MyBashScripts

Bash utilities for Kali and other Debian-based systems. Built for helpdesk and junior security work on a machine you already administer: create a local user, install a script as a command, and apply package updates.

Authorized use. These scripts change accounts and files on the machine where you run them. Use them only on systems you administer.

Contents

• Features
• Prerequisites
• Install
• How it works
• Usage
• Screenshots
• License

Features

• Create a local account with zsh as the login shell, with or without sudo
• Install a script file as a command in /usr/bin
• Optional root-only command (chmod 700, owner root)
• Reject command names that contain / or .., so the write cannot leave /usr/bin
• Refuse to replace a command that is already installed
• Stop newuser, stc, and updatemykali unless they are run as root
• Run apt update and apt full-upgrade -y from one command

Prerequisites

• A Debian-based system with apt (developed on Kali Linux)
• zsh (sudo apt install zsh). newuser will not continue without it, because it sets that shell on the new account
• Root, or a user who can sudo. installallnow calls sudo itself. The other three commands must be started as root

Install

git clone https://github.com/avitwil/MyBashScripts.git
cd MyBashScripts
./installallnow

installallnow copies these commands into /usr/bin:

Command	Source	What it does
newuser	newuser	Create a user and optionally add them to the sudo group
stc	scripttocommand.sh	Install a script file as a command
updatemykali	updatemykali	apt update and apt full-upgrade -y

You can also run a script from the checkout without installing it, for example sudo ./newuser.

How it works

newuser checks the effective user id, checks that zsh is on PATH, then asks for a username and a y or n sudo answer. It creates the account with adduser, sets the shell with usermod -s /usr/bin/zsh, and on y adds the account to the sudo group. It finishes by printing the matching /etc/passwd and /etc/group lines.

stc (scripttocommand.sh) checks root, checks that the source file exists, and rejects a command name that contains / or ... It writes the file to /usr/bin/<name> and sets mode 755. A third argument of sudo changes that to mode 700 and owner root. An existing path under /usr/bin is left untouched.

updatemykali checks root, then runs apt update and apt full-upgrade -y. It takes no arguments and does not ask for confirmation.

installallnow finds newuser, scripttocommand.sh, and updatemykali next to itself, copies them to /usr/bin (scripttocommand.sh becomes stc), and sets each one mode 700 and owner root. If a copy fails, it stops instead of printing success.

Usage

Examples below are from a local lab run. Paths are /tmp and a fictional account named acmehelp. User ids in the newuser transcript come from that lab machine.

Root is required

./newuser
./scripttocommand.sh /tmp/acme-hello.sh acmehello
./updatemykali

Each command prints this and exits 1:

This script must be run as root (use sudo).

newuser

sudo newuser

The script prompts for the username and for sudo access. adduser then asks for a password (not echoed) and the usual name and phone fields. Answer y to put the account in the sudo group, or n to leave it as a normal user.

Lab run, answer n, full name ACME Helpdesk:

User creation script by Avi Twil. Please wait...
Enter new user name: acmehelp
Do you want this user to have "sudo" privileges? [y/n]: n
info: Adding user `acmehelp' ...
info: Selecting UID/GID from range 1000 to 59999 ...
info: Adding new group `acmehelp' (1001) ...
info: Adding new user `acmehelp' (1001) with group `acmehelp (1001)' ...
info: Creating home directory `/home/acmehelp' ...
info: Copying files from `/etc/skel' ...
New password:
Retype new password:
passwd: password updated successfully
Changing the user information for acmehelp
Enter the new value, or press ENTER for the default
	Full Name []: ACME Helpdesk
	Room Number []:
	Work Phone []:
	Home Phone []:
	Other []:
Is the information correct? [Y/n] Y
info: Adding new user `acmehelp' to supplemental / extra groups `users' ...
info: Adding user `acmehelp' to group `users' ...
acmehelp in passwd file
-------------------------------
acmehelp:x:1001:1001:ACME Helpdesk,,,:/home/acmehelp:/usr/bin/zsh
-------------------------------
acmehelp in group file
-------------------------------
users:x:100:acmehelp
acmehelp:x:1001:
-------------------------------
User creation complete

adduser's info: lines vary by distribution. The prompts and the passwd line are the part to check: the shell should be /usr/bin/zsh.

stc

sudo stc /tmp/acme-hello.sh acmehello
sudo stc /tmp/acme-hello.sh acmehello sudo

• First argument: path to the script file.
• Second argument: command name. It must not contain / or ...
• Third argument: sudo for a root-only command. Omit it for mode 755.

Missing arguments, a missing file, a name that would escape /usr/bin, and a name that is already taken all exit 1:

$ sudo stc
missing script file path
 correct format : sudo stc [script] [command] [sudo/nothing]
  sudo stc /tmp/acme-hello.sh command
                or
  sudo stc /tmp/acme-hello.sh command sudo

$ sudo stc /tmp/no-such-acme.sh acmehello
file /tmp/no-such-acme.sh does not exist
 correct format : sudo stc [script] [command] [sudo/nothing]
  sudo stc /tmp/acme-hello.sh command
                or
  sudo stc /tmp/acme-hello.sh command sudo

$ sudo stc /tmp/acme-hello.sh ../acmehello
invalid command name

$ sudo stc /tmp/acme-hello.sh bash
command bash already exists
try another command name

A successful install prints one line, and the new command runs from PATH:

$ sudo stc /tmp/acme-hello.sh acmehello
command acmehello created successfully
$ acmehello
ACME lab command is installed

/tmp/acme-hello.sh in that run was a two-line script:

#!/bin/bash
echo "ACME lab command is installed"

Passing sudo as the third argument prints the same success line, then sets mode 700 and owner root.

updatemykali

sudo updatemykali

Runs apt update, then apt full-upgrade -y, and exits with apt's status. There is no extra prompt. Without root it exits 1 with the message shown above.

installallnow

./installallnow

Installing commands by Avi Twil...
Installing "newuser" command...
Installing "stc" command...
Installing "updatemykali" command...
Installation complete
--------------------------------------------------------------------------------------------------------
 newuser -- create a new user
 stc [script file] [command name] [sudo/nothing] -- install a script as a command
 updatemykali -- run apt update and full-upgrade; no input needed
--------------------------------------------------------------------------------------------------------
Enjoy

After that, newuser, stc, and updatemykali are on the default PATH.

Screenshots

Terminal captures from the lab runs above.

Root is required

Create a user

stc checks

Install a command

Install all three commands

License

MIT. See LICENSE.