Linux: set date through command line

Use date -s:

date -s '2014-12-25 12:34:56'

Run that as root or under sudo. Changing only one of the year/month/day is more of a challenge and will involve repeating bits of the current date. There are also GUI date tools built in to the major desktop environments, usually accessed through the clock.

To change only part of the time, you can use command substitution in the date string:

date -s "2014-12-25 $(date +%H:%M:%S)"

will change the date, but keep the time. See man date for formatting details to construct other combinations: the individual components are %Y, %m, %d, %H, %M, and %S.

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 --systohc

Or the system time to the hardware clock

hwclock --hctosys

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