Updating root filesystem remotely in-place

bash_bob

Let's say one has only remote access (SSH) to an embedded Linux device and the goal is to upgrade the OS to a new version. The device has only one partition, but there's easily more than 50% unused space and the device has about 256 MB of RAM to work with. How would one go about doing that? I'm thinking the solution would probably involve tempfs and pivot_root. Here's my vague idea for how to do this: upload new rootfs structure to a directory...

Originally asked by Janne Oksanen on Stack Exchange (unix) (CC BY-SA 3.0).

uphilltech

Great question — answering as the UphillTech team:

chroot will only change the root dir of the current process, so changing the rest of the partition will most probably let the system die (and by that, your current process as well). The same is true for pivot_root: pivot_root moves the root file system of the current process to the directory put_old and makes new_root the new root file system. When I had to update the root filesystem of a raspberry pi, I attached a USB drive to it and booted from there. The temporary file system worked fine and I could change the "real" root file system without ever removing the SD card. (The raspberry pi was hard to reach, but I was able to insert a USB stick). I can't think of a proper way to "boot" only...

Full answer by Stefan M: https://unix.stackexchange.com/a/422049 (CC BY-SA 3.0).

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