gtf

gtf Hpixels Vlines refresh [-x|-r|-c|-D|-M|-F]

-x
    Generate interlaced timings

-r
    Use reduced blanking timings

-c
    Composite sync timings

-D
    Force DMT (Display Monitor Timings) mode

-M
    Generate minimal timings

-F
    Force framebuffer timings

-h
    Display help summary

-v
    Print version information

The gtf command is a utility for generating modelines based on the VESA Generalized Timing Formula (GTF), used to define custom video timings for X11 displays. It computes parameters such as pixel clock, horizontal/vertical sync timings, and blanking intervals from input resolution (horizontal pixels, vertical lines) and refresh rate.

Modelines output by gtf are directly usable in xorg.conf(5) Monitor sections or with xrandr(1) commands like xrandr --newmode followed by --addmode and --mode. This is essential for non-standard resolutions, high refresh rates, or older CRT monitors where default modes fail.

Unlike cvt(1), which uses the more modern Coordinated Video Timings (CVT) reducing overscan, gtf adheres to the original GTF standard for potentially wider hardware compatibility, though it may produce slightly larger blanking periods. Always verify timings on target hardware to avoid damage.

Modelines may cause hardware stress or damage if invalid; test incrementally with xrandr. GTF timings can have more overscan than CVT; not guaranteed on all GPUs/monitors. Deprecated in favor of CVT for LCDs.

Always starts with # HxV refresh (GTF) comment, followed by Modeline "name" pixclock params string.

gtf 1024 768 60
# 1024x768 59.92 Hz (GTF) hsync: 47.71 kHz; pclk: 63.50 MHz
Modeline "1024x768" 63.50 1024 1080 1176 1328 768 771 775 798 -hsync +vsync

Originated in XFree86 (pre-2004 X.Org split), based on VESA GTF 1.1 spec (1999). Integrated into X.Org Server utils package; remains in x11-utils for legacy support as CVT supersedes it.

cvt(1), xrandr(1), xorg.conf(5)