I've been meaning to try out fish on several occasions (years apart), but I always stumble upon this issue.

On my system (various versions of Ubuntu, currently 19.10) I do

• sudo apt install fish
• fish

and what happens next:

• no output
• no prompt
• laptop's fan spins up
• nothing else happens for several minutes
• I panic and kill fish that is eating all the CPU

On second run fish starts instantly.

I'm not sure how to reset the state so this happens again.

fish version: 3.0.2
OS: Ubuntu 19.10
$TERM: xterm-256color
Terminal emulator: gnome-terminal 3.34.0 (VTE 0.58.2)

I cannot reproduce this with sh -c 'env HOME=$(mktemp -d) fish'! But if I try to close the shell I spawned that way, I get a warning about active jobs, which might be a Clue.

Welcome to fish, the friendly interactive shell
mg@blynas /h/m/s/z/BTrees>
There are still jobs active:
   PID  Command
 25573  $py $update_args >/dev/null 2>&1 &
A second attempt to exit will terminate them.
Use 'disown PID' to remove jobs from the list without terminating them.
mg@blynas /h/m/s/z/BTrees>

(this also leaves my terminal in a noecho mode, which is annoying but unrelated)

It seems that something in my home directory (its sheer size? some config file somewhere?) is causing this, but I don't know what.