getpass(3)

1GETPASS(3)                 Linux Programmer's Manual                GETPASS(3)
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NAME

6       getpass - get a password
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SYNOPSIS

9       #include <unistd.h>
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11       char *getpass( const char *prompt);
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13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15       getpass():
16           Since glibc 2.2.2:
17               _BSD_SOURCE ||
18                   (_XOPEN_SOURCE >= 500 ||
19                       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED) &&
20                   !(_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
21           Before glibc 2.2.2:
22               none
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DESCRIPTION

25       This  function  is obsolete.  Do not use it.  If you want to read input
26       without terminal echoing enabled, see the description of the ECHO  flag
27       in termios(3).
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29       The  getpass() function opens /dev/tty (the controlling terminal of the
30       process), outputs the string prompt, turns off echoing, reads one  line
31       (the  "password"),  restores  the  terminal  state  and closes /dev/tty
32       again.
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RETURN VALUE

35       The function getpass() returns a pointer to a static buffer  containing
36       (the  first  PASS_MAX  bytes of) the password without the trailing new‐
37       line, terminated by a null byte ('\0').  This buffer may be overwritten
38       by  a  following call.  On error, the terminal state is restored, errno
39       is set appropriately, and NULL is returned.
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ERRORS

42       The function may fail if
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44       ENXIO  The process does not have a controlling terminal.
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FILES

47       /dev/tty
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ATTRIBUTES

50   Multithreading (see pthreads(7))
51       The getpass() function is not thread-safe.
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CONFORMING TO

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

57       For libc4 and libc5, the prompt is  not  written  to  /dev/tty  but  to
58       stderr.   Moreover,  if /dev/tty cannot be opened, the password is read
59       from stdin.  The static buffer has length 128 so that  only  the  first
60       127  bytes  of  the password are returned.  While reading the password,
61       signal generation (SIGINT, SIGQUIT, SIGSTOP, SIGTSTP) is  disabled  and
62       the  corresponding  characters (usually control-C, control-\, control-Z
63       and control-Y) are transmitted as part of  the  password.   Since  libc
64       5.4.19  also  line  editing is disabled, so that also backspace and the
65       like will be seen as part of the password.
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67       For glibc2, if /dev/tty cannot be opened,  the  prompt  is  written  to
68       stderr  and  the password is read from stdin.  There is no limit on the
69       length of the password.  Line editing is not disabled.
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71       According to the SUSv2, the value of PASS_MAX must be defined in  <lim‐
72       its.h>  in  case  it is smaller than 8, and can in any case be obtained
73       using sysconf(_SC_PASS_MAX).  However, POSIX.2 withdraws the  constants
74       PASS_MAX and _SC_PASS_MAX, and the function getpass().  Libc4 and libc5
75       have  never  supported  PASS_MAX  or  _SC_PASS_MAX.    Glibc2   accepts
76       _SC_PASS_MAX and returns BUFSIZ (e.g., 8192).
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BUGS

79       The  calling  process  should  zero the password as soon as possible to
80       avoid leaving the cleartext password visible in the  process's  address
81       space.
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COLOPHON

87       This  page  is  part of release 3.53 of the Linux man-pages project.  A
88       description of the project, and information about reporting  bugs,  can
89       be found at http://www.kernel.org/doc/man-pages/.
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93Linux                             2013-06-21                        GETPASS(3)