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man pages section 3: Basic Library Functions

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Updated: Friday, August 13, 2021



getlogin, getlogin_r - get login name


#include <unistd.h>

char *getlogin(void);
int getlogin_r(char *name, size_t namesize);
POSIX.1c Draft 6
       cc [ flag ... ] file... –D__USE_DRAFT6_PROTOTYPES__ [ library ... ]
char *getlogin_r(char *name, int namelen);


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 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 size namesize to store the result. The name buffer must be at least _POSIX_LOGIN_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. Otherwise 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.


The getlogin_r() function will fail if:


The size of the buffer is smaller than the result to be returned.


And entry for the current user was not found in the /var/adm/utmpx file.

The getlogin() and getlogin_r() functions may fail if:


There are {OPEN_MAX} file descriptors currently open in the calling process.


The maximum allowable number of files is currently open in the system.


The calling process has no controlling terminal.


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.



user access and administration information


See attributes(7) for descriptions of the following attributes:

Interface Stability
See below.

See Also

geteuid(2), getuid(2), getpwnam(3C), cuserid(3C), getgrnam(3C), getpwuid(3C), utmpx(5), attributes(7), standards(7)


The getlogin() function is safe to use in multithreaded applications, but is discouraged. The getlogin_r() function should be used instead.

Prior to Oracle Solaris 11.4, the default compilation environment provided 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 obsolete Draft-6 interfaces to continue to be compiled and run, the __USE_DRAFT6_PROTOTYPES__ macro must be defined:


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.