network applications throwing "Servname not supported for ai_socktype"

Question

Why are some network application failing with this error message?

$ whois example.com
getaddrinfo(whois.verisign-grs.com): Servname not supported for ai_socktype

Solution

This can occur when, due to misconfiguration, an unprivileged user does not have read access to /etc/services. Check with:

ls -l /etc/services

It should look like -rw-r--r-- 1 root root ...

The file should be installed from the Priority: important package netbase and have exactly these permissions. If not, fix it with:

sudo chown root:root /etc/services
sudo chmod 644 /etc/services

Nothing about the files contents is confidential or expected to change often. The file lists IANA-registered or common protocol port number associations for TCP, UDP, DCCP, and SCTP.