How to print kernel time from command line

Write to /dev/kmsg (not /proc/kmsg as suggested by @Nils). See linux/kernel/printk/printk.c devkmsg_writev for the kernel-side implementation and systemd/src/journal/journald-kmsg.c server_forward_kmsg for an example of usage.

The following commands work with Python 2.7.15rc1 on my Mint 19.
They will display the uptime excluding sleep time.

python3 -c 'import time;print(f" {(time.clock_gettime(time.CLOCK_MONOTONIC))}")'

The above shows the time in seconds with a decimal.

python3 -c 'import time;second=int(time.clock_gettime(time.CLOCK_MONOTONIC));print(f" {second} seconds")'

The above shows the time in seconds with no decimal.

python3 -c 'import time;second=int(time.clock_gettime(time.CLOCK_MONOTONIC));minute=second//60;print(f" {minute} minutes")'

The above shows the time in minutes.

python3 -c 'import time;s=int(time.clock_gettime(time.CLOCK_MONOTONIC));h=s//3600;m=(s-h*3600)//60;print(f"{h} hours {m} minutes")'

The above shows the time in hours and minutes.

python3 -c 'import time,datetime;print(datetime.timedelta(seconds=time.clock_gettime(time.CLOCK_MONOTONIC)))'

The above shows the time in hours, minutes, and seconds.

python3 -c 'import time,datetime;d=datetime.datetime(1,1,1)+datetime.timedelta(seconds=time.clock_gettime(time.CLOCK_MONOTONIC));print(f"{d.day-1} days, {d.hour} hours, {d.minute} minutes")'

The above shows the time in days, hours, and minutes.

I have used CLOCK_MONOTONIC and Awk to create a script that will calculate the total time if my Mint has been started more than once on the same date. The Awk command can even be used to calculate the total time in one week/month/year.