GETLOGIN(3) Linux Programmer's Manual GETLOGIN(3)
getlogin, getlogin_r, cuserid - get username
int getlogin_r(char *buf, size_t bufsize);
char *cuserid(char *string);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getlogin_r(): _POSIX_C_SOURCE >= 199506L
Since glibc 2.24:
(_XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
Up to and including glibc 2.23:
getlogin() returns a pointer to a string containing the name of the user logged in on the controlling terminal of the process, or a null
pointer if this information cannot be determined. The string is statically allocated and might be overwritten on subsequent calls to this
function or to cuserid().
getlogin_r() returns this same username in the array buf of size bufsize.
cuserid() returns a pointer to a string containing a username associated with the effective user ID of the process. If string is not a
null pointer, it should be an array that can hold at least L_cuserid characters; the string is returned in this array. Otherwise, a
pointer to a string in a static area is returned. This string is statically allocated and might be overwritten on subsequent calls to this
function or to getlogin().
The macro L_cuserid is an integer constant that indicates how long an array you might need to store a username. L_cuserid is declared in
These functions let your program identify positively the user who is running (cuserid()) or the user who logged in this session (getlo-
gin()). (These can differ when set-user-ID programs are involved.)
For most purposes, it is more useful to use the environment variable LOGNAME to find out who the user is. This is more flexible precisely
because the user can set LOGNAME arbitrarily.
getlogin() returns a pointer to the username when successful, and NULL on failure, with errno set to indicate the cause of the error. get-
login_r() returns 0 when successful, and nonzero on failure.
EMFILE The per-process limit on the number of open file descriptors has been reached.
ENFILE The system-wide limit on the total number of open files has been reached.
ENXIO The calling process has no controlling terminal.
ERANGE (getlogin_r) The length of the username, including the terminating null byte ('