GETLOGIN(3C) Standard C Library Functions GETLOGIN(3C)
NAME
getlogin, getlogin_r - get login name
SYNOPSIS
#include <unistd.h>
char *getlogin(
void);
char *getlogin_r(
char *name,
int namelen);
Standard conforming
cc [
flag ... ]
file...
-D_POSIX_PTHREAD_SEMANTICS [
library ... ]
int getlogin_r(
char *name,
size_t namesize);
DESCRIPTION
The
getlogin() function returns a pointer to the login name as found in
/var/adm/utmpx. It can be used in conjunction with
getpwnam(3C) to locate
the correct password file entry when the same user
ID is shared by
several login names.
The login name plus the terminating null byte can be up to 33 characters
in length. Newly-compiled programs should use the
LOGIN_NAME_MAX symbol,
defined in <
limits.h>, to size the buffer. Older programs that call
getlogin() expect only the legacy 9-character length. These
automatically link to a version of the
getlogin() functions that
truncates longer login names. It's also possible to compile new programs
that link to truncating versions of these functions by defining
__USE_LEGACY_LOGNAME__ in the compile environment.
Some older programs will correctly handle long login names returned by
the
getlogin() function. For this case, the user compatibility library
/usr/lib/getloginx.so.1 redirects to a version of the
getlogin() function
that returns the long name. This library should be added to such an
application at runtime using
LD_PRELOAD.
If
getlogin() 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
cuserid(3C), or to call
getlogin() and if it fails to call
getpwuid(3C).
The
getlogin_r() function has the same functionality as
getlogin() except
that the caller must supply a buffer
name with length
namelen to store
the result. The
name buffer should be at least
LOGIN_NAME_MAX bytes in
size (defined in <
limits.h>). The POSIX version (see
standards(7)) of
getlogin_r() takes a
namesize parameter of type
size_t. If the size of
the supplied buffer is less than the size of
LOGIN_NAME_MAX and the name,
including the null terminator, does not fit inside the buffer, than an
error will be generated. Otherwise, the buffer
name will be updated with
the login name.
RETURN VALUES
Upon successful completion,
getlogin() 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
errno to indicate the error.
The standard-conforming
getlogin_r() returns
0 if successful, or the
error number upon failure.
ERRORS
The
getlogin_r() function will fail if:
ERANGE The size of the buffer is smaller than the result to be
returned.
EINVAL And entry for the current user was not found in the
/var/adm/utmpx file.
The
getlogin() and
getlogin_r() functions may fail if:
EMFILE There are {
OPEN_MAX} file descriptors currently open in the
calling process.
ENFILE The maximum allowable number of files is currently open in the
system.
ENXIO The calling process has no controlling terminal.
The
getlogin_r() function may fail if:
ERANGE The size of the buffer is smaller than the result to be
returned.
USAGE
The return value of
getlogin() points to thread-specific data whose
content is overwritten on each call by the same thread.
Three names associated with the current process can be determined:
getpwuid(geteuid()) returns the name associated with the effective user
ID of the process;
getlogin() returns the name associated with the
current login activity; and
getpwuid(getuid()) returns the name
associated with the real user ID of the process.
FILES
/var/adm/utmpx user access and administration information
/usr/lib/getloginx.so.1 A compatibility library that returns long login names
to older applications.
/usr/lib/64/getloginx.so.1 A 64-bit compatibility library to return long login
names.
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | See below. |
+--------------------+-----------------+
SEE ALSO
geteuid(2),
getuid(2),
cuserid(3C),
getgrnam(3C),
getpwnam(3C),
getpwuid(3C),
utmpx(5),
attributes(7),
standards(7)NOTES
When compiling multithreaded programs, see
Intro(3).
The
getlogin() function is safe to use in multithreaded applications, but
is discouraged. The
getlogin_r() function should be used instead.
Solaris 2.4 and earlier releases provided a
getlogin_r() as specified in
POSIX.1c Draft 6. The final POSIX.1c standard changed the interface as
described above. Support for the Draft 6 interface is provided for
compatibility only and may not be supported in future releases. New
applications and libraries should use the standard-conforming interface.
March 15, 2014
GETLOGIN(3C)