SSHFS on the Nexus 9

This is documentation for getting SSHFS working on the Nexus 9 (flounder). My main motivation was to get my NAS mounted to the Android filesystem outside or inside my LAN, so I didn't have to rely on cloud services. Google is trying really hard to force cloud services. I'm using Dirty Unicorns 5.1.1, so this is only tested with that. It should work with other roms and kernels, so long as you are rooted.

First task is to get SSH working. Dropbear binaries are included in repo, thanks to tonyb486 at xda. All commands should be run as root with / writable.

Dropbear

• Put dropbear binaries in correct directory

mount -o remount,rw /system
cp /sdcard/Download/dropbearmulti /system/xbin/

• Create symlinks to the dropbearmulti binary

ln -s dropbearmulti dropbear
ln -s dropbearmulti dropbearkey

• Try to ssh from the android terminal. Make sure / is writable because this binary creates a /.ssh directory to store the known hosts file

ssh USER@HOST

• Once connected, exit back to android local and backup the /.ssh directory because it gets deleted on boot. We want to save the known_hosts file so we don't get an unknown host prompt every reboot

cp -r /.ssh /sdcard/.ssh

• Generate public/private keys so we can login in without a password, this is almost a necessity for auto mounting. We can do this with dropbear

dropbearkey -t rsa -f /data/.ssh/id_rsa

• Save the public key to a file

dropbearkey -y -f /data/.ssh/id_rsa | grep ssh-rsa > /tmp/pubkey

• and add the key to your authorized_keys file on your server by uploading the pubkey file, then

cat pubkey >> ~/.ssh/authorized_keys

• You should be able to SSH to your server without a password prompt. Be sure to specify your key file with -i

ssh -i /data/.ssh/id_rsa USER@HOST

Now we can get SSHFS working

SSHFS

• Drop the binary in the correct path

mount -o remount,rw /system
cp /sdcard/Download/sshfs /system/xbin/

• Test connection, these are the options that worked best for me. You can find more from the orginal source: https://github.com/l3iggs/android_external_sshfs

mkdir /mnt/sshfs
chmod 777 /mnt/sshfs
sshfs -o allow_other -o ro -o follow_symlinks -o StrictHostKeyChecking=no -o reconnect -o TCPKeepAlive=no -o ssh_command="ssh -i /data/.ssh/id_rsa" USER@HOST:/path/on/server /mnt/sshfs

You should have working SSHFS right now! But you may have noticed that the contents of the mounted directory is only visible to the terminal app. To fix this, uncheck "Mount namespace separation" in superSU settings. Now mount commands run by root are shared across all apps. https://su.chainfire.eu/#how-mount

Automounting

• I use tasker to autorun some scripts for automounting. I've created a startup script and mount nas script that's included in the repo. Contents of startup_script.sh will create your mount directory and copy the previously backed up known_hosts ssh file that dropbear needs. I used tasker to run this on boot, and also run the mount script when wifi is up. The mount script will make the sshfs connection.

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Important links

• http://forum.xda-developers.com/nexus-9/development/useful-64-bit-aarch64-binaries-busybox-t2931373

• https://github.com/iMilnb/docs/blob/master/dropbear%2Bsftp-android.md

• https://github.com/l3iggs/android_external_sshfs

• https://github.com/lotan/android_sshfs_bin

• https://yorkspace.wordpress.com/2009/04/08/using-public-keys-with-dropbear-ssh-client/

• http://forum.xda-developers.com/showthread.php?t=2106480

• https://play.google.com/store/apps/details?id=os.tools.scriptmanager&hl=en

• https://su.chainfire.eu/#how-mount