mirror of https://github.com/mkerrisk/man-pages
250 lines
6.5 KiB
Groff
250 lines
6.5 KiB
Groff
.\" Copyright 1995 James R. Van Zandt <jrv@vanzandt.mv.com>
|
|
.\"
|
|
.\" %%%LICENSE_START(VERBATIM)
|
|
.\" 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.\" manual page may be incorrect or out-of-date.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.
|
|
.\" %%%LICENSE_END
|
|
.\"
|
|
.\" Changed Tue Sep 19 01:49:29 1995, aeb: moved from man2 to man3
|
|
.\" added ref to /etc/utmp, added BUGS section, etc.
|
|
.\" modified 2003 Walter Harms, aeb - added getlogin_r, note on stdin use
|
|
.TH GETLOGIN 3 2019-03-06 "GNU" "Linux Programmer's Manual"
|
|
.SH NAME
|
|
getlogin, getlogin_r, cuserid \- get username
|
|
.SH SYNOPSIS
|
|
.B #include <unistd.h>
|
|
.PP
|
|
.B "char *getlogin(void);"
|
|
.br
|
|
.BI "int getlogin_r(char *" buf ", size_t " bufsize );
|
|
.PP
|
|
.B #include <stdio.h>
|
|
.PP
|
|
.BI "char *cuserid(char *" string );
|
|
.PP
|
|
.RS -4
|
|
Feature Test Macro Requirements for glibc (see
|
|
.BR feature_test_macros (7)):
|
|
.RE
|
|
.PP
|
|
.BR getlogin_r ():
|
|
.\" Deprecated: _REENTRANT ||
|
|
_POSIX_C_SOURCE\ >=\ 199506L
|
|
.PP
|
|
.BR cuserid ():
|
|
.nf
|
|
Since glibc 2.24:
|
|
(_XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
|
|
|| _GNU_SOURCE
|
|
Up to and including glibc 2.23:
|
|
_XOPEN_SOURCE
|
|
.fi
|
|
.SH DESCRIPTION
|
|
.BR getlogin ()
|
|
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
|
|
.BR cuserid ().
|
|
.PP
|
|
.BR getlogin_r ()
|
|
returns this same username in the array
|
|
.I buf
|
|
of size
|
|
.IR bufsize .
|
|
.PP
|
|
.BR cuserid ()
|
|
returns a pointer to a string containing a username
|
|
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
|
|
.BR getlogin ().
|
|
.PP
|
|
The macro \fBL_cuserid\fP is an integer constant that indicates how
|
|
long an array you might need to store a username.
|
|
\fBL_cuserid\fP is declared in \fI<stdio.h>\fP.
|
|
.PP
|
|
These functions let your program identify positively the user who is
|
|
running
|
|
.RB ( cuserid ())
|
|
or the user who logged in this session
|
|
.RB ( getlogin ()).
|
|
(These can differ when set-user-ID programs are involved.)
|
|
.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 RETURN VALUE
|
|
.BR getlogin ()
|
|
returns a pointer to the username when successful,
|
|
and NULL on failure, with
|
|
.I errno
|
|
set to indicate the cause of the error.
|
|
.BR getlogin_r ()
|
|
returns 0 when successful, and nonzero on failure.
|
|
.SH ERRORS
|
|
POSIX specifies:
|
|
.TP
|
|
.B EMFILE
|
|
The per-process limit on the number of open file descriptors has been reached.
|
|
.TP
|
|
.B ENFILE
|
|
The system-wide limit on the total number of open files has been reached.
|
|
.TP
|
|
.B ENXIO
|
|
The calling process has no controlling terminal.
|
|
.TP
|
|
.B ERANGE
|
|
(getlogin_r)
|
|
The length of the username, including the terminating null byte (\(aq\e0\(aq),
|
|
is larger than
|
|
.IR bufsize .
