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00:56 Sponsor: Proton Mail
02:32 Software and updates
04:04 Services and SSH
06:38 User management
10:10 Physical Security
11:35 SELinux, AppArmor, and firewall
14:04 Parting Thoughts
15:15 Sponsor: Get a PC made to run Linux
16:30 Support the channel
Password complexity tips: https://www.networkworld.com/article/2726217/how-to-enforce-password-complexity-on-linux.html
Tips to secure SSH: https://www.cyberciti.biz/tips/linux-unix-bsd-openssh-server-best-practices.html
The more software you use, the larger the attack surface for your Linux install is. It’s always good to take a look at all the installed applications, and libraries, and remove what you don’t use anymore. You can also remove packages that aren’t linked to anything else and aren’t used by anything.
On Debian or Ubuntu, for example, you can find these by running sudo apt autoremove
And on a desktop, you probably already apply updates, or your distro has auto updates enabled. But on a server, it’s easy to let things slide, and forget to log in regularly and make sure things are up to date. I’m guilty of that myself.
And just like with packages, libraries, and apps, you should also make sure you only run the services you actually use. You can list all services running with:
To stop a service you don’t need, you can run
systemctl stop SERVICE
To stop the service from starting with the system, you can run
systemctl disable SERVICE
If you’re on a server, the general rule of thumb is also NOT to run a graphical desktop on it. It will often be much more secure to use SSH to log in to the server remotely.
But you might also need to secure SSH first. If you have multiple users, make sure only the ones who need it have SSH access. To do that, you can edit the /etc/ssh/sshd_config file, and type AllowUsers then the names of the users that will actually have access to SSH.
Now, something that might be useful in general, for a server or a desktop, is making sure all the users are correctly handled. The first thing will be to disable root login.
If you decide to disable the root account, make sure at least one user has admin privileges though, or you’ll have a system without any way to access any task with sudo. Once you’re certain everything is ok, you can use the following method:
Edit /etc/passwd, and change the first line, by replacing /bin/bash, or whatever other shell root currently logs into, by /sbin/nologin (or /usr/sbin/nologin depending on the distro)
If you prefer, you can simply disable root login through SSH, so the account is still there if you want it locally, but remote attackers won’t be able to login as root. To do so, you can edit /etc/ssh/sshd_config, and uncomment the PermitRootLogin line, and then set its value to no. Restart SSH with sytemctl restart sshd, and you’re done.
To remove the ability to use USB, Thunderbolt or Firewire, you can add the following lines to their respective files (create them if need be). To revert this, just remove the lines that have been added in the various files by the commands.
Add: install usb-storage /bin/true to /etc/modprobe.d/disable-usb-storage.conf
Add blacklist firewire-core to /etc/modprobe.d/firewire.conf
Add blacklist thunderbolt to /etc/modprobe.d/thunderbolt.conf