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rt_sigaction - install or confirm action for specified signal.


rt_sigaction is a system call that changes the action taken by a process on receipt of a specific signal. Signal actions are explained in signal(7).

Using rt_sigaction, a process can specify the action to be taken when a specific signal is delivered. This can include ignoring the signal, catching it with a signal handler, or setting a flag in the process's signal mask.

rt_sigaction is available on Linux systems and is a more recent, improved way of setting signal handlers compared to signal syscall. It can be used to install signal handlers that take an extra parameter, an ucontext_t *, which will be used by the handler to store the context of the signal where it was caught.

The main advantage of using this system call over the signal syscall is that it allows for the setting of a real-time signal, in addition to the usual POSIX signals. A critical limitation of the signal syscall is that it does not provide a way to set real-time signals, which are useful for applications needing to respond quickly to events.

rt_sigaction is also useful for working with signals that have been registered using sigaction. For example, sigaction can be used to register a signal handler, but rt_sigaction is the only way to retrieve the currently installed signal handler.


  • signum:int[K] - Signal to be handled, which can either be a POSIX signal or real-time signal.
  • act:const struct sigaction*[K] - New signal action, or NULL to restore default action.
  • oldact:struct sigaction*[K] - Output parameter which will return the previous signal action, or NULL if not required.
  • sigsetsize:size_t[K] - Size of the sigset specified by act in bytes.

Available Tags

  • K - Originated from kernel-space.
  • U - Originated from user space (for example, pointer to user space memory used to get it)
  • TOCTOU - Vulnerable to TOCTOU (time of check, time of use)
  • OPT - Optional argument - might not always be available (passed with null value)






Hook function to capture signal handler changes made using rt_sigaction syscall.





Hook function to capture signals as they are delivered to the process.

Example Use Case

rt_sigaction can be used to enable a process to react quickly to a signal sent from another process, or another thread in the same process. For example, a signal handler can be registered with rt_sigaction that sets a flag when the signal is received. The flag can then be checked in an application loop, and its presence will trigger an action.


It is possible to register a signal handler using rt_sigaction that does not take an additional parameter for the ucontext_t *, even though this parameter is required for real-time signals. While this will work for most OS versions without failing, this may cause unexpected results or failures on some systems.

signal, rt_sigprocmask

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.