Introduce small time library based on clock_gettime - #21

Thank you for your PR. Have wall clock adjustments been a problem for you? While it is true that CLOCK_BOOTTIME is better for this purpose, the fallback (CLOCK_MONOTONIC) does not increment during sleep. Point is, unless there is an actual problem with time(NULL) I don't want to fix something that's not broken.

Have wall clock adjustments been a problem for you? While it is true that CLOCK_BOOTTIME is better for this purpose, the fallback (CLOCK_MONOTONIC) does not increment during sleep.

In my case, the system allowed users to adjust the system clock, so using a clock source immune to wall‑clock changes was a better approach. Since I was working on Linux, I knew CLOCK_BOOTTIME would be available. However, because it is Linux‑specific, I added CLOCK_MONOTONIC as a POSIX‑compliant fallback. While that fallback avoids problems caused by manual time adjustments, it indeed has the drawback you mentioned.

I'm still not entirely sure that this is a condition that SSHGuard can and should handle. On most systems, you have to be root to change time. If the user is root, what else can they change? Can you be more specific about why you need SSHGuard specifically to handle time changing?

I'm still not entirely sure that this is a condition that SSHGuard can and should handle. On most systems, you have to be root to change time. If the user is root, what else can they change? Can you be more specific about why you need SSHGuard specifically to handle time changing?

I’ve checked and found that the only configurable option is the timezone in the system I was working on, which does not affect time(NULL). However, I still believe that using clock_gettime() with a monotonic clockid_t is a standard systems‑programming best practice for measuring elapsed time.