With fail2ban, what is a "jail"?
A. A netfilter rules chain blocking offending IP addresses for a particular service
B. A group of services on the server which should be monitored for similar attack patterns in the log files
C. A filter definition and a set of one or more actions to take when the filter is matched
D. The chroot environment in which fail2ban runs
題解
「fail2ban」可以用來掃描記錄檔，來檢查密碼嘗試次數過過多的IP位址，並且將其阻擋。「jail」是fail2ban的設定檔，定義了要如何匹配IP以及一些動作。
所以答案是選項「C」。