GETLOGIN(2) BSD Programmer's Manual GETLOGIN(2)NAME
getlogin, getlogin_r, setlogin - get/set login name
SYNOPSIS
#include <unistd.h>
char *
getlogin(void);
int
getlogin_r(char *buf, size_t size);
int
setlogin(const char *name);
DESCRIPTION
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.)
The getlogin_r() function is a reentrant version of the traditional
getlogin() function. Instead of using a static buffer, it places the
name into the supplied buffer buf of the given size, which should be at
least LOGIN_NAME_MAX bytes long.
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-
voked).
RETURN VALUES
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 re-
turns NULL. If a call to getlogin_r() succeeds, it returns 0; otherwise
it returns an error code as described below. 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.
ERRORS
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-
per-user.
[ERANGE] The buffer supplied to getlogin_r() was too small to hold
the login name.
SEE ALSOsetsid(2)BUGS
Login names are limited in length by setlogin(). However, lower limits
are placed on login names elsewhere in the system (UT_NAMESIZE in
<utmp.h>).
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.
HISTORY
The getlogin() function first appeared in 4.4BSD.
The getlogin() and getlogin_r() functions conform to IEEE Std1003.1-1996
(``POSIX'').
4.2 Berkeley Distribution June 9, 1993 2
