Scrollback

Scrollback is the portion of a terminal's output that can be viewed by scrolling up after new output has appeared. It is implemented as a scrollback buffer that stores previously displayed lines, allowing users to review past messages, errors, or commands without re-running them.

In most modern terminal emulators, the scrollback length is configurable. Common defaults range from several thousand to hundreds of thousands of lines, with memory usage rising roughly in proportion to the number of lines and the width of the display, since each line can have color attributes and wide characters.

Scrollback is distinct from a shell's command history. The scrollback buffer contains program output, while command history records the commands entered. Some applications use an alternate screen buffer to avoid disturbing the main scrollback; when a program avoids writing to the main buffer, its full-screen interfaces do not affect the normal scrollback.

Features often include searching within the scrollback, copying text to the clipboard, and, in some terminals, preserving scrollback between sessions or across reopenings. Some terminals also allow clearing or truncating the buffer manually.

Different systems and applications implement scrollback differently. Xterm, GNOME Terminal, Konsole, iTerm2, and Windows Terminal provide large, configurable buffers. Terminal multiplexers like tmux and GNU Screen maintain their own scrollback for each pane, which can be independent of the terminal emulator's buffer.

Limitations exist: very large buffers consume memory, and some programs may clear or manipulate the display in ways that reduce useful scrollback. Understanding a system's scrollback behavior helps with debugging long-running processes and reviewing log output.