The --link flag is a legacy feature of Docker: 'Error: unknown flag: --link'

[simonsigre]

The reference to --link should be modified as --link is a deprecated feature .

$ docker run -ti -d -p 80:80 -e MYSQL_ENV_MYSQL_ROOT_PASSWORD=my-secret-pw --name ipam --link phpipam-mysql:mysql pierrecdn/phpipam

Warning: The --link flag is a legacy feature of Docker. It may eventually be removed. Unless you absolutely need to continue using it, we recommend that you use user-defined networks to facilitate communication between two containers instead of using --link. One feature that user-defined networks do not support that you can do with --link is sharing environment variables between containers. However, you can use other mechanisms such as volumes to share environment variables between containers in a more controlled way.
``` - https://docs.docker.com/network/links/

This feature has already been removed from stable builds of `podman` ... will endeavour to propose a solution shortly. For search purposes the following error is observed;

Error: unknown flag: --link