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+.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" Historical remark, aeb, 2004-06-05
+.TH getuid 2 2023-03-30 "Linux man-pages 6.05.01"
+.SH NAME
+getuid, geteuid \- get user identity
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <unistd.h>
+.PP
+.B uid_t getuid(void);
+.B uid_t geteuid(void);
+.fi
+.SH DESCRIPTION
+.BR getuid ()
+returns the real user ID of the calling process.
+.PP
+.BR geteuid ()
+returns the effective user ID of the calling process.
+.SH ERRORS
+These functions are always successful
+and never modify
+.\" https://www.austingroupbugs.net/view.php?id=511
+.\" 0000511: getuid and friends should not modify errno
+.IR errno .
+.SH STANDARDS
+POSIX.1-2008.
+.SH HISTORY
+POSIX.1-2001, 4.3BSD.
+.PP
+In UNIX\ V6 the
+.BR getuid ()
+call returned
+.IR "(euid << 8) + uid" .
+UNIX\ V7 introduced separate calls
+.BR getuid ()
+and
+.BR geteuid ().
+.PP
+The original Linux
+.BR getuid ()
+and
+.BR geteuid ()
+system calls supported only 16-bit user IDs.
+Subsequently, Linux 2.4 added
+.BR getuid32 ()
+and
+.BR geteuid32 (),
+supporting 32-bit IDs.
+The glibc
+.BR getuid ()
+and
+.BR geteuid ()
+wrapper functions transparently deal with the variations across kernel versions.
+.PP
+On Alpha, instead of a pair of
+.BR getuid ()
+and
+.BR geteuid ()
+system calls, a single
+.BR getxuid ()
+system call is provided, which returns a pair of real and effective UIDs.
+The glibc
+.BR getuid ()
+and
+.BR geteuid ()
+wrapper functions transparently deal with this.
+See
+.BR syscall (2)
+for details regarding register mapping.
+.SH SEE ALSO
+.BR getresuid (2),
+.BR setreuid (2),
+.BR setuid (2),
+.BR credentials (7)