true, partitioning

unpacking includes target
source is easy, even internet ones
package selection is easy, also more of a gui thing (gui was not mentioned)
filesystem goes into partitioning
boot config is easy since you have all the data you need to do it
fstab (that includes swap) is easy when you do partitioning

i'm against using anaconda as an example as apparently it is so incredibly complex that very competent programmers can't rid it of bugs

slackwares installer is much much simpler and does it all except the partitioning part
(a gui version of it is a matter of making a gui more then anything else)
k, it doesn't do encryption and lvm

depends on the configuration of the LVM/partitioning. Anaconda is complex, as it is trying to do the whole install/configuration/configuration tasks. It has to be complex. That is one of the nice things about Slakware - it doesn't try to do everything. But then, the person installing has to know more.

In the case of btrfs, there are storage pools to be considered which can be one or more disks/partitions.

In the case of xfs/ext4 there are optimization configurations...

As far as not using something that has already been done..
Up to you. NIH exists in lots of forms.

Boot configuration depends on what you are dealing with - BIOS/UEFI, grub/grub2/lilo/elilo... and then there are signing issues for secureboot, unless that is disabled...

Lots of variables and combinations.

Slackware is much simpler in packaging too. But it depends on what you are doing. It is considered more complex since it doesn't directly deal with dependency lists...

When you're installing an OS, you have to be root user because you are creating partitions, file systems, etc. Or to be more precise, there's no users (other than the 'implicit root') at that time.

Just to add to what NevemTeve has written. The reason an installer requests a password is not to become root, since you already are root to do the install, but to add the password to the password file.

This is turning into much larger affair

Are you making a Linux installer or an application/applet/etc installer. If it is Linux installer, the installer is running in a live environment and the root account is created on the partition the will contains the new /etc/ and as such it can be created with a password that supplied by the "installing person" via the fact that you are root in the installer or that you are a user that can do su or sudo commands.

That is what happens with a system level installer. There are a LOT details to get right.

That is why people usually reuse existing installers.

Thank you all.

I had a derp moment!

This is what I learned:

The initramfs is unpacked
and therefore in kernel space.
Which in turn gives you
"automatic admin" rights.

OS-installation is always happening in admin mode, initramfs notwithstanding (packed or otherwise).
Mind you, the installer program isn't part of the kernel.

Right on!

Just to clarify:
The initial initramfs in the root of
the .iso will start up my installer.
I will use dracut at the end of the
install to make another initramfs on
the HD

Thaks all for your help.

Linux and the LQ forum have been
very good to me!