GETLOGIN(2) | System Calls Manual | GETLOGIN(2) |
getlogin
, getlogin_r
,
setlogin
—
#include <unistd.h>
char *
getlogin
(void);
int
getlogin_r
(char
*name, size_t
len);
int
setlogin
(const
char *name);
getlogin
() 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.)
The getlogin_r
() function provides the
same service as getlogin
(), however the caller must
provide the buffer name with length
len bytes to hold the result. The buffer should be at
least MAXLOGNAME
bytes in length.
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 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).
NOTE: There is only one login name per session.
It is CRITICALLY important to ensure that
setlogin
() 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
setsid
() function. The
daemon
() function calls
setsid
() which is an ideal way of detaching from a
controlling terminal and forking into the background.
In particular, neither
ioctl
(ttyfd,
TIOCNOTTY, ...) nor
setpgid
(...) is 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
setlogin
(), even though it is not the session
leader. Beware, however, that ALL processes in the session
will change their login name at the same time, even the parent.
This is different from traditional UNIX privilege 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.
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 getlogin_r
() function returns zero if
successful, or the error number upon failure.
EFAULT
]EINVAL
]MAXLOGNAME
(from
⟨sys/param.h⟩) characters, currently
16.EPERM
]ERANGE
]getlogin
() and getlogin_r
()
functions conform to ISO/IEC 9945-1:1996
(“POSIX.1”).
getlogin
() function first appeared in
4.4BSD.
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 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
this check.
January 6, 2009 | NetBSD 9.2 |