When the resolver is not configured properly, ssh shows a "Success" error message:

/etc/nsswitch.conf:
hosts:      files dns xyz


$ ssh nohost
ssh: Could not resolve hostname nohost: Success

The message "Success" doesn't make sense given that it's in fact a system error. It's an issue of ssh_gai_strerror() which can't handle a situation when getaddrinfo() returns EAI_SYSTEM but errno is not set/is set to 0.

A potential fix:

--- a/misc.c
+++ b/misc.c
@@ -127,7 +127,7 @@ unset_nonblock(int fd)
 const char *
 ssh_gai_strerror(int gaierr)
 {
-       if (gaierr == EAI_SYSTEM)
+       if (gaierr == EAI_SYSTEM && errno != 0)
                return strerror(errno);
        return gai_strerror(gaierr);
 }