TIME(9)

💖 TIME(9) — Kernel Developer's Manual, bestie edition 💖

okay so you're in the 9 section, which is where the kernel developer girlies live, and this page is literally just three global variables that run the whole clock situation. no cap. let's go 🕐✨

🌸 NAME 🌸

boottime, time_second, time_uptime — the system time variables, aka the three icons keeping track of when things are happening 👑

✨ SYNOPSIS ✨

#include <sys/time.h>

extern struct timeval boottime;
extern time_t time_second;
extern time_t time_uptime;

that's it. that's the whole cast. three externs and a header. slay 💅

🦋 DESCRIPTION 🦋

okay so boom, meet the trio:

• boottime — this one holds the system boot time. like, the exact moment the system woke up and said "hi bestie, I'm alive" 🌅. it's a struct timeval, so she's got sub-second precision energy.
• time_second — this is the system's “wall time” clock, rounded to the second. the vibes clock. the one you glance at. ⏰
• time_uptime — the number of seconds since boot. not the time of day, just how long have we been up, like a "days since last incident" sign but for your kernel 🔥

now here's the tea, bestie 🫖 — if you want the current time and you want it accurate and atomic (no half-updated nonsense, no race conditions sneaking in like a toxic ex), use these instead:

bintime(9), getbintime(9), microtime(9), getmicrotime(9), nanotime(9), and getnanotime(9) — they give you the current time more accurately and in an atomic manner. periodt ✨

and if what you actually want is how much time has elapsed since boot, also accurate, also atomic, hit up:

binuptime(9), getbinuptime(9), microuptime(9), getmicrouptime(9), nanouptime(9), and getnanouptime(9) — these give you the time elapse since boot, more accurately and in an atomic manner 🧚

but boottime? she's different. the boottime variable may be read and written without special precautions. lowkey the most chill of the three. no locking drama, no atomic requirements, just vibes 🫶

👑 SEE ALSO 👑

the whole friend group, alphabetized, no one left out:

• clock_settime(2)
• ntp_adjtime(2)
• settimeofday(2)
• bintime(9)
• binuptime(9)
• getbintime(9)
• getbinuptime(9)
• getmicrotime(9)
• getmicrouptime(9)
• getnanotime(9)
• getnanouptime(9)
• microtime(9)
• microuptime(9)
• nanotime(9)
• nanouptime(9)

and the required reading for the academic girlies 📚:

• Poul-Henning Kamp, “Timecounters: Efficient and precise timekeeping in SMP kernels”, Proceedings of EuroBSDCon 2002, Amsterdam, /usr/share/doc/papers/timecounter.ascii.gz.
• Marshall Kirk McKusick and George V. Neville-Neil, The Design and Implementation of the FreeBSD Operating System, Addison-Wesley, 57-61,65-66, July 2004.

and that's the whole page bestie!! this one came from Debian, dated September 17, 2004, and honestly for a manpage that old she's still serving 💜 go read bintime(9) if you want the atomic upgrade, love u bye 🎀✨