man3/getpass.3

.\" Copyright (c) 2000 Andries Brouwer (aeb@cwi.nl)
.\"
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.TH GETPASS 3  2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
getpass \- get a password
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.PP
.BI "char *getpass(const char *" prompt );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR getpass ():
.nf
    Since glibc 2.2.2:
        _XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L)
            || /* Glibc since 2.19: */ _DEFAULT_SOURCE
            || /* Glibc <= 2.19: */ _BSD_SOURCE
    Before glibc 2.2.2:
        none
.fi
.SH DESCRIPTION
This function is obsolete.
Do not use it.
If you want to read input without terminal echoing enabled,
see the description of the
.I ECHO
flag in
.BR termios (3).
.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\e0\(aq).
This buffer may be overwritten by a following call.
On error, the terminal state is restored,
.I errno
is set to indicate the error, 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 ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR getpass ()
T}	Thread safety	MT-Unsafe term
.TE
.hy
.ad
.sp 1
.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.
.
In the GNU C library implementation, 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 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 .
The glibc version 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)