get/set login name
() routine returns the login name of
the user associated with the current session, as previously set by
(). 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
() routine is a reentrant version of
(). It is functionally identical to
() except that the caller must provide a
, in which to store the user's
login name and a corresponding length parameter,
, that specifies the size of the
buffer. The buffer should be large enough to store the login name and a
trailing NUL (typically
() 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 invoked).
: There is only one login name per session.
It is CRITICALLY
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 ONLY
way to do this is via the
() function. The
() function calls
() which is an ideal way of detaching from
a controlling terminal and forking into the background.
In particular, neither
sufficient to create a new session.
Once a parent process has called setsid
(), it is
acceptable for some child of that process to then call
(), even though it is not the session
leader. Beware, however, that ALL
the session will change their login name at the same time, even the parent.
This is different from traditional UNIX
inheritance and as such can be counter-intuitive.
Since the setlogin
() 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
. If a call to
() succeeds, a value of 0 is returned,
else the error number is returned. If a call to
() succeeds, a value of 0 is returned. If
() fails, a value of -1 is returned and
an error code is placed in the global location
() will succeed unless:
- The name parameter points
to an invalid address.
In addition, getlogin_r
() may return the following
- The value of namelen is
not large enough to store the user's login name and a trailing NUL.
() may return the following errors:
- The name parameter pointed
to a string that was too long. Login names are limited to
LOGIN_NAME_MAX-1 characters, currently
- The caller tried to set the login name and was not the
() functions conform to
IEEE Std 1003.1-2008
() function 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
() could not be trusted without checking
the user ID. Portable programs should probably still make this check.