TIL that you can tell systemd to run any ExecStartPre and ExecStopPost scripts as root instead of the user the service is supposed to run under.

At the same time we can touch on how to create an override for a service. In my case, I wanted to override how Redis is started on a system to ensure hugepage was set correctly, per their documentation. Creating an override for a service is super simple:

systemctl edit <service>

In my case this means:

systemctl edit redis

Since I know that the name of the service I want to edit is redis. From here, I am presented with my favorite editor where I can input the following:

[Service]
PermissionsStartOnly=true
ExecStartPre=/usr/local/sbin/hugepage.sh

Here I am defining two things. First, I want the permissions to only apply to the ExecStart command, not the others. Next, I am specifying an ExecStartPre that calls a script. This script is simply outputting:

/bin/echo never > /sys/kernel/mm/transparent_hugepage/enabled

Once complete, save out the file and restart your service. Your changes will now take affect.

If you are running a newer release of systemd (231+) then you can use the following format as well:

ExecStartPre=+/usr/local/sbin/hugepage.sh