Root File System Questions

[Greg Ludewig]

I was told to post this on the forum by Jeff Blees, who said Jesse would be able to answer some of these questions for me.

If I flash the kernel but not the root filesystem, I won’t lose any of the files I have stored on the device, but if I flash the root filesystem I’ll lose any saved files, right? Is there any way to download a new file to the filesystem as part of the flashing process?

Also, how much space is available in the root filesystem, if we’re not using an SD card? Does it depend on how much space is taken up by the kernel image, such that we’ll have less space in the root filesystem the more packages we include in the kernel? Is there a way to tell how much free space is left in the root filesystem?

[Jesse Gilles]

Hi Greg,

> If I flash the kernel but not the root filesystem, I won’t lose any of the files I have stored on the device, but if I flash the root filesystem I’ll lose any saved files, right?

Correct, flashing the linux kernel does not touch the root filesystem at all. If you flash the root filesystem, it will replace the entire filesystem, so any changes will be lost. If you need to store files and have them persist after flashing the root filesystem, they should either be put into your filesystem image, stored on the SD card, or if they are small, they can be stored in /var/config, which is a separate partition on the NAND flash.

> Is there any way to download a new file to the filesystem as part of the flashing process?

No, not as part of the flashing process itself. If you have an application/files that you want to be flashed in, you will need to write a bitbake recipe to package it and include in a custom image recipe. There are some basic examples on this site as to how to do that.

> Also, how much space is available in the root filesystem, if we’re not using an SD card?

The root filesystem partition is rather large, it’s about 230MB in total size. To see how much space is available, run ‘df -h’ on the unit and will print out the size and free space for all partitions.

> Does it depend on how much space is taken up by the kernel image, such that we’ll have less space in the root filesystem the more packages we include in the kernel?

No, the linux kernel image is stored in a separate partition in the flash. You will most likely not need to change anything with the kernel itself, unless you need to enable certain drivers that are not included by default or make custom patches. The linux kernel itself is only about 2MB.

Hope that helps,
Jesse

[Greg Ludewig]

Jesse,

thanks, this does help alot. It sounds like it’s not a simple process to transfer a file to the filesystem via the debug port.

Greg

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