getlogin man page on 4.4BSD

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GETLOGIN(2)		    BSD System Calls Manual		   GETLOGIN(2)

     getlogin, setlogin — get/set login name

     #include <unistd.h>

     char *

     setlogin(const char *name);

     The getlogin() routine returns the login name of the user associated with
     the current session, as previously set by setlogin().  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.)

     Setlogin() sets the login name of the user associated with the current
     session to name.  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

     If a call to getlogin() succeeds, it returns a pointer to a null-termi‐
     nated string in a static buffer.  If the name has not been set, it
     returns NULL.  If a call to setlogin() succeeds, a value of 0 is
     returned.	If setlogin() fails, a value of -1 is returned and an error
     code is placed in the global location errno.

     The following errors may be returned by these calls:

     [EFAULT]		The name parameter gave an invalid address.

     [EINVAL]		The name parameter pointed to a string that was too
			long.  Login names are limited to MAXLOGNAME (from
			⟨sys/param.h⟩) characters, currently 12.

     [EPERM]		The caller tried to set the login name and was not the


     Login names are limited in length by setlogin().  However, lower limits
     are placed on login names elsewhere in the system (UT_NAMESIZE in

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

     The getlogin() function first appeared in 4.4BSD.

4.2 Berkeley Distribution	 June 9, 1993	     4.2 Berkeley Distribution

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