Auto Login Linux Mint

curl -fsSL https://engineerisaac.com/download/mint_enable_autologin.sh | head -n 20

#!/usr/bin/env bash
set -euo pipefail

if [[ "${EUID}" -ne 0 ]]; then
    exec sudo -E bash "$0" "$@"
fi

ts() { date +"%Y%m%d_%H%M%S"; }
die() { echo "ERROR: $*" >&2; exit 1; }

backup_file() {
    local f="$1"
    [[ -f "$f" ]] || return 0
    local b="${f}.bak.$(ts)"
    cp -a "$f" "$b"
    echo "Backup: $b"
}

guess_user() {
    if [[ -n "${1:-}" ]]; then
        echo "$1"
        return 0
    fi
    if [[ -n "${SUDO_USER:-}" && "${SUDO_USER}" != "root" ]]; then
        echo "${SUDO_USER}"
        return 0
    fi
    local ln
    ln="$(logname 2>/dev/null || true)"
    if [[ -n "$ln" && "$ln" != "root" ]]; then
        echo "$ln"
        return 0
    fi
    die "Could not determine target username. Run: sudo $0 YOUR_USERNAME"
}

detect_dm() {
    if [[ -f /etc/X11/default-display-manager ]]; then
        local dm_path
        dm_path="$(cat /etc/X11/default-display-manager 2>/dev/null || true)"
        case "$dm_path" in
            *lightdm*) echo "lightdm"; return 0 ;;
            *gdm3*)    echo "gdm3"; return 0 ;;
            *sddm*)    echo "sddm"; return 0 ;;
        esac
    fi

    if systemctl list-unit-files 2>/dev/null | grep -qE '^lightdm\.service'; then echo "lightdm"; return 0; fi
    if systemctl list-unit-files 2>/dev/null | grep -qE '^gdm3\.service'; then echo "gdm3"; return 0; fi
    if systemctl list-unit-files 2>/dev/null | grep -qE '^sddm\.service'; then echo "sddm"; return 0; fi

    die "Could not detect display manager (lightdm/gdm3/sddm)."
}

choose_session() {
    local desired="${SESSION:-}"
    if [[ -n "$desired" ]]; then
        echo "$desired"
        return 0
    fi

    if [[ -d /usr/share/xsessions ]]; then
        [[ -f /usr/share/xsessions/cinnamon.desktop ]] && { echo "cinnamon"; return 0; }
        [[ -f /usr/share/xsessions/