Why separated /usr partition?

[pingtoo]

Hi,

Still working on design initramfs, come to a point where many existing initramfs script have option to mount /usr. And I notice some of long time gentoo user also choose to have separated /usr, I wonder why?

In old day when I/O slow and system crash you want to be able to get back to console as soon as possible, you separate / (root) into its own partition so the fsck can finish early and get console prompt, but now I/O are fast, many system structure are not designed to support a separated /usr in mind but some of you still choose so, why? Is it and old habits? or there are some benefit doing so?

And why not separate others, for example /var or /tmp?

Thank you very much for taking time to share.

[eccerr0r]

It was a historical thing IMHO. Mainly because disk sizes were limited coupled with random people using the machine would not care or explicitly trying to crash the system by filling the disk up. Could also be an inadvertent disk fill. Also filling logfiles with junk can be a way to exploit DoS'ing a machine.

Also some ancient un*x had user homes in /usr instead of /home ... and user accounts shared disk space with /usr/bin. /usr/adm (which was a historical place for logfiles before they got stuck in /var/log) which had an additional DoS vector by unscrupulous users.

Fast forward to today and disk sizes have gotten huge. Partitioning is not the only way, logical volume management and resizeable partitions are common. Disk quotas are something. Keeping /home separate meant easier management of keeping user data and system data separate.

Same problems still exist today but different ways of solving them are available. Technically with disk sizes so big today your initramfs should be your recovery image and system binaries including distribution sourced software may well share the same rootfs partition. Keeping a separate /home partition may still be prudent.

Old habits die hard.
_________________
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[alamahant]

I suppose the only benefit would be to mount it RO for protection.
But special care should be taken to have it mounted before the kernel invokes "init",ie you DO need an initrd for that.
Otherwise you may have trouble.
It feels an obsolete paradigm in contrast to /home /var /boot which fully or partially can reside in separate partitions.
Ie
/var/lib/docker
/var/lib/mysql
/var/lib/lxd
/var/lib/flatpak

/home also is common.
If you wish to maintain it accross installations or maybe even in centralized network auth situations where it might even be mounted @user-login via pam,autofs,nfs etc etc.
This is my very incomplete understanding on this issue.
Personally I only have /boot and parts of /home and parts of /var on separate partitions.
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[NeddySeagoon]

pingtoo,

Once upon a time, sharing the same /usr, read only, to lots of systems, over NFS was popular.
That was about the same time that "thin clients" were in fashion too.

Its a mild security thing too, since you can have different mount options for separate filesystems.
My /usr is still separate because I've always done it that way.

[pjp]

[eccerr0r]

A lot of the times if you screw up one partition, it tends to mean a reinstall regardless as accounting is separated where they should be treated as a unit. All those packages you installed on Gentoo in /usr/bin or even /bin are kept in /var/db. Why (in this case) should they be kept on different partitions, if they ever differ due to a mismatched backup restore, your package accounting is no longer valid.

Another thing that boggles the mind is why mysql data is by default kept in /var along with apache root webpage data... These are not system data, it's user data. Things like print spooler data make sense... Then there's the old mbox standard...this too should not technically be in /var ...

Granted there are other user-created and (most) logfiles that can/should be stored on a different partition as long as the accounting data does not reference a different disk.

In the end flexibility is there, you choose what you want to do to make your life simpler, but what's simpler may actually be more convoluted.
_________________
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What am I supposed watching?

[Naib]

[eccerr0r]

Yes cached and pseudo-temporary (state) data belongs in /var. But every time you change /var/db/pkg it means you also changed something in /usr or somewhere else too, so they are all equally "variable". So they belong on the same partition if not different use characteristics.

And still does not explain mysql and apache data as it has nothing to do with the base system data.
_________________
Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?

[pingtoo]

[pingtoo]

Many thanks to everyone sharing your thoughts/ideas.

A follow up question from initramfs design point of view, Do you think mounting /usr | /var | /tmp | ... in initramfs is good thing? assume those are separated partition/volumes. obviously if we do mount them in initramfs we will also need to move them to NEWROOT.

