panel 1:

One weird thing about DNS is that different programs on a single computer can get different results for the same domain name.

Let’s talk about why!

Illustration of a program, represented by a box with a smiley face, and a resolver (server), represented by a box with a smiley face holding a magnifying glass. Between them is a function, represented by a rectangle with squiggly lines on it. There are arrows going back and forth between the function and both the program and the resolver (server).

The function is the problem.

reason 1: many (but not all!!) programs use the function getaddrinfo for DNS lookups…

ping, represented by a box with a smiley face: I use getaddrinfo! dig, also represented by a box with a smiley face: I don’t!

So if you see an error message like “getaddrinfo: nodename or servname not provided...”, that’s a DNS error.

and not using getaddrinfo might give a different result

• the program might not use /etc/hosts (dig doesn’t)
• the program might use a different DNS resolver (some browsers do this)

reason 2: there are many different versions of getaddrinfo…

• the one in glibc
• the one in musl libc
• the one in Mac OS

And of course, they all behave slightly differently :)

you can have multiple getaddrinfos on your computer at the same time

For example on a Mac, there’s your system getaddrinfo, but you might also be running a container that’s using musl.

glibc and musl getaddrinfo are configured with /etc/resolv.conf

IP of resolver to use

# Generated by NetworkManager
nameserver 192.168.1.1 
nameserver fd13: d987:748a::1

On a Mac, /etc/resolv.conf exists, but it’s not used by the system getaddrinfo.