— get/set login name
routine returns the login name of the user associated with the current
session, as previously set by
setlogin(). The name
is normally 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.)
routine is a reentrant version of
getlogin(). It is
functionally identical to
getlogin() except that the
caller must provide a buffer, name, in which to store
the user's login name and a corresponding length parameter,
namelen, that specifies the size of the buffer. The
buffer should be large enough to store the login name and a trailing NUL
sets the login name of the user associated with the current session to
name. This call is restricted to the superuser, and is
normally 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
NOTE: There is only one login name per session.
important to ensure that
is only ever called after the process has taken adequate steps to ensure
that it is detached from its parent's session. The
to do this is via the
setsid() function. The
setsid() which is an ideal way of
detaching from a controlling terminal and forking into the background.
In particular, neither
TIOCNOTTY, ...) nor
is sufficient to create a new session.
Once a parent process has called
is acceptable for some child of that process to then call
setlogin(), even though it is not the session
leader. Beware, however, that
processes in the session will change their login name at the same time, even
This is different from traditional UNIX privilege inheritance and as such can be counter-intuitive.
routine is restricted to the super-user, it is assumed that (like all other
privileged programs) the programmer has taken adequate precautions to
prevent security violations.
If a call to
getlogin() succeeds, it
returns a pointer to a NUL-terminated string in a static buffer. If the name
has not been set, it returns
NULL. If a call to
getlogin_r() succeeds, a value of 0 is returned,
else the error number is returned. 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.
setlogin() will succeed unless:
- The name parameter points to an invalid address.
getlogin_r() may return the
- The value of namelen is not large enough to store the user's login name and a trailing NUL.
setlogin() may return the following
- The name parameter pointed to a string that was too
long. Login names are limited to
LOGIN_NAME_MAX-1characters, currently 31.
- The caller tried to set the login name and was not the superuser.
getlogin_r() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
getlogin() function which used
utmp(5) first appeared in Version 7 AT&T
setlogin() system calls first appeared 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 controlling 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