I have a machine running Ubuntu which I SSH to from my Fedora 14 machine. I want to forward X from the Ubuntu machine back to Fedora so I can run graphical programs remotely. Both machines are on a LAN.
I know that the -X option enables X11 forwarding in SSH, but I feel like I am missing some of the steps.
What are the required steps to forward X from a Ubuntu machine to Fedora over SSH?
X11 forwarding needs to be enabled on both the client side and the server side.
On the client side, the -X (capital X) option to ssh enables X11 forwarding, and you can make this the default (for all connections or for a specific connection) with ForwardX11 yes in ~/.ssh/config.
On the server side, X11Forwarding yes must be specified in /etc/ssh/sshd_config. Note that the default is no forwarding (some distributions turn it on in their default /etc/ssh/sshd_config), and that the user cannot override this setting.
The xauth program must be installed on the server side. If there are any X11 programs there, it's very likely that xauth will be there. In the unlikely case xauth was installed in a nonstandard location, it can be called through ~/.ssh/rc (on the server!).
Note that you do not need to set any environment variables on the server. DISPLAY and XAUTHORITY will automatically be set to their proper values. If you run ssh and DISPLAY is not set, it means ssh is not forwarding the X11 connection.
To confirm that ssh is forwarding X11, check for a line containing Requesting X11 forwarding in the output of ssh -v -X. Note that the server won't reply either way, a security precaution of hiding details from potential attackers.
To get X11 forwarding working over SSH, you'll need three things in place:
If you have both #1 and #2 in place but are missing #3, then you'll end up with an empty DISPLAY environment variable.
Soup-to-nuts, here is how to get X11 forwarding working:
On your server, make sure /etc/ssh/sshd_config contains:
X11Forwarding yes
X11DisplayOffset 10
You may need to SIGHUP sshd so it picks up these changes.
cat /var/run/sshd.pid | xargs kill -1
On your server, make sure you have xauth installed.
belden@skretting:~$ which xauth
/usr/bin/xauth
If you do not have xauth installed, you will run into the empty DISPLAY environment variable problem.
On your client, connect to your server. Be certain to tell ssh to allow X11 forwarding. I prefer
belden@skretting:~$ ssh -X blyman@the-server
but you may like
belden@skretting:~$ ssh -o ForwardX11=yes blyman@the-server
or you can set this up in your ~/.ssh/config.
I was running into this empty DISPLAY environment variable earlier today when ssh'ing into a new server that I do not administer. Tracking down the missing xauth part was a bit fun. Here is what I did, and what you can do too.
On my local workstation, where I am an administrator, I verified that /etc/ssh/sshd_config was set up to forward X11. When I ssh -X back in to localhost, I do get my DISPLAY set correctly.
Forcing DISPLAY to get unset was not too hard. I just needed to watch what sshd and ssh were doing to get it set correctly. Here is the full output of everything I did along the way.
blyman@skretting:~$ mkdir ~/dummy-sshd
blyman@skretting:~$ cp -r /etc/ssh/* ~/dummy-sshd/
cp: cannot open `/etc/ssh/ssh_host_dsa_key' for reading: Permission denied
cp: cannot open `/etc/ssh/ssh_host_rsa_key' for reading: Permission denied
Instead of using sudo to force copying my ssh_host_{dsa,rsa}_key files into place, I used ssh-keygen to create dummy ones for myself.
blyman@skretting:~$ ssh-keygen -t rsa -f ~/dummy-sshd/ssh_host_rsa_key
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/blyman/dummy-sshd/ssh_host_rsa_key.
Your public key has been saved in /home/blyman/dummy-sshd/ssh_host_rsa_key.pub.
Rinse-and-repeate with -t dsa:
blyman@skretting:~$ ssh-keygen -t dsa -f ~/dummy-sshd/ssh_host_dsa_key
# I bet you can visually copy-paste the above output down here
Edit ~/dummy-sshd/sshd_config to point to the correct new ssh_host key files.
