If you want to use different source IP addresses based on the logged in user or running service on a Linux computer you can use these simple commands:
/sbin/ifconfig eth0:1 NEW-IP-ADDRESS netmask YOUR-NORMAL-NETMASK /sbin/iptables -t nat -A POSTROUTING -m owner --uid-owner USERNAME -j SNAT --to-source NEW-IP-ADDRESS
You can use this if the source IP is necessary for remote firewall filter lists, or to separate IP traffic from services that don’t allow to configure the outgoing source IP.
Add these lines to /etc/rc.local to make it permanent.
Version: Should work on every Linux kernel of the last 10 years, tested on Linux 4.11.1