How to interpret results of `last reboot` command?

Question

I was supposed to left my device always on since Monday

last reboot

give me

 reboot   system boot  4.4.0-98-generic Wed Dec  6 08:52   still running
 reboot   system boot  4.4.0-98-generic Mon Dec  4 09:40 - 18:12 (1+08:31)

is it correct?

Answer 1

See man last:

last searches back through the /var/log/wtmp file (or the file designated by the -f option) and displays a list of all users logged in (and out) since that file was created. One or more usernames and/or ttys can be given, in which case last will show only the entries matching those arguments. Names of ttys can be abbreviated, thus last 0 is the same as last tty0.

For your command last reboot:

The pseudo user reboot logs in each time the system is rebooted. Thus last reboot will show a log of all the reboots since the log file was created.

Shows you number of reboots the system went through, and reboot and shutdown are pseudo-users for system reboot and shutdown, respectively.