getpass (3) - glibc

Split from the chapter glibc: Low-Level Terminal Interface into the per-function layout; see the method page and the glibc ledger for coverage status.

Declaration and gates

#include <unistd.h>

char *getpass(const char *prompt);

The declaration is inside the #if defined __USE_MISC || (defined __USE_XOPEN && !defined __USE_XOPEN2K) block of /usr/include/unistd.h (lines 974-982). The man page’s historical gate: since glibc 2.2.2 _XOPEN_SOURCE && !(_POSIX_C_SOURCE >= 200112L) or _DEFAULT_SOURCE (before 2.19: _BSD_SOURCE) (getpass(3)).

Semantics

getpass opens /dev/tty, prints prompt, turns off terminal echo, reads one line, restores the terminal state and closes /dev/tty again. It returns a pointer to a static buffer holding the first PASS_MAX bytes of the password without the trailing newline, or NULL on error with errno set and the terminal state restored (getpass(3)). In the glibc implementation, when /dev/tty cannot be opened the prompt goes to stderr and the line is read from stdin; there is no length limit and line editing is not disabled (getpass(3) NOTES).

Errors

ENXIO: the process has no controlling terminal (getpass(3) ERRORS).

Gotchas and portability

• Obsolete by design: the man page opens with “This function is obsolete. Do not use it.” and points to the ECHO flag of termios(3) for hand-rolled no-echo input.
• Static return buffer: MT-Unsafe and trampled by the next call; the buffer is not zeroized, and the man page BUGS section tells callers to clear the password as soon as possible.
• PASS_MAX / sysconf(_SC_PASS_MAX) are withdrawn (POSIX.2); glibc accepts _SC_PASS_MAX and returns BUFSIZ (getpass(3) NOTES).
• musl 1.2.5: present in src/legacy/getpass.c, declared in include/unistd.h under _GNU_SOURCE || _BSD_SOURCE.

References

• glibc manual: terminal.texi (terminal modes behind the echo toggle)
• man3: getpass(3)
• headers: /usr/include/unistd.h
• symbols: nm -D --with-symbol-versions libc.so.6