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README update.

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Johannes Findeisen 2026-01-13 00:20:45 +01:00
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chkusr is a set of programs (chkgrp, chkpwd and chkpwr) to verify information about a user and/or group on UNIX based systems.
Go over to [https://hanez.org/project/chkusr/](https://hanez.org/project/chkusr/) for details...
## THE FOLLOWING DOCUMENTATION WILL NOT WORK ACTUALLY! YOU NEED TO READ THE CODE! SORRY...
* [The idea](#the-idea)
* [Requirements](#requirements)
* [Configuration](#configuration)
* [Building chkusr](#building-chkusr)
* [Installation](#installation)
* [Uninstall](#uninstall)
* [Programs](#programs)
* [chkgrp](#chkgrp)
* [chkpwd](#chkpwd)
* [Usage](#usage)
* [Return codes](#return-codes)
* [Examples](#examples)
* [Interactive mode asking for a username and a password](#interactive-mode-asking-for-a-username-and-a-password)
* [Interactive mode only asking for a password](#interactive-mode-only-asking-for-a-password)
* [None interactive mode with username and password provided as arguments to chkpwd](#none-interactive-mode-with-username-and-password-provided-as-arguments-to-chkpwd)
* [Request the result from the above commands](#request-the-result-from-the-above-commands)
* [Custom build](#custom-build)
* [chkpwr](#chkpwr)
* [Links](#links)
* [License](#license)
### The idea
I needed some programs to verify some information about users and groups on a Linux/UNIX system just returning 0 on success and 1 on error. Nonetheless, some programs also return a message.
#### Requirements
You need the PAM development package installed. On Alpine it is named linux-pam-dev, on Debian based systems it is named libpam0g-dev. Not all programs require PAM but you need to edit the Makefile to disable PAM based programs in the build process.
#### Configuration
chkusr needs to be configured before compilation. Always look at config.h for configuration options. I did it this way because I need the programs as small and simple as possible, and I don't want to parse a configuration file.
#### Building chkusr
```
git clone https://git.xw3.org/hanez/chkusr.git
cd chkusr
make
```
#### Installation
**WARNING:** Install this software with care. chkpwd could easily be used for bruteforcing passwords from local users!
```
sudo make install
```
chkusr programs are installed to /usr/bin/.
chkpwd.h is installed to /usr/include/ for use in other applications.
#### Uninstall
```
sudo make uninstall
```
### Programs
#### chkgrp
chkgrp is a program to verify if a user is a member of a group.
More information will follow... Actually there are multiple programs with some different behavior. I will write more about this, but for now I will not.
#### chkpwd
chkpwd is a program that checks the validity of a users password on a UNIX/[PAM](https://en.wikipedia.org/wiki/Pluggable_Authentication_Module)-based system.
Currently chkpwd is only tested on Linux, but it should work on a [AIX](https://en.wikipedia.org/wiki/IBM_AIX), [DragonFly BSD](https://www.dragonflybsd.org/), [FreeBSD](https://www.freebsd.org/), [HP-UX](https://en.wikipedia.org/wiki/HP-UX), [Linux](https://kernel.org/), [macOS](https://en.wikipedia.org/wiki/MacOS), [NetBSD](https://netbsd.org/) and [Solaris](https://en.wikipedia.org/wiki/Oracle_Solaris) operating system too.
The code only supports verifying passwords for user id 1000 by default. Look at the file chkpwd.h for some compile time options!
##### 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
chk 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 $?
```
##### Custom build
Set MAX_UID and MIN_UID at compile time:
```
gcc -Wall -DMAX_UID=1000 -DMIN_UID=1000 -o chkpwd chkpwd.c -lpam -lpam_misc
```
#### chkpwr
A program that checks if an input string validates a password rule. More to come... look at the code!
### Links
- [https://git.xw3.org/hanez/chkusr](https://git.xw3.org/hanez/chkusr)
- [https://github.com/shadow-maint/shadow](https://github.com/shadow-maint/shadow)
- [https://github.com/linux-pam/linux-pam](https://github.com/linux-pam/linux-pam)
- [https://www.man7.org/linux/man-pages/man8/unix_chkpwd.8.html](https://www.man7.org/linux/man-pages/man8/unix_chkpwd.8.html)
- [https://cr.yp.to/checkpwd.html](https://cr.yp.to/checkpwd.html)
- [https://pamtester.sourceforge.net/](https://pamtester.sourceforge.net/)
- [https://github.com/AlexanderZhirov/chkpass](https://github.com/AlexanderZhirov/chkpass)
- [https://github.com/ViKingIX/pam_test](https://github.com/ViKingIX/pam_test)
- [https://github.com/Dareka826/chk_pw](https://github.com/Dareka826/chk_pw)
### License
chkusr is licensed under the Apache License, Version 2.0.
See LICENSE for details.