sshd
SSHPackage: openssh-server
The SSH server itself. sshd -t validates the configuration before a restart and sshd -T prints what actually applies, first obtained value per keyword — which the file does not show.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
sshd -t- Checks the configuration and keys without restarting the service. Run it before reloading sshd, or risk losing access.
sshd -T- Extended test mode: checks the configuration, then prints the one actually in force — one keyword per line, lower-cased, defaults included. Needs root, because it checks the host keys too. It is the only reliable way to see what sshd keeps once the includes have been read.
sshd -f- The configuration file to read, instead of
/etc/ssh/sshd_config. With-t, it is what lets you check a candidate file before it becomes the live configuration. sshd -C- Describes a hypothetical connection (
user=,host=,addr=,laddr=,lport=,rdomain=) so that-Tapplies theMatchblocks that would fire for it. Without it, only the global section is printed.
Lessons that teach it
- Editing a file without breaking itLinux Fundamentals
- Moving SSH to key authenticationUsers, sudo and SSH access
- A key is a line, and the line takes optionsUsers, sudo and SSH access
- The redirection empties the file firstBash scripting for administrators
- Hardening the SSH daemon without locking yourself outFirewall and hardening