Overview

This feature is designed for environments where the root user navigates through different user home directories. It automatically switches the root user to the appropriate user when entering their home directory and logs out when exiting /home, ensuring correct file ownership and permissions.


This feature relies on the /etc/profile.d directory used by Bourne and compatible shells. It might not work in non-compatible shells.

Implementation details

  1. Script location

    The script is placed in the /etc/profile.d directory to ensure it is sourced for all users during login.

  2. Script name

    virtualmin-switch-user-on-cd.sh

  3. Script content

    # Extract username from the home directory
get_username_from_home() {
    local home_dir="$1"
    local username=$(awk -F: -v home="$home_dir" '$6 == home {print $1}' /etc/passwd)
    echo "$username"
}

# Function to switch user on cd
switch_user_on_cd() {
    # If root is forced under for whatever reason exit
    if [ -n "$ROOT" ]; then
        return
    fi

    # Check if the current directory is not under /home
    if [[ "$PWD" != /home/* ]]; then
        if [[ -n "$ORIGINAL_USER" && "$(whoami)" != "root" ]]; then
            exit
        fi
    else
        # Extract the username from the home directory if it's under /home
        username=$(get_username_from_home "$PWD")
        if [[ -n "$username" ]]; then
            if [[ "$(whoami)" != "$username" ]]; then
                export ORIGINAL_USER=$(whoami)
                export ORIGINAL_USER_PWD=$PWD
                export ORIGINAL_USER_OLDPWD=$OLDPWD
                sudo -H -u "$username" bash -c 'export ORIGINAL_USER='"$ORIGINAL_USER"'; \
                    export ORIGINAL_USER_PWD='"$ORIGINAL_USER_PWD"'; \
                    export ORIGINAL_USER_OLDPWD='"$ORIGINAL_USER_OLDPWD"'; \
                    exec bash -l'

                if [ "$PWD" = "$ORIGINAL_USER_PWD" ]; then
                    cd "$ORIGINAL_USER_OLDPWD"
                fi
                unset ORIGINAL_USER
                unset ORIGINAL_USER_PWD
                unset ORIGINAL_USER_OLDPWD
            fi
        fi
    fi
}

# Set the PROMPT_COMMAND to call the switch_user_on_cd function
PROMPT_COMMAND=switch_user_on_cd

  4. Script installation

    source /etc/profile.d/virtualmin-switch-user-on-cd.sh

How it works

  • User detection

    • When the root user navigates to a directory under /home, the script uses the get_username_from_home function to extract the username based on the home directory path from the /etc/passwd file.
    • The script then switches to the identified user using the sudo -H -u username command.

  • Logout mechanism

    • When the user navigates outside the /home directory, the script checks if the ORIGINAL_USER variable is set.
    • If set, and the current user is not root, the script logs out the user, reverting control back to the root user.

  • Disable mechanism

    • Setting the environment variable ROOT=1 will disable the automatic user switch and logout behavior.
    • This can be done in the shell by executing export ROOT=1.

Testing and validation

  1. Navigate to a user’s home directory

    cd /home/charles
    • Expected result: The shell switches to charles user.

  2. Navigate outside the /home directory

    cd /
    • Expected result: The shell logs out the current user if ORIGINAL_USER was set, reverting control back to the root user.

  3. Disable automatic switching

    export ROOT=1
cd /home/charles
cd /
    • Expected result: No user switching or logging out occurs due to the ROOT=1 variable.

Benefits

  • Ensures correct file ownership and permissions under user home directories.
  • Provides an automated mechanism for user context switching.