4.4BSD/usr/share/man/cat2/getlogin.0

GETLOGIN(2)                 BSD Programmer's Manual                GETLOGIN(2)

NNAAMMEE
     ggeettllooggiinn, sseettllooggiinn - get/set login name

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<uunniissttdd..hh>>

     _c_h_a_r _*
     ggeettllooggiinn(_v_o_i_d);

     _i_n_t
     sseettllooggiinn(_c_o_n_s_t _c_h_a_r _*_n_a_m_e);

DDEESSCCRRIIPPTTIIOONN
     The ggeettllooggiinn() routine returns the login name of the user associated with
     the current session, as previously set by sseettllooggiinn().  The name is nor-
     mally associated with a login shell at the time a session is created, and
     is inherited by all processes descended from the login shell.  (This is
     true even if some of those processes assume another user ID, for example
     when su(1) is used.)

     SSeettllooggiinn() sets the login name of the user associated with the current
     session to _n_a_m_e. This call is restricted to the super-user, and is nor-
     mally used only when a new session is being created on behalf of the
     named user (for example, at login time, or when a remote shell is in-
     voked).

RREETTUURRNN VVAALLUUEESS
     If a call to ggeettllooggiinn() succeeds, it returns a pointer to a null-
     terminated string in a static buffer.  If the name has not been set, it
     returns NULL. If a call to sseettllooggiinn() succeeds, a value of 0 is returned.
     If sseettllooggiinn() fails, a value of -1 is returned and an error code is
     placed in the global location _e_r_r_n_o.

EERRRROORRSS
     The following errors may be returned by these calls:

     [EFAULT]      The _n_a_m_e parameter gave an invalid address.

     [EINVAL]      The _n_a_m_e parameter pointed to a string that was too long.
                   Login names are limited to MAXLOGNAME (from <_s_y_s_/_p_a_r_a_m_._h>)
                   characters, currently 12.

     [EPERM]       The caller tried to set the login name and was not the su-
                   per-user.

SSEEEE AALLSSOO
     setsid(2)

BBUUGGSS
     Login names are limited in length by sseettllooggiinn().  However, lower limits
     are placed on login names elsewhere in the system (UT_NAMESIZE in
     <_u_t_m_p_._h>).

     In earlier versions of the system, ggeettllooggiinn() failed unless the process
     was associated with a login terminal.  The current implementation (using
     sseettllooggiinn()) allows getlogin to succeed even when the process has no con-
     trolling terminal.  In earlier versions of the system, the value returned
     by ggeettllooggiinn() could not be trusted without checking the user ID.
     Portable programs should probably still make this check.

HHIISSTTOORRYY
     The ggeettllooggiinn() function first appeared in 4.4BSD.

4.2 Berkeley Distribution        June 9, 1993                                1