[systemd-devel] emergency, rescue and single-user

[Lennart Poettering]

On Tue, 09.12.14 13:43, Jan Synáček (jsynacek at redhat.com) wrote:

> Hello,
> 
> what is the difference between emergency, rescue and single-user?
> On F21, systemd-216-12.fc21.x86_64, they all boot into something that
> presents itself as "Welcome to emergency mode!" and they all require a
> root password. In case of booting into emergency.target, I can see
> "Starting Emergency Shell" in the console output. In single-user and
> rescue.target, I can see "Starting Rescue Shell", but they all look the
> same. systemd.special(7) doesn't help much.

"rescue" is simply how we call the old sysv "single user" mode. This
means all early-boot services are started, but no later boot
service. File systems are hence checked, udev is started, and so
on. You get your shell right after sysinit.target but before
basic.target basically.

"emergency" maps to the "emergency" mode that sysvinit already knew:
it just starts a shell, and does nothing else. No early-boot services
are run. No udev, no file system checks, no nothing.

Lennart

-- 
Lennart Poettering, Red Hat