Crostini is the Linux (LXD, a project initiated by Ubuntu publisher Canonical) container for ChromeOS. When enabled it creates a new container with the hostname "penguin" and an initial user whose user/login name is derived from the Gmail alias of the logged in Google account.
This is incovenient for a lot of reasons, not the least of which is that it makes working with NFSv3 shares and ssh keys on and for other hosts tedious (userids are everything to NFSv3, as login names are for ssh).
These are the steps to rename that default user and group:
In what follows "oldusername" is your existing username in penguin, while "newusername" is what you want it to be.
- Enter crosh with Ctrl-Alt-t