[NeddySeagoon]

pingtoo,

If you will use udev or one of its clones, /usr needs to be mounted before it starts.
There is a patch to Openrc to start udev after localmount but I don't knew if it still works.

As I gave up udev and friends an most of the autoblackmagic some years ago now, letting localmount mount /usr just works.

[pjp]

[pjp]

[szatox]

[Zucca]

[dmpogo]

[dmpogo]

One other things with partitions, was that they assured that a particular set of data is kept physically in a particular area of a disk (which were rotating disks, of course).

That allowed to

1) Hope that if the disk is physically damaged, the damage will be limited only to one partition, and the rest of data can be recovered
2) Set of files within a partition are physically close, and the search between them is faster. /var on a separated partition was a good candidate for such configuration, since it may require fast random access between mailboxes, for instance
3) There were consideration where to put the most demanding partition for faster access. For instance sequential read from outer layers of a disk maybe faster than from the inner ones. I remember people (justifiably or not) putting swap at the outer sectors.
4) You can run different file systems on diffrent partitions, tuned to the use ( /var many tiny files for read and write, /usr basically read only, /home, well, your /home was probably not on your computer anyway (*)

I did not benchmark any of these, but this were the discussions.

(*) And, of course, Unix was geared for networked environment. X was network transparent, disks were shared via NSF. And once you start sharing, you do want partitions, since you do not want to share everything on your disk.
I remember as a postdoc at University, I had no idea where all those disks I am using are actually attached to, and what computer runs mailboxes I am reading from

[dmpogo]

[spica]

[eccerr0r]

[Naib]

people who backup their data would be performing an sql dump as backing up the raw relational db is going to cause consistency issues if you do not backup/restore concisely .

Likewise those that are serious about backups already consider /var as an extremely critical area ( like /home and /etc)
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[technotorpedo]

[figueroa]

I was an early adopter of Linux, first downloading and installing Slackware 1.0 (over a Hayes 1200 modem) with what I think were 24 720k diskettes. (Downloading and writing to those diskettes was a miracle.) Then for quite a few years I'd buy Slackware boxed sets at MicroCenter or pick up diskettes/CDs at computer/ham radio shows. Around 2000 I used Red Hat (with a GUI) from a CD bound into a book, then Mandrake, and finally Gentoo in 2004.

I was just a user. I didn't start out as a Unix system administrator, but I had been a Unix user (ordinary user) from 1985.

Throughout these experiences, primarily single-user systems, I never felt encouraged to install any system directories to separate partitions, believing that any system directories on other partitions added significant complexity for system backup and restore, which early on had to be done with disgusting regularity, often from tape. I never bought into the arguments for any separate system partitions. I still feel that way. I keep current system backups (stage4 equivalents, one zstd compressed tar archive per system directory, in total occupying about 4 GB), and I know how to use them, though I seem to seldom need them these days thanks to increased hardware reliability and operating system stability.

I do keep separate /home and another data partition, plus multiple backup partitions across different drives, but the entire OS is in /. I'm happy with this arrangement.
_________________
Andy Figueroa
hp pavilion hpe h8-1260t/2AB5; spinning rust x3
i7-2600 @ 3.40GHz; 16 gb; Radeon HD 7570
amd64/23.0/split-usr/desktop (stable), OpenRC, -systemd -pulseaudio -uefi

[greyspoke]

My first install (10+ years ago) had a separate /usr because that was recommended. That worked without an intramfs until it didn't. I didn't get on with an initramfs, so now I have just a separate /home, /tmp in ram, /var/db separate for reasons that now escape me probably to do with when I had a smaller disk, /var/tmp/portage in ram and a part of /home on a separate (spinning plate type) disk for photos and video etc. cos I am a cheapskate should have got a bigger ssd (see /var/db supra). Oh and a separate /boot which is FAT32 so it works for UEFI boot (I don't have a bootloader either).

This is for a personal use desktop system.

[dmpogo]