When a program in Ubuntu such as crontab -e or dch -i, is used to edit a file, it uses a helper program called sensible-editor.
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Any user that has physical access to the keyboard can simply use the Ctrl+Alt+Delete key combination to reboot the server without having to log on. Sure, someone could simply unplug the power source, but you should still prevent the use of this key combination on a production server. This forces an attacker to take more drastic measures to reboot the server, and will prevent accidental reboots at the same time.
The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123 as its transport layer. It is designed particularly to resist the effects of variable latency (Jitter).
Nginx (pronounced "engine x") is a free, open-source, high-performance HTTP server and reverse proxy, as well as an IMAP/POP3 proxy server. Written by Igor Sysoev in 2005, Nginx now hosts between 1% and 4% of all domains worldwide. Although still in beta, Nginx is known for its stability, rich feature set, simple configuration, and low resource consumption.