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getlogin(3c)
getlogin(3C) Standard C Library Functions getlogin(3C)
NAME
getlogin, getlogin_r - get login name
SYNOPSIS
#include <unistd.h>
char *getlogin(void);
int getlogin_r(char *name, size_t namesize);
POSIX.1c Draft 6
#define __USE_DRAFT6_PROTOTYPES__
#include <grp.h>
char *getlogin_r(char *name, int namelen);
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 lo‐
cate 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() ex‐
cept that the caller must supply a buffer name with size namesize to
store the result. The name buffer must be at least _POSIX_LO‐
GIN_NAME_MAX bytes in size (defined in <limits.h>).
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. Other‐
wise it returns a null pointer and sets errno to indicate the error.
The getlogin_r() function returns 0 if successful, or the error number
upon failure. It does not set errno.
ERRORS
The getlogin_r() function will fail if:
ERANGE The size of the buffer is smaller than the result to be re‐
turned.
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.
USAGE
The return value of getlogin() points to thread-specific data whose
content is overwritten on each call by the same thread, and which must
not be referenced after the termination of the thread which called get‐
login().
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(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSee below. _
StandardSee standards(7).
The getlogin() function is safe to use in multithreaded applications,
but is discouraged. The getlogin_r() function should be used instead.
SEE ALSO
geteuid(2), getuid(2), getpwnam(3C), cuserid(3C), getgrnam(3C),
getpwuid(3C), utmpx(5), attributes(7), standards(7)
NOTES
Prior to Oracle Solaris 11.4, the default compilation environment pro‐
vided a definition of the getlogin_r() function as specified in
POSIX.1c Draft 6. The final POSIX.1c standard changed the interface for
getlogin_r(). To allow applications that were written to use the obso‐
lete Draft-6 interfaces to continue to be compiled and run, the
__USE_DRAFT6_PROTOTYPES__ macro must be defined:
cc -D__USE_DRAFT6_PROTOTYPES__ ...
Support for the Draft-6 interfaces is provided for source compatibility
only and might not be supported in future releases. Old applications
should be converted to use the standard definitions.
HISTORY
Oracle Solaris 11.4.0 made the standards-conforming version of getlo‐
gin_r() the default definition, removing the requirement to define
_POSIX_C_SOURCE or _POSIX_PTHREAD_SEMANTICS before including the
header, and adding the requirement to define __USE_DRAFT6_PROTOTYPES__
to expose the Draft 6 version instead. Solaris 11.4.0 also removed the
requirement to define _REENTRANT before including the header to expose
the _r function variant.
In Solaris 2.5, the final POSIX.1c standard version of getlogin_r() was
added, but only exposed in the header if _POSIX_C_SOURCE was set to
199506 or higher, or _POSIX_PTHREAD_SEMANTICS was defined, before in‐
cluding the <unistd.h> header.
Solaris 2.3 added a definition of the getlogin_r() function as speci‐
fied in POSIX.1c Draft 6. This definition was only exposed in the
header if _REENTRANT was defined before including the <unistd.h>
header.
The getlogin() function has been included in all Sun and Oracle re‐
leases of Solaris.
Oracle Solaris 11.4 27 Aug 2025 getlogin(3C)