GETPASS(3) Linux Programmer's Manual GETPASS(3)
getpass - get a password
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This function is obsolete.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 termi-
nal 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 NUL. This buffer may
be overwritten by a following call. On error, the terminal state is restored, errno is
set appropriately, and NULL is returned.
The function may fail if
ENXIO The process does not have a controlling terminal.
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 cor-
responding characters (usually control-C, control-\, control-Z and control-Y) are trans-
mitted 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
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).
A getpass function appeared in Version 7 AT&T UNIX.
The calling process should zero the password as soon as possible to avoid leaving the
cleartext password visible in the process's address space.
Linux Manpage 2000-12-05 GETPASS(3)