Creating invisible users in Mac OS-X (Snow)Leopard

Recently I wanted to install a software no my Mac that required a dedicated user. So I created a user via the GUI-Interface and noted, that the user now was visible in the login-screen, which I didn’t want to happen.

So after a bit of research I came up with the following:
In MacOS-X you can hide users with a user-id below 500, so I had to check which number below the 500 was free.

Using the following commands I got a list of all IDs for the users and the groups and found, that – at least on my system – everything from 300 through 399 was free, so I will settle for the 300 in this example.

# List all User-IDs
dscl . list /Users UniqueID | sed -E "s/ +/ /g" | cut -d " " -f 2 \
    | sort
# List all Group-IDs
dscl . list /Groups PrimaryGroupID | sed -E "s/ +/ /g" \ 
    | cut -d " " -f 2 |sort

That given I had to create the group and the user as well as set the user as member of the group

USERNAME="MyUserName"
GIDNUMBER=300
UIDNUMBER=300
PASSWORD="secretPassword"
# Create the group
sudo dscl . create /Groups/$USERNAME
sudo dscl . create /Groups/$USERNAME PrimaryGroupID $GIDNUMBER
# Create the user
sudo dscl . create /Users/$USERNAME
sudo dscl . create /Users/$USERNAME PrimaryGroupID $GIDNUMBER
sudo dscl . create /Users/$USERNAME UniqueID $UIDNUMBER
sudo dscl . create /Users/$USERNAME UserShell /bin/bash
# Set the users pasword
sudo dscl . passwd /Users/$USERNAME $PASSWORD
# Add the user to the group
sudo dscl . append /Groups/$USERNAME GroupMembership $USERNAME

That’s that!

Group created, User created, User as Group-Member set, what’s next?

Oh yes, I have to set the flag to hide users with ID below 500, and some stuff like that.

# Hide all users with a user-ID below 500
sudo defaults write /Library/Preferences/com.apple.loginwindow \
    Hide500Users -bool TRUE
# Add the user to the list of users to be hidden
sudo defaults write /Library/Preferences/com.apple.loginwindow \
    HiddenUsersList -array $USERNAME
# Remove the 'other...' string from the login-screen
sudo defaults write /Library/Preferences/com.apple.loginwindow \
     SHOWOTHERUSERS_MANAGED -bool FALSE

Finished.

The created User ‘MyUserName’ now should not show up in the login-screen.

For more Information see this MacWorld-Hint