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+.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
+.TH "GETLOGIN" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.\" getlogin 
+.SH NAME
+getlogin, getlogin_r \- get login name
+.SH SYNOPSIS
+.LP
+\fB#include <unistd.h>
+.br
+.sp
+char *getlogin(void);
+.br
+\fP
+.LP
+\fBint getlogin_r(char *\fP\fIname\fP\fB, size_t\fP \fInamesize\fP\fB);
+\fP
+\fB
+.br
+\fP
+.SH DESCRIPTION
+.LP
+The \fIgetlogin\fP() function shall return a pointer to a string containing
+the user name associated by the login activity with
+the controlling terminal of the current process. If \fIgetlogin\fP()
+returns a non-null pointer, then that pointer points to the
+name that the user logged in under, even if there are several login
+names with the same user ID.
+.LP
+The \fIgetlogin\fP() function need not be reentrant. A function that
+is not required to be reentrant is not required to be
+thread-safe.
+.LP
+The \fIgetlogin_r\fP() function shall put the name associated by the
+login activity with the controlling terminal of the current
+process in the character array pointed to by \fIname\fP. The array
+is \fInamesize\fP characters long and should have space for
+the name and the terminating null character. The maximum size of the
+login name is {LOGIN_NAME_MAX}.
+.LP
+If \fIgetlogin_r\fP() is successful, \fIname\fP points to the name
+the user used at login, even if there are several login
+names with the same user ID. 
+.SH RETURN VALUE
+.LP
+Upon successful completion, \fIgetlogin\fP() shall return a pointer
+to the login name or a null pointer if the user's login
+name cannot be found. Otherwise, it shall return a null pointer and
+set \fIerrno\fP to indicate the error.
+.LP
+The return value from \fIgetlogin\fP() may point to static data whose
+content is overwritten by each call.
+.LP
+If successful, the \fIgetlogin_r\fP() function shall return zero;
+otherwise, an error number shall be returned to indicate the
+error. 
+.SH ERRORS
+.LP
+The \fIgetlogin\fP() and \fIgetlogin_r\fP() functions may fail if:
+.TP 7
+.B EMFILE
+{OPEN_MAX} file descriptors are currently open in the calling process.
+.TP 7
+.B ENFILE
+The maximum allowable number of files is currently open in the system.
+.TP 7
+.B ENXIO
+The calling process has no controlling terminal.
+.sp
+.LP
+The \fIgetlogin_r\fP() function may fail if:
+.TP 7
+.B ERANGE
+The value of \fInamesize\fP is smaller than the length of the string
+to be returned including the terminating null character. 
+.sp
+.LP
+\fIThe following sections are informative.\fP
+.SH EXAMPLES
+.SS Getting the User Login Name
+.LP
+The following example calls the \fIgetlogin\fP() function to obtain
+the name of the user associated with the calling process,
+and passes this information to the \fIgetpwnam\fP() function to get
+the associated user
+database information.
+.sp
+.RS
+.nf
+
+\fB#include <unistd.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <stdio.h>
+\&...
+char *lgn;
+struct passwd *pw;
+\&...
+if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
+    fprintf(stderr, "Get of user information failed.\\n"); exit(1);
+    }
+\fP
+.fi
+.RE
+.SH APPLICATION USAGE
+.LP
+Three names associated with the current process can be determined:
+\fIgetpwuid\fP( \fIgeteuid\fP()) shall return the name associated
+with the effective user ID of the process;
+\fIgetlogin\fP() shall return the name associated with the current
+login activity; and \fIgetpwuid\fP( \fIgetuid\fP()) shall return the
+name associated with the real user ID of the process.
+.LP
+The \fIgetlogin_r\fP() function is thread-safe and returns values
+in a user-supplied buffer instead of possibly using a static
+data area that may be overwritten by each call.
+.SH RATIONALE
+.LP
+The \fIgetlogin\fP() function returns a pointer to the user's login
+name. The same user ID may be shared by several login
+names. If it is desired to get the user database entry that is used
+during login, the result of \fIgetlogin\fP() should be used to
+provide the argument to the \fIgetpwnam\fP() function. (This might
+be used to determine
+the user's login shell, particularly where a single user has multiple
+login shells with distinct login names, but the same user
+ID.)
+.LP
+The information provided by the \fIcuserid\fP() function, which was
+originally defined in the POSIX.1-1988 standard and
+subsequently removed, can be obtained by the following:
+.sp
+.RS
+.nf
+
+\fBgetpwuid(geteuid())
+\fP
+.fi
+.RE
+.LP
+while the information provided by historical implementations of \fIcuserid\fP()
+can be obtained by:
+.sp
+.RS
+.nf
+
+\fBgetpwuid(getuid())
+\fP
+.fi
+.RE
+.LP
+The thread-safe version of this function places the user name in a
+user-supplied buffer and returns a non-zero value if it
+fails. The non-thread-safe version may return the name in a static
+data area that may be overwritten by each call.
+.SH FUTURE DIRECTIONS
+.LP
+None.
+.SH SEE ALSO
+.LP
+\fIgetpwnam\fP() , \fIgetpwuid\fP() , \fIgeteuid\fP() , \fIgetuid\fP()
+, the Base Definitions volume of
+IEEE\ Std\ 1003.1-2001, \fI<limits.h>\fP, \fI<unistd.h>\fP
+.SH COPYRIGHT
+Portions of this text are reprinted and reproduced in electronic form
+from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
+-- Portable Operating System Interface (POSIX), The Open Group Base
+Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
+Electrical and Electronics Engineers, Inc and The Open Group. In the
+event of any discrepancy between this version and the original IEEE and
+The Open Group Standard, the original IEEE and The Open Group Standard
+is the referee document. The original Standard can be obtained online at
+http://www.opengroup.org/unix/online.html .