I have a machine I changed the hostname of. I changed it in /etc/hosts, /etc/sysconfig/network, and with hostname command. hostname returns the correct shortname, hostname --fqdn returns the expected FQDN, but hostname -A returns an old name. I changed the IP address of the machine to make sure it wasn't external DNS cache.

If I open python and run

import socket

Both return the old hostname/fqdn, the same as hostname -A

From the hostname man page it appears --fqdn just takes the shortname and domain and puts them together.

Display the FQDN (Fully Qualified Domain Name). A FQDN consists of a short host name and the DNS domain name. Unless you are using bind or NIS for host lookups you can change the FQDN and the DNS domain name (which is part of the FQDN) in the /etc/hosts file.

What is the difference between these commands and how can I better troubleshoot why the old hostname is sticking around.

  • 1
    How about the specific linux/unix and version identification. There are cases where this information resides elsewhere and is setup at boot time from other configuration files.
    – mdpc
    Commented Aug 12, 2014 at 23:27
  • Red Hat Enterprise Linux 6.4 Commented Aug 13, 2014 at 15:19

1 Answer 1


hostname returns the configured hostname or nodename. In practice, it can either be a short name (in most configurations) or a long name (normally the FQDN in this case). The short name is given by hostname --short.

hostname --fqdn returns the FQDN, which is gethostbyname on the nodename (as returned by the uname system call, see uname(2) man page).

hostname -A is something obscure and non-intuitive. In particular, despite its name and description ("all FQDNs"), it doesn't give the standard FQDN, by design. Thus I would say: do not use it. One reason is that it misses valid IP addresses of the machine, such as, with which the FQDN may be associated in the /etc/hosts file (this is currently the default under Debian and Ubuntu, for instance). Another issue with the hostname -A method is that the reverse resolution of an IP address doesn't necessarily give a FQDN; it can just be a short name.

Concerning your problem with python, it may be a bug there. I don't know. I suggest that you try the following Perl script:

#!/usr/bin/env perl

use strict;
use POSIX;

my $nodename = (POSIX::uname)[1];
print "Nodename: $nodename\n";

my @ghbn = gethostbyname $nodename;
print "FQDN: $ghbn[0]\n";

$ghbn[0] !~ /\./ && $ghbn[1] =~ /(\S+\.\S+)/
  and print "Fixed FQDN from aliases: $1\n";
  • So where does hostname -A get its information? I was having a problem with other software installed on the system that I couldn't fix until hostname -A showed the correct name. Commented Aug 13, 2014 at 15:17
  • ps, I tried to fix your address to but edits require 6 characters minimum. Maybe you can fix it. Commented Aug 13, 2014 at 15:18
  • 2
    @Rothgar hostname -A looks at the configured interfaces and reverse-resolves them (well, this is the information given in its man page). is the right IP address in my answer, not The fact that is used for the FQDN (instead of is one cause of the problem with hostname -A.
    – vinc17
    Commented Aug 13, 2014 at 15:31
  • @vinc17: I don't think nodename is relative here. The main difference is hostname -f use /etc/hosts, while hostname -A use dns lookup. See more here: bugs.debian.org/cgi-bin/bugreport.cgi?bug=718393
    – cuonglm
    Commented Aug 13, 2014 at 19:46
  • 1
    @vinc17: run strace hostname -A to see what happen.
    – cuonglm
    Commented Aug 14, 2014 at 6:30

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