Everything that hardens an ordinary Linux server hardens this one: key-based SSH, no root logins, a firewall that denies by default, automatic security updates, rate limiting on repeated failures. Securing a VPS goes over those, and they are the foundation.
What a dedicated server adds is hardware, and one piece of it is a computer in its own right.
The management controller
Every server-class machine has one: IPMI, BMC, iDRAC, iLO, depending on the manufacturer. It is a small independent system inside the server with its own processor, its own firmware, its own network address and its own credentials.
It can power the machine on and off, present a virtual console, and mount installation media: regardless of what the operating system is doing, including when the operating system is not running at all.
Hardening the operating system does nothing to protect it. Your firewall rules live inside a machine this thing controls.
That makes it, in practice, the most valuable target on a dedicated server and the one most administrators have never logged into.
Three things it needs
It must not be reachable from the internet. Management interfaces are scanned continuously and have a long history of serious vulnerabilities. It belongs on a management network, reached over a private connection, and nowhere else.
The default credentials must be changed. Controllers ship with known defaults, published in manuals. A controller still using them is not protected by anything.
Its firmware must be updated separately. Operating system updates do not touch it. A controller running years-old firmware is an unpatched machine on your network that nobody is watching.
Using IPMI and out-of-band management covers the interface itself, which is genuinely useful. It is how you recover a machine that will not boot.
Firmware generally
Beyond the controller, the machine has firmware in its BIOS, its storage controller and its network cards.
None of it updates automatically, none of it is covered by the package manager, and storage controller firmware in particular has fixed data-corruption faults across its history.
The realistic approach is to check at each planned maintenance window rather than to chase releases. Planning maintenance windows explains having one.
Physical access is real here
On a virtual machine, the physical layer is somebody else's concern. On a dedicated server it is a genuine part of the threat model, even in a good facility.
Encrypting data at rest is the measure that survives a drive leaving the building. It costs a little performance and it means a stolen or improperly disposed-of disk is not a disclosure.
Which leads to the item people forget entirely: drive disposal. When a disk fails and is replaced, the old one still holds your data. Establish with the provider what happens to failed drives, and prefer secure destruction over return. Decommissioning a server safely explains the same question at the end of the machine's life.
Reduce what is listening
ss -tlnp
A dedicated server accumulates services nobody chose; a database listening on all addresses, a monitoring agent, a mail server enabled by default.
Anything that only serves the machine itself should listen on the loopback address rather than every address. That is more effective than a firewall rule, because it does not depend on the firewall being correct.
And check both address families: rules written for IPv4 alone leave IPv6 entirely unfiltered, which is a common and invisible gap. Understanding IPv6 has the detail.
Separate what you can
A single machine running everything means one compromise reaches everything.
Where the workload allows it, separate the database from the web server, or run untrusted workloads in containers. This does not prevent a compromise; it limits what one becomes.
Backups assume all of this failed
Every measure here reduces the chance of a compromise. Backups are what you have when one happens anyway.
They must be somewhere the server cannot reach. A server that can delete its own backups will, if something on it decides to. Backups and disaster recovery for dedicated servers goes into arranging that.
Console access is a credential too
The management interface offers a virtual console, and that console is frequently logged into as root without a second factor, because it is thought of as hardware rather than as a login.
Anyone reaching it can restart the machine into a recovery mode and change the root password, regardless of how well the operating system is secured. It is a complete bypass of every measure inside the machine.
Which is the strongest argument for keeping the interface off any network the public can reach, and for treating its password with the same seriousness as root's. A shared or default credential there undoes everything else on this page.
Encrypt the traffic between your own machines
Servers in the same rack are frequently configured to talk to each other in plain text (a web server to a database, an application to a cache) on the assumption that the internal network is private.
It is private from the internet and not from anything else in that facility, or from any other machine of yours that is compromised.
Where the services support it, enable encryption between them. Where they do not, bind them to the loopback address and reach them through an SSH tunnel rather than across the network. For arranging that cleanly, see SSH config, jump hosts and key agents.
Decide what happens when a disk leaves
Disks leave a server in three ways, and all three are disclosure paths on hardware you own.
A failed disk returned to the manufacturer under warranty. A disk replaced during an upgrade. The whole machine at the end of its life.
Full-disk encryption resolves all three at once, and it must be set up at installation, adding it later means moving all the data off and back. That timing is why it belongs in the build rather than in a hardening pass afterwards. Installing an operating system on a dedicated server explains the decision.
Failing that, agree with the provider in writing that failed drives are destroyed rather than returned, and confirm it when one actually fails. Decommissioning a server safely explains the end of the machine's life.
Check what changed, on a schedule
rpm -Va 2>/dev/null | head -20 # RHEL family debsums -c 2>/dev/null | head -20 # Debian family
These compare installed files against what the packages say they should be. Differences are either your own edits (which you should recognise) or something you did not do.
Run it monthly and read the output. On a server nobody has touched, it should be short and familiar. A file in a system binary directory that does not match its package is not ambiguous.