git@github.com: Permission denied (publickey).

[michaelfliegner]

mf@Michis:~/nixkell$ niv update
Updating all packages
Package: nixpkgs
Package: gitignore
Package: treefmt
FATAL: Could not read the output of 'git'.
command: git ls-remote git@github.com:numtide/treefmt.git refs/heads/master
stdout:
stderr: git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

This is a bug. Please create a ticket:
https://github.com/nmattia/niv/issues/new
Thanks! I'll buy you a beer.
FATAL: One or more packages failed to update:
treefmt: ExitFailure 1
ERROR: ExitFailure 1

[nmattia]

Hi! I suggest removing your treefmt entry and adding it like this:

$ niv add numtide/treefmt

or adding you SSH key to your SSH agent. Niv is calling git to update the repo and git is expecting an SSH key since the repo is adding with the ssh protocol.