This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
How to Harden SSH on openSUSE / SLES is one lab change on a openSUSE / SLES host you administer. Hardening SSH is a second session first, then one setting. Root login and empty passwords are the settings you are leaving.
openSUSE or SLES. zypper is the package tool. dnf and apt are the wrong commands. The network path on this host is: the network tool this host already uses. Read whether it is NetworkManager or wicked before you paste nmcli. It is not netplan. The firewall, if this change touches it, is firewalld.
AppArmor is the usual confinement tool. Do not disable it to make a package start. Do not assume SELinux is enforcing unless getenforce on this host says so. Do not restart sshd from the only session. Do not cut off the prefix you are using. The auditor reads a paste. It does not connect. A new session still logs in with the key, and the setting you changed matches the ticket.
The generator drafts a script. It does not log in. 192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.
The change you can finish
Apply nothing while you are writing the note. When the lab window opens, it is one change on the host named in the ticket. Read the draft, then the host, then decide.
Rollback is the file, the package version, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.
- Write the hostname and confirm you administer it.
- Save the current file, package list, or snapshot before any draft is applied.
- Generate the draft and delete every line this ticket did not name.
- Remove documentation addresses, example.com, and any secret.
- Apply one change only when the lab window is open and a console or a second session exists.
- Read the result back and compare it with the ticket.
- Stop. The next change is a different page.
Mistakes that outlive the command
Harden SSH on openSUSE / SLES goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- Pasting a draft you did not read.
- The wrong hostname.
- A secret in the ticket or in git.
- Two changes in one window.
- No copy saved before the change.
- A documentation address left on a host that is leaving the lab.
- Disabling a firewall, AppArmor, or SELinux to make a check pass.
- Calling the generator output a finished production change.
- Do not restart sshd from the only session. Do not cut off the prefix you are using. The auditor reads a paste. It does not connect.
Decisions to write down
One decision for Harden SSH on openSUSE / SLES: The hostname matches. The change is only Harden SSH. The platform habit was followed: openSUSE / SLES. A console or a second session exists. No secret is in the note. And the proof is: A new session still logs in with the key, and the setting you changed matches the ticket.
Checks before you call it done
Confirm this before you call the change done: The hostname matches. A rollback copy exists. The draft was edited. Documentation values were removed before any apply. Management still works. And a second person can say what changed. If one of those fails, stop.
# openSUSE / SLES. Harden SSH.
# zypper. the network tool this host already uses. Read whether it is NetworkManager or wicked before you paste nmcli. It is not netplan.
# prompt-for-this is not a password.
# 192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.Before you leave the host
How to Harden SSH on openSUSE / SLES ends when the hostname in the prompt matches the hostname in the ticket. If it does not, you are on the wrong host. Stop. A command that succeeded on the wrong host is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the host and does not know which disk is empty. You delete a line that names a host, a path, or an account you did not write down.
192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save in the ticket or in git. The real secret stays in the password store.
One change is the window. If two things move and the result is wrong, you will not know which one did it. The next change waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied change produces a host nobody can rebuild. Restore the copy you took first.
A second person reads the hostname and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the host alone.
Tools for this guide
These tools run in the browser on this site. They do not log into your machines.
Related pillar guides
More in this cluster
The pillar for this page, and the next published pages filed with it.
- Pillar: openSUSE / SLES Server Administration Guide
- How-To: How to Set Up firewalld on openSUSE / SLES
- How-To: How to Add a Package Repository on openSUSE / SLES
- How-To: How to Enable Automatic Security Updates on openSUSE / SLES
Companion: Security: Linux Server Hardening Checklist.