.\" Copyright (c) 2000 Andries Brouwer (aeb@cwi.nl)
.\"
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
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.\"
.TH GETPASS 3  2010-09-20 "Linux" "Linux Programmer's Manual"
.SH NAME
getpass \- get a password
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "char *getpass( const char *" prompt );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR getpass ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.2.2:
.nf
_BSD_SOURCE ||
    (_XOPEN_SOURCE\ >=\ 500 ||
        _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED) &&
    !(_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600)
.TP 4
.fi
Before glibc 2.2.2: none
.PD
.RE
.ad b
.SH DESCRIPTION
This function is obsolete.
Do not use it.
.PP
The
.BR getpass ()
function opens
.I /dev/tty
(the controlling terminal of the process), outputs the string
.IR prompt ,
turns off echoing, reads one line (the "password"),
restores the terminal state and closes
.I /dev/tty
again.
.SH "RETURN VALUE"
The function
.BR getpass ()
returns a pointer to a static buffer containing (the first
.B PASS_MAX
bytes of) the password without the trailing
newline, terminated by a null byte (\(aq\\0\(aq).
This buffer may be overwritten by a following call.
On error, the terminal state is restored,
.I errno
is set appropriately, and NULL is returned.
.SH ERRORS
The function may fail if
.TP
.B ENXIO
The process does not have a controlling terminal.
.SH FILES
.I /dev/tty
.\" .SH HISTORY
.\" A
.\" .BR getpass ()
.\" function appeared in Version 7 AT&T UNIX.
.SH "CONFORMING TO"
Present in SUSv2, but marked LEGACY.
Removed in POSIX.1-2001.
.SH NOTES
For libc4 and libc5, the prompt is not written to
.I /dev/tty
but to
.IR stderr .
Moreover, if
.I /dev/tty
cannot be opened, the password is read from
.IR stdin .
The static buffer has length 128 so that only the first 127
bytes of the password are returned.
While reading the password, signal generation
.RB ( SIGINT ,
.BR SIGQUIT ,
.BR SIGSTOP ,
.BR SIGTSTP )
is disabled and the corresponding characters
(usually control-C, control-\e, control-Z and control-Y)
are transmitted as part of the password.
Since libc 5.4.19 also line editing is disabled, so that also
backspace and the like will be seen as part of the password.
.PP
For glibc2, if
.I /dev/tty
cannot be opened, the prompt is written to
.I stderr
and the password is read from
.IR stdin .
There is no limit on the length of the password.
Line editing is not disabled.
.PP
According to the SUSv2, the value of
.B PASS_MAX
must be defined in
.I <limits.h>
in case it is smaller than 8, and can in any case be obtained using
.IR sysconf(_SC_PASS_MAX) .
However, POSIX.2 withdraws the constants
.B PASS_MAX
and
.BR _SC_PASS_MAX ,
and the function
.BR getpass ().
Libc4 and libc5 have never supported
.B PASS_MAX
or
.BR _SC_PASS_MAX .
Glibc2 accepts
.B _SC_PASS_MAX
and returns
.B BUFSIZ
(e.g., 8192).
.SH BUGS
The calling process should zero the password as soon as possible to avoid
leaving the cleartext password visible in the process's address space.
.SH "SEE ALSO"
.BR crypt (3)
.SH COLOPHON
This page is part of release 3.44 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.