SSH Login Failed After Adding "AllowUsers" and "AllowGroups" Directives into /etc/ssh/sshd_config

Applies To:

Oracle Cloud Infrastructure - Version N/A and later

Linux OS - Version Oracle Linux 6.0 and later

Linux x86-64

Symptoms:

SSH client like PuTTY can return a failure like this:

disconnected: no supported authentication methods available (server sent: publickey, gssapi-with-mic)

Changes:

Added "AllowUsers" and "AllowGroups" directives into /etc/ssh/sshd_config.

Cause:

When adding "AllowUsers" and "AllowGroups", the target user must fulfill both directives, by its user name matching one of the patterns in the AllowUsers list AND by belonging to a group matching one of the patterns in the AllowGroups list.

SSHD_CONFIG(5) states:

The allow/deny directives are processed in the following order: DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups.  All of the specified user and group tests must succeed, before user is allowed to log in.