getpass — get a password
#include <unistd.h>
char
*getpass( |
const char * | prompt) ; |
This function is obsolete. Do not use it.
The getpass
() function opens
/dev/tty
(the controlling
terminal of the process), outputs the string prompt
, turns off echoing,
reads one line (the "password"), restores the terminal state
and closes /dev/tty
again.
The function getpass
()
returns a pointer to a static buffer containing the (first
PASS_MAX bytes of) the password without the trailing newline,
terminated by a null byte ('\0'). This buffer may be
overwritten by a following call. On error, the terminal state
is restored, errno
is set
appropriately, and NULL is returned.
For libc4 and libc5, the prompt is not written to
/dev/tty
but to stderr
. Moreover, if /dev/tty
cannot be opened, the password is
read from 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 (SIGINT, SIGQUIT, SIGSTOP, SIGTSTOP) is disabled
and the corresponding characters (usually control-C,
control-\, 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.
For glibc2, if /dev/tty
cannot be opened, the prompt is written to stderr
and the password is read from
stdin
. There is no limit on the
length of the password. Line editing is not disabled.
According to the SUSv2, the value of PASS_MAX must be
defined in <limits.h>
in case it
is smaller than 8, and can in any case be obtained using
sysconf(_SC_PASS_MAX)
.
However, POSIX.2 withdraws the constants PASS_MAX and
_SC_PASS_MAX, and the function getpass
(). Libc4 and libc5 have never
supported PASS_MAX or _SC_PASS_MAX. Glibc2 accepts
_SC_PASS_MAX and returns BUFSIZ (e.g., 8192).
The calling process should zero the password as soon as possible to avoid leaving the cleartext password visible in the process's address space.
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