How do I enable the "remote control" in JOSM?

In the JOSM menu select Edit/Preferences.../ or press F12

Click on the remote control icon

Select "Enable Remote Control" and click OK.

(If you have a JOSM version older than 3715, then RemoteControl is only available as a plugin. You can either get the plugin, or update JOSM.)

If the problem is NoScript then you can to allow the request through the ABE blocker rules as follows:

1) Open the NoScripts options dialog,
2) Goto the Advanced pane then the ABE sub-pane
3) Change the SYSTEM rule to read:

Site http://127.0.0.1:8111
Accept from *.openstreetmap.org
Deny

Site LOCAL
Accept from LOCAL
Deny

If you are using Opera there are also security issues in the browser that you need to address. The warning it would normally show is hidden in an invisible iframe so the edit option silently fails. To overcome this you can go into Preferences (Ctrl-F12), Advanced, Security, Trusted Websites, Secure Internal Hosts and add 127.0.0.1 (openstreetmap.org edit option) and localhost (OSM Inspector). I guess there may be security issues that permanently flagging the sites as secure may raise, but as the links work with other browsers I don't think that it can be a major risk.

I had another problem with remote control not working today. Here is what I did to troubleshoot it:

First, I started JOSM, and verified it had "Enable remote control" and "Enable HTTPS support" enabled. It was, so I didn't need to enable it and restart JOSM. Next I did in shell:

telnet localhost 8112

if it said the following:

Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.

Then it would mean that JOSM, networking and local firewall on the machine are working, and that the problem is somewhere in the web browser (for which I'd then try to open "https://localhost:8112/" to debug further, whitelist certicates etc).

But in my case it hanged after "Trying 127.0.0.1..." and never showed "Connected to 127.0.0.1", which indicated that the problem is either JOSM or network/firewall. Then I did:

netstat -tlpn

to verify if JOSM is listening (that is on Debian GNU/Linux,on MS-windows it would be something like "netstat -a"?):

It should output something like:

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp6       0      0 ::1:8111                :::*                    LISTEN      20297/java
tcp6       0      0 127.0.0.1:8111          :::*                    LISTEN      20297/java
tcp6       0      0 ::1:8112                :::*                    LISTEN      20297/java
tcp6       0      0 127.0.0.1:8112          :::*                    LISTEN      20297/java

to indicate JOSM is listening on both port 8111 and 8112. But in my case the list was empty. If it wasn't empty, it would strongly indicate problem in local firewall, so I'd try disabling firewall and trying "telnet" again. But as it was empty, it indicated that problem is that JOSM didn't listen on that port - which is either problem in JOSM (less likely, as I was running stable version and lots of people would be making noise about it) or a problem in local machine networking.

I found a log in ~/.xsession-errors, and it contained:

WARNING: Cannot start IPv4 remotecontrol server on port 8111: Cannot assign requested address (Bind failed)
WARNING: Cannot start IPv6 remotecontrol server on port 8111: Cannot assign requested address (Bind failed)
WARNING: Cannot start IPv4 remotecontrol https server on port 8112: Cannot assign requested address (Bind failed)
WARNING: Cannot start IPv6 remotecontrol https server on port 8112: Cannot assign requested address (Bind failed)

then I started JOSM manually under strace with:

strace -o /tmp/log.txt -s999 -tt -f java -jar josm-tested.jar
grep -w 8112 /tmp/log.txt

and it showed:

bind(38, {sa_family=AF_INET6, sin6_port=htons(8112), inet_pton(AF_INET6, "::ffff:127.0.0.1", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, 28) = -1 EADDRNOTAVAIL (Cannot assign requested address)

"EADDRNOTAVAIL" means that no network interface on computer has requested address (127.0.0.1 in this case). I did "ip addr show" and found out that my computer really did not have "127.0.0.1" as the "lo" interface was down due to some other problem. So simple "/etc/init.d/networking start" fixed it (which is unlikely to be anybody elses problem, but hopefully those troubleshooting steps would help to narrow down problem).