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I'm trying to setup a one-time SSH tunnel which instantiates x11vnc on a logged-in display.

ssh -f -t -L 5900:localhost:5900 user@10.1.10.1 'sudo /usr/bin/x11vnc -safer -once -nopw -display :0 -auth /home/user/.Xauthority'

/etc/sudoers:

user@myhost:~$ sudo cat /etc/sudoers
[sudo] password for user: 
#
# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/
# instead of directly modifying this file.
#
Defaults:user   !requiretty
Defaults        env_reset
Defaults        secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

root    ALL=(ALL:ALL) ALL
user  ALL=(ALL:ALL) NOPASSWD: /usr/bin/x11vnc

%admin ALL=(ALL) ALL

%sudo   ALL=(ALL:ALL) ALL

The end result is this:

Pseudo-terminal will not be allocated because stdin is not a terminal.
bind: Address already in use
channel_setup_fwd_listener: cannot listen to port: 5900
Could not request local forwarding.
ebz@icarus:~ $ sudo: no tty present and no askpass program specified
Sorry, try again.
sudo: no tty present and no askpass program specified
Sorry, try again.
sudo: no tty present and no askpass program specified
Sorry, try again.
sudo: 3 incorrect password attempts

It does say bind: Address already in use, but I feel this is not true and unrelated:

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 10.1.10.1:domain        *:*                     LISTEN      -               
tcp        0      0 *:ssh                   *:*                     LISTEN      -                   
tcp6       0      0 xxxx::xxxx:xxxx::domain [::]:*                  LISTEN      -               
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN      -               

Safe to say we can ignore that message. Also, removing the sudo entry for user has no effect, either.

Thanks, guys. Cheers.

P.S. The solution here - No TTY present when running commands over SSH.. - didn't work :(

Also, a side note, THIS IS SERVER RELATED (BACKGROUND REGARDING A CUSTOM LXC VMM IMPLEMENTATION FOR OPENNEBULA). Please DO NOT mark this off-topic as this is a valid application use case.

UPDATE

Plus -tt, minus -f -t switches:

$ ssh -tt -L 5900:localhost:5900 user@10.1.10.1 'sudo /usr/bin/x11vnc -safer -once -nopw -display :0 -auth /home/user/.Xauthority'
bind: Address already in use
channel_setup_fwd_listener: cannot listen to port: 5900
Could not request local forwarding.
[sudo] password for user: 

But it prompts for a password? It works after I enter the password though.

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1 Answer 1

up vote 2 down vote accepted

Make sure that user isn't in either of the groups admin or sudo or put the sudoers line for user after the group lines.

From the sudoers man page

When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).

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