According to version 5 of the LPIC-1 Exam 101 objectives, which was published in October 2018, you need to be familiar with a number of concepts and commands that are are alternatives to each other. Most notably, these are:
- init systems: both systemd-related concepts and commands (e.g. boot targets,
systemctl) and the older SysVinit (e.g. runlevels,
/etc/init.d/, etc.). Upstart is also still listed but much less important now, especially after Ubuntu switched to systemd for compatibility with Debian, which had also switched to systemd.
- Package management: you need to be able to do package management with Debian tools (dpkg, apt-get, apt-cache, etc.), and with RPM-related tools, not just yum but also zypper.
So which distributions can you use?
- If you use Debian or a Debian-based distribution such as Ubuntu, you can practise with systemd and with Debian tools for package management.
- If you use Fedora or one of its derivatives (e.g. Cent OS), you can practise with systemd and with RPM tools for package management.
- If you use openSUSE, you can practise with systemd and Zypper.
- This still leaves us with the question which distribution to use for SysVinit. There are still a number of distros that use SysVinit, most notably Devuan, which forked from Debian, but also Gentoo (Gentoo offers systemd as an alternative) and Slackware. For other distrinbutions with SysVinit, consult the webpage Linux distributions without systemd.
Harald Maaßen, whose book LPIC-1. Sicher zur erfolgreichen Linux-Zertifizierung (2018) is up-to-date with version 5 of the exam objectives, recommands using a Debian-based distro (e.g. Debian, Ubuntu or Mint) and a Red Hat-based distro (e.g. Scientific, Cent OS or Fedora). His book's introduction doesn't mention OpenSUSE (for zypper) or any distro that still uses SysVinit. It appears that you need at least three distributions to get experience with the concepts and tools listed at the beginning of my answer, e.g.
- Fedora or one of its derivatives will bring systemd and RPM-based package management tools,
- openSUSE will also allow you to practise with zypper (in addition to systemd),
- Devuan will allows you to practise with SysVinit and the apt-based tools that you also get on Debian and Ubuntu.
Of course, you can run these distributions as virtualised machines, e.g. using VirtualBox.
Devuan may be an unexpected choice, but you can see how I arrived at it.