Make sure you have ffmpeg installed.

$ sudo apt install ffmpeg

You can use x11 to record your screen using the following command in a shell. To complete the recording just press Ctrl-C and the file recording.mp4 will be saved in your current working directory.

$ ffmpeg -hide_banner -loglevel error -f x11grab -i :0 -q:v 0 -r 30 -vcodec mpeg4 recording.mp4

If you have multiple monitors connected you need to update the input to :1 to get all screens. I made a screen recording script which defaults to your primary display in qrandr but also lets you specify what screen you want to record.

# FPS     - Records the screen in 144 fps
# DELAY   - Puts 1s delay before recording starts
# MONITOR - Only record the monitor connected to HDMI-1.
#   To see available monitors run: $ qrandr -q.
#   If you omit `MONITOR` it will use your primary monitor.

$ FPS=144 DELAY=1 MONITOR=HDMI-1 ./screenrec

For the latest version of the script see screenrec in my dotfiles. The script will store the recording in ~/recordings named as the current date with seconds (2021-04-09_14:18:30.mp4).

#!/usr/bin/env bash

# params as env vars
#   FPS=n
#   DELAY=n 
#   MONITOR=<monitor id>
FPS=${FPS:-60}
DELAY=${DELAY:-0}
MONITOR=${MONITOR:-primary}

sleep "$DELAY"

DATE="$(date +%Y-%m-%d)_$(date +%H:%M:%S)"
OUTPUT_DIR="$(xdg-user-dir VIDEOS)/recordings"
OUTPUT="$OUTPUT_DIR/$DATE.mp4"
mkdir -p $OUTPUT_DIR

size_pos=$(xrandr -q | grep $MONITOR | grep -Eo "[[:digit:]]*x[[:digit:]]*\+[[:digit:]]*\+[[:digit:]]*" | awk -F+ '{print " -s " $1 " -i :1+"$2"+"$3}')

echo "Starting recording. Ctrl-C to stop recording."
ffmpeg -hide_banner -loglevel error -f x11grab $size_pos -q:v 0 -r $FPS -vcodec mpeg4 "$OUTPUT"

echo "Recording saved: $OUTPUT"