how-to create (and use) extra partition on USB-installation stick

Why not install Ubuntu to the USB and then use that as you require? You can install the installer application to the USB stick too and use it when you want to put Ubuntu on a system.

Thanks for your idea Andrew,

i have some questions:

running Xubuntu on my PC,
which program do i use to install life-running Xubuntu on the entire USB ?
( /usr/bin/usb-creator-gtk let me only create a bootable installer-USB of 1,6 Gb without using the extra space )

At the end of the installation process the command /usr/sbin/update-grub is putting ALL boot-images in the grub-config-file /boot/grub/grub.cfg , so
.1. during creation of the Xubuntu-USB-stick also my boot-images on my hard disk are added in the USB-grub
.2. during installation on an other PC on that hard disk the boot-images of the USB-stick are added in grub

The same question for the UEFI-partition too ...

Thanks for your answers!

to install Ubuntu to USB you just choose it at install time. The OS doesn't care how the disk is attached. It's just

it's just a disk (knocked mouse by accident there).

You will need to tell the installer to go on the USB too so that it is bootable. USB creator doesn't install Ubuntu to the USB per-se. It simply copies the ISO data and makes it bootable. This is slightly different to a real install.

I don't know about UEFI. If Ubuntu is the only OS on the system then I suggest you don't use it. If you have *buntu on the internal drive already and is installed with UEFI enabled then don't change this as the installed OS won't boot if you switch this.

On a PC running on Xubuntu-18.04.5 (32 bit, so i386 version) i downloaded ubiqity.

When i start ubiquity, the only choice is to install Kubuntu (KDE including all programs).
This 'life' version needs more than 8 Gb !

But i want to create an USB running Xubuntu-18.04 (XFCE) life
with the possibility to boot from that USB and install Xubuntu on other 32-bit systems.
On old Xubuntu-Cd's there was a non-graphic installation program...

What should i download to create such an USB (it's size is 8 Gb, which is larger than the 1,6 Gb used by the installation DVD; so this must be sufficient)

Tips are welcome!

Have you tried creating the USB stick with unetbootin https://unetbootin.github.io/ ?
This should allow adding a persistent area up to 4 GB size.

@andrew-woodhead666 about UEFI:

booting in (old) BIOS starts the PC in a way that only disks smaller than 2 Tb are correctly accessed, it uses the old MBR-partition of disks.
booting in (new) UEFI boots from a disk with GPT-partitions (under which one special containing only the UEFI boot-files); booted this way, the accessible disks can be larger than 2 Tb.
More info at
  https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface

@m-hampl about uNetBootin:
i am going to give it a try and describe my findings here;
thanks for your hint.

If 2Tb is all that is present or needed, then it's not so bad. It's quite common to have a smaller. SSD with the OS on and larger drives which have casual user data on.

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