Today, after doing updates in Debian Stretch, I have noticed it started displaying this warnings when restarting the ssh service with my current config:/etc/ssh/sshd_config line 17: Deprecated option KeyRegenerationInterval/etc/ssh/sshd_config line 18: Deprecated option ServerKeyBits/etc/ssh/sshd_config line 29: Deprecated option RSAAuthentication/etc/ssh/sshd_config line 36: Deprecated option RhostsRSAAuthentication[....] Restarting OpenBSD Secure Shell server: sshd/etc/ssh/sshd_config line 17: Deprecated option KeyRegenerationInterval/etc/ssh/sshd_config line 18: Deprecated option ServerKeyBits/etc/ssh/sshd_config line 29: Deprecated option RSAAuthentication/etc/ssh/sshd_config line 36: Deprecated option RhostsRSAAuthenticationWhat is happening here?
Deprecated options when restarting openssh in Stretch
debian;openssh
In the current Stretch update, openssh version changed from 7.3 to 7.4, released on 2016-Dec-19.As it can be inferred from the Release notes, and from @Jakuje comments, OpenSSH maintainers have removed the corresponding configuration options for good, as they are obsolete.So the lines can be safely removed.Also, take head of:Future deprecation noticeWe plan on retiring more legacy cryptography in future releases,  specifically:In approximately August 2017, removing remaining support for the  SSH v.1 protocol (client-only and currently compile-time disabled).In the same release, removing support for Blowfish and RC4 ciphers   and the RIPE-MD160 HMAC. (These are currently run-time disabled).Refusing all RSA keys smaller than 1024 bits (the current minimum  is 768 bits)The next release of OpenSSH will remove support for running sshd(8)  with privilege separation disabled.The next release of portable OpenSSH will remove support for  OpenSSL version prior to 1.0.1.