GETPASS(3)

NAME
getpass - get a password

LIBRARY
libc

SYNOPSIS
#include <unistd.h>
char *
getpass(const char *prompt);
char *
getpass_r(const char *prompt, char *buf, size_t buflen);
char *
getpassfd(const char *prompt, char *buf, size_t buflen, int *fd, int flags, int timeout);

DESCRIPTION
The getpass() function displays a prompt to, and reads in a password from, /dev/tty. If this file is not accessible, getpass() displays the prompt on the standard error output and reads from the standard input.

The password may be up to sysconf(3) _SC_PASS_MAX characters in length. Any additional characters and the terminating newline character are discarded.

getpass() turns off character echoing while reading the password.

getpass_r() is similar to getpass() only it puts its result in buf for up to buflen characters. If the buf argument is NULL, then a buffer will be dynamically allocated.

The getpassfd() function allows one to specify the three file descriptors corresponding to stdin, stdout, and stderr in the fd argument, or if fd is NULL, getpassfd() first attempts to open /dev/tty and if that fails, defaults to STDIN_FILENO for input and STDERR_FILENO for output.

The behavior of getpassfd() is controlled by the flags argument:

GETPASS_NEED_TTY
    Fail if we are unable to set the tty modes like we want.

GETPASS_FAIL_EOF
    Fail if we get the end-of-file character instead of returning the result so far.

GETPASS_BUF_LIMIT
    Beep when the buffer limit is reached, instead of silently absorbing it.

GETPASS_NO_SIGNAL
    Don't make ttychars send signals.

GETPASS_NO_BEEP
    Don't beep if we erase past the beginning of the buffer or we try to enter past the end.

GETPASS_ECHO_STAR
    Echo a ‘*’ for each character entered.

GETPASS_ECHO
    Echo characters as they are typed.

GETPASS_ECHO_NL
    Echoes a newline if successful.

GETPASS_7BIT
    Mask the high bit for each entered character.

GETPASS_FORCE_LOWER
    Lowercase each entered character.

GETPASS_FORCE_UPPER
    Uppercase each entered character.

Finally if the timeout argument is non zero, getpassfd() will wait for timeout seconds for input after each character before returning an error, instead of waiting forever.

RETURN VALUES
The getpass() function returns a pointer to the NUL terminated password, or an empty string on error. The getpass_r() and getpassfd() functions return a pointer to the NUL terminated password, or NULL on error.

FILES
/dev/tty

SEE ALSO
crypt(3)

STANDARDS
The getpass() function appeared in susv2, but it was already marked as legacy. The function was removed in the p1003.1-2001 standard.

HISTORY
A getpass() function appeared in AT&T UNIX. The getpass_r() and getpassfd() functions appeared in NetBSD 7.0.

BUGS
The getpass() function leaves its result in an internal static object and returns a pointer to that object. Subsequent calls to getpass() will modify the same object.

SECURITY CONSIDERATIONS
The calling process should zero the password as soon as possible to avoid leaving the cleartext password visible in the process's address space.

Historically getpass accepted and returned a password if it could not modify the terminal settings to turn echo off (or if the input was not a terminal). In this implementation, only terminal input is accepted.