9.54 setuids ¶

int setuids(uid_t uid, uid_t euid);

This syscall sets the UID and effective UID of the calling process. If the calling process has the MAC_CAP_SETUID capability, it will set both the EUID and UID, else, it will only try to set EUID to values matching the process’s UID. If any of them is -1, it will not be modified.

The syscall returns 0 on success or -1 on failure, with the following errno:

EPERM

MAC did not allow this.