phoenix detach in gitlabci

somebody run phoenix used detached mode in gitlab ci ?
i tryed to run command below and my stage hang

elixir --erl "-detached" -e "File.write! 'tmp/', :os.getpid" -S mix phx.server

cant uderstand wtf… what i doing wrong ?? why stage hanged, why in bash all work how expected.

Iam not use docker, all run in centos shell without virtualization.

stage: build_phoenix_gateway
extends: .default_options
- cd ${GW_ROOT}
- elixir --erl “-detached” -e “File.write! ‘tmp/’, :os.getpid” -S mix phx.server

example my stage