register_sys_off_handler(9)

💅 register_sys_off_handler(9) 💅

okay bestie, welcome to the Kernel API Manual — this is the page where we learn how to get a callback to fire when the system powers off or restarts. yes, that kind of handler. very main character energy for your machine's final moments. 🫶

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✨ NAME ✨

register_sys_off_handler — literally just "Register sys-off handler" 🎀

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🌸 SYNOPSIS 🌸

struct sys_off_handler * register_sys_off_handler (enum sys_off_mode
mode , int priority , int (*callback)(struct sys_off_data *data) , void
*cb_data );

like. that's the whole signature. four args. slay. ✨

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🦋 ARGUMENTS 🦋

• mode — the Sys-off mode, i.e. which step of the shutdown/restart saga your handler gets to show up at 👑
• priority — Handler priority. where you stand in line, basically. no cutting, gorgeous 💅
• callback — Callback function. this is the little function that actually does the thing when it's your turn 🔥
• cb_data — Callback argument. the little gift bag you hand to your callback 🎁

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💖 DESCRIPTION 💖

so here's the tea ☕: this registers a system power-off or restart handler, and it gets invoked at the step corresponding to the given sys-off mode. matching vibes, matching moment. 💫

your handler's callback should return NOTIFY_DONE to permit execution of the next handler in the call chain — yes, the chain keeps going, be a team player — or NOTIFY_STOP to break the chain (in error case for example). dramatic exit, honestly iconic. 💀

multiple handlers can be registered at the default priority level. the more the merrier, fr fr 🫶

but. only one handler can be registered at the non-default priority level, otherwise ERR_PTR(-EBUSY) is returned. so like… pick one. not me showing up twice to the non-default priority party 🙈

Returns a new instance of struct sys_off_handler on success, or an ERR_PTR-encoded error code otherwise. 🍓

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👑 SEE ALSO 👑

• Kernel file ./kernel/reboot.c
• emergency_restart(9)
• register_reboot_notifier(9)
• unregister_reboot_notifier(9)
• register_restart_handler(9)
• unregister_restart_handler(9)
• do_kernel_restart(9)
• kernel_restart(9)
• kernel_halt(9)
• unregister_sys_off_handler(9)
• devm_register_sys_off_handler(9)
• devm_register_power_off_handler(9)
• devm_register_restart_handler(9)
• register_platform_power_off(9)
• unregister_platform_power_off(9)
• do_kernel_power_off(9)
• kernel_can_power_off(9)
• kernel_power_off(9)
• orderly_poweroff(9)
• orderly_reboot(9)
• hw_failure_emergency_action_func(9)
• hw_failure_emergency_schedule(9)
• __hw_protection_trigger(9)

like, read them. all of them. iykyk 💅

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okay that's the page!! it lives in ./kernel, the version vibes are October 2026, and yes the header and footer both say register_sys_off_handler(9) because symmetry is cute. go register something responsibly bestie 🧚‍♀️💜