.\" Hey Emacs! This file is -*- nroff -*- source. .\" .\" Copyright 1995 James R. Van Zandt .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" Changed Tue Sep 19 01:49:29 1995, aeb: moved from man2 to man3 .\" added ref to /etc/utmp, added BUGS section, etc. .TH GETLOGIN 3 "3 September, 1995" "Linux 1.2.13" "Linux Programmer's Manual" .SH NAME getlogin, cuserid \- get user name .SH SYNOPSIS .B #include .sp .BI "char * getlogin ( void );" .sp .B #include .sp .BI "char * cuserid ( char *" string " );" .SH DESCRIPTION \fBgetlogin\fP returns a pointer to a string containing the name of the user logged in on the controlling terminal of the process, or a null pointer if this information cannot be determined. The string is statically allocated and might be overwritten on subsequent calls to this function or to \fBcuserid\fP. .PP \fBcuserid\fP returns a pointer to a string containing a user name associated with the effective user ID of the process. If \fIstring\fP is not a null pointer, it should be an array that can hold at least \fBL_cuserid\fP characters; the string is returned in this array. Otherwise, a pointer to a string in a static area is returned. This string is statically allocated and might be overwritten on subsequent calls to this function or to \fBgetlogin\fP. .PP The macro \fBL_cuserid\fP is an integer constant that indicates how long an array you might need to store a user name. \fBL_cuserid\fP is declared in \fBstdio.h\fP. .PP These functions let your program identify positively the user who is running (\fBcuserid\fP) or the user who logged in this session (\fBgetlogin\fP). (These can differ when setuid programs are involved.) The user cannot do anything to fool these functions. .PP For most purposes, it is more useful to use the environment variable \fBLOGNAME\fP to find out who the user is. This is more flexible precisely because the user can set \fBLOGNAME\fP arbitrarily. .SH ERRORS .TP .B ENOMEM Insufficient memory to allocate passwd structure. .SH FILES .nf \fI/etc/passwd\fP password database file .fi \fI/etc/utmp\fP (or \fI/var/adm/utmp\fP, or wherever your \fIutmp\fP file lives these days - the proper location depends on your libc version) .SH "CONFORMING TO" POSIX.1. System V has a \fBcuserid\fP function which uses the real user ID rather than the effective user ID. The \fBcuserid\fP function was included in the 1988 version of POSIX, but removed from the 1990 version. .SH BUGS Unfortunately, it is often rather easy to fool getlogin(). Sometimes it does not work at all, because some program messed up the utmp file. Often, it gives only the first 8 characters of the login name. The user currently logged in on the controlling tty of our program need not be the user who started it. .LP Nobody knows precisely what cuserid() does - avoid it in portable programs - avoid it altogether - use getpwuid(geteuid()) instead, if that is what you meant. DO NOT USE cuserid(). .SH "SEE ALSO" .BR geteuid "(2), " getuid (2)