Virtual Machines – Saint's Log

2026-07-10 —Categories: Linux, Virtual Machines

Peeking into Ubuntu Crash Handling

I recently turned on an Ubuntu VM I had not used in a while and was greeted by this error dialog about a system program problem. I looked up this message and got a reference to Apport – Ubuntu project documentation explaining that the crash reports are in /var/crash.

There were 3 files in that folder. Although I couldn’t initially read them since I wasn’t root, it was interesting seeing the callout warning me not to start VS Code as a super user.

saint@ubuntuvm3:~$ ls -l /var/crash
total 7428
-rw------- 1 root whoopsie  158635 Jul  1 15:35 python3.10.0.crash
-rw-r----- 1 root whoopsie 2995487 Jul  9 12:50 _usr_lib_cnf-update-db.0.crash
-rw-r----- 1 root whoopsie 4444576 Jul  1 15:35 _usr_lib_python3.10_py_compile.py.0.crash
saint@ubuntuvm3:~$ head -10 /var/crash/_usr_lib_cnf-update-db.0.crash 
head: cannot open '/var/crash/_usr_lib_cnf-update-db.0.crash' for reading: Permission denied
saint@ubuntuvm3:~$ sudo code /var/crash/_usr_lib_cnf-update-db.0.crash 
mkdir: cannot create directory ‘’: No such file or directory
You are trying to start Visual Studio Code as a super user which isn't recommended. If this was intended, please add the argument `--no-sandbox` and specify an alternate user data directory using the `--user-data-dir` argument.

I copied one of the files to my home folder and tried to open it without fixing the permissions. Several warnings appeared in VS Code, which was interesting to me because I never take this path in VS Code (taking me back to my full-time QA days).

2026-07-09 18:06:17.921 [error] [Window] Error: Unable to read file '/home/saint/cnf.txt' (NoPermissions (FileSystemError): An unknown error occurred. Please consult the log for more details.)
    at Kkt.G (vscode-file://vscode-app/snap/code/215/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3828:65903)
...
2026-07-09 18:06:18.102 [error] [Window] [File Watcher (node.js)] Failed to watch /home/saint/cnf.txt for changes using fs.watch() (Error: EACCES: permission denied, watch '/home/saint/cnf.txt')
...

Nothing chmod couldn’t take care of.

saint@ubuntuvm3:~$ ls -l cnf.txt 
-rw-r----- 1 root root 2995487 Jul  9 18:06 cnf.txt
saint@ubuntuvm3:~$ sudo chmod o+r cnf.txt 
saint@ubuntuvm3:~$ ls -l cnf.txt 
-rw-r--r-- 1 root root 2995487 Jul  9 18:06 cnf.txt

An interesting aspect of the crash was that it looked like all 3 files were related to cnf-update-db. Per sources like Why do lines with “c-n-f Metadata” appear in the output of `sudo apt update`? – Ask Ubuntu, this is related to the command not found system that suggests packages to install to get the command you’re trying to use.

saint@ubuntuvm3:~$ sudo head -20 /var/crash/_usr_lib_cnf-update-db.0.crash 
ProblemType: Crash
Architecture: amd64
Date: Thu Jul  9 12:50:33 2026
DistroRelease: Ubuntu 22.04
ExecutablePath: /usr/lib/cnf-update-db
ExecutableTimestamp: 1638960799
InterpreterPath: /usr/bin/python3.10
ProcCmdline: /usr/bin/python3 /usr/lib/cnf-update-db
ProcCwd: /tmp
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 LANG=en_US.UTF-8
ProcMaps:
 6087ac793000-6087ac800000 r--p 00000000 08:02 1442737                    /usr/bin/python3.10

I knew that I needed to update everything on this VM. Firefox was on version 146.0.1. The strange thing was that the Software Updater app didn’t even start! Nothing happened when clicking on its icon. I ran apt update anyway.

