On 01/09/15 17:21, Goffredo Baroncelli wrote: > I discovered that bootctl assume as default mount point for the ESP > partition the /boot directory. Instead it seems to me that the most part > of distributions prefers /boot/efi.
For some context, the reasoning for /boot/efi is: In some distributions (presumably including the (Fedora-based?) ones where this feature was developed), /boot is traditionally treated as mutable and unpackaged, like /var; so the packages include the kernel in /usr or /lib or something, and copy it into /boot. The cost of this is one extra copy of the kernel on-disk, which used to be a significant amount of space, although on modern disks it doesn't really matter. In other distributions (like Debian and its derivatives), the OS packages for kernels traditionally include /boot/vmlinux-whatever and /boot/config-whatever as packaged files; the corresponding initramfs is generated at install time and placed alongside them. In these distributions, there is no second copy of the kernel in /usr or /lib. This saves some space, although, again, the amount of space saved is negligible on current hardware. On BIOS systems, either way was fine, because /boot was either part of the root filesystem, or a separate small ext2 partition near the beginning of the drive (to work around BIOS disk-addressability limitations) for use by lilo or grub or whatever. Similarly, on non-x86, the bootloader would traditionally either load the kernel from a non-filesystem like a raw flash partition, or from the root filesystem or a separate /boot partition; either would be fine. However, it starts to matter with the move to EFI (on x86 and elsewhere), or on non-EFI systems where the bootloader also reads a FAT partition (such as the Raspberry Pi). If the OS packages for kernels include files in /boot, then having a non-Unix filesystem for /boot becomes a problem, because the package manager (e.g. dpkg) can't use the same hardlink-based atomic-overwrite that it would use for robustness on a proper Unix filesystem. The ESP is FAT, which is not a full Unix filesystem, so you can't do that sort of thing. That's why Debian and its derivatives mount the ESP at /boot/efi instead of /boot, and why <http://sjoerd.luon.net/posts/2015/02/debian-jessie-on-rpi2/> mounts the ESP-equivalent at /boot/firmware. AIUI, /boot/efi also makes it a bit easier to have the ESP remain unmounted or read-only when not in active use, which is good for its own robustness; a system crash corrupting an unmounted partition is less likely than corrupting a mounted filesystem. In principle, it should be possible for the ESP to never be mounted at all, copying files in with mtools (or equivalent) when required. -- Simon McVittie Collabora Ltd. <http://www.collabora.com/> _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel