I have a dilemma. In my learning curve or learning how to use and install Arch Linux, I have always installed everything under /mnt (/mnt/home /mnt/var, etc).
Recently, I wanted to use a /boot partition and someone said it's better for toubleshooting if you just install everything under it's own directory (/boot /home /var)

I wrote verything down for my installation instructions for Arch and they don't work with the new partitions:
pacstrap /boot grub
pacstrap /mnt base base-devel
genfstab -p /mnt >> /mnt/etc/fstab
arch-chroot /mnt
mkinitcpio -p linux

I do not know how to execute grub-mkconfig -o /dev/sdb (sdb because I'm installing on a USB)

It makes sense to me that the base and all other packages should be in /mnt but grub cannot find any /etc directories and thus can't complete mkconfig.
What should I chroot into and what else am I missing?

Hope this makes sense. Thanks for taking the time to consider my question :-)

I don't agree with that statement but anyway...

You need to mount your main partition:
Create the /boot directory (the filesystem package is not installed yet so you need to do this manually):
Create any other mountpoint directories you wish to use at this point.

Then mount your /boot partition:
https://wiki.archlinux.org/index.php...the_partitions

Replace "X" with the drive letter assigned to your main system drive (probably "b" if it is a USB stick), replace "Y" with the partition number you wish to use for your root partition ("/") and replace "Z" with the partition number you wish to use for /boot -- use `lsblk` to list all attached drives and their sizes.

Mount any other partitions you wish to use at this point.

Then select a mirror by un-commenting the nearest entries from /etc/pacman.d/mirrorlist
https://wiki.archlinux.org/index.php...elect_a_mirror

Then run the `pacstrap` script to install the base system (and any other packages you need):
https://wiki.archlinux.org/index.php...he_base_system

Then generate the fstab and configure the system (timezones, keyboard configuration, boot loader/manager. etc).

For configuring GRUB you should use:
https://wiki.archlinux.org/index.php...S_motherboards
EDIT: This command should be run after using the `arch-chroot` command.
https://wiki.archlinux.org/index.php...he_base_system

Finally, please refer to the Beginner's Guide (see my signature) when installing Arch as it covers all these steps very clearly.

As noted above, to install Arch you have to read the (excellent) Arch doco.
Your command is a composite of grub-install and grub-mkconfig. It can never work. Just follow the Guide - it's not just for beginners, we all refer back to it on occasion.

someone didn't read the wiki

I did but I guess the whole /boot /home thing threw me off.
I asked on another forum about partitioning sizes for a USB Linux and some guy said he didn't understand why I was doing /mnt/home.. The reason being for if your /mnt partition goes bad the /home doesn't need to be affected. I thought I'd try it but grub wouldn't work.

I sorted it, now. using /mnt/boot and it works fine. Many thanks for pointing it out and for the useful tips :-)