xterm

xterm is the standard terminal emulator of the X Window System. It was first developed in the mid-1980s to provide DEC VT102 and Tektronix 4014 compatible terminals for programs that cannot use the window system directly, and it has been maintained by Thomas E. Dickey since the mid-1990s. It is for users who want a stable, highly compatible terminal on Linux, the BSDs and other Unix systems.

Emulation is xterm's strength. The man page documents complete VT52 emulation, fairly complete VT102, VT220 complete except for soft fonts, and VT420 as the default level, with rectangle operations and left/right margins. It also implements selected VT320, VT420 and VT520 features and a separate Tektronix 4014 graphics window. ISO/ANSI color uses background color erase, and the preferred terminal description has moved from VT102 (until 1996) to VT220 (until 2012) to VT420 today. The emulation level can be set with -ti or the decTerminalID resource. Sixel and ReGIS graphics are available when xterm is built with that support. The maintainer also develops vttest, a test program for VT100-family terminals.

Configuration uses X resources (the XTerm class, set in ~/.Xresources or app-defaults files) and command-line options. Fonts can be X core bitmap fonts or, through Xft and FreeType, TrueType fonts selected with -fa or faceName. The uxterm wrapper starts xterm in UTF-8 mode, and other encodings are handled through luit. Settings can also be changed at runtime from popup menus opened with Ctrl and a mouse button, or from an optional toolbar. Secure Keyboard mode protects password entry. Resources such as allowWindowOps control which window-manipulation escape sequences are honored.

xterm keeps to one terminal per window, with each window a separate process, and has no tabs, splits, GPU rendering or ligatures. It relies on the window manager or a multiplexer for those. Several features, including Sixel and ReGIS graphics and FreeType fonts, depend on build-time options, so distribution packages can differ.