Cubic custom ISO which executes shell script at startup

Question

I'm trying to customise an Ubuntu ISO with Cubic to run a couple of shell scripts when the Live user logs in. I've been following a bunch of tutorials with a ton of instructions and I eventually had it working at one point. Unfortunately, I'm not able to recreate the setup and worse still, I've deleted the particular ISO thinking I won't be needing it. So far, I've moved my shell scripts to the /etc/skel directory through the chroot environment in Cubic and modified the the crontab by adding an @reboot command. After that, I let Cubic create my ISO and I flashed it to a USB. I booted it up but realised the scripts hadn't been executed. I checked the home directory (since thats where the contents of /etc/skel are supposed to go) and all my scripts were present. How can I get this working?

Answer 1

Instead of using chron, you can use an autostart script to connect to the remote machine.

You should setup key based authentication to the remote machine, so no user interaction is required.

In the instructions below, replace the following values as needed.

• LOCAL - the IP address or host name of your local computer (where you are running Cubic)
• REMOTE - the IP address or host name of the remote computer
• n00dles - the user name on the local computer and/or the remote computer
• REMOTE_LOCATION_PATH - the path of the directory you want to mount on the remote computer

1. Generate public and private keys for your local machine.

   These keys will be used in your custom ISO. Be aware of the security implications. Anyone who gets a hold of your customized USB will be able to login to your remote machine.

   Execute the following commands on your local machine (e.g. not in Cubic).

   cd ~
   ssh-keygen -t rsa
   

   Accept the defaults. The output will look something like this.

   Generating public/private rsa key pair.
   Enter file in which to save the key (/home/n00dles/.ssh/id_rsa): 
   Enter passphrase (empty for no passphrase):
   Enter same passphrase again:
   Your identification has been saved in /home/n00dles/.ssh/id_rsa
   Your public key has been saved in /home/n00dles/.ssh/id_rsa.pub
   The key fingerprint is:
   SHA256:G48dcTOXpUhzWxuzwn8pgdOTP9WmlLtXBCJkkiSEywk n00dles@LOCAL
   The key's randomart image is:
   +---[RSA 3072]----+
   |     xxxxxx x xxx|
   |  x x  xxxxxxxxxx|
   |   x x    xxxxxxx|
   |    x      xxxxxx|
   |  x     x x  xxxx|
   |         x x  xxx|
   |  x     x x   x x|
   |               x |
   |  x              |
   +----[SHA256]-----+
   

2. Setup remote login.

   Copy the public key to the remote machine. Be aware of the security implications. This will allow remote connections from any computer using the corresponding private key.

   ssh-copy-id -i .ssh/id_rsa.pub user@host
   

   Create a new known_hosts file that you will copy to the customized ISO. This will allow the Live environment to connect to the remote machine without prompting the user to confirm.

   Temporarily backup your current known_hosts file. Remember to replace n00dles@REMOTE and REMOTE_LOCATION_PATH as necessary.

   mv ~/.ssh/known_hosts ~/.ssh/known_hosts.original
   
   # Login to the remote machine to automatically create a new `known_hosts` file.
   sudo mkdir /mnt/remote
   sshfs [email protected]:/REMOTE_LOCATION_PATH/ /mnt/remote/
   
   ECDSA key fingerprint is SHA256:XXXX.
   Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
   
   # Unmount the remote machine.
   fusermount -u /mnt/remote
   sudo rmdir /mnt/remote
   
   # Save the new known_hosts file.
   mv ~/.ssh/known_hosts ~/
   
   # Revert the original known_hosts file.
   mv ~/.ssh/known_hosts.original ~/.ssh/known_hosts
   

3. Customize the ISO using Cubic.

   Launch Cubic and do the following on the Terminal page.

   Make sure sshfs is installed so we can connect to remote machines.

   apt install sshfs
   

   Copy the keys and the new known_hosts file to the custom OS.

   cd /etc/skel
   mkdir .ssh
   chmod u=rwx,g=,o= .ssh
   cd .ssh
   

   Open a file browser such as Nautilus and navigate to your local ~/.ssh directory.

   Select id_rsa and id_rsa.pub and drag them onto the Cubic window to copy them into the current directory, /etc/skel.ssh.

