RHEL family tutorials

Check whether an x86 CPU supports 2 MB or 1 GB HugePages, find the current HugeTLB default size, and change default_hugepagesz persistently with grubby on RHEL.

Increase or shrink tmpfs on Linux with size=, /etc/fstab, and mount -o remount. Covers /dev/shm, /run, and systemd /run/user limits on RHEL-family systems.

Install dnsmasq on RHEL 10, cache DNS on loopback, point upstream resolvers at a dedicated file, persist 127.0.0.1 through NetworkManager, and verify cache behavior with dig and tcpdump.

Authorize Samba shares for Active Directory users and groups on a RHEL 10 Winbind member server: valid users, Unix permissions, POSIX ACLs, SELinux, firewall, and Windows access tests.

Authenticate vsftpd FTP logins with Active Directory on RHEL 10 through PAM and SSSD, with deprecation notes, SELinux, passive ports, and tests—prefer SFTP for new deployments.

Let Active Directory users transfer files over SFTP on RHEL 10 after a realmd and SSSD join: sshd, PAM, home directories, optional chroot, and verification from Linux clients.

Join RHEL 10 to Active Directory with Samba Winbind using realm join or net ads join, verify wbinfo and getent, and publish an AD-authenticated Samba share.

Join RHEL 10 or Rocky Linux 10 to Windows Server 2025 Active Directory with realmd, adcli, and SSSD. Discover the domain, run realm join, verify Kerberos, and control AD logins.

Enroll RHEL 10 in Active Directory with adcli join, then configure SSSD, authselect, and NSS yourself—without realm join—for full control of the AD computer account.

Learn how to check whether SSH is using protocol 1 or 2, what OpenSSH version strings such as OpenSSH_7.4p1 mean, and how to read SSH-2.0 banners and verbose SSH output.

Automate password-based SSH and SCP in Linux using sshpass, Expect, and SSH_ASKPASS, with safer password input, host-key handling, and key-based alternatives.

Mount a remote Linux directory over SSH with SSHFS on RHEL, Ubuntu, and Windows. Covers install, user mounts, permissions, fstab, jump hosts, SSHFS-Win UNC paths, and troubleshooting.

Configure OpenSSH host-based authentication on Linux with HostbasedAuthentication, ssh-keysign, shosts.equiv, and verified host keys—plus hostname/DNS checks and safer alternatives.

Test SSH connectivity in Linux step by step: check port 22, verify that sshd responds, test authentication, inspect server-side sshd status, and troubleshoot common SSH errors.

Connect to private Linux servers through an SSH jump or bastion host using ProxyJump, ssh -J, ProxyCommand, and scp -J, with multi-hop routes and troubleshooting examples.

SSH from your host into a Linux VirtualBox VM using NAT port forwarding (recommended), host-only networking, or a bridged adapter — with a mode decision table, guest SSH checks, and troubleshooting for 10.0.2.15 and VPN …

Use OpenSSH host certificates so clients trust one host CA through @cert-authority in known_hosts instead of enrolling every server host key — create a host CA, sign with ssh-keygen -h, configure HostCertificate on sshd, …

Understand sshd ssh-rsa algorithm is disabled on RHEL 9 and 10, when RSA-SHA2 logins still work, and when to upgrade clients or allow a scoped ssh-rsa exception.

Sign files with ssh-keygen -Y sign, verify them with an allowed_signers file, signer identity, namespace, and stdin — no sshd or GPG required on OpenSSH 8.2 and later.

Fix SSH no matching key exchange method found by reading Their offer:, enabling the required KEX algorithm safely, and resolving follow-on host-key or cipher errors.

Fix SSH "Bad server host key: Invalid key length" caused by 1024-bit RSA host keys, RequiredRSASize, RHEL crypto policies, or stale known_hosts entries.

Fix userauth_pubkey: key type ssh-rsa not in PubkeyAcceptedKeyTypes by using rsa-sha2 with the same RSA key, or Ed25519, before any legacy ssh-rsa exception.

Create and update an OpenSSH Key Revocation List (KRL), revoke SSH certificates by serial, Key ID, or fingerprint, revoke plain public keys, and make sshd enforce RevokedKeys.

Set up OpenSSH user certificate authentication with an SSH CA: create TrustedUserCAKeys, sign keys with principals and expiry, verify login, revoke with a KRL, then map principals with AuthorizedPrincipalsFile.

Configure OpenSSH authentication in sshd_config: password, public key, keyboard-interactive, host-based, GSSAPI, AuthenticationMethods, and Match blocks on Linux.

Why Redis packages are gone on RHEL 10, how to install Valkey, and how to migrate a real Redis OSS RDB dump into Valkey with ownership and SELinux fixes.

Step by step instructions to install redis on Rocky Linux 9

Why dhclient and dhcp-client are gone on RHEL 10, what replaces them, how to configure and reacquire DHCP with NetworkManager, and how to fix old dhcp=dhclient settings.

OpenSSH PerSourcePenalties on Linux: how sshd temporarily refuses noisy source addresses, how to read defaults with sshd -T, how to fix Not allowed at this time, and how exemptions and MaxAuthTries differ from Fail2ban.

Understand RPM signing changes on RHEL 10 and 10.1: Sequoia PGP verification, RPMv6 signatures, multiple signatures, OpenPGP v6, and hybrid ML-DSA-87+Ed448 post-quantum signing with tested commands.