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)