   Open a file browser such as Nautilus and navigate to your home directory.

   Select the new known_hosts file and drag it onto the Cubic window to copy it into the current directory, /etc/skel/.ssh.

   Make sure the permissions are correctly set for these files; this is very important. In Cubic, execute the following:

   chmod u=rw,g=,o= id_rsa
   chmod u=rw,g=r,o=r id_rsa.pub
   chmod u=rw,g=r,o=r known_hosts
   
   ls -la
   
   -rw------- 1 root root 2602 Jun  7 09:35 id_rsa
   -rw-r--r-- 1 root root  566 Jun  7 09:35 id_rsa.pub
   -rw-r--r-- 1 root root  222 Jun  7 09:35 known_hosts
   

   Create a mount point for the remote location, make sure it can be used by all users, and add a link named Remote in each user's home directory.

   mkdir /mnt/remote
   chmod a+rw /mnt/remote
   ln -s /mnt/remote /etc/skel/Remote
   

4. Create a script to mount the remote location.

   nano /opt/mount_remote.sh
   

   Add the following to the script. Remember to replace n00dles@REMOTE and REMOTE_LOCATION_PATH as necessary.

   #!/bin/bash
   # Mounts the remote location.
   # To mount use: sshfs [email protected]:/REMOTE_LOCATION_PATH/ /mnt/remote
   # To unmount use: fusermount -u /mnt/remote
   for i in {1..5}; do
       if mountpoint /mnt/remote; then
           echo "[email protected]:/REMOTE_LOCATION_PATH is mounted."
           break
       else
           # Attempt to mount the remote location to /mnt/remote
           echo "Attempt # $i to mount [email protected]:/REMOTE_LOCATION_PATH."
           sleep $i
           sshfs [email protected]:/REMOTE_LOCATION_PATH/ /mnt/remote
       fi
   done
   if mountpoint /mnt/remote; then
       echo "Successfully mounted [email protected]:/REMOTE_LOCATION_PATH."
   else
       echo "Unable to mount [email protected]:/REMOTE_LOCATION_PATH."
   fi
   

   Type CTRLX, Y, Enter to save the file.

   You can use environment variables such as $HOME in the script, if you need to.

   Make the script executable.

   chmod +x /opt/mount_remote.sh
   

5. Create an autostart file that will run for each user after login.

   nano ~/mount_remote.desktop
   

   For XUbuntu 20.04+ or older versions of Ubuntu, add the following to the file.

   [Desktop Entry]
   Encoding=UTF-8
   Version=0.9.4
   Type=Application
   Name=mount_remote
   Comment=Mount remote location
   Exec=/opt/mount_remote.sh
   OnlyShowIn=XFCE;
   RunHook=0
   StartupNotify=false
   Terminal=false
   Hidden=false
   

   For Ubuntu 20.04+, add the following to the file.

   [Desktop Entry]
   Type=Application
   Exec=/opt/mount_remote.sh
   Hidden=false
   NoDisplay=false
   X-GNOME-Autostart-enabled=true
   Name[en_US]=Mount Remote
   Name=Mount Remote
   Comment[en_US]=Mount remote location
   Comment=Mount remote location
   

   Type CTRLX, Y, Enter to save the file.

   You can add Terminal=true to the *.desktop file for debugging purposes, but the remote location will be immediately unmounted once the terminal window automatically closes.

6. Move the autostart file to the correct location. You have two options.

   • If you want to use a global autostart file, move it to /etc/xdg/autostart.

     mv ~/mount_remote.desktop /etc/xdg/autostart
     

   • If you want each user to have thier own copy of the autostart file, move it to /etc/skel/.config/autostart. (Users will be able to delete this file because it will be placed in their home folder).

     mkdir -p /etc/skel/.config/autostart
     mv ~/mount_remote.desktop /etc/skel/.config/autostart
     

7. Continue customizing your OS, and generate a new ISO.

8. Testing

   If you use the remote host name instead of the IP address, when you test the generated ISO, make sure DNS resolution works. In VirtualBox, I usually set the Network to use the "Bridge Adapter" instead of the default "NAT" adapter.