CloudLinux OS is a Linux distribution built for servers that host many customers' websites side by side. It is AlmaLinux with a modified kernel that puts every hosting account in its own resource container, plus a set of tools around that kernel. This post explains the problem it solves, what each edition gives you, and when you do not need it at all.
The problem on a shared server
On a plain Linux server with a control panel, every account's PHP processes compete for the same CPU, memory and disk. One WordPress site with a broken plugin, a runaway cron job or a bot hammering xmlrpc.php can take all of it. Every other site on the box slows down or stops, and the panel's own limits (disk space, bandwidth, number of domains) do nothing about it, because none of them measure what an account is doing right now.
The usual answer is to find the culprit by hand with top, suspend it, and apologise to everyone else. CloudLinux exists so that this stops happening.
What CloudLinux does about it
CloudLinux is a RHEL-family distribution from CloudLinux Inc. Today it comes as CloudLinux 9 (tracking AlmaLinux 9, kernel 5.14) and CloudLinux 10 (tracking AlmaLinux 10, kernel 6.12), x86-64 only. You do not install it from an ISO; you convert an existing AlmaLinux, Rocky or RHEL server with one script and reboot into the CloudLinux kernel. Everything already on the server, including the control panel and the accounts, stays where it is.
The kernel is the point. It adds LVE (Lightweight Virtual Environment), a container per account with limits on CPU, memory, disk IO, number of processes and concurrent requests. When a site hits its limit, that site slows down or returns an error; the rest of the server does not notice. How each limit behaves is covered in LVE explained.
Around the kernel sit the components people usually mean when they say "CloudLinux":
- CageFS gives each user a virtualised filesystem, so they cannot see other users' files, other users' processes in
/proc, or the real layout of the server. - PHP Selector lets every account pick its own PHP version and extensions, from 5.6 through 8.5, without the administrator rebuilding anything.
- Node.js, Python and Ruby Selectors do the same for application runtimes, with a Passenger-based app wizard in the panel.
- MySQL Governor accounts for database load per user and throttles the accounts that abuse it.
- mod_lsapi is a fast PHP handler for Apache that works with all of the above.
- HardenedPHP backports security fixes to PHP versions that are officially end of life.
- KernelCare live-patches the kernel, so security updates do not need a reboot. It is included in the licence.
The four editions
CloudLinux OS Shared is the classic product: everything above, licensed per server, aimed at shared and reseller hosting. If you run a DirectAdmin or cPanel server with dozens of accounts, this is the one.
CloudLinux OS Shared Pro adds the tooling a busier host wants: X-Ray autotracing that flags slow sites without being asked, AccelerateWP for WordPress caching and image optimisation, centralised monitoring across servers, and reseller limits so a reseller can divide a pool of resources among their own customers. It costs more per server, and some AccelerateWP features are paid extras on top.
CloudLinux OS Solo is for a server with one tenant: an agency box, one busy WordPress site, a company's own server. There are no per-user LVE limits, because there is nobody to isolate from, but you keep X-Ray, AccelerateWP and the PHP and Node.js selectors.
CloudLinux OS Admin sits in between, for a VPS with a handful of accounts: LVE isolation for up to five users, plus the selectors and X-Ray.
Licences are per server and there is a trial, so you can convert a test server and watch the effect before paying.
Which panels it works with
cPanel, Plesk and DirectAdmin all have first-class integration. A CloudLinux Manager appears in the admin area, users get Select PHP Version and Resource Usage pages, and limits attach to hosting packages. It also runs without a panel. The DirectAdmin procedure is in installing CloudLinux on a DirectAdmin server.
The cost logic
Per server, CloudLinux costs less than a couple of hours of an engineer's time each month. Most of the value shows up as things that stop happening: the 3 a.m. "server is slow" ticket, the weekly hunt for the account that ate the CPU, the customer lost because their site was down through someone else's fault. A close second is the sales side: once you can promise a customer a defined amount of CPU and memory, you can sell tiers that mean something.
When plain AlmaLinux is enough
If a server hosts only your own sites, or a few sites you fully control, you already know who the noisy neighbour is: you. Plain AlmaLinux 9 with a panel, sensible PHP-FPM pool limits and a firewall is fine, and you keep the licence fee.
The same goes for a single-application server. One Laravel app or one shop should use all the resources it can; there is nothing to isolate it from.
The tipping point is the first account you do not control. The moment a server hosts a paying customer, a client's site, or a reseller's customers, isolation stops being a nice-to-have, because the cost of one bad plugin is now every other customer's uptime. On a VPSPioneer managed VPS we can convert the server to CloudLinux for you when that moment comes.