POSIX 7 http://pubs.opengroup.org/onlinepubs/9699919799/utilities/date.html
Get system date:
date
Sample output:
Sun Feb 1 12:21:15 CET 2015
Format current time and output it:
date '+%Y-%m-%d_%H:%M:%S'
Sample output:
2015-02-01 12:21:52
Saner RFC-3339 format:
date --rfc-3339=seconds
Sample output:
2015-02-08 15:42:37+01:00
Set the system date:
sudo date -s "1 JUN 2012 09:30:00"