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.
If getlogin() is called within a process that is not attached to a ter‐
minal, 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 must be at least
_POSIX_LOGIN_NAME_MAX bytes in size (defined in <limits.h>). The POSIX
version (see standards(5)) of getlogin_r() takes a namesize parameter
of type size_t.
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. Oth‐
erwise 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: get‐
pwuid(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
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │See below. │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOgeteuid(2), getuid(2), cuserid(3C), getgrnam(3C), getpwnam(3C), getp‐
wuid(3C), utmpx(4), attributes(5), standards(5)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 inter‐
face.
SunOS 5.10 18 May 2004 getlogin(3C)
