GETLOGIN(2) BSD Programmer's Manual GETLOGIN(2)
getlogin, setlogin - get/set login name
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 in-
If a call to getlogin() 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 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 su-
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.
Portable programs should probably still make this check.
The getlogin() function first appeared in 4.4BSD.
4.2 Berkeley Distribution June 9, 1993 1