Skip to content



setreuid - set real and effective user IDs.


The setreuid() system call allows a process to set both its real user ID and its effective user ID.

This provides flexibility in managing user-based privileges, especially for processes that need to toggle between different levels of privileges temporarily. In Unix-like systems, the real user ID identifies the user who launched the process, whereas the effective user ID dictates the permissions for process operations.

By modifying these IDs selectively, processes can execute specific tasks under one identity and then revert to another, thereby enhancing system security by minimizing the time a process runs with elevated privileges.


  • ruid:uid_t[K] - The real user ID to be set. If this argument is -1, the real UID is not changed.
  • euid:uid_t[K] - The effective user ID to be set. If this argument is -1, the effective UID is not changed.

Available Tags

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




Tracepoint (through sys_enter).


To observe and trace when the setreuid() system call is executed, capturing information about the changes made to the real and effective user IDs.

Example Use Case

Monitoring privilege transitions is crucial in environments that prioritize security, particularly when tracking potential privilege escalation scenarios or processes that are expected to change their operational context frequently.


If misused or if programs leveraging setreuid() contain vulnerabilities, they can be exploited to gain unauthorized privileges, leading to potential security breaches.

  • setuid() - Set the effective user ID of the calling process.
  • setresuid() - Set real, effective, and saved user IDs.
  • seteuid() - Set effective user ID.

This document was automatically generated by OpenAI and reviewed by a Human.