Comment 83 for bug 32906

Lance Berry (dunixdude) wrote :

I had this problem as well.

Another fix

I fixed mine by modifying the alias in the /etc/hosts file. When the Network wizard added my host to /etc/host, it forced itself to add the fully qualified domain name (myhost.ubuntu.com), while sudo is looking for the short name (myhost).

I booted into Recovery mode, modified /etc/hosts to reflect the correct alias, i.e.
{ipaddress} {Fully qualified name} {alias}
113.23.42.21 myhost.ubuntu.com myhost

Now Synaptic works fine for me.