initramfs / busybox cron (Ubuntu 18.04)

Note: full busybox installation is needed:
https://www.ullright.org/ullWiki/show/install-full-busybox-in-initramfs-ubuntu-18-04

• mkdir -p /var/spool/cron/crontabs
• busybox2 crontab -e

  •   SHELL=/bin/bash
      */2 * * * *date >> /date.txt

• mkdir -p /var/log/
• busybox2 crond --help

  • BusyBox v1.27.2 (Ubuntu 1:1.27.2-2ubuntu3.2) multi-call binary.
    
    Usage: crond -fbS -l N -L LOGFILE -c DIR
    
        -f    Foreground
        -b    Background (default)
        -S    Log to syslog (default)
        -l N    Set log level. Most verbose 0, default 8
        -L FILE    Log to FILE
        -c DIR    Cron dir. Default:/var/spool/cron/crontabs

• busybox2 crond -L /var/log/crond.log
• ps | grep crond
  • 352 root      2320 S    busybox2 crond --L /var/log/crond.log
• busybox2 killall busybox2
  • -> cron killed
• restart cron:
  • busybox2 killall busybox2; busybox2 crond -L /var/log/crond.log
• show log:
  • tail -f -n 100 /var/log/crond.log

Hints

• To log cron output redirect to stderr:   date >&2
• To log to vga terminal:   date > /dev/tty0
• To log to both:   date | tee /dev/tty0 >&2