CPU_REBOOT(9)

💅 CPU_REBOOT(9) — the kernel developer's manual, but make it make sense 💅

okay bestie, so this page is CPU_REBOOT(9) from the Kernel Developer's Manual — section 9, kernel-adjacent, very "final boss of the boot sequence" energy. It's the function that literally hits the lights or restarts the whole vibe. Let's get into it 🫶

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✨ NAME ✨

cpu_reboot — halt or reboot the system. that's it. that's the whole job. the end-of-day function. the "we're closing, please make your way to the exit" of kernel space 💀

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🎀 SYNOPSIS 🎀

#include <sys/reboot.h>

void
cpu_reboot(int howto, char *bootstr);

so it takes an int howto and a char *bootstr, and it returns void — meaning it does not give you anything back. it's giving "I am the last thing that happens, there is no return, there is no after." main character energy fr fr 👑

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🌸 DESCRIPTION 🌸

The cpu_reboot() function handles the final system shutdown, and then either halts or reboots the system. Which one it picks depends on two things, no cap:

• the flags you pass in howto
• whether or not the system has finished autoconfiguration

Two whole paths. Two whole vibes. Let's go.

🔥 if the system HAS finished autoconfiguration

then cpu_reboot() does the following, in this exact order (the order matters, do not shuffle, this is not a playlist):

1. Sets the boothowto system variable (see boothowto(9)) from the howto argument. lowkey just recording what you asked for, so the next boot knows the lore 📝
2. If this is the first invocation of cpu_reboot() and the RB_NOSYNC flag is not set in howto, it syncs and unmounts the system disks by calling vfs_shutdown(9), and sets the time of day clock by calling resettodr(9). this is the "save your work before I close the laptop" step and it is so important 😭
3. Disables interrupts. everyone quiet, the adults are talking 🤫
4. If rebooting after a crash (i.e., if RB_DUMP is set in howto, but RB_HALT is not), it saves a system crash dump. yes bestie, we're preserving the evidence 🔍
5. Runs any shutdown hooks by calling pmf_system_shutdown(9). hooks get to say their goodbyes 🥹
6. Prints a message indicating that the system is about to be halted or rebooted. a little announcement, a little "going down in 3, 2, 1" 📢
7. If RB_HALT is set in howto, it halts the system. Otherwise, it reboots the system. that's the fork in the road, the whole plot twist, the moment ✨

🌈 if the system has NOT finished autoconfiguration

then it's a whole different situation, and honestly it's simpler: cpu_reboot() runs any shutdown hooks by calling pmf_system_shutdown(9), prints a message, and halts the system.

that's it. no disk sync step listed here, no dump step listed here — the page only says hooks, message, halt. don't go adding steps that aren't in the original, i'm watching you 👀

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🦋 one more thing: bootstr

If RB_STRING is set in howto, then the parameter bootstr is passed to the system boot loader on some ports. not all ports! some. iykyk 🧚

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👑 SEE ALSO 👑

the whole friend group, assembled:

• boothowto(9)
• dumpsys(9)
• pmf_system_shutdown(9)
• resettodr(9)
• vfs_shutdown(9)

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💜 sign-off 💜

that's the whole page, bestie — go forth and reboot responsibly 🌟 this little icon was brought to you by Debian, dated February 11, 2010, from the CPU_REBOOT(9) page in the Kernel Developer's Manual. periodt 💅🎀