saint@ubuntuvm3:~$ sudo apt update
Hit:1 https://download.docker.com/linux/ubuntu jammy InRelease
Hit:2 http://security.ubuntu.com/ubuntu jammy-security InRelease                                       
Hit:3 http://us.archive.ubuntu.com/ubuntu jammy InRelease                                              
Get:4 http://us.archive.ubuntu.com/ubuntu jammy-updates InRelease [128 kB]
Hit:5 http://us.archive.ubuntu.com/ubuntu jammy-backports InRelease
Get:6 http://us.archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages [3,624 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu jammy-updates/main i386 Packages [1,039 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu jammy-updates/universe i386 Packages [814 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu jammy-updates/universe amd64 Packages [1,277 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu jammy-updates/universe Translation-en [321 kB]
Fetched 7,203 kB in 2s (4,014 kB/s)                             
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
7 packages can be upgraded. Run 'apt list --upgradable' to see them.
saint@ubuntuvm3:~$ apt list --upgradable
Listing... Done
docker-compose-plugin/jammy 5.3.1-1~ubuntu.22.04~jammy amd64 [upgradable from: 5.2.0-1~ubuntu.22.04~jammy]
fwupd/jammy-updates 2.0.20-1ubuntu2~22.04.2 amd64 [upgradable from: 2.0.20-1ubuntu2~22.04.1]
iproute2/jammy-updates 5.15.0-1ubuntu2.2 amd64 [upgradable from: 5.15.0-1ubuntu2]
libfwupd3/jammy-updates 2.0.20-1ubuntu2~22.04.2 amd64 [upgradable from: 2.0.20-1ubuntu2~22.04.1]
python3-distupgrade/jammy-updates,jammy-updates 1:22.04.21 all [upgradable from: 1:22.04.20]
ubuntu-release-upgrader-core/jammy-updates,jammy-updates 1:22.04.21 all [upgradable from: 1:22.04.20]
ubuntu-release-upgrader-gtk/jammy-updates,jammy-updates 1:22.04.21 all [upgradable from: 1:22.04.20]
saint@ubuntuvm3:~$ uname -a
Linux ubuntuvm3 6.8.0-90-generic #91~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov 20 15:20:45 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
saint@ubuntuvm3:~$ sudo apt upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
  libfwupd2 libfwupdplugin5 libgcab-1.0-0 libslirp0 libsmbios-c2 libwpe-1.0-1 libwpebackend-fdo-1.0-1 slirp4netns
Use 'sudo apt autoremove' to remove them.
The following packages have been kept back:
  fwupd libfwupd3 python3-distupgrade ubuntu-release-upgrader-core ubuntu-release-upgrader-gtk
The following packages will be upgraded:
  docker-compose-plugin iproute2
2 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
Need to get 9,172 kB of archives.
After this operation, 72.7 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 https://download.docker.com/linux/ubuntu jammy/stable amd64 docker-compose-plugin amd64 5.3.1-1~ubuntu.22.04~jammy [8,100 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu jammy-updates/main amd64 iproute2 amd64 5.15.0-1ubuntu2.2 [1,072 kB]
Fetched 9,172 kB in 2s (5,743 kB/s)                  
Preconfiguring packages ...
(Reading database ... 181925 files and directories currently installed.)
Preparing to unpack .../iproute2_5.15.0-1ubuntu2.2_amd64.deb ...
Unpacking iproute2 (5.15.0-1ubuntu2.2) over (5.15.0-1ubuntu2) ...
Preparing to unpack .../docker-compose-plugin_5.3.1-1~ubuntu.22.04~jammy_amd64.deb ...
Unpacking docker-compose-plugin (5.3.1-1~ubuntu.22.04~jammy) over (5.2.0-1~ubuntu.22.04~jammy) ...
Setting up iproute2 (5.15.0-1ubuntu2.2) ...
Setting up docker-compose-plugin (5.3.1-1~ubuntu.22.04~jammy) ...
Processing triggers for man-db (2.10.2-1) ...

These were not as many packages as I expected to have updates! The next question was therefore how to determine whether I was on the latest security release. 22.04.5 appears to be the latest build, which is what cat /etc/lsb-release showed to my relief. Unfortunately, I didn’t check this value before I ran apt upgrade so I don’t know if this was already the version I was running when I started.

saint@ubuntuvm3:~$ uname -r
6.8.0-90-generic
saint@ubuntuvm3:~$ uname -a
Linux ubuntuvm3 6.8.0-90-generic #91~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov 20 15:20:45 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
saint@ubuntuvm3:~$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.5 LTS"

At this point, I decided to abandon the VM and create a new one with the latest release. I downloaded the 26.04 ISO from Ubuntu 24.04.4 (Noble Numbat) and verified its entry in the SHASUMS file. I ran into some errors setting up the VM in Hyper V so I ended my experiment with VMs there.

2023-01-17 —Categories: Linux, Virtual Machines

Installing CentOS on Hyper-V

A few months ago I set out to install CentOS on a VM on my Windows 11 desktop. I selected the x86_64 RPM link on the CentOS Download page (centos.org), which linked to the CentOS Mirror. Browsing to the isos/x86_64 directory presented a list of mirrors with ISO images. I selected the MIT mirror: Index of /centos/7.9.2009/isos/x86_64/ (mit.edu) then downloaded the DVD-2009 ISO.

Next, I created a new VM in Hyper-V and set the downloaded ISO as the boot disk. This was not sufficient to start the VM. Hyper-V failed to boot because the signed image’s hash is not allowed.

