STRUCT K_ITIMER(9)

👑 struct k_itimer(9) — the Kernel API Manual glow-up

okay bestie, sit down, hydrate, and get comfy, because we're talking about struct k_itimer from the Kernel API Manual (yes, the (9) section, we're fancy now 💅). This is literally the POSIX.1b interval timer structure — the main character of the posix timer world. no cap.

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✨ NAME ✨

struct k_itimer — the POSIX.1b interval timer structure. that's it, that's the vibe. 🎀

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🌸 SYNOPSIS 🌸

here's the whole thing, copied exactly, because we do not touch the source in this house:

struct k_itimer {
    struct hlist_node       t_hash;
    struct hlist_node       list;
    timer_t it_id;
    clockid_t it_clock;
    int it_sigev_notify;
    enum pid_type           it_pid_type;
    struct signal_struct    *it_signal;
    const struct k_clock    *kclock;
    spinlock_t it_lock;
    int it_status;
    bool it_sig_periodic;
    s64 it_overrun;
    s64 it_overrun_last;
    unsigned int            it_signal_seq;
    unsigned int            it_sigqueue_seq;
    ktime_t it_interval;
    struct hlist_node       ignored_list;
    union {
      struct pid              *it_pid;
      struct task_struct      *it_process;
    };
    struct sigqueue         sigq;
    rcuref_t rcuref;
    union {
      struct {
        struct hrtimer  timer;
      } real;
      struct cpu_timer        cpu;
      struct {
        struct alarm    alarmtimer;
      } alarm;
    } it;
    struct rcu_head         rcu;
 };

look at all those fields. she's got range. 🌈

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🦋 Members 🦋

time to meet the cast, one field at a time. no skipping, we love an exhaustive list here:

• t_hash — entry in the posix timer hash table. she's indexed, she's findable, she's on the map 🗺️
• list — list node for binding the timer to tsk::signal::posix_timers. keeping the friend group together fr fr.
• it_id — the posix timer id for identifying the timer. it's giving government-name realness 🪪
• it_clock — the posix timer clock id. which clock is she on? that one. ⏰
• it_sigev_notify — the notify word of sigevent struct for signal delivery. the "how do we tell you" field 📣
• it_pid_type — the type of the PID. gotta know what flavor of pid we're dealing with.
• it_signal — pointer to the creator's signal struct. hi creator bestie 🫶
• kclock — pointer to the k_clock struct handling this timer. the manager of the whole situation, lowkey iconic.
• it_lock — lock protecting the timer. do not touch without the lock, that's the rule 🔒
• it_status — the status of the timer. current mood: field-encoded 💀
• it_sig_periodic — the periodic status at signal delivery. is she repeating? this tells you.
• it_overrun — the overrun counter for pending signals. the "oops we're behind" tally 😭
• it_overrun_last — the overrun at the time of the last delivered signal. receipts from last time 🧾
• it_signal_seq — sequence count to control signal delivery. numbers keep it orderly.
• it_sigqueue_seq — the sequence count at the point where the signal was queued. timestamped-ish, snapshotted, slay ✨
• it_interval — the interval for periodic timers. the again? how often? value 🔁
• ignored_list — list node for tracking ignored timers in tsk::signal::ignored_posix_timers. yes she has a whole separate list for the ignored ones. the way that's so real 🙈
• {unnamed_union} — anonymous. that's the whole description. anonymous. she's mysterious, she's unnamed, she's that girl 🕵️‍♀️
  • it_pid — the pid of the process/task targeted by the signal 🎯
  • it_process — the task to wakeup on clock_nanosleep (CPU timers). rise and shine bestie ☀️
• sigq — embedded sigqueue. she brought her own queue, prepared queen 👑
• rcuref — reference count for life time management. literally keeping her alive 🫶
• it — union representing the various posix timer type internals. all the internal lore in one union 🌈
• rcu — RCU head for freeing the timer. the graceful-exit era, we love a clean teardown 💜

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💖 SEE ALSO 💖

• Kernel file ./include/linux/posix-timers.h
• struct cpu_timer(9)

go read those, iykyk 🔥

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quick vibe check: every flag, field, and path above is exactly as it appears in the original — no invented behavior, no guessing, no drama we didn't source. the drama is editorial. 💅

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and that's the page, bestie!! 🎀 this gem came out of ./include/linux, October 2026 edition — go off, kernel docs, periodt. ⭐💖