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getuid, geteuid — get user identification
Standard C Library (libc, -lc)
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
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.
The getuid() and geteuid() system calls are always successful, and no
return value is reserved to indicate an error.
getgid(2), issetugid(2), setgid(2), setreuid(2), setuid(2)
The geteuid() and getuid() system calls are expected to conform to
ISO/IEC 9945-1:1990 (“POSIX.1”).
The getuid() and geteuid() functions appeared in Version 7 AT&T UNIX.