geteuid(2)

geteuid2

Get user identification

Part of getuid(2).

Usage

#include <unistd.h>

uid_t

getuid(void);

uid_t

geteuid(void);

Library

Standard C Library (libc, -lc)

Overview

The getuid() system call returns the real user ID of the calling process. The geteuid() system call returns the effective user ID of the calling process.

The real user ID is that of the user who has invoked the program. As the effective user ID gives the process additional permissions during execution of “set-user-ID” mode processes, getuid() is used to determine the real-user-id of the calling process.

Errors

The getuid() and geteuid() system calls are always successful, and no return value is reserved to indicate an error.

Releases

87 releases since FreeBSD 2.0.5-RELEASE; the text changed 45 times.

  1. 2.0.5–2.1.7.1
  2. 2.2.2–2.2.5
  3. 2.2.6–2.2.8
  4. 2.2.9
  5. 3.0–3.2
  6. 3.3–3.4
  7. 3.5–3.5.1
  8. 4.0
  9. 4.1–4.3
  10. 4.4
  11. 4.5–4.11
  12. 5.0
  13. 5.1–6.3
  14. 6.4
  15. 7.0
  16. 7.1
  17. 7.2
  18. 7.3
  19. 7.4
  20. 8.0
  21. 8.1
  22. 8.2
  23. 8.3
  24. 8.4
  25. 9.0
  26. 9.1
  27. 9.2
  28. 9.3
  29. 10.0
  30. 10.1
  31. 10.2
  32. 10.3
  33. 10.4
  34. 11.0
  35. 11.1
  36. 11.2
  37. 11.3
  38. 11.4
  39. 12.0
  40. 12.1
  41. 12.2
  42. 12.3
  43. 12.4
  44. 13.0–13.2
  45. 13.3–14.5
  46. 15.0–16.0

Standards

The geteuid() and getuid() system calls are expected to conform to ISO/IEC 9945-1:1990 (“POSIX.1”).

History

The getuid() function appeared in Version 1 AT&T UNIX. The geteuid() function appeared in Version 4 AT&T UNIX.

From base 16.0-CURRENT-20261027-61c70dc16a79 in FreeBSD 16.0-CURRENT (2026-10-27). Parsed by carta from the page's mdoc source.