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.TH GETLOGIN 3C "Mar 15, 2014"
.SH NAME
getlogin, getlogin_r \- get login name
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>

\fBchar *\fR\fBgetlogin\fR(\fBvoid\fR);
.fi

.LP
.nf
\fBint\fR \fBgetlogin_r\fR(\fBchar *\fR\fIname\fR, \fBsize_t\fR \fInamesize\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBgetlogin()\fR function returns a pointer to the login name as found in
\fB/var/log/utmpx\fR. It can be used in conjunction with \fBgetpwnam\fR(3C) to
locate the correct password file entry when the same user \fBID\fR is shared by
several login names.
.sp
.LP
The login name plus the terminating null byte can be up to 33 characters
in length.
Newly-compiled programs should use the \fBLOGIN_NAME_MAX\fR symbol,
defined in <\fBlimits.h\fR>, to size the buffer.
.sp
.LP
If \fBgetlogin()\fR is called within a process that is not attached to a
terminal, it returns a null pointer. The correct procedure for determining the
login name is to call \fBcuserid\fR(3C), or to call \fBgetlogin()\fR and if it
fails to call \fBgetpwuid\fR(3C).
.sp
.LP
The \fBgetlogin_r()\fR function has the same functionality as \fBgetlogin()\fR
except that the caller must supply a buffer \fIname\fR with length \fInamesize\fR
to store the result.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fBgetlogin()\fR returns a pointer to the login
name or a null pointer if the user's login name cannot be found.  Otherwise it
returns a null pointer and sets \fBerrno\fR to indicate the error.
.sp
.LP
\fBgetlogin_r()\fR returns \fB0\fR if successful, or the error number upon
failure.
.SH ERRORS
.sp
.LP
The \fBgetlogin_r()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBERANGE\fR\fR
.ad
.RS 10n
The size of the buffer is smaller than the result to be returned.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
And entry for the current user was not found in the \fB/var/log/utmpx\fR file.
.RE

.sp
.LP
The \fBgetlogin()\fR and \fBgetlogin_r()\fR functions may fail if:
.sp
.ne 2
.na
\fB\fBEMFILE\fR\fR
.ad
.RS 10n
There are {\fBOPEN_MAX\fR} file descriptors currently open in the calling
process.
.RE

.sp
.ne 2
.na
\fB\fBENFILE\fR\fR
.ad
.RS 10n
The maximum allowable number of files is currently open in the system.
.RE

.sp
.ne 2
.na
\fB\fBENXIO\fR\fR
.ad
.RS 10n
The calling process has no controlling terminal.
.RE

.sp
.LP
The \fBgetlogin_r()\fR function may fail if:
.sp
.ne 2
.na
\fB\fBERANGE\fR\fR
.ad
.RS 10n
The size of the buffer is smaller than the result to be returned.
.RE

.SH USAGE
.sp
.LP
The return value of \fBgetlogin()\fR points to thread-specific data whose
content is overwritten on each call by the same thread.
.sp
.LP
Three names associated with the current process can be determined:
\fBgetpwuid(\fR\fBgeteuid()\fR\fB)\fR returns the name associated with the
effective user ID of the process; \fBgetlogin()\fR returns the name associated
with the current login activity; and \fBgetpwuid(\fR\fBgetuid()\fR\fB)\fR
returns the name associated with the real user ID of the process.
.SH FILES
.sp
.ne 2
.na
\fB\fB/var/log/utmpx\fR\fR
.ad
.RS 18n
user access and administration information
.RE

.sp
.ne 2
.na
\fB\fB/usr/lib/getloginx.so.1\fR\fR
.ad
.RS 18n
A compatibility library that returns long login names to older applications.
.RE

.sp
.ne 2
.na
\fB\fB/usr/lib/64/getloginx.so.1\fR\fR
.ad
.RS 18n
A 64-bit compatibility library to return long login names.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	See below.
.TE

.SH SEE ALSO
.sp
.LP
\fBgeteuid\fR(2), \fBgetuid\fR(2), \fBcuserid\fR(3C), \fBgetgrnam\fR(3C),
\fBgetpwnam\fR(3C), \fBgetpwuid\fR(3C), \fButmpx\fR(4), \fBattributes\fR(5),
\fBstandards\fR(5)
.SH NOTES
.sp
.LP
When compiling multithreaded programs, see \fBIntro\fR(3).
.sp
.LP
The \fBgetlogin()\fR function is safe to use in multithreaded applications, but
is discouraged. The \fBgetlogin_r()\fR function should be used instead.