If the Linux Development Environment isn’t starting normally for you, you might see if you can start it manually.

Start by pulling up the Chrome OS developer shell (Ctrl + Alt + T) and executing vmc list. If it’s there, you should see information about the termina VM returned.

If it’s not currently running, the output looks like this:

crosh> vmc list
termina (322123612160 bytes, raw)
Total Size (bytes): 322123612160

If it is running, it’ll be more like this:

crosh> vmc list
termina (322123612160 bytes, min shrinkable size 179911524352 bytes, raw) running
Total Size (bytes): 322123612160

If termina is not yet running, try manually starting it with vmc start termina:

crosh> vmc start termina
(termina) chronos@localhost ~ $

If termina is already running (and/or vmc start termina yields a timeout error), use vsh termina to access a shell in the already-running VM instead:

crosh> vsh termina
(termina) chronos@localhost ~ $

From the (termina) prompt, check for the default Linux container (named penguin) with lxc list:

(termina) chronos@localhost ~$ lxc list
To start your first container, try: lxc launch ubuntu:18.04
 
+---------+---------+------+------+------------+-----------+
|  NAME   |  STATE  | IPV4 | IPV6 |    TYPE    | SNAPSHOTS |
+---------+---------+------+------+------------+-----------+
| penguin | STOPPED |      |      | PERSISTENT | 0         |
+---------+---------+------+------+------------+-----------+

If the penguin container is listed, you can then try manually starting it as well - but you’ll want to logout back to the crosh prompt and then execute vmc container termina penguin:

(termina) chronos@localhost ~ $ logout
crosh> vmc container termina penguin
username@penguin:~$ 

If vmc container termina penguin doesn’t work, you can go back into termina and try to run it with lxc start penguin and then lxc exec penguin bash. That should give you a root shell in the container, though without any of the nice ChromeOS integrations. You might be able to fix things from there.

These commands may or may not fix the problem but I hope they will at least provide a bit more information about the issue(s) you’re encountering and perhaps allow you to troubleshoot it further.