the iMac again. No luck.

An unexpected error occurred while signing in. Failure.

Turns out I have to restart the recovery installer to log in again. Great job, Apple. So I restart, sign in again, and get the same message as before, saying “This Apple ID has not yet been used with the App Store”.

You need iTunes

Apparently, I don’t have to review my account information as the message says, I have to accept the license agreement. How do you do that? The forums told me to use iTunes. What the heck, again?!

So, I fire up a disposable virtual machine, install Apple’s bloated music/store software, log in, accept the license agreement, restart the iMac again and log in with the account once more.


This item is temporarily unavailable. Please try again later.

Who’s the previous owner?

According to the Apple forums, the reason for the above error message is that my freshly created Apple ID is not associated with the version of Mac OS (El Capitan) I’m installing on this machine. I haven’t bought it, which is obviously true, as it’s simply what was on this machine that was in storage.

Various people have solved this by using the Apple ID that was originally used to install the machine. Not an option. I have no idea who originally installed this machine.

Full reinstall from a USB stick

Some more time on Google told me that a clean install from a USB stick was the way around this account issue. So now I need the El Capitan installation image. This used to be available in the App Store, but of course Apple removed that.

So, more Google, and I found the .dmg image on allpcworld.com. I tried various processes to get this image onto a USB stick, but in the end the only method that produced a bootable stick was to mount the .dmg on another mac, and then run an adaptation of the following commands:

$ cd /Volumes/Install\ OS\ X\ El\ Capitan/Install\ OS\ X\ El\ Capitan.app/Contents/Resources
$ sudo ./createinstallmedia --volume /Volumes/My\ USB\ Stick/ --applicationpath /Volumes/Install\ OS\ X\ El\ Capitan/Install\ OS\ X\ El\ Capitan.app/

This created a USB stick the iMac would boot. Not in any given USB port, mind you. For the USB stick to be detected, I needed to put it in the rightmost USB port when the iMac is viewed from the back.

Holding the “alt” (“option”) key on the keyboard when turning the iMac on made the USB stick show up as a bootable drive.

This copy can’t be verified

That’s right. Cue more hurdles.

This copy of the Install OS X El Capitan application can't be verified. It may have been corrupted or tampered with during downloading.

So the iMac boots from the USB stick, but it can’t verify the image. Turns out this is because the date and time on the machine is wrong. Obviously.

Luckily, there’s a terminal available on the utilities menu at the top of the screen. I set the date using the “date” command. The solution was found in this rather shaky video.

# date 0202020216
Tue 2 Feb 2016 02:02:00 CET

Then you can close the terminal and run the installer again.

Finally installed

The rest of the installation took ages, probably due to the rather slow USB stick I selected for the job. Regardless, the rest of the procedure was fairly uneventful.

The iMac is up and running, and I like Apple even less than I did previously.

The trust relationship between this workstation and the primary domain failed

So, you resurrected a VM from the cold, damp crypts of the deepest backup dungeons, and now you can’t log in because the VM doesn’t trust the domain server anymore?

That’s alright. The Windows Domain will rotate its keys from time to time, and an offline VM snapshot will not know about it.

You don’t have to re-join the domain to fix this. Simply log in with a local admin account, or a cached domain login that’s somehow an administrator of the machine. Open a PowerShell session as said administrator, and run the following command:


That’s it!

This answer was found at implbits.com (local archive).

Finding the first (default) IPv4 gateway in a Windows batch script

I recently had to whip out my Windows batch scripting skills to grab the default gateway for a routing script. Here’s what I ended up with:

route print | findstr /R /C:"^[ ][ ]*[ ]" | for /f "tokens=3" %%i in ('more') do (echo %%i & exit) >gw.tmp
set /P gw=<gw.tmp
del gw.tmp
echo "%gw%"

This does, unfortunately, use a temporary file (gw.tmp), and I didn’t find a non-clunky way around that. But it works, for now 🙂

Suggestions on more elegant ways of doing this in a pure batch script are welcome.

Recovering versioned files from Owncloud’s data directory

Tasked with recovering files you don’t have access to through the web interface, you can always find these through the file system if you’re the operator. You could, of course, give yourself access, but let’s save that for another time. Right now we want the files our users removed and/or can’t find.

We start by looking for them in Owncloud’s data directory.

# find /mnt/data/owncloud/ -name "AWOL Excel file.xlsm*"
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542980717
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542029758
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542303810
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542631862
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1541686827
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1543226434
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542889051
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1541775363
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542722172
/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1541922874

Oh hey, there they are!

So, now we could simply copy them and ship them to our user, but let’s be a bit more fancy, since we can.

# FILE_SUFFIX=".xlsm"
# find /mnt/data/owncloud/ -name "AWOL Excel file.xlsm*" |
>   grep -E "\.v[0-9]+(\.d[0-9]+)?$" |
>   while read -r file; do
>       ts="${file##*.v}"; ts="${ts%.*}";
>       date=$(date --date="@${ts}" +"%Y%m%dT%H%M%S")
>       base="$(basename "${file%.v*}")"
>       name="${base%${FILE_SUFFIX:-}}"
>       echo "${name}-${date}${FILE_SUFFIX:-}"
>   done
AWOL Excel file-20181123T134517.xlsm
AWOL Excel file-20181112T133558.xlsm
AWOL Excel file-20181115T174330.xlsm
AWOL Excel file-20181119T125102.xlsm
AWOL Excel file-20181108T142027.xlsm
AWOL Excel file-20181126T100034.xlsm
AWOL Excel file-20181122T121731.xlsm
AWOL Excel file-20181109T145603.xlsm
AWOL Excel file-20181120T135612.xlsm
AWOL Excel file-20181111T075434.xlsm

So that’s the list of our files, with all the names neatly timestamped (translated from the UNIX timestamp at the end of Owncloud’s file names).
Not setting the $FILE_SUFFIX variable will work fine too, but you will end up with names such as “AWOL Excel file.xlsm-20181126T100034

Now, let’s copy the files to their new names in our current directory.

