You change the date with the date command. However, the command expects a full date as the argument:

# date -s "20141022 09:45"
Wed Oct 22 09:45:00 BST 2014

To change part of the date, output the current date with the date part that you want to change as a string and all others as date formatting variables. Then pass that to the date -s command to set it:

# date -s "$(date +'%Y12%d %H:%M')"
Mon Dec 22 10:55:03 GMT 2014

changes the month to the 12th month – December.

The date formats are:

• %Y – Year
• %m – Month
• %d – Day
• %H – Hour
• %M – Minute

System time

You can use date to set the system date. The GNU implementation of date (as found on most non-embedded Linux-based systems) accepts many different formats to set the time, here a few examples:

set only the year:

date -s 'next year'
date -s 'last year'

set only the month:

date -s 'last month'
date -s 'next month'

set only the day:

date -s 'next day'
date -s 'tomorrow'
date -s 'last day'
date -s 'yesterday'
date -s 'friday'

set all together:

date -s '2009-02-13 11:31:30' #that's a magical timestamp

Hardware time

Now the system time is set, but you may want to sync it with the hardware clock:

Use --show to print the hardware time:

hwclock --show

You can set the hardware clock to the current system time:

hwclock --hctosys

Or the system time to the hardware clock

hwclock --systohc

For ones like me running ESXI 5.1, here’s what the system answered me

~ # date -s "2016-03-23 09:56:00"
date: invalid date '2016-03-23 09:56:00'

I had to uses a specific ESX command instead :

esxcli system time set  -y 2016 -M 03 -d 23  -H 10 -m 05 -s 00

I used the date command and time format listed below to successfully set the date from the terminal shell command performed on Android Things which uses the Linux Kernal.

date 092615002017.00

MMDDHHMMYYYY.SS

MM – Month – 09

DD – Day – 26

HH – Hour – 15

MM – Min – 00

YYYY – Year – 2017

.SS – second – 00

The command to to change the system date is date.

There are two ways to call the date command(in Linux):

   date [OPTION]... [+FORMAT]
   date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

Easy

The easiest way is to use date -s as it allows the use of simple relative dates

 $ date -s yesterday; date
 date: cannot set date: Operation not permitted
 Sat Jan  5 07:21:07 EST 2019
 Sun Jan  6 07:21:07 EST 2019

The date did not change because it was executed with a limited user $. If you actually want the date changed, use root (#) or sudo:

 $ sudo date -s yesterday; date
 Sat Jan  5 07:21:07 EST 2019
 Sat Jan  5 07:21:07 EST 2019

So, changing any part of a relative date is as easy as naming it:

 $ date -s "5 years ago"
 Mon Jan  6 08:26:26 EST 2014

 $ date -s "+6 months"
 Sat Jul  6 08:28:39 EDT 2019

 $ date -s "+3 hours -13 minutes"
 Sun Jan  6 11:16:59 AST 2019

Absolute dates are a bit more complex as they need more detail:

 $ date -s "2001-07-23 10:11:12"

Or, you can use the date command twice:

 $ date -s "$(date +'%Y-%m-%d %H:%M:%S')"

replace any of the % by a valid value and the date will be set (only as root).

 $ date -s "$(date +'%Y-11-%d %H:%M:%S')"
 Wed Nov  6 08:37:15 EST 2019

direct

The second date call form is used to directly change the system date.

 date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

So :

 date 11230812              # MMDDhhmm

Will set the date to the 23th of November at 08h and 12min.

BSD has a similar command but a different format ([[[[[cc]yy]mm]dd]HH]MM[.ss]).

Try date as a limited user to see what it would do (without changing anything):

 $ date 11230812
 date: cannot set date: Operation not permitted
 Sat Nov 23 08:12:00 EST 2019

Or, if you actually want to change the date, as root:

 # date 11230812
 # date
 Sat Nov 23 08:12:00 EST 2019

Note that services like NTP or chrony will be affected. And, if restarted will reset the date back to the real one.

Add a YY to set the year:

 $ date 1123081222
 date: cannot set date: Operation not permitted
 Wed Nov 23 08:12:00 EST 2022

Or a CCYY to set year and century:

 $ date 112308121982
 date: cannot set date: Operation not permitted
 Tue Nov 23 08:12:00 EST 1982

As of December 2022:

You may disable NTP sync before actual date change:

sudo timedatectl set-ntp 0
sudo timedatectl set-time "2022-12-03 $(date +%H:%M:%S)"

When date modification is no longer necessary, you should enable NTP sync again to auto update system date:

sudo timedatectl set-ntp 1