docker-baseimage-ubuntu/root/etc/cont-init.d/10-adduser

#!/usr/bin/with-contenv bash

PUID=${PUID:-911}
PGID=${PGID:-911}

groupmod -o -g "$PGID" abc
usermod -o -u "$PUID" abc

echo '
-------------------------------------
          _     _ _
         | |___| (_) ___
         | / __| | |/ _ \ 
         | \__ \ | | (_) |
         |_|___/ |_|\___/
               |_|

Brought to you by linuxserver.io
We gratefully accept donations at:
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-------------------------------------
GID/UID
-------------------------------------'
echo "
User uid:    $(id -u abc)
User gid:    $(id -g abc)
-------------------------------------
"
chown abc:abc /app
chown abc:abc /config
chown abc:abc /defaults