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GETPASS(3) Linux Programmer's Manual GETPASS(3)

NAME

getpass - get a password

SYNOPSIS

#include <unistd.h>

char *getpass( const char *prompt);


Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getpass():

_BSD_SOURCE ||


    (_XOPEN_SOURCE >= 500 ||


        _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&


    !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
none

DESCRIPTION

This function is obsolete. Do not use it. If you want to read input without terminal echoing enabled, see the description of the ECHO flag in termios(3).

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.

RETURN VALUE

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.

ERRORS

The function may fail if

The process does not have a controlling terminal.

FILES

/dev/tty

ATTRIBUTES

Multithreading (see pthreads(7))

The getpass() function is not thread-safe.

CONFORMING TO

Present in SUSv2, but marked LEGACY. Removed in POSIX.1-2001.

NOTES

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, SIGTSTP) 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).

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.

SEE ALSO

crypt(3)

COLOPHON

This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

2013-06-21 Linux