[systemd-devel] systemd boot sequence doubt

[Mantas Mikulėnas]

On Thu, Oct 22, 2015 at 9:37 AM, kennedy <kennedyhan at 163.com> wrote:

> what is systemd booting sequence?
>
> how is Systemd support both sysV's runlevel script and systemd's target
> file at the same time?
>

systemd first runs its "generators", which generate .mount units from
/etc/fstab (systemd-fstab-generator), .service units from /etc/rc?.d
(systemd-sysv-generator), and so on.

(The auto-generated units live in /run/systemd/generator; the
package-distributed ones in /usr/lib/systemd/system; the user-provided ones
in /etc/systemd/system.)

systemd then starts with "default.target" (usually symlinked to
multi-user.target), creates a dependency tree (based on Wants= or Requires=
in the unit files, symlinks in *.wants/, or drop-ins in *.d/), and starts
all units that default.target depends on:

$ systemctl list-dependencies multi-user.target
multi-user.target
 ├─apache2.service
 ├─bind9.service
 ├─binfmt-support.service
 ├─cron.service
 ├─dbus.service

See also manual pages for bootup(7), systemd.unit(5)

-- 
Mantas Mikulėnas <grawity at gmail.com>
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