于 2014年05月08日 19:37, John Ferlan 写道:
On 05/08/2014 05:01 AM, Xu Wang wrote:

于 2014年04月14日 23:05, John Ferlan 写道:

On 04/14/2014 02:15 AM, Xu Wang wrote:

于 2014年04月05日 00:12, John Ferlan 写道:

Rather than default to socket.gethostbyaddr(socket.gethostname())[0] to
get full_hostname(), go through a sequence of steps to get a more
correct result

NOTE:
See http://www.redhat.com/archives/libvirt-cim/2013-November/msg00082.html
for more details and history.

Signed-off-by: John Ferlan <jferlan@redhat.com>
---
   lib/VirtLib/live.py | 11 ++++++++---
   1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/VirtLib/live.py b/lib/VirtLib/live.py
index c929e71..e9cafc1 100644
--- a/lib/VirtLib/live.py
+++ b/lib/VirtLib/live.py
@@ -100,6 +100,11 @@ def hostname(server):
       return out
   
   def full_hostname(server):
-    """To return the fully qualifiec domain name(FQDN) of the system"""
-
-    return socket.gethostbyaddr(socket.gethostname())[0]
+    """To return the fully qualified domain name(FQDN) of the system"""
+
+    if socket.getfqdn().find('.') >= 0:
+        return socket.getfqdn()
+    elif socket.gethostname().find('.') >= 0:
+        return socket.gethostname()
+    else:
+        return socket.gethostbyaddr(server)[1][0]

I got an error here. The content of my /etc/hosts is,

# cat /etc/hosts
127.0.0.1 RH64wenchao localhost localhost.localdomain localhost4
localhost4.localdomain4 #RH64wenchao


I don't see the same results if I add a different name to /etc/hosts. I
didn't restart my network and that may make a difference.  I did restart
my tog-pegasus, but that shouldn't make a difference, but who knows at
this point.

There's 3 places that use the returned data.  I'll play with this some
more and see what happens

John

Dear John,
   I installed several absolutely new systems to test it, and got 
different results.
I have a question here. Why don't we use socket.gethostname() directly? 
It seems
work well on my systems. Is there any other situation it could not handle?

Thanks,
   Xu Wang

The code currently does the following

def full_hostname(server):
    """To return the fully qualifiec domain name(FQDN) of the system"""

    return socket.gethostbyaddr(socket.gethostname())[0]


$ python

import socket
help(socket.getfqdn)

Help on function getfqdn in module socket:

getfqdn(name='')
    Get fully qualified domain name from name.
    
    An empty argument is interpreted as meaning the local host.
    
    First the hostname returned by gethostbyaddr() is checked, then
    possibly existing aliases. In case no FQDN is available, hostname
    from gethostname() is returned.
Dear John,
  This is the description I got from https://docs.python.org/2/library/socket.html

  socket.getfqdn([name])
  Return a fully qualified domain name for name. If name is omitted or empty,
  it is interpreted as the local host. To find the fully qualified name, the
  hostname returned by gethostbyaddr() is checked, followed by aliases for
  the host, if available. The first name which includes a period is selected.
  In case no fully qualified domain name is available, the hostname as returned
  by gethostname() is returned.
  New in version 2.0.

  and

  socket.gethostname()
  Return a string containing the hostname of the machine where the Python
  interpreter is currently executing.
    If you want to know the current machine’s IP address, you may want
  to use gethostbyname(gethostname()). This operation assumes that there is
  a valid address-to-host mapping for the host, and the assumption does not
  always hold.
  Note: gethostname() doesn’t always return the fully qualified domain name;
  use getfqdn() (see above).

  I think socket.gethostname() returns the hostname of the machine where the
Python interpreter is currently executing contains potential issue. That is if
cimtest runs on different system with libvirt-cim, hostname maybe different.
Another point, gethostname() doesn't always return the fully qualified domain
name (Note mentioned, maybe different from getfqdn(). libvirt-cim set hostname
by calling get_fqdn(), in set_host_system_properties()).

  Hence, I agree with you about the getfqdn() is a proper choice.
help(socket.gethostbyaddr)

Help on built-in function gethostbyaddr in module _socket:

gethostbyaddr(...)
    gethostbyaddr(host) -> (name, aliaslist, addresslist)
    
    Return the true host name, a list of aliases, and a list of IP addresses,
    for a host.  The host argument is a string giving a host name or IP number.


Thus the byaddr probably does what you asked for before in returning
the aliaslist (e.g. the [1] entry) and then being able to do some sort of
"if myname in aliaslist:" test. 

I still content getfqdn() is the proper action for the full_hostname()
method.  A new method could be added "aliaslist" which could return all
names in order to be checked.  It's just a matter of taking the time to
do the code, check all the callers, etc.  Time that I haven't had lately.

FWIW:
My host (f20) returns:


print socket.getfqdn()

localhost.localdomain

print socket.gethostname()

localhost.localdomain

print socket.gethostbyaddr(socket.gethostname())

('localhost', ['localhost.localdomain', 'localhost6', 'localhost6.localdomain6'], ['::1'])
I got an interesting result if I changed the hostname when system starting the first time.

>>> import socket
>>> print socket.getfqdn()
zBX.testing
>>> print socket.gethostname()
zBX.testing
>>> print socket.gethostbyaddr(socket.gethostname())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
socket.gaierror: [Errno -2] Name or service not known

But my /etc/hosts was not changed (just as default),

  # cat /etc/hosts
  127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
  ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

  Just the system with default hostname was changed from localhost.localdomain into
others could happened that. If we use getfqdn() that situation would not occur. But
I still don't know the reason why the error happened.

Thanks,
  Xu Wang
print socket.getfqdn()

localhost.localdomain


I've done no manipulation of my /etc/hosts

John

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