[systemd-devel] Ask some questions about overlay+/dev/mtdblock?

[Lennart Poettering]

On Mo, 02.03.20 16:21, www (ouyangxuan10 at 163.com) wrote:

> Dear all,
>
>
> Systemd is used in the embedded system. and some mounting information is as follows:
>
>
> dev on /dev type devtmpfs (rw,relatime,size=221372k,nr_inodes=55343,mode=755)
> sys on /sys type sysfs (rw,relatime)
> proc on /proc type proc (rw,relatime)
> tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
> /dev/mtdblock4 on /run/initramfs/ro type squashfs (ro,relatime)
> /dev/mtdblock5 on /run/initramfs/rw type jffs2 (rw,relatime)
> cow on / type overlay (rw,relatime,lowerdir=run/initramfs/ro,upperdir=run/initramfs/rw/cow,workdir=run/initramfs/rw/work)
> tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
>
>
> I have a question, why can overlayfs directly save the information in block4 and block5 (such as the running information of SYSTEMd) after I uninstall block4 and block5 with umount command？
> Who knows why, or gives some advice?

It's a feature of overlayfs that it keeps its own references to the
underlying file systems, and they can be unmounted while the overlayfs
itself stays accessible.

if you don't want that, unmount the overlayfs too?

Lennart

--
Lennart Poettering, Berlin