Slackware Linux has been my all time favorite Linux distribution for over 24 years, having been the very first distro I used when Slackware was first released as a beta, Slackware pre-1.0 beta, and have since continued to use for all my servers! In those first days, it took a big stack of 3-1/2 inch floppy disks, and a LOT of time!
When adding new users from the command line Slackware Linux utility "adduser" command, which is unique to Slackware, you are given the opportunity to add the new user to additional groups, which makes it very easy to do so at user account creation! Simply add all the additional groups you want the new user to be a member of, separated by one space, and that is all that it takes!
You can confirm your new user account has been added to the additionally required groups by looking at the /etc/group file.
After creating a new account from the command line tool "adduser",
There will be more Slackware Linux info to come as I have the time to add it here!
Thanks for checking back often for new cool tips, tricks and HowTo's!