# before
blyman@skretting:~$ grep ssh_host /home/blyman/dummy-sshd/sshd_config
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
# after
blyman@skretting:~$ grep ssh_host /home/blyman/dummy-sshd/sshd_config
HostKey /home/blyman/dummy-sshd/ssh_host_rsa_key
HostKey /home/blyman/dummy-sshd/ssh_host_dsa_key
Fire up sshd on a new port in non-detach mode:
blyman@skretting:~$ sshd -p 50505 -f ~/dummy-sshd/sshd_config -d
sshd re-exec requires execution with an absolute path
Whoops, better correct that path:
blyman@skretting:~$ /usr/sbin/sshd -p 50505 -f ~/dummy-sshd/sshd_config -d
debug1: sshd version OpenSSH_5.5p1 Debian-4ubuntu6
debug1: read PEM private key done: type RSA
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: private host key: #0 type 1 RSA
debug1: read PEM private key done: type DSA
debug1: Checking blacklist file /usr/share/ssh/blacklist.DSA-1024
debug1: Checking blacklist file /etc/ssh/blacklist.DSA-1024
debug1: private host key: #1 type 2 DSA
debug1: setgroups() failed: Operation not permitted
debug1: rexec_argv[0]='/usr/sbin/sshd'
debug1: rexec_argv[1]='-p'
debug1: rexec_argv[2]='50505'
debug1: rexec_argv[3]='-f'
debug1: rexec_argv[4]='/home/blyman/dummy-sshd/sshd_config'
debug1: rexec_argv[5]='-d'
Set /proc/self/oom_adj from 0 to -17
debug1: Bind to port 50505 on 0.0.0.0.
Server listening on 0.0.0.0 port 50505.
debug1: Bind to port 50505 on ::.
Server listening on :: port 50505.
Pop a new terminal and ssh into localhost on port 50505:
blyman@skretting:~$ ssh -p 50505 localhost
The authenticity of host '[localhost]:50505 ([::1]:50505)' can't be established.
RSA key fingerprint is 81:36:a5:ff:a3:5a:45:a6:90:d3:cc:54:6b:52:d0:61.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '[localhost]:50505' (RSA) to the list of known hosts.
Linux skretting 2.6.35-32-generic #67-Ubuntu SMP Mon Mar 5 19:39:49 UTC 2012 x86_64 GNU/Linux
Ubuntu 10.10
Welcome to Ubuntu!
* Documentation: https://help.ubuntu.com/
1 package can be updated.
0 updates are security updates.
Last login: Thu Aug 16 15:41:58 2012 from 10.0.65.153
Environment:
LANG=en_US.UTF-8
USER=blyman
LOGNAME=blyman
HOME=/home/blyman
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
MAIL=/var/mail/blyman
SHELL=/bin/bash
SSH_CLIENT=::1 43599 50505
SSH_CONNECTION=::1 43599 ::1 50505
SSH_TTY=/dev/pts/16
TERM=xterm
DISPLAY=localhost:10.0
Running /usr/bin/xauth remove unix:10.0
/usr/bin/xauth add unix:10.0 MIT-MAGIC-COOKIE-1 79aa9275ced418dd445d9798b115d393
Look at the last three lines there. I fortuitously had DISPLAY set, and had those two nice-looking lines from /usr/bin/xauth.
From there it was child's play to move aside my /usr/bin/xauth to /usr/bin/xauth.old, disconnect from ssh and stop the sshd, then launch sshd and ssh back in to localhost.
When /usr/bin/xauth was gone, I did not see DISPLAY reflected in my environment.
There is nothing brilliant going on here. Mostly I got lucky in choosing a sane approach to try reproducing this on my local machine.
Make sure that:
xauth installed on the server (see: xauth info/xauth list).On the server your /etc/ssh/sshd_config file have these lines:
X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost no
On the client side your ~/.ssh/config file have these lines:
Host *
ForwardAgent yes
ForwardX11 yes
On the client side, you've X server installed (e.g. macOS: XQuartz; Windows: Xming).
Then to do X11 forwarding using SSH, you need to add -X to your ssh command, e.g.
ssh -v -X user@host
then verify that your DISPLAY is not empty by:
echo $DISPLAY
If it is, then having verbose parameter for ssh (-v), check for any warnings, e.g.
debug1: No xauth program.
Warning: untrusted X11 forwarding setup failed: xauth key data not generated
In case you've got untrusted X11 as shown above, then try -Y flag instead (if you trust the host):
ssh -v -Y user@host
In case you've warning: No xauth data, you may try to generate a new .Xauthority file, e.g.
xauth generate :0 . trusted
xauth list
See: Create/rebuild a new .Xauthority file
If you've got a different warnings than above, follow the further clues.
