Boost.Python error in job 'bootldr'
<class 'FileNotFoundError'>
[Errno 2] No such file or directory:'/tmp/calamares-root-hef_wg21/boot/loader/entries/KaOS_2018.04.conf'

Installation almost finished, it's failed.

GPT, UEFI.
I have esp partition with esp and boot checked. Linuxmint and Solus, the two sys are ok.
I create a new partition mounted point with '/boot' and another mounted point with '/'.
rosa-image-writer or rufus(dd mod), all failed.
ISO sha256, it's ok.
What's the problem?

The above error indicates an issue with installation media. For one, Rufus in regular mode is known to fail 100 % (dd method in Rufus seems to be OK).
But installation.log will be needed to rule out other issues:
http://kaosx.us/docs

    demm
    Where to find the installation.log?
    And thank you.

    I looked up installation.log at the right partition failed installation in my Solus, there's pacman.log and tallylog, no installation.log.
    It seems I need to install and fail again to get the installation.log.

    If Linux Mint and Solus are still functioning, boot into the OS with the 'controlling grub' and do an update-grub. If KaOS is otherwise installed properly (except for loader entries), that should include KaOS in the grub.cfg and boot KaOS.

    Then boot up KaOS and do a 'sudo bootctl install'. Check first with 'findmnt /boot' to make sure the new $esp you created for KaOS is correct. You may have to create an entry for KaOS in /boot/loader/entries/KaOS.conf if an entry for KaOS is not created.

    It succeeded with only one change.
    I set the esp partition with mount point /boot.
    Well, it's different from my knowledge.
    Other linux distributions don't do the same way.
    Anyway, plasma is beautiful, I begin to love it than gnome.
    Thanks!

    As linked for you in my previous post, it is explained there where to get the installation log.

    That KaOS uses systemd-boot and /boot for ESP is explained to you during the installation. It actually is shown to you in bold text.......

      demm
      I got you.Uhahahahahh

      In the meantime, it explain why my boot menu have only two os(KaOs and Solus) after successful installation.
      Solus uses systemd-boot too. Now, I have to boot Linuxmint by F12 boot menu.
      Is there any way to fix this? I mean let Linuxmint be on KaOS boot menu. I installed rEFInd in Linuxmint, it didn't work.

        By the way, I heard a joke.
        It's about KaOS, they said KaOS, choas.It's a bad thing. They don't want any trouble, couldn't use KaOS.

        rv415s05 In the meantime, it explain why my boot menu have only two os(KaOs and Solus) after successful installation.
        Solus uses systemd-boot too. Now, I have to boot Linuxmint by F12 boot menu.
        Is there any way to fix this? I mean let Linuxmint be on KaOS boot menu. I installed rEFInd in Linuxmint, it didn't work.

        Systemd-boot can only pick up OS's in the same $esp. So if Linux-mint $esp is not the same as KaOS and Solus, it won't be picked up. The same applies for rEFInd. But it (refind) can detect efi files in other $esp's and boot them up. But that means it will boot through their own efi files and that usually means through their grubs. Grub 2 can detect other OS's not in their own $esp and boot them.

        There can be ways to boot other OS's not in the same $esp in systemd-boot. That involves copying over their vmlinuz and initrd files to systemd-boot. You have to copy as sym-links won't work on fat32 format partitions.
        Another way is to copy over the core.efi files and the boot will 'chainload' to that efi file effectively going through their grub (usually).

        I would advise against using Ubuntu (and derivatives) in systemd-boot as their kernel generation makes a sym-link (vmlinuz) to root directory. As said, sym-links won't work. Also if using same name vmlinuz and intrd files, like arch and kaos, (both using vmlinuz-linux and initramfs-linux.img) or like Ubuntu and Linux Mint, have them in the same $esp (/boot), systemd-boot would be perilous (same as in rEFInd). But grub 2 will present no such problem for any multitude of OS's.