Where is the global auth.json from composer located on linux?
Composer global files can usually be found at your home directory:
In a *nix system that is:
~/.composer # early composer 0/1 and 2 upgraded from it
~/.config/composer # composer 1/2+
auth.json is in there as well (if there is a global one).
In a more general sense, on any system, you should be able to find this by executing:
composer config --global home
On my system this results in:
/Users/yivi/.composer