2022-11

SSH connection with authentication using public key cryptographyCreate public and private key pairsCreate a public/private key pair for a user connecting to a Linux server using OpenSSH.Use ssh-keygen to create the key pair.The creation of a public/private key pair must be done as a user with remote login privileges.If you do not specify the destination and file name, id_ed25519 and id_eed25519.pub will be created in /home/(user name)/.ssh/. On the way, enter the password for the key.

1.SSH remote connectionSSH is a service for connecting remotely to a server and is basically running immediately after the OS is installed, but the default settings are somewhat insecure.Here we will configure the default settings to increase the security of ssh connections.1.1 SSH service configuration file changes2.How to set up a firewall (firewalld)In AlmaLinux, the firewall is set to firewalld by default and is enabled during OS installation.4.NTP ServerBuild an NTP server to synchronize the server time with Japan Standard Time

1.Disabling SELinuxFirst, disable selinux. selinux is a feature that improves auditing and security in Linux, but when enabled, it places considerable restrictions on the behavior of services and on what can be configured. Therefore, it is basically disabled in many cases.①Disable SELinux while it is activated but no policy is loaded2.Modernize the systemPackage updates are performed as soon as possible immediately after OS installation.However, when a dnf update is performed, a kernel update is also performed at the same time.Performing a kernel update may require rebooting the system or stopping services, or worse, a kernel panic may occur and the system may not boot. It is wiser to exclude the kernel from the update.By running dnf -y update with "--exclude=kernel*" behind itkernel can be excluded from the update target.

AlmaLinux 9.0 InstallAlmaLinux OS is a project launched by CloudLinux in the US as an alternative to CentOS. Currently, the AlmaLinux OS Foundation is the development parent organization.Following the general availability of Red Hat Enterprise Linux 9.0, AlmaLinux 9.0 was released on May 26, 2022.Like Red Hat Enterprise Linux 9, AlmaLinux 9 utilizes the same package versions as the Linux 5.14 kernel, GCC 11, Python 3.9, and RHEL9.Cockpit web management interface, enhanced kernel live patching, improved container and cloud integration, OpenSSL 3, and other security improvements.