Next week I'll be getting a new desktop, my old one having just died. This means moving from a 32-bit computer to a 64-bit and from CentOS 6 to CentOS 7. Ideally, I should also be moving from BIOS to UEFI, but I may chicken out!

I shall be installing on a 120GB SSD, with no other operating system. My questions are

1. How much space do I need for root?

2. The installation guide refers to a /boot partition. Is that just because they assume that you will follow their advice and use LVM, which I shan't be doing?

3. The CentOS documentation refers to the ESP partition as mounted at /boot/efi. Other distros say it doesn't need a mount point. Any explanations?

4. Will CentOS still install Grub, despite the fact that UEFI can boot an OS directly? I do like the idea of still having Grub, in case I need to alter anything.

I would just follow the installer's guidance for EUFI, use LVM if it's default and then worry about whether to use the remaining space as one large partition (easier if your OS grows beyond what you expact) or seperate 30GB root (perhaps 20, certainly no more than 30) and the rest /home for easier install without losing your data from home.
Personally, I'd buy another drive of some kind either for home or backups of data (and make sure I made them) then just use the "all one partition" scheme.

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/boot has nothing to do with LVM. The guide refers to a /boot partition because you will normally get one (I don't know if it's possible to run Centos without a boot partition).
/boot/efi contains grub and grub.cfg, so yes, you need it.
Yes it will.

It all depends on what packages/programs you install. Potential size of databases etc

Legacy grub could not read a LVM and therefore a separate /boot partition was required. grub2 can but CentOS still automatically creates a separate partition. Yes it is possible to run without a separate /boot. If you want a separate /home as suggested a min of 20GB for /(root) would be ok.

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Use UEFI - don't even consider not using it.
I haven't installed CentOS in a while, but it will presumably format the disk as gpt. This is also what you want - msdos (MBR) format is a thing of the past.

Welcome to your future.

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I could be misremembering, but the last time I installed CentOS 7, I think from memory it wanted to use LVM by default. I chose MBR partitioning instead - as I currently have no need for LVM or GPT partitioning.

Slightly different scenarios. msdos (aka MBR) and gpt are partitioning systems of physical hard disk/SSD (whatever). LVM is a block device emulation that (typically) sits on top of that partitioning. Each can exist without the others, but usually MBR/gpt defines the underlying architecture.

Nothing is ever as simple as it first seems ... now I wonder when have I said that before ?

@michaelk Thank you for answering my first question.

@273 Why tell me to use LVM when I've just said I have no intention of doing so? Why tell me I need another drive? I bought a 120GB drive because that's all I need.

@berndbausch You can run CentOS without /boot — I've been doing it for years. If CentOS puts Grub on the EFI partition, that would explain the need for a mount point, but since you don't seem familiar with CentOS, I shall seek confirmation elsewhere.

Owing to your placement of the comma and question mark that communicated uncertainty rather than the emphatic rejection you intended. I can see why 273 might have thought you were soliciting opinion on LVM.

"Is that just because they assume that you will follow their advice and use LVM? Which I shan't be doing." -- here the intent is much clearer.

@DavidMcCann: that is what, in my experience, makes a smoother install.
If you don't want LVM then don't use it, I assume you know why you don't want to use it?
The seperate drive issue is that, simply, things are much easier if you keep your data (products of your computer use you want to keep) seperate from your OS. If you don't want to, or cannot, then you must simply back up any data you want and, then, it matters not what you do because the important things are triplicated, at least.

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if you use LVM is will be much better in future , like you can easily extend disk size if your partitioning run out of spaces.

and for root you can give 2G of space would be enough.

First, this thread had been closed for months before you reopened it. And telling someone that having 2GB for a root "/" file system is a HORRIBLE idea, since most distros take up more space than that, not to mention any updates/patches/additions they may need later.

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