I'm using buildroot 2022.02.1 under x86 embedded SBC. 

The root file system is located on the on-board disk. 

The boot argument contains 'ro' (checked with /proc/cmdline after login) but the disk is not read-only. 

When I used the same boot args with busybox, it worked fine.

Of course with busybox I had to tailor all other mandatory files and directories. 

I need read-only rootfs to defend this embedded system in case of power-down / cold reset. 

Beyond the default configuration, the rootfs also contains ntp client, httpd, pci tools. 

Thank you,

Zvika