Linux provides 'capabilities' used to grant specific commands the ability to do things that are normally only allowed for a root account. Instead of granting the ability to a specific user, capabilities are granted to a specific command. It may be convenient to enable the server to listen on privileged ports while running as a non-root user.

The setcap command is used to assign capabilities to an application. The cap_net_bind_service capability enables a service to bind a socket to privileged ports (port numbers less than 1024). If Java is installed in /ds/java (and the Java command to run the server is /ds/java/bin/java), the Java binary can be granted the cap_net_bind_service capability with the following command:

$ sudo setcap cap_net_bind_service=+eip /ds/java/bin/java

The java binary needs an additional shared library (libjli.so) as part of the Java installation. More strict limitations are imposed on where the operating system will look for shared libraries to load for commands that have capabilities assigned. So it is also necessary to tell the operating system where to look for this library. This can be done by creating the file /etc/ld.so.conf.d/libjli.conf with the path to the directory that contains the libjli.so file. For example, if the Java installation is in /ds/java, the contents of that file should be:

/ds/java/lib/amd64/jli

Run the following command for the change to take effect:

$ sudo ldconfig -v