virtualbox.org

I have a windows 10 host and Ubuntu guest. Whenever I start virtual machine I have to enter password for my username, for example "User". But when I try to execute something from my host command line: vboxmanage guestcontrol "My VM" run --username user --password xxxxx --exe "/bin/ls", I have to use lowercase "user" as my username, not uppercase "User", otherwise I get a error: The specified user was not able to logon. I opened the file in guest system, it seems my username is "user". So why is that?

There should not be any special setting causing one capitalization of the username to work differently than another intentionally caused through the 'vboxmanage guestcontrol' command.

I tried guestcontrol but couldn't make it work on a Linux guest. But on an XP guest with user 'SnC' I got SnC, snc, and SNC to work. Unless there's a bit flipped in your local setup I'd say there is no case imposed by Virtualbox.

Maybe your guest is case-sensitive?

Like in most OSs, a Linux user has a username and a full name. GUI login screens often allow you to use the full name instead of the username. CLI logins require the username most of the time.