|
|
.PP
|
|
Linux/glibc also has:
|
|
.TP
|
|
.B ENOENT
|
|
There was no corresponding entry in the utmp-file.
|
|
.TP
|
|
.B ENOMEM
|
|
Insufficient memory to allocate passwd structure.
|
|
.TP
|
|
.B ENOTTY
|
|
Standard input didn't refer to a terminal.
|
|
(See BUGS.)
|
|
.SH FILES
|
|
.TP
|
|
\fI/etc/passwd\fP
|
|
password database file
|
|
.TP
|
|
\fI/var/run/utmp\fP
|
|
(traditionally \fI/etc/utmp\fP;
|
|
some libc versions used \fI/var/adm/utmp\fP)
|
|
.SH ATTRIBUTES
|
|
For an explanation of the terms used in this section, see
|
|
.BR attributes (7).
|
|
.TS
|
|
allbox;
|
|
lb lb lb
|
|
l l l.
|
|
Interface Attribute Value
|
|
T{
|
|
.BR getlogin ()
|
|
T} Thread safety T{
|
|
MT-Unsafe race:getlogin race:utent
|
|
.br
|
|
sig:ALRM timer locale
|
|
T}
|
|
T{
|
|
.BR getlogin_r ()
|
|
T} Thread safety T{
|
|
MT-Unsafe race:utent sig:ALRM timer
|
|
.br
|
|
locale
|
|
T}
|
|
T{
|
|
.BR cuserid ()
|
|
T} Thread safety MT-Unsafe race:cuserid/!string locale
|
|
.TE
|
|
.sp 1
|
|
In the above table,
|
|
.I utent
|
|
in
|
|
.I race:utent
|
|
signifies that if any of the functions
|
|
.BR setutent (3),
|
|
.BR getutent (3),
|
|
or
|
|
.BR endutent (3)
|
|
are used in parallel in different threads of a program,
|
|
then data races could occur.
|
|
.BR getlogin ()
|
|
and
|
|
.BR getlogin_r ()
|
|
call those functions,
|
|
so we use race:utent to remind users.
|
|
.SH CONFORMING TO
|
|
.BR getlogin ()
|
|
and
|
|
.BR getlogin_r ():
|
|
POSIX.1-2001, POSIX.1-2008.
|
|
.PP
|
|
System V has a
|
|
.BR cuserid ()
|
|
function which uses the real
|
|
user ID rather than the effective user ID.
|
|
The
|
|
.BR cuserid ()
|
|
function
|
|
was included in the 1988 version of POSIX,
|
|
but removed from the 1990 version.
|
|
It was present in SUSv2, but removed in POSIX.1-2001.
|
|
.PP
|
|
OpenBSD has
|
|
.BR getlogin ()
|
|
and
|
|
.BR setlogin (),
|
|
and a username
|
|
associated with a session, even if it has no controlling terminal.
|
|
.SH BUGS
|
|
Unfortunately, it is often rather easy to fool
|
|
.BR 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 terminal
|
|
of our program need not be the user who started it.
|
|
Avoid
|
|
.BR getlogin ()
|
|
for security-related purposes.
|
|
.PP
|
|
Note that glibc does not follow the POSIX specification and uses
|
|
.I stdin
|
|
instead of
|
|
.IR /dev/tty .
|
|
A bug.
|
|
(Other recent systems, like SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8
|
|
all return the login name also when
|
|
.I stdin
|
|
is redirected.)
|
|
.PP
|
|
Nobody knows precisely what
|
|
.BR cuserid ()
|
|
does; avoid it in portable programs.
|
|
Or avoid it altogether: use
|
|
.I getpwuid(geteuid())
|
|
instead, if that is
|
|
what you meant.
|
|
.B Do not use
|
|
.BR cuserid ().
|
|
.SH SEE ALSO
|
|
.BR logname (1),
|
|
.BR geteuid (2),
|
|
.BR getuid (2),
|
|
.BR utmp (5)
|