sshfs with x forwarding?

Question

I've been using sshfs to mount directories from servers on my laptop.

I also have the following in my ~/.ssh/config: ControlMaster auto

I set this because it keeps a single ssh connection alive whenever I ssh into a server. I do this particularly for fast browsing in emacs using tramp.

Since I have sshfs in my /etc/fstab, the ssh connection from sshfs is the one that stays alive. A lot of times I also need X11 forwarding (ssh -X -Y -C), and since I'm always using the original connection from sshfs, X11 isn't forwarded.

X11 works when I remove the sshfs mount from my fstab, and I ssh into my servers manually with the -X -Y -C option.

Is there a way to turn on -X -Y -C (or the likes) for sshfs? I tried adding ForwardX11 yes ForwardX11Trusted yes

in ~/.ssh/config and /etc/ssh/ssh_config to force the option to always be on (might have security issue). However, sshfs in /etc/fstab does not pick this up.

Do you have any suggestions? Thanks!

Answer 1

The way around this problem is to use script in place of ssh command.

man pages of sshfs (at least since 2.0 April 2008)

-o ssh_command=CMD
  execute CMD instead of 'ssh'

Like this:

sshfs user@remote: mountpoint -o ssh_command='/path/to/sshcmd -Y -X -C '

And here's sshcmd

#!/bin/bash

# declare array for ssh options
declare -a CLEANED_SSH_OPTS
declare -a ADD_OPTIONS

# add options to be automatically added to the ssh command here.
# example
#ADD_OPTIONS=( '-C' )
# empty default
ADD_OPTIONS=(  )

for OPT in "$@"; do 
  # add list of values to be removed
  # from sshfs ssh options
  case $OPT in
    "-x")
     # this and these like this will be removed
    ;;
    "-a")
    ;;
    "-oClearAllForwardings=yes")
    ;;
    *)
      # These are ok.. add
      NUM=${#CLEANED_SSH_OPTS[@]}
      CLEANED_SSH_OPTS[$NUM]="$OPT"
    ;;
  esac
done

# Start ssh with CLEANED options
exec ssh ${ADD_OPTIONS[@]} ${CLEANED_SSH_OPTS[@]}
# replace above exec with the next one if you ssh tunneling to run as your 
# local user. Like when using automatic mounts from fstab.
# Please note that this has some extra security issues.
#exec su YourUserName -c "ssh ${ADD_OPTIONS[@]} ${CLEANED_SSH_OPTS[@]}"

Adding something like this to fstab should allow automatic mounting of sshfs and enable forwarding. Do note that when mount happens it's usually root user so you might have to make appropriate changes to sshcmd (see last line of sshcmd).

sshfs#USERID@HOST:/TARGETPATH /MOUNT_POINT fuse _netdev,user,ssh_command=/path/to/sshcmd\040-Y\040-X 0 0

Answer 2

Try this:

sshfs -ossh_command="ssh -A me@host1_wan_ip ssh $@" me@host2_lan_ip:/ /media/me/mount1

Answer 3

Yesterday I had exactly the same problem. I've modified sshcmd so that nows it also tries to contact the user's ssh-agent. Thanks Manwë!

#!/bin/bash
# Open a ssh connection as a given user, thus using his/hers authentication
# agent and/or config files.
: ${ADDOPTS:="-2Ax"}
: ${LOCAL:="kreator"}
export SSH_AUTH_SOCK=$(find /tmp/ssh-* -type s -user ${LOCAL} -name agent* | tail -1)
declare -a options=( $* )

# Remove unwanted options
for (( i=0,fin=${#options[*]} ; i < fin ; i++ ))
do
    case ${options[$i]} in
            (-a|-oClearAllForwardings=*)    unset options[$i]
                                            ;;
    esac
done

exec /bin/su ${LOCAL} -c "$(which ssh) ${ADDOPTS} ${options[*]}"