I'm trying to do a couple of tests where I need to set the computer time backward or forward depending on some external values. I know that I can do this using clock_settime() in time.h.
I've encountered the problem that when needing to set the time backward, the operation fails.
The documentation for clock_settime states that
Only the CLOCK_REALTIME clock can be set, and only the superuser may do so. If the system securelevel is greater than 1 (see init(8)), the time may only be advanced. This limitation is imposed to prevent a malicious superuser from setting arbitrary time stamps on files. The system time can still be adjusted backwards using the adjtime(2) system call even when the system is secure.
I require nanosecond precision, and adjtime() as far as I understand, does not allow nanosecond precision. The other problem with ajdtime() is that it does not set the clock outright, rather slows it down, until the clock catches up to the set value.
I've done some reading on init() but I'm not sure how to lower the securelevel, and frankly I'd rather not be forced to do this, however, if there's no other way, I'm willing to try it.
Thanks in advance
Update 1
I started looking into altering securelevel and now i'm not even sure if that's something that can be done on Ubuntu. Around the web, I have come across mentions of editing /etc/init/rc-sysinit.conf, /etc/init/rc.conf, or /etc/sysctl.conf and, again, I'm not sure what needs to be added in order to lower the securelevel if, in fact, this is something that can be done. Especially since I could not find a 'rc.securelvel' file.