Linux

RedHat, CentOS, Debian, Ubuntu.

All are good choices.

Ubuntu, RedHat, AWS Linux, Arch. Honestly distros in production are pretty similar since they're all headless and pretty pared-down. If you just know the logistics of a few package managers and init systems you'll be good.

Depends on context.

If you want to get a job as a "Linux admin" then Red Hat is basically what you want as a "default". Fedora will give you something you can use at home that's broadly similar. You will need to learn more than just that though.

To tag onto this, what makes RHEL so special? Is it just the support you get from Red Hat or is there something about the distro that makes it so widely used?

I'd suggest RedHat and SUSE as well.

Debian.

I once worked in for a small publishing company years ago, circa 2005, where they used CentOS on the desktop and server environments. Deploying a new desktop was as simple as using kickstart. They had their infrastructure down to a science.

Mostly mission critical server that I deployed in the past, all use RHEL/Clones because their LTS, and stability across packages version.

If for hobbyist, it's Ubuntu. I think you need to learn more about ansible, container/podman/openshift, and SDN for work. Nowdays, there are some use APT in production, but mostly they switch to dnf because dnf have better way to do downgrade, undo, redo, and config package in production.

This applied mostly for ERP project such as SAP Hanna, SQL Server, DB2, etc... Like it not, Red Hat Dwindling isn't now, probably 5-10 years ahead, but I'm not sure, as mostly rant about RHEL are in Community. I do know regional linux user group in Indonesia, some are leaving EL group, but they still can't rip apart most mission critical server on top of RHEL/Clones... so it's still worth learning RHEL/Clones, and use Fedora for day 2 day task, and learn ubuntu, as well ubuntu pro, for learn deploying critical production server.

Debian and Ubuntu are near, and ubuntu is derived from debian, but if you talk spirit, they are different... If you are conscious about what Red Hat do, stay away from it, but if you are working in corporate, you can't go without learning it.

Where I'm at, that would be Ubuntu, followed by Debian.

I work for a well known internet company, and its 98% redhat (or derivative) with some alpine and ubuntu scattered about randomly

It really depends. I work for a large company and we use Ubuntu, Oracle, RedHat, and SLES. We were moving from Oracle to Ubuntu but now we are going back to RedHat.

Currently we deploy like this: Ubuntu: PostgreSQL, web servers, some engineering workstations, and big data Oracle & RedHat: web servers, security applications, and network systems

So just having a fundamental understanding of Linux and you will be fine SUSE: SAP and HR software

All of my personal servers are Debian. My last company switched their entire production fleet from centos to Debian. I think a lot of people switched to Debian back when the Centos Stream debacle went down.

If you want to learn more than one distro, try setting up Docker containers for various services. The base distros in the containers use the same commands as on the base metal

I've been seeing a lot of alpine based containers recently. Used to see a lot of Ubuntu, debian, redhat.

I think a lot of it depends on if you are spinning a lot of containers up.

Nobody said Alpine? Youre debugging k8s containers your gonna find Alpine, Ubuntu/Debian and CentOS.

Once you know package managers and basic images you're gonna be able to get what you need.

The two distros I've seen in the workplace most often were Redhat (because support contracts can be purchased) and Ubuntu (because AWS and Digital Ocean treat Ubuntu VMs as first-class citizens).

100% sure its Debian.

Not Linux but there are still a of Unix System V systems out there too. AIX, Solaris and HP-UX. Harder to learn as very much not open source software (although there is the Illumos project with distros like OpenIndiana).

Almost always use Ubuntu in production. Also a bit of Centos at one point.

Ive worked a couple fortune 500s that used ubuntu. If im using aws ill stick with their distro but most of time im happy with ubuntu. I think distro choice matters less and less. Most of the systems ive run recently have had ansible to configure them or have just run docker containers. Most of the gov contracts iveworked on insisted on red hat but honestly the teams making those decsions seemed the least technically capeable ive worked with and it was just a red tape issue to change distros

I work at NASA and we use redhat a lot for development work.

The default Linux image on AWS (Amazon Linux) is RPM-based; but the default image on Google Cloud currently appears to be Debian "bullseye" (the April 2023 release) with an option for "bookworm" (brand new this month). I'm not sure about Microsoft Azure but their docs suggest a Debian default as well.

So that's one impression. Knowing both dpkg/apt and rpm will serve you well.

Major tech companies have their own internal distributions in their production datacenters, which focus much more on their specific needs. Any major tech company using Linux in datacenters will have an engineering team specifically building what they need.

My experience in my career has been all RHEL/CentOS. The meat of Linux admin isn't going to hugely change between most distros tho. Different package mgmt, how the network is configured, etc... Spin up an VM, install it from scratch, and just learn those differences.

A company I worked at 2016-2022 used mainly CentOS and Ubuntu for all their servers at customers' sites

I'm seeing a lot of very interesting answers but I'm wondering what you mean by "production environment".

Do you mean VFX Production? (English not my first language so if "production" is used in different industries, well, I didn't know).

I'm new to the industry and worked for small companies that don't use Linux. But my VFX peeps use Rocky, Mint, and Ubuntu ( stronger preference for Rocky in studios).