# FILE_SUFFIX=".xlsm"
# find /mnt/data/owncloud/ -name "AWOL Excel file.xlsm*" |
>   grep -E "\.v[0-9]+(\.d[0-9]+)?$" |
>   while read -r file; do
>       ts="${file##*.v}"; ts="${ts%.*}";
>       date=$(date --date="@${ts}" +"%Y%m%dT%H%M%S")
>       base="$(basename "${file%.v*}")"
>       name="${base%${FILE_SUFFIX:-}}"
>       cp -v "$file" "${name}-${date}${FILE_SUFFIX:-}"
>   done
'/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542980717' -> 'AWOL Excel file-20181123T134517.xlsm'
'/mnt/data/owncloud/files/user/files_versions/Important/Stuff/AWOL Excel file.xlsm.v1542029758' -> 'AWOL Excel file-20181112T133558.xlsm'
[... and so on ... ]


Here it is as a one-liner, which your browser might add a line break to anyway, in case you’re interested:

FILE_SUFFIX=".xlsm"; find /mnt/data/owncloud/ -name "AWOL Excel file.xlsm*" | grep -E "\.v[0-9]+(\.d[0-9]+)?$" | while read -r file; do ts="${file##*.v}"; ts="${ts%.*}"; date=$(date --date="@${ts}" +"%Y%m%dT%H%M%S"); base="$(basename "${file%.v*}")"; name="${base%${FILE_SUFFIX:-}}"; cp -v "$file" "${name}-${date}${FILE_SUFFIX:-}"; done

Who deleted the files from the Windows file server?

Classic whodunit – the file is gone. Who deleted it?

Well, unless you’ve already prepared for this, Windows has no log for you. Sorry.
The good news is that this is an excellent time to prepare for the next time. So let’s do that.

Enable the auditing of file operations to the Windows Event Log

Netwrix has documented the procedure for this. The relevant steps for us are:

  1. Navigate to the file share, right-click it and select “Properties” Select the “Security” tab → “Advanced” button → “Auditing” tab → Click “Add” button:
    • Select Principal: “Everyone”; Select Type: “All”; Select Applies to: “This folder, subfolders and files”; Select the following “Advanced Permissions”: “Delete subfolders and files” and “Delete”.
  2. Run gpedit.msc, create and edit new GPO → Computer Configuration → Policies → Windows Settings → Security Settings → Go to Local Policies → Audit Policy:
    • Audit object access → Define → Success and Failures.
  3. Go to “Advanced Audit Policy Configuration” → Audit Policies → Object Access:
    • Audit File System → Define → Success and Failures
    • Audit Handle Manipulation → Define → Success and Failures.
  4. Link new GPO to File Server and force the group policy update.
  5. Open Event viewer and search Security log for event ID 4656 with “File System” or “Removable Storage” task category and with “Accesses: DELETE” string. “Subject: Security ID” will show you who has deleted a file.

Extract the logs

I wrote a short PowerShell script to do this. It’s not very efficient, but it does the job, and is relatively readable 🙂

"Chewing through the log files..."
Get-WinEvent -LogName "Security" | Where-Object { $_.Id -eq 4656 } | ForEach-Object { [xml]($_.ToXml()) } | Select -ExpandProperty "Event" | Where-Object `
    ( $_.EventData.Data | Where-Object { $_.Name -eq "AccessList" -and $_."#text" -like "*%%1537*" } ) -and `
    ( $_.EventData.Data | Where-Object { $_.Name -eq "ObjectName" -and $_."#text" -like "R:\*" } )
} | ForEach-Object `
    New-Object PSObject -Property (@{
        "TimeStamp"  = ($_.System.TimeCreated.SystemTime)
        "UserName"   = ($_.EventData.Data | Where-Object { $_.Name -eq "SubjectUserName" } | Select -ExpandProperty "#text")
        "UserDomain" = ($_.EventData.Data | Where-Object { $_.Name -eq "SubjectDomainName" } | Select -ExpandProperty "#text")
        "ObjectType" = ($_.EventData.Data | Where-Object { $_.Name -eq "ObjectType" } | Select -ExpandProperty "#text")
	"ObjectName" = ($_.EventData.Data | Where-Object { $_.Name -eq "ObjectName" } | Select -ExpandProperty "#text")
} | Format-Table TimeStamp,UserDomain,UserName,ObjectType,ObjectName -AutoSize
"Press <enter> to quit"
Read-Host | Out-Null

Pro tip: For faster printout (line by line) but worse formatting, remove the -AutoSize parameter to Format-Table

This script specifically looks for files on R:\, but you can change this to whatever you want, or remove that condition all together.

Sample output

And there you go! 🙂