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timerfd_settime32 - sets or reads the expiration and interval settings of a timer created by timerfd_create3


This syscall is used to set or read the expiration and interval settings of a timer created by timerfd_create3, a timer that is awoken when a time elapses until the timer is reset with a new expiration time. This syscall is called with two pointers to struct old_itimerspec32 objects, utmr and otmr, which store the values of the timer both before and after it being set. A ufd and flags are also passed to the function, ufd corresponding to the file descriptor associated to the timer, and flags, an options field.

One advantage of using this syscall is that it provides an easy (and fast) way of setting and managing a timer. It is particularly handy when used with a CLOCK_MONOTONIC clock, since it will neither gain nor lose time. On top of that, timers set with timerfd_settime will never expire earlier than its intended time, which can be quite useful when working with time-sensitive tasks.

One drawback is that if Linux kernel is modified with a newer version of it, applications need to be recompiled against newer version in order for timerfd_settime32 to be used properly.


  • ufd: int - The file descriptor associated with the timer.
  • flags: int - Option flags to indicate whether the new settings are affected at expiration or after current expiration.
  • utmr: struct old_itimerspec32* - Pointer to a struct old_itimerspec32 object defining the new timer settings.
  • otmr: struct old_itimerspec32*[OPT] - Pointer to a struct old_itimerspec32 object where the previous settings of the timer are stored.

Available Tags

  • K - Originated from kernel-space.
  • TOCTOU - Vulnerable to TOCTOU (time of check, time of use)
  • OPT - Optional argument - might not always be available (passed with null value)




kprobe + nop


To trace the syscall timerfd_settime32 with the intention of monitoring when the timer is set and gather information about the duration of time for which the user is expecting the timer to expire.

Example Use Case

One example use case for this syscall is when we need to keep track of time needed for certain tasks. This can be particularly useful when we are doing performance analysis, as we can use this to check which operations are taking more time.

For example, we can measure how much time it takes to perform a certain task by setting a timer with this funciton and checking how much time it takes for the timer to expire.


One common issue with using timerfd_settime32 is that we are relying on the accuracy of the system timer. In a system with an unstable clock, maybe due to scheduling, this could cause our timer to expire earlier or later than it is supposed to.

  • timerfd_create3: Used to create the timer associated with timerfd_settime32.
  • epoll_wait: Used to wait for timers to expire.
  • timer_gettime: Used to access or alter the timer's expiration settings.

This document was automatically generated by OpenAI and needs review. It might not be accurate and might contain errors. The authors of Tracee recommend that the user reads the "events.go" source file to understand the events and their arguments better.