Unable to insert the virtual optical disk in an Ubuntu virtual machine

When you try to install a new version of the VirtualBox Guest Addition on an Ubuntu virtual machine you may get the error message Unable to insert the virtual optical disk C:\Program Files\Oracle\VirtualBox\VBoxGuestAdditions.iso into the machine Ubuntu 64. Could not mount the media/drive ‘C:\Program Files\Oracle\VirtualBox\VBoxGuestAdditions.iso’ (VERR_PDM_MEDIA_LOCKED). Result Code: E_FAIL (0x80004005) Component: ConsoleWrap Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed} […]

Raw-mode is unavailable courtesy of Hyper-V error in VirtualBox

For VirtualBox to be able to start virtual machines, Hyper-V has to be turned off in Windows 10. If you get the error message when you try to launch a virtual machine in VirtualBox Raw-mode is unavailable courtesy of Hyper-V Check the Hyper-V setting Open a command prompt as an administrator, Execute the command: bcdedit […]

Set up a user to connect to a Linux server with a private-public key pair

To secure a Linux server, disable password authentication on it. This way only those users can connect to it, who have access to an authorized private key. To enable users to connect to a Linux server with a private-public key pair Generate an RSA key pair In a Bash terminal on your workstation execute ssh-keygen Follow […]

Error loading table definition of a PostgreSQL table

When a PostgreSQL table name contains uppercase letters there is no known way to get the table definition SQL script. When we right-click a table name in SQLPro for Postgres the has an uppercase letter and select Script as, CREATE to, New query window we get the error message /* * Error loading table definition. * ERROR: […]

Copy files between Linux machines

The rsync command allows you to copy files using SSH connection, between your workstation and another Linux machine. You have to be logged into one of the machines, this command cannot copy files between two remote machines. To copy a file from your local machine to a remote server rsync -avz -e “ssh -i SSH_KEY_FILE -o […]

Using tmux terminal multiplexer

The tmux terminal multiplexer allows us to open multiple terminal windows in the same SSH session and continue the command execution even when we log out of the SSH session. This way we can execute long-running copy commands overnight without keeping the SSH session open. Install tmux On CentOS family Linux yum install tmux To start tmux […]

Copy files between Windows and Linux computers

There are many tools to copy files between Windows and Linux computers, I have found this method the simplest. It does not require any software installation on the Windows machine, and only one package installation on the Linux machine. Share a folder on the Windows machine Share a folder on the Windows machine and allow […]

delimited by end-of-file (wanted `EOF’)

When you create a file in a script and use an end of file delimiter, if … cat <<EOF> $chef_dir/attrib.json $json EOF fi and you indent the word EOF to look nicer, you will get the error message warning: here-document at line … delimited by end-of-file (wanted `EOF’) STDERR> …: line …: syntax error: unexpected end of file […]

org.apache.jasper.JasperException: java.lang.IllegalStateException: No output folder

This error can happen on Linux and Windows, and the cause could be the same. On Windows Server 2012R2 I opened a command prompt. To be able to delete a directory from the Tomcat webapps folder, I have issued the shutdown command. When I started the server with the startup command, and navigated to my local […]