Getting "unknown host" on hostname despite adding it to /etc/hosts

Question

I have an Ubuntu server called crow:

$ hostname
crow

But when I try to ping it (from itself), I get unknown host:

$ ping crow
ping: unknown host crow

This is despite explicitly adding crow to /etc/hosts:

$ sudo cat /etc/hosts
127.0.0.1       localhost crow

What am I doing wrong?

Additional info in response to comments:

The hosts line of /etc/nsswitch.conf looks like this:

hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

Solution

Check permissions on /etc/hosts and /etc/nsswitch.conf files. They should be world-readable.

Comments

[Username]

Have you rebooted/restarted networking services after making the edit to your hosts file?

[Sameer]

Modification of hosts file doesn't require restart of network services.

[David Mackintosh]

What does the hosts line in /etc/nsswitch.conf look like?

[Nicola Boccardi]

where do you ping it, from the server itself or from another machine in the same lan?

[sanity]

I've edited to answer these questions

[Johan]

As reference I once had this problem since I by mistake "lost" the s in hosts (in nsswitch.conf). So a faulty nsswitch.conf can cause this problem as well...

[UncleAdam]

And what if they are already world readable, however you still can't ping localhost?