Eclipse help won't show under Ubuntu

Question

Whenever I open some help within eclipse I get a page saying:

Server Error. The following error occurred: [code=CANT_CONNECT_LOOPBACK] Cannot connect due to potential loopback problems

I'm running Ubuntu 10.04.

Any ideas what this can be?

UPDATE Some commands outputs (some private info replaced):

$ ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:xx:xx:xx:xx:xx  
          inet addr:123.12.123.235  Bcast:123.12.456.255  Mask:255.255.254.0
          inet6 addr: fe80::xxx:eff:xxxx:xxxx/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1343040 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1133672 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:829265876 (829.2 MB)  TX bytes:242912202 (242.9 MB)
          Memory:f3200000-f3220000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:125 errors:0 dropped:0 overruns:0 frame:0
          TX packets:125 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:15910 (15.9 KB)  TX bytes:15910 (15.9 KB)

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
123.12.123.0    0.0.0.0         255.255.254.0   U     1      0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eth0
0.0.0.0         123.12.456.254  0.0.0.0         UG    0      0        0 eth0

$ sudo netstat -anp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      765/portmap     
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      871/sshd        
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      1181/cupsd      
tcp        0      0 0.0.0.0:52068           0.0.0.0:*               LISTEN      786/rpc.statd   
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      1186/mysqld     
tcp        0      0 0.0.0.0:53709           0.0.0.0:*               LISTEN      -               
tcp        0      0 123.12.123.235:755      123.12.5.48:2049        ESTABLISHED -               
tcp        0      0 123.12.123.235:60793    123.12.5.129:8080       ESTABLISHED 2264/firefox-bin
tcp        0      0 123.12.123.235:57940    123.12.5.43:8080        ESTABLISHED 2264/firefox-bin
tcp        0      0 123.12.123.235:57928    123.12.5.43:8080        CLOSE_WAIT  2247/google-chrome
tcp        0      0 123.12.123.235:35767    123.12.5.129:8080       ESTABLISHED 2247/google-chrome
tcp        0      0 123.12.123.235:57930    123.12.5.43:8080        ESTABLISHED 2247/google-chrome
tcp        0      0 123.12.123.235:57931    123.12.5.43:8080        CLOSE_WAIT  2247/google-chrome
tcp6       0      0 :::80                   :::*                    LISTEN      1278/apache2    
tcp6       0      0 :::22                   :::*                    LISTEN      871/sshd        
tcp6       0      0 ::1:631                 :::*                    LISTEN      1181/cupsd      
tcp6       0      0 :::55934                :::*                    LISTEN      1956/eclipse    
tcp6       0      0 :::5900                 :::*                    LISTEN      1792/vino-server
udp        0      0 0.0.0.0:35631           0.0.0.0:*                           912/avahi-daemon: r
udp        0      0 0.0.0.0:962             0.0.0.0:*                           786/rpc.statd   
udp        0      0 0.0.0.0:68              0.0.0.0:*                           1575/dhclient   
udp        0      0 0.0.0.0:46149           0.0.0.0:*                           -               
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           912/avahi-daemon: r
udp        0      0 0.0.0.0:111             0.0.0.0:*                           765/portmap     
udp        0      0 0.0.0.0:36211           0.0.0.0:*                           786/rpc.statd   
udp        0      0 123.12.123.235:123      0.0.0.0:*                           1689/ntpd       
udp        0      0 127.0.0.1:123           0.0.0.0:*                           1689/ntpd       
udp        0      0 0.0.0.0:123             0.0.0.0:*                           1689/ntpd       
udp6       0      0 fe80::227:eff:fe07::123 :::*                                1689/ntpd       
udp6       0      0 ::1:123                 :::*                                1689/ntpd       
udp6       0      0 :::123                  :::*                                1689/ntpd       

Active UNIX domain sockets (servers and established) due to post size limit.

UPDATE 2 My proxy bypass settings:

Answer 1

I know this is a late answer, but I had the same problem and resolved it, so to tie up this one...

This is a combination of two bugs:

(i) Eclipse's internal help browser doesn't use the Eclipse proxy settings! See: https://bugs.eclipse.org/bugs/show_bug.cgi?id=318969

(and the bugs referenced in comment #7 therein)

(ii) Ubuntu's proxy support is horribly broken in certain subtle ways. See: https://bugs.launchpad.net/ubuntu/+bug/300271

The fix/workaround is to manually set the no_proxy environment variable before running eclipse (as reported in the Eclipse #308035 bug referenced from the 318969 one) e.g.

export no_proxy=127.0.0.1,localhost
eclipse &

Help then launches correctly within Eclipse. Of course, once Eclipse is launched (thus running its own internal HTTP server), you can also access the local help manually from another browser (or, if within the 'can't access 127.0.0.1' screen, there's an icon at the top to launch in an external window --> default system browser).

This may well apply on other Linux distros using Gnome.

[Couldn't post the 308035 bug link because my low reputation means I can only post 2 hyperlinks :-( Getting excited at this privilege come 10 reputation points :-)]

Answer 2

Basically, this error means that Eclipse is failing to establish a TCP/IP connection to your localhost using 127.0.0.1 (Eclipse starts a server for the Help).

If you are using some specific proxy settings (either global at the OS level or local at the Eclipse level), double check that you are bypassing the proxy for localhost and 127.0.0.1.

If this doesn't help, try setting the hostname that help uses to localhost when starting eclipse (either on the command line or in the eclipse.ini):

eclipse -vmargs -Dserver_host=localhost