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JaR
Asked: 2012-01-17 10:05:45 +0800 CST

X11 forwarding broken

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I cant for the life of me get x11forwarding to work. I did everything 'by the book'... Both client and server is running ubuntu 11.04. Both have ssh, vnc, x11 and FW ports open

/etc/ssh/ssh_config

   ForwardAgent yes
   ForwardX11 yes
   ForwardX11Trusted yes

/etc/ssh/sshd_config

X11Forwarding yes
X11DisplayOffset 10

apt-get install xauth
xauth is already the newest version.
  • installed tightvncserver
  • ran xauth list
  • rebooted
  • connected with ssh server -Xvl user

echo $DISPLAY return blank xterm returns xterm Xt error: Can't open display:

xterm:  DISPLAY is not set
  • FW is open
  • VNCserver running
  • sshd running
  • X11 running
  • ssh config files ok
  • verbose output from ssh login shows all ok, no errors

Still nothing works...

So i did export DISPLAY=localhost:10.0 Then echo $DISPLAY returns localhost:10.0 but xterm returns xterm Xt error: Can't open display: localhost:10.0

Now here's the weird part. if i do export DISPLAY=:0.0 then xterm gives no error, but no GUI is displayed...

Tried everything except reinstalling the OS. Even reinstalled ssh and copied fresh config files from a working install...

Putting here the verbose output:

user@jupiter:~$ ssh -v -X [email protected] env
OpenSSH_5.8p1 Debian-1ubuntu3, OpenSSL 0.9.8o 01 Jun 2010
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.0.1 [192.168.0.1] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/id_rsa type -1
debug1: identity file /home/user/.ssh/id_rsa-cert type -1
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: identity file /home/user/.ssh/id_dsa-cert type -1
debug1: identity file /home/user/.ssh/id_ecdsa type -1
debug1: identity file /home/user/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.8p1 Debian-1ubuntu3
debug1: match: OpenSSH_5.8p1 Debian-1ubuntu3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.8p1 Debian-1ubuntu3
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ECDSA 31:52:3e:91:b2:b2:74:cf:3e:65:37:a7:78:b9:3a:9e
debug1: Host '192.168.0.1' is known and matches the ECDSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:4
debug1: ssh_ecdsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /home/user/.ssh/id_rsa
debug1: Trying private key: /home/user/.ssh/id_dsa
debug1: Trying private key: /home/user/.ssh/id_ecdsa
debug1: Next authentication method: password
debug1: Authentication succeeded (password).
Authenticated to 192.168.0.1 ([192.168.0.1]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: Requesting X11 forwarding with authentication spoofing.
debug1: Requesting authentication agent forwarding.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug1: Sending command: env
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype [email protected] reply 0
SHELL=/bin/bash
XDG_SESSION_COOKIE=5867400390852a975845598400000005-1329602079.30299-1173119600
SSH_CLIENT=192.168.0.14 34691 22
USER=user
SSH_AUTH_SOCK=/tmp/ssh-bPyNW11158/agent.11158
MAIL=/var/mail/user
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
PWD=/home/user
LANG=en_US.UTF-8
SHLVL=1
HOME=/home/user
LOGNAME=user
SSH_CONNECTION=192.168.0.14 34691 192.168.0.1 22
_=/usr/bin/env
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 1960, received 1968 bytes, in 0.1 seconds
Bytes per second: sent 19601.4, received 19681.4
debug1: Exit status 0
x11-forwarding

3 Answers

  1. I spend more a few hours looking into this one and tryed almost everything.

    Very experienced at using SSH.
    Odd it was adding this line that made it work /etc/ssh/sshd_config X11UseLocalhost no

    • 6

  2. Not sure if you still care this long after you asked, but I solved the same problem today.

    You need to add: X11UseLocalhost no to /etc/ssh/sshd_config and restart the SSH server.

    You may need to also add the .Xauthority file for the connecting host to the remote X host:

    xauth add {ip}:0 . {32byte code from `xauth list` on the connecting host}

    where {ip} is the IP of remote X host and xauth list is run on the local connecting host.

    • 3

  3. Well, I don't have any problems, I've always been able to get it working pretty easily, but maybe I can help by comparing my working connection. I connect to my server system, named "myserver", with login name "myname", using rsa, not a password (names have been changed). By the way, this is easy to do with a couple of commands on the local system.

    $ ssh -v -X myserver env
OpenSSH_5.8p1 Debian-7ubuntu1, OpenSSL 1.0.0e 6 Sep 2011
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to myserver [192.168.1.111] port 22.
debug1: Connection established.
debug1: identity file /home/myname/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/myname/.ssh/id_rsa-cert type -1
debug1: identity file /home/myname/.ssh/id_dsa type -1
debug1: identity file /home/myname/.ssh/id_dsa-cert type -1
debug1: identity file /home/myname/.ssh/id_ecdsa type -1
debug1: identity file /home/myname/.ssh/id_ecdsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3p1 Debian-3ubuntu7
debug1: match: OpenSSH_5.3p1 Debian-3ubuntu7 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.8p1 Debian-7ubuntu1
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA de:ad:be:ef:00:ff:00:5c:1a:65:8e:01:73:4a:96:da
debug1: Host 'myserver' is known and matches the RSA host key.
debug1: Found key in /home/myname/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/myname/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 279
debug1: Authentication succeeded (publickey).
Authenticated to myserver ([192.168.1.111]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: Requesting X11 forwarding with authentication spoofing.
debug1: Sending environment.
debug1: Sending env LC_MESSAGES = en_US.UTF-8
debug1: Sending env LC_COLLATE = en_US.UTF-8
debug1: Sending env LANG = en_US.UTF-8
debug1: Sending env LC_CTYPE = en_US.UTF-8
debug1: Sending command: env
SHELL=/bin/bash
XDG_SESSION_COOKIE=d509ffb7a28e82163e2349554bdbc5ab-1329602932.440753-1239879281
SSH_CLIENT=192.168.1.110 48888 22
USER=myname
MAIL=/var/mail/myname
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
LC_MESSAGES=en_US.UTF-8
LC_COLLATE=en_US.UTF-8
PWD=/home/myname
LANG=en_US.UTF-8
SHLVL=1
HOME=/home/myname
LOGNAME=mynage
SSH_CONNECTION=192.168.1.110 48888 192.168.1.111 22
LC_CTYPE=en_US.UTF-8
DISPLAY=localhost:10.0
_=/usr/bin/env
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: client_input_channel_req: channel 0 rtype [email protected] reply 0
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 2912, received 2760 bytes, in 0.5 seconds
Bytes per second: sent 5503.1, received 5215.8
debug1: Exit status 0

    Edit: Oh, yes, the config files: ssh_config... None of the three were set at all; commented out.

    Only these were set:

    SendEnv LANG LC_*
HashKnownHosts yes
GSSAPIAuthentication yes
GSSAPIDelegateCredentials no

    sshd_config... Same as yours, with addition of this at the end:

    UsePAM yes

    Oh, and on the remote host:

    $ echo $DISPLAY
localhost:10.0
    • 2