On Thu, May 28, 2015 at 4:55 PM, <cov...@ccs.covici.com> wrote: > Canek Peláez Valdés <can...@gmail.com> wrote: [...] > > As I said, I did the following tests: > > > > 1. Adding "emergency" to the kernel command line, with a valid root=. > > 2. Adding "rescue" to the kernel command line, with a valid root=. > > 2. Leaving root= invalid without adding neither "emergency" nor "rescue". > > > > If root= is valid, with emergency systemd drops you to a shell with your > > root filesystem mounted read-only. With rescue, systemd drops you to a > > shell with all your filesystems mounted read-write. > > > > If root= is invalid, it doesn't matter if you use emergency, rescue, or > > neither, *dracut* drops you to a shell, still inside the initramfs > > obviously. It takes a while; I didn't took the time, but I think it was 3 > > minutes. Inside this shell, you can use systemd normally, and if you manage > > to mount the root filesystem, I'm sure you could continue the normal boot > > process. You'll have to pivot root manually, though. > > > > Hope that makes it clear. > > How do you pivot route manually?
Basically, with pivot_root(8) [1]. Be aware that systemd does some things before and after pivot_root'ing; in particular, it switches from the instance running inside the initramfs to an instance running in the real filesystem. I'm not sure how it does it, but the switching code is relatively simple [2]. Regards. [1] http://linux.die.net/man/8/pivot_root [2] http://cgit.freedesktop.org/systemd/systemd/tree/src/shared/switch-root.c -- Canek Peláez Valdés Profesor de asignatura, Facultad de Ciencias Universidad Nacional Autónoma de México
