Permission denied on port 80 or 443

On Linux, a program needs a special right to listen on a port below 1024.

What you see

ferryd

Error: cannot listen on 0.0.0.0:80 (proxy address)

Caused by:
    Permission denied (os error 13)

On Linux, only a program with special rights can listen on a port below 1024.

Do not run ferryd as root. Give it the capability CAP_NET_BIND_SERVICE.

With systemd, add this line to the unit of ferryd. See Production setup.

systemd unit

AmbientCapabilities=CAP_NET_BIND_SERVICE

As an alternative, set the capability on the file of the program.

Terminal

sudo setcap cap_net_bind_service=+ep /usr/local/bin/ferryd

Run setcap again after each upgrade of ferryd.

A port is in use

ferryd cannot listen on an address, because another program has it.

Another ferryd uses the data directory

Only one ferryd can use a data directory at a time.