The fix is to add this line to your /etc/ssh/sshd_config:
X11UseLocalhost no
https://joshua.hoblitt.com/rtfm/2013/04/how_to_fix_x11_forwarding_request_failed_on_channel_0/
ssh -X to get a GUI environment on a remote serverInstall all the following. On Window, install Xming. On Ubuntu in the terminal, use sudo apt install to install ssh xauth xorg.
sudo apt install ssh xauth xorg
Go to the folder contains ssh_config file, mine is /etc/ssh.
Edit ssh_config as administrator(USE sudo). Inside ssh_config, remove the hash # in the lines ForwardAgent, ForwardX11, ForwardX11Trusted, and set the corresponding arguments to yes.
# /etc/ssh/ssh_config
Host *
ForwardAgent yes
ForwardX11 yes
ForwardX11Trusted yes
In ssh_config file, remove the front hash # before Port 22 and Protocol 2, and also append a new line at the end of the file to state the xauth file location, XauthLocation /usr/bin/xauth, remember write your own path of xauth file.
# /etc/ssh/ssh_config
# IdentifyFile ...
Port 22
Protocol 2
# Cipher 3des
# ...
# ...
...
...
GSSAPIDelegateCredentials no
XauthLocation /usr/bin/xauth
Now since we are done editing ssh_config file, save it when we leave the editor. Now go to folder ~ or $HOME, append export DISPLAY=localhost:0 to your .bashrc file and save it.
# ~/.bashrc
...
...
export DISPLAY=localhost:0
We are almost done. Restart your bash shell, open your Xming program and use ssh -X yourusername@yourhost. Then enjoy the GUI environment.
ssh -X yourusername@yourhost
The problem is also in Ubuntu subsystem on Windows, and the link is at
https://gist.github.com/DestinyOne/f236f71b9cdecd349507dfe90ebae776
Add X11UseLocalhost no to /etc/ssh/sshd_config and restart the SSH server.
If you get no DISPLAY, check if xauth is installed correctly and then try it again.
RHE/CEntos doesn't have this issue, this is a Ubuntu thing!
If you are doing ssh from Windows (10) to a Linux system - do yourself a favour and use a SSH client like Putty ( regular ssh -X etc does not work).
Step 1: Install a XServer in Windows : Example XMing Server (listens on localhost:0.0)
Step 2: In putty enable X11 forwarding
Step 3: Connect to remote Linux server
Make sure all conditions here are met in Linux server - that is X11Forwarding is yes and xauth is present as explained in the answer https://unix.stackexchange.com/a/12772/121634
Fire up XClock and wait a minute for the display to appear in your Windows machine
Note - If from this Linux server you are connecting to another server and want to forward X11 back to your Windows, you just need to connect to the next in chain with ssh -X.
That is
[Windows] Putty (with X11forwarding) --> [Server1] (xclock works) --> ssh -X [Server 2] (xclock works)
X11Forwarding must be set on the SSH server (in your case the Ubuntu box) in its sshd_config, and you must allow X11 to be forwarded for the SSH client (your Fedora box) by passing the -X option or editing the ssh_config file to add the ForwardX11 default.
For me the problem was in nodev mount option for /tmp filesystem. X11 needs a special file to be created in there.
So check what are the mount options for /tmp filesystem if you use a separate partition or disk for that.
xauth can get locked.
-b This option indicates that xauth should attempt to break any authority file locks before proceeding. Use this
option only to clean up stale locks.
Using
xauth -b
On the machine that I was trying to ssh into broke the lock on xauth. Logging out of the ssh session after issuing xauth -b then logging back in finally allowed me to successfully echo $DISPLAY. Definitely try this before re-creating .Xauthority
To add to the previous excellent answers (setting up ~/.ssh/config and checking to see if the DISPLAY environment variable is set on the client, setting up /etc/ssh/sshd_config and installing xauth on the server), also make sure xterm is installed on the client, e.g.
sudo apt-get install xterm
unix-like OS
/etc/ssh/sshd_config you have yes line
X11Forwarding yes
sudo systemctl restart ssh
macOS
xterm
brew install --cask xquartz
ssh -Y user@host
chromium http://google.com
If you're using connection sharing, you need to close all existing connections before any changes to your client ssh options will take effect.
I was using a script to connect to a remote machine with these options set.
-oControlPath=${control_path}
-oControlMaster=auto
I was trying to change my client ssh options to enable X11 forwarding and couldn't figure out why they weren't taking effect. I had to close the existing connections and reconnect with the new client ssh options for enabling X11 forwarding for it to work. You could also just open a new connection by removing any options for setting the control path.
Took me awhile to figure this out. Hope this helps someone.
