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wait4 - wait for a process to change state.


The wait4() system call suspends execution of the calling process until a specified process has changed state, or until a signal is received, or until the delay, as specified by an argument, has passed. This syscall allows to retrieve information about the child process which changed from the provided parameters. The main purpose of this call is to allow the process to wait for the termination of a child that it created using one of the fork() syscall family functions.

The wait4() syscall attempts to return the exit status of the process specified by pid. If pid is equal to -1, it matches any process whose process group ID is equal to the process group ID of the caller, or any process when it is not a member of a process group.

When options is set to 0, the status is returned immediately. If pid is equal to 0, wait4() matches any process with the same process group ID as the caller.

If rusage is not NULL, the resource usage of the terminating process and its children is returned as part of rusage.


  • pid:pid_t[K] - the process ID of a child process for which status is requested.
  • wstatus:int*[K] - the address of a buffer where the status of the terminated process is to be stored.
  • options:int[K] - the options argument can be used to change the behavior of wait4().
  • rusage:struct rusage*[K] - a pointer to a struct rusage where the resource usage information of the terminated process (and its children) will be stored.

Available Tags

  • K - Originated from kernel-space.




Kprobe + Kretprobe


Hooked to trace information about a process and collect the return code value of wait4().

Example Use Case

The wait4() syscall is useful whenever processes need to be monitored. It can be used to track the execution of a child process and react accordingly if it fails. For example, an Alert rule can be triggered if the child process leaves the system in an unexpected state.


It should be noted that wait4()'s status value is the same as that of the wait() syscall.

  • exit()
  • wait()
  • fork()

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.