chkpwd

chkpwd is a program that checks the validity of a users password on a UNIX/PAM-based system.

Currently chkpwd is only tested on Linux, but it should work on a AIX, DragonFly BSD, FreeBSD, HP-UX, Linux, macOS, NetBSD and Solaris operating system too.

The idea

I needed a program to verify passwords of users on Linux/UNIX systems using PAM that just returns 0 on success and 1 on error.

Requirements

You need the PAM development package installed. On Alpine it is named linux-pam-dev, on Debian based systems it is libpam0g-dev.

Building chkpwd

git clone https://git.xw3.org/hanez/chkpwd.git
cd chkpwd
make

The code only supports verifying passwords for user id 1000 by default. Look at the file chkpwd.h for some compile time options!

Custom build example

Set MAX_UID and MIN_UID at compile time:

gcc -Wall -DMAX_UID=1000 -DMIN_UID=1000 -o chkpwd chkpwd.c -lpam -lpam_misc

Installation

WARNING: Install this software with care. chkpwd could easily be used for bruteforcing passwords from local users!

sudo make install

chkpwd is installed to /usr/bin/.

chkpwd.h is installed to /usr/include/ for use in other applications.

Uninstall

sudo make uninstall

Usage

chkpwd -h
Usage: chkpwd [-u <username>] [-p <password>] [-v] [-V] [-h]

Options:
  -u <username>  Set username.
  -p <password>  Set password.
  -v             Enable verbose mode.
  -V             Print program version.
  -h             Show this help.

You can also use chkpwd even without installing by just running the following command:

./chkpwd

Return codes

chkpwd returns 0 on success, 1 otherwise.

Examples

Interactive mode asking for a username and a password

chkpwd

Interactive mode only asking for a password

chkpwd -u hanez

None interactive mode with username and password provided as arguments to chkpwd

chkpwd -u hanez -p password

Request the result from the above commands

echo $?

License

chkpwd is licensed under the Apache License, Version 2.0.

See LICENSE for details.

Links

• https://git.xw3.org/hanez/chkpwd
• https://linux.die.net/man/8/unix_chkpwdd
• https://cr.yp.to/checkpwd.html
• https://pamtester.sourceforge.net/