getpass(3) -- Linux man page



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This function is obsolete.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 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
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 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).  






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.