{"id":18127,"date":"2016-12-28T11:19:24","date_gmt":"2016-12-28T19:19:24","guid":{"rendered":"https:\/\/blog.digilentinc.com\/?p=18127"},"modified":"2021-06-11T10:58:15","modified_gmt":"2021-06-11T17:58:15","slug":"using-the-chroot-ssh-trick","status":"publish","type":"post","link":"https:\/\/digilent.com\/blog\/using-the-chroot-ssh-trick\/","title":{"rendered":"Using the Chroot SSH trick"},"content":{"rendered":"

Recently\u00a0I created a LabVIEW graphical interface for my LIRC<\/a> Raspberry PI<\/a> Universal remote<\/a>. The first step in this process was getting LIRC to work in the chroot <\/a>that runs on the Raspberry Pi. You can think of the chroot as a super lightweight virtual machine that\u00a0LabVIEW<\/a> runs in. Many folders have been mapped so they are shared between the host OS and the chroot, but LV cannot run a command (i.e. invoke an executable) that is outside the chroot. There is, however, one cheat though that would allow me to interact with LIRC when it is outside the chroot.\u00a0This cheat involves downloading an ssh client to your chroot and then using a System Exec VI to run commands outside of the chroot. This is potentially very powerful because it allows LINX<\/a> users to run programs that aren\u2019t compatible with the chroot.<\/p>\n

\"\"<\/p>\n

First, let\u2019s talk about what a chroot is exactly. A\u00a0chroot<\/a>\u00a0is a Linux construct that allows a process (like the LabVIEW run-time engine) set to run as if an arbitrary directory is the root directory. The way that we use a chroot with the LabVIEW run-time engine is to act as if LV was running within a very lightweight virtual machine. There are 2 reasons that LabVIEW runs within a chroot on the BeagleBone Black or Raspberry Pi 2:<\/p>\n

    \n
  1. Using a chroot we can make one installer which will run on several different Linux distributions and devices since the chroot contains its own set of system libraries and other operating system files.<\/li>\n
  2. The LabVIEW run-time engine is compiled with options that make it incompatible with the system libraries that are included in the default operating system images used with the BBB and RPi2\/3, so the chroot allows us to include a set of system libraries for LabVIEW to use that are compiled with options that are compatible.<\/li>\n<\/ol>\n

    \"\"<\/p>\n

    Since the LIRC wasn’t\u00a0compatible with the chroot yet I spent some time on LabVIEW MakerHub<\/a>, and I found a technique\u00a0referred\u00a0to as the “Chroot SSH Trick<\/a>”\u00a0This technique allows LabVIEW to run commands outside of its chroot on a LINX 3.0 (BBB or RPi2) target. This can be useful for interacting with commands that are unavailable inside the chroot, I have detailed the steps below.<\/p>\n

      \n
    1. \n
      Install an SSH client to your chroot:<\/div>\n