How can I replace upstart with systemd?

Wily Werewolf (15.10) and newer:

You don't have to do anything. You are using systemd by default.

Trusty (14.04) and older:

You are out of luck. Ubuntu repositories do not provide the systemd binaries for versions before Utopic, despite the fact that their sources do generate the files. You can learn more about this in this answer.

add these ppas

sudo add-apt-repository ppa:ondrej/systemd
sudo apt-get update

systemd requires the directory /sys/fs/cgroup as a mountpoint. It doesn't exist in the current Ubuntu kernel (2.6.35). It can't be created with mkdir either because sysfs doesn't allow that. To create the directory this patch from the 2.6.36 kernel must be backported. A suitably patched kernel can be pulled via apt-get

sudo apt-get install linux-image-2.6.35-23-generic=2.6.35-23.41ppa1 linux-headers-2.6.35-23-generic=2.6.35-23.41ppa1 linux-headers-2.6.35-23=2.6.35-23.41ppa1

then install systemd

 sudo apt-get install systemd libpam-systemd systemd-gui systemd-extra-units

for more information go to this link