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Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)getlogin.2 8.1 (Berkeley) 6/9/93 .\" $FreeBSD: src/lib/libc/sys/getlogin.2,v 1.14.2.6 2001/12/14 18:34:00 ru Exp $ .\" .Dd December 1, 2019 .Dt GETLOGIN 2 .Os .Sh NAME .Nm getlogin , .Nm getlogin_r , .Nm setlogin .Nd get/set login name .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In unistd.h .Ft char * .Fn getlogin void .In sys/param.h .Ft int .Fn getlogin_r "char *name" "size_t len" .Ft int .Fn setlogin "const char *name" .Sh DESCRIPTION The .Fn getlogin routine returns the login name of the user associated with the current session, as previously set by .Fn 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 .Xr su 1 is used). .Pp .Fn getlogin_r provides the same service as .Fn getlogin except the caller must provide the buffer .Fa name with length .Fa len bytes to hold the result. The buffer should be at least .Dv MAXLOGNAME bytes in length. .Pp .Fn Setlogin sets the login name of the user associated with the current session to .Fa 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). .Pp .Em NOTE : There is only one login name per session. .Pp It is .Em CRITICALLY important to ensure that .Fn 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 .Fn setsid system call is the .Em ONLY way to do this. The .Fn daemon library call calls .Fn setsid which is an ideal way of detaching from a controlling terminal and forking into the background. .Pp In particular, doing a .Fn ioctl ttyfd TIOCNOTTY ...\& or .Fn setpgrp ...\& is .Em NOT sufficient. .Pp Once a parent process does a .Fn setsid call, it is acceptable for some child of that process to then do a .Fn 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. .Pp This is not the same as the traditional .Ux behavior of inheriting privilege. .Pp Since the .Fn 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. .Sh RETURN VALUES If a call to .Fn getlogin succeeds, it returns a pointer to a null-terminated string in a static buffer, or .Dv NULL if the name has not been set. .Fn getlogin_r returns zero if successful, or the error number upon failure. .Pp .Rv -std setlogin .Sh ERRORS The following errors may be returned by these calls: .Bl -tag -width Er .It Bq Er EFAULT The .Fa name parameter gave an invalid address. .It Bq Er EINVAL The .Fa name parameter pointed to a string that was too long. Login names are limited to .Dv MAXLOGNAME (from .In sys/param.h ) characters, currently 17 including null. .It Bq Er EPERM The caller tried to set the login name and was not the super-user. .It Bq Er ERANGE The size of the buffer is smaller than the result to be returned. .El .Sh SEE ALSO .Xr setsid 2 , .Xr daemon 3 .Sh STANDARDS .Fn getlogin and .Fn getlogin_r conform to .St -p1003.1-96 . .Sh HISTORY The .Fn getlogin function first appeared in .Bx 4.4 . The return value of .Fn getlogin_r was changed from earlier versions of .Fx to be conformant with .St -p1003.1-96 . .Sh BUGS In earlier versions of the system, .Fn getlogin failed unless the process was associated with a login terminal. The current implementation (using .Fn setlogin ) allows getlogin to succeed even when the process has no controlling terminal. In earlier versions of the system, the value returned by .Fn getlogin could not be trusted without checking the user ID. Portable programs should probably still make this check.