Partitioning scheme

General support questions
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Jeffgi
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Joined: 2023/02/04 02:48:58

Partitioning scheme

Post by Jeffgi » 2023/02/05 02:00:34

Hello.
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.

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TrevorH
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Re: Partitioning scheme

Post by TrevorH » 2023/02/05 02:09:38

I would not install CentOS 7 at this point in its life. It will be going EOL in less than 18 months so you'll need to start over again when that happens. You'd be far better installing either el8 or el9 as they have a longer lifespan left. As there are no newer versions of CentOS than 7, you will need to use Rocky/Alma/OEL or even RHEL itself. You can get a free developer RHEL subscription that lasts for a year until you have to repeat the process to get an extension. That lets you run up to 16 instances of RHEL.

If your machine in in UEFI mode at install time then the installer will offer to create all the relevant partitions for you. I'd also urge you to reconsider the LVM choice as it is far more flexible and much easier to use and to change. If I recall correctly it will create /boot/efi as 200MB, then /boot as 1GB.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

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jlehtone
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Location: Finland

Re: Partitioning scheme

Post by jlehtone » 2023/02/05 10:43:05

Jeffgi wrote:
2023/02/05 02:00:34
4. Will CentOS still install Grub, despite the fact that UEFI can boot an OS directly?
Yes.

The GRUB executable is installed into the ESP. The UEFI loads and runs that executable. The OS does not need to access the ESP, except to update files; the GRUB packages do get occasional updates. Hence mounting ESP is not required for running the system, but is necessary for maintenance.

The GRUB loads kernel and initramfs image from /boot. In el7 and el8 the grub.cfg is entirely in ESP, but in el9 there is only a stub that includes /boot/grub2/grub.cfg. The GRUB of el8 and el9 does use BLS (Boot Loader Specification) that places the grub entries in /boot/loader/entries/.

The GRUB the executable must be able to access the filesystem(s) that it loads files from. That is one reason for separate /boot that is not on LVM, on encrypted volume, etc.


The RHEL 8 doc recommends 10 GiB for /. https://access.redhat.com/documentation ... -reference

However, that does depend on how much applications (packages) you do install. Furthermore, /tmp and /var are on / filesystem by default. Databases, virtual guest images, /var/www, mock environments, etc, and logs are under /var (if you do use any).

I did install CentOS 7 systems around 2016 with 16 GiB /. That was eventually not enough with lots of desktop applications (including texlive, some Software Collections, and CUDA). A still quite fresh and basic el9 GNOME workstation seems to have about 8 GiB in /. I have those (Alma) el9 with 24 GiB /.


The el9 does require x86_64-v2 CPU micro-architecture. If your CPU is very old, then it might not support el9.


The default filesystem on e7-el9 is XFS. It is not possible to shrink XFS on the fly.


The UEFI works with GPT. Unlike MBR, the GPT is not limited to four partitions (although MBR could have multiple logical drives in one of the four partitions). Nevertheless, the LVM does add flexibility. GPT+LVM is great.

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