geteuid (2) - Linux Man Pages
geteuid: get user identity
getuid, geteuid - get user identity
DESCRIPTIONgetuid() returns the real user ID of the calling process.
ERRORSThese functions are always successful.
CONFORMING TOPOSIX.1-2001, POSIX.1-2008, 4.3BSD.
HistoryIn UNIX V6 the getuid() call returned (euid << 8) + uid. UNIX V7 introduced separate calls getuid() and geteuid().
The original Linux getuid() and geteuid() system calls supported only 16-bit user IDs. Subsequently, Linux 2.4 added getuid32() and geteuid32(), supporting 32-bit IDs. The glibc getuid() and geteuid() wrapper functions transparently deal with the variations across kernel versions.
On Alpha, instead of a pair of getuid() and geteuid() system calls, a single getxuid() system call is provided, which returns a pair of real and effective UIDs. The glibc getuid() and geteuid() wrapper functions transparently deal with this. See syscall(2) for details regarding register mapping.
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