Problem
Issuing the following commend caused the system to be unreachable via SSH:
chmod a+rwx / -R
Here the entire filesystem, and all mounted partitions, were modified to be world-writable. One immediate consequence of this is that ssh logins fail:
ssh_exchange_identification: Connection closed by remote host
Looking in /var/log/auth.log upon the host we can see the cause of this failure:
error: Could not load host key: /etc/ssh/ssh_host_rsa_key
error: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
error: @ WARNING: UNPROTECTED PRIVATE KEY FILE! @
error: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
error: Permissions 0777 for '/etc/ssh/ssh_host_dsa_key' are too open.
error: It is recommended that your private key files are NOT accessible by others.
error: This private key will be ignored.
error: bad permissions: ignore key: /etc/ssh/ssh_host_dsa_key
error: Could not load host key: /etc/ssh/ssh_host_dsa_key
fatal: /var/run/sshd must be owned by root and not group or world-writable.
Solution
These errors are fixable fairly easily unless we are not disallowed to access linux machine otherwise then through SSH:
(none):~# chmod 600 /var/run/sshd
(none):~# chmod 600 /etc/ssh/ssh_host_*
