Editing Init (section)

== {{Anchor|STARTUP-SCRIPTS}}Research Unix-style/BSD-style ==
[[Research Unix]] init runs the initialization [[shell script]] located at <code>/etc/rc</code>,<ref>{{man|8|init|v7}}</ref> then launches [[getty (Unix)|getty]] on terminals under the control of <code>/etc/ttys</code>.<ref>{{man|5|ttys|v7}}</ref> There are no runlevels; the <code>/etc/rc</code> file determines what programs are run by init. The advantage of this system is that it is simple and easy to edit manually. However, new software added to the system may require changes to existing files that risk producing an unbootable system.

[[Berkeley Software Distribution|BSD]] init was, prior to 4.3BSD, the same as Research UNIX's init;<ref>{{man|8|init|4.2BSD}}</ref><ref>{{man|5|ttys|4.2BSD}}</ref> in [[4.3BSD]], it added support for running a [[windowing system]] such as [[X Window System|X]] on graphical terminals under the control of <code>/etc/ttys</code>.<ref>{{man|8|init|4.3BSD}}</ref><ref>{{man|5|ttys|4.3BSD}}</ref> To remove the requirement to edit <code>/etc/rc</code>, BSD variants have long supported a site-specific <code>/etc/rc.local</code> file that is run in a sub-shell near the end of the boot sequence.

A fully modular system was introduced with [[NetBSD]] 1.5 and ported to [[FreeBSD]] 5.0 and successors. This system executes scripts in the <code>/etc/rc.d</code> directory. Unlike System V's script ordering, which is derived from the filename of each script, this system uses explicit dependency tags placed within each script.<ref>{{cite web | url = http://aplawrence.com/Basics/unix-startup-scripts-2.html | title = Unix and Linux startup scripts, Part 2 | author = Andrew Smallshaw | date = 7 December 2009 | access-date = 6 June 2011 | archive-date = 18 December 2009 | archive-url = https://web.archive.org/web/20091218083059/http://aplawrence.com/Basics/unix-startup-scripts-2.html | url-status = live }}</ref> The order in which scripts are executed is determined by the ''rcorder'' utility based on the requirements stated in these tags.