Editing Scroll Lock (section)

===Console scrolling===
Pressing the {{keypress|Scroll Lock}} key in the [[Linux console]] while the text is scrolling through the screen freezes the console output (but not input) during which no further text is sent to the screen, while the program continues running as usual — or becomes blocked at the {{mono|write}} [[syscall]] when too much data is prevented from reaching the terminal, causing the tty's output queue to become full if the tty file descriptor is not using non-blocking I/O. When {{keypress|Scroll Lock}} is pressed again, the screen is unfrozen and all text generated during the freeze is displayed at once and the program continues to run normally. This allows the user to pause the display and read long log messages that scroll through the screen too quickly to read, such as when the system is [[booting up]] (provided the keyboard [[Device driver|driver]] has already been loaded). Unless configured otherwise or in raw mode, {{keypress|Ctrl|S}} (DC3 in ASCII) and {{keypress|Ctrl|Q}} (DC1 in ASCII) can be used instead of Scroll Lock in Unix-like systems to freeze and unfreeze the tty output respectively.

This behavior emulates the Hold Screen key or similar flow control mechanisms on computer terminal hardware.

The behavior should be distinguished from pressing the [[Pause key]] during [[Power-on self-test|POST]] or under [[DOS]], which, by default, has the effect of temporarily halting the running process.

On the [[FreeBSD]] system console, the {{keypress|Scroll Lock}} key not only pauses output, but additionally enables scrolling: after pressing {{keypress|Scroll Lock}}, one can use {{keypress|Page Up}} and {{keypress|Page Down}} to scroll up or down. Pressing {{keypress|Scroll Lock}} again disables this mode and moves back to the bottom of the output. The Linux console implemented this behaviour by using {{keypress|Shift|Page Up}} and {{keypress|Shift|Page Down}}, not requiring {{keypress|Scroll Lock}} to be active; this behavior has been removed due to a vulnerability (CVE-2020-14390).<ref>{{Cite web |title=Linux 5.9 Dropping Soft Scrollback Support From FB + VGA Console Code |url=https://www.phoronix.com/news/Linux-5.9-Drops-Soft-Scrollback |access-date=2022-12-22 |website=www.phoronix.com |language=en}}</ref> The [[NetBSD]] console can be scrolled either with {{keypress|Shift|Page Up}}/ {{keypress|Shift|Page Down}} or by pressing {{keypress|Scroll Lock}} then {{keypress|Page Up}}/{{keypress|Page Down}} .