setcap to allow a program to listen on privileged ports

caveats

setcap grants root-like permissions, so there's additional constraints on the binary.

It ignores LD_PRELOAD and LD_LIBRARY_PATH environment variables, so if you used these, you'll have to find another way.

One option is to use the RPATH piece of the Dynamic section of an ELF binary.

example

# Ubuntu is weird and calls the 'nc' binary 'nc.openbsd' - that's a rant for another time.

% nc.openbsd -l 123                                   
nc.openbsd: Permission denied
 % sudo setcap cap_net_bind_service=+ep /bin/nc.openbsd
% nc.openbsd -l 123                                   
works....
^C