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GETLOGIN(2) | System Calls Manual | GETLOGIN(2) |
NAME¶
getlogin
,
getlogin_r
,
setlogin
—
get/set login name
LIBRARY¶
Standard C Library (libc, -lc)SYNOPSIS¶
#include
<unistd.h>
char *
getlogin
(void);
#include
<sys/param.h>
int
getlogin_r
(char
*name, int
len);
int
setlogin
(const
char *name);
DESCRIPTION¶
Thegetlogin
() 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
() except 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.
The setlogin
() system call sets the login
name of the user associated with the current session to
name. This system 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. Making a setsid
() system
call is the ONLY way to do this. The
daemon(3) function calls
setsid
() which is an ideal way of detaching
from a controlling terminal and forking into the background.
In particular, doing a
ioctl
(ttyfd,
TIOCNOTTY,
...) or
setpgrp
(...)
is NOT sufficient.
Once a parent process does a setsid
() system
call, it is acceptable for some child of that process to then do a
setlogin
() even though it is not the
session leader, but beware that ALL processes in the session will change their
login name at the same time, even the parent.
This is not the same as the traditional UNIX behavior of inheriting privilege.
Since the setlogin
() system call 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.
RETURN VALUES¶
If a call togetlogin
() succeeds, it returns
a pointer to a null-terminated string in a static buffer, or
NULL
if the name has not been set. The
getlogin_r
() function returns zero if
successful, or the error number upon failure.
The
setlogin
() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate
the error.
ERRORS¶
The following errors may be returned by these calls:- [
EFAULT
] - The name argument gave an invalid address.
- [
EINVAL
] - The name argument pointed to a string
that was too long. Login names are limited to
MAXLOGNAME
(from<sys/param.h>
) characters, currently 17 including null. - [
EPERM
] - The caller tried to set the login name and was not the super-user.
- [
ERANGE
] - The size of the buffer is smaller than the result to be returned.
SEE ALSO¶
setsid(2), daemon(3)STANDARDS¶
Thegetlogin
() system call and the
getlogin_r
() function conform to
ISO/IEC 9945-1:1996
(“POSIX.1”).
HISTORY¶
Thegetlogin
() system call first appeared in
4.4BSD. The return value of
getlogin_r
() was changed from earlier
versions of FreeBSD to be conformant with
ISO/IEC 9945-1:1996
(“POSIX.1”).
BUGS¶
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.June 9, 1993 | Debian |