The solution to this is from this article: Hyper-V Boot Error: The Image’s Hash and Certificate Are not Allowed (bobcares.com). Uncheck the Enable Secure Boot option in the VM’s settings then reboot the VM.

Setup is now straightforward. Here are the screenshots of the setup process. I selected the Server with GUI Base Environment with the Performance Tools and System Administration Tools add-ons.

Once setup completed, CentOS booted and prompted me to accept the license as shown in these screenshots.

This was my first time using CentOS in more than a decade so I was pleased that there wasn’t anything particularly jarring about the experience.

2022-11-02 —Categories: Linux, Virtual Machines

Sharing Files with Ubuntu Guest on Hyper-V Host

Of the many ways to transfer files to an Ubuntu guest on Hyper-V, running these PowerShell commands (as admin) suffices for a one-off file transfer. See 4 Ways to Transfer Files to a Linux Hyper-V Guest (altaro.com) for more details about this approach.

Enable-VMIntegrationService -VMName 'Ubuntu 22.04 LTS' -Name 'Guest Service Interface'

Copy-VMFile -Name 'Ubuntu 22.04 LTS' -SourcePath 'dumpfile.gz' -DestinationPath '/home/saint/Downloads' -FileSource Host

Backstory

Yesterday I had a core dump from a Linux process that I wanted to specifically inspect in an Ubuntu VM. My host machine is a Windows 11 (10.0.22621.674) machine. The simple question of how to share files with my Ubuntu VM took me all over the map. Searching for hyper-v share files linux guest led me to Shared Folders over Hyper-V Ubuntu Guest (linuxhint.com). This had me enabling SMB 1.0/CIFS File Sharing Support (already had SMB Direct enabled) and Public folder sharing.

I then created an empty directory and turned on sharing on it as instructed. However, accessing it from Ubuntu turned out to be the problem. These are the suggested commands:

sudo apt install cifs-utils
mkdir ~/SharedFolder
sudo mount.cifs //<NAME OF YOUR PC>/<SHARED FOLDER NAME>
~/SharedFolder -o user=<YOUR WINDOWS USERNAME>

mount.cifs failed though.

saint@linuxvm:~$ sudo mount.cifs //DEVICENAME/virtual-machines
~/shared -o user=USERNAME
Password for USERNAME@//DEVICENAME/virtual-machines: ***
mount error(13): Permission denied
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs) and kernel log messages (dmesg)

There doesn’t seem to be anything particularly interesting at mount.cifs(8) – Linux man page (die.net). Running dmesg showed these messages:

[  425.318905] CIFS: Attempting to mount \\DEVICENAME\virtual-machines
[  425.318905] CIFS: Status code returned 0xc000006d STATUS_LOGON_FAILURE
[  425.318905] CIFS: VFS: \\DEVICENAME Send error in SessSetup = -13
[  425.318905] CIFS: VFS: cifs_mount failed w/return code = -13

cifs status_logon_failure – Search (bing.com) leads to a comment at STATUS_LOGON_FAILURE (0xc000006d) · Issue #478 · hierynomus/smbj (github.com) stating that STATUS_LOGON_FAILURE means that your credentials were rejected. This error code (and others) at [MS-CIFS]: SMB Error Classes and Codes | Microsoft Learn. The Windows event logs do not contain any entries related to this (surprisingly). So I pivot to the next result from my search for hyper-v share files linux guest.

4 Ways to Transfer Files to a Linux Hyper-V Guest (altaro.com) instructs you to enable the file copy guest service (either using PowerShell or the GUI). Apparently a power cycle of the VM is not necessary. See article for more info.

Enable-VMIntegrationService -VMName LinuxVM3 -Name 'Guest Service Interface'

Copy-VMFile -Name LinuxVM3 -SourcePath 'dumpfile.gz' -DestinationPath '/home/saint/Downloads' -FileSource Host

Unfortunately, Copy-VMFile fails. The VM is running Ubuntu 20.04.1 (x86_64) with kernel 5.15.0-52-generic.

It shouldn’t be this hard to just get a file into a guest VM. Looking up the docs again and Use local resources on Hyper-V virtual machine with VMConnect | Microsoft Learn suggests VMConnect but looks like enhanced session mode and Type Clipboard text are only available on VMs running a recent Windows OS. For Ubuntu, that article points to Changing Ubuntu Screen Resolution in a Hyper-V VM | Microsoft Learn. At this point, I decide to create a new VM using Hyper-V’s quick create and perhaps that will have the proper configuration for what I’m trying to do.

Creating an Ubuntu VM

Click on Hyper-V’s Quick Create… command to start creating a VM. Select the latest Ubuntu LTS (22.04). Unfortunately, the only options available are the VM name and the network switch to use. Clicking on Create Virtual machine creates a VM on the primary/OS disk. I was pleasantly surprised to find that the Ubuntu 22.04 VM appeared to support enhanced session mode when Hyper-V asked for the screen resolution when connecting to it:

The enhanced session gives this xrdp login window:

The window disappears when I enter my credentials and nothing happens for some time. I used the “Basic Session” toolbar button to switch back to the normal mode I’m used to. These are some of the errors I encounter:

The error report points out that I have obsolete packages, among them gnome-shell (which crashed). I run sudo apt upgrade and says yes to the 368 upgrades (826 MB of archives). That is not sufficient to address this rdp bug so I stay in Basic Session mode for the rest of the time.

This leads me back to the PowerShell commands I used above. Lo and behold, they work this time! This is despite the fact that there don’t appear to be any processes displayed by ps -u root | grep hyper as described at 4 Ways to Transfer Files to a Linux Hyper-V Guest (altaro.com).

Enable-VMIntegrationService -VMName 'Ubuntu 22.04 LTS' -Name 'Guest Service Interface'

Copy-VMFile -Name 'Ubuntu 22.04 LTS' -SourcePath 'dumpfile.gz' -DestinationPath '/home/saint/Downloads' -FileSource Host

This is when I discover that I do not have enough space on the VM to expand my .gz file.

Unfortunately, the disk for the VM is only 12 GB (confirmed by launching Ubuntu and running out of space). Therefore, once the installation completes, expand the disk from 12 GB to a more reasonable size (e.g. 127 GB). If the default drive Quick Create used for the VM’s virtual disk does not have sufficient space, you will need to move the virtual hard disk to another drive then expand the partition in Ubuntu to use the whole virtual disk.

Moving Ubuntu VM to a Bigger Disk

My main desktop has a 500 GB SSD that had only about 20GB of space free. How unpleasant to then discover that Quick Create simply dumped the new VM on it AND created such a small disk to start with, all without asking. Turns out I’m not the only one that finds this behavior less than ideal: hyperv quick create disk size – Search (bing.com) pointed me to Hyper-V Ubuntu 18.04 Quick Create disk size is too small · Issue #82 · microsoft/linux-vm-tools (github.com) and unfortunately, doesn’t look like there’s a resolution of this issue. My solution was to create a new virtual disk on my secondary 3.5 TB hard drive.

Turn off the virtual machine.
Open the virtual machine’s settings and select the VM’s Hard Drive. Click on the “New” button.

Select the disk type, e.g. “Dynamically Expanding“
Specify the name and location of the virtual hard disk file. This is where I selected a hard drive with lots of space for expansion for the VM.
In the Configure Disk section, select the option to “Copy the contents of the specified virtual hard disk” and select the virtual machine’s current .vhdx file.

Verify that all parameters are correctly set then click on Finish.

If the VM was still running, this error dialog will most likely be displayed.

The new hard disk will be created with the content of the currently

After starting the VM again, I still didn’t have enough space to decompress my .gz file.

Fortunately, there is a useful site explaining how to Expand Ubuntu disk after Hyper-V Quick Create – Anton Karl Ingason (linguist.is):

sudo apt install cloud-guest-utils
sudo growpart /dev/sda 1
sudo resize2fs /dev/sda1

growpart failed the first time I ran it. The disk was still 12 GB!

I had to turn off the VM, wait for the disk “merging” status to go away, then go to edit the disk in Hyper-V:

Some scary warnings about data loss that I promptly ignored and marched forward since I didn’t yet have any critical data on that disk.

Once the expansion completes, the growpart command can now be successfully exeuted as shown below.

Open Questions

Why does mount.cifs fail (on both VMs)?
Why does Copy-VMFile work on Ubuntu 22 VM but not Ubuntu 20?

2010-07-09 —Categories: Linux, Virtual Machines

Changing Screen Resolution of Ubuntu in Virtual Box

As suggested on one of the Ubuntu forums, the key here is to install the VirtualBox guest additions. Having done so on my system, I ran these commands:

cd /media/VBOXADDITIONS_3.2.6_63112/
sudo ./VBoxLinuxAdditions-x86.run

Rebooting my virtual machine and maximizing the VirtualBox window left me running Ubuntu at my native screen resolution of 1680×1050 :).

Update: On VirtualBox 4.1.2, use the virtual machine’s Devices -> Install Guest Additions … menu item. The ISO Disc should be automatically mounted, and allowing autorun to continue should complete the installation. The Virtualbox website has more information on guest additions.