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28 .\" @(#)getlogin.2 8.1 (Berkeley) 6/9/93
29 .\" $FreeBSD: src/lib/libc/sys/getlogin.2,v 1.14.2.6 2001/12/14 18:34:00 ru Exp $
38 .Nd get/set login name
47 .Fn getlogin_r "char *name" "size_t len"
49 .Fn setlogin "const char *name"
54 returns the login name of the user associated with the current session,
57 The name is normally associated with a login shell
58 at the time a session is created,
59 and is inherited by all processes descended from the login shell.
60 (This is true even if some of those processes assume another user ID,
66 provides the same service as
68 except the caller must provide the buffer
73 to hold the result. The buffer should be at least
78 sets the login name of the user associated with the current session to
80 This call is restricted to the super-user, and
81 is normally used only when a new session is being created on behalf
83 (for example, at login time, or when a remote shell is invoked).
86 There is only one login name per session.
90 important to ensure that
92 is only ever called after the process has taken adequate steps to ensure
93 that it is detached from its parent's session.
102 which is an ideal way of detaching from a controlling terminal and
103 forking into the background.
105 In particular, doing a
106 .Fn ioctl ttyfd TIOCNOTTY ...\&
113 Once a parent process does a
115 call, it is acceptable for some child of that process to then do a
117 even though it is not the session leader, but beware that ALL processes
118 in the session will change their login name at the same time, even the
121 This is not the same as the traditional
123 behavior of inheriting privilege.
127 system call is restricted to the super-user, it is assumed that (like
128 all other privileged programs) the programmer has taken adequate
129 precautions to prevent security violations.
133 succeeds, it returns a pointer to a null-terminated string in a static buffer,
136 if the name has not been set.
138 returns zero if successful, or the error number upon failure.
142 The following errors may be returned by these calls:
153 pointed to a string that was too long.
154 Login names are limited to
158 characters, currently 17 including null.
160 The caller tried to set the login name and was not the super-user.
162 The size of the buffer is smaller than the result to be returned.
176 function first appeared in
180 was changed from earlier versions of
182 to be conformant with
185 In earlier versions of the system,
187 failed unless the process was associated with a login terminal.
188 The current implementation (using
190 allows getlogin to succeed even when the process has no controlling terminal.
191 In earlier versions of the system, the value returned by
193 could not be trusted without checking the user ID.
194 Portable programs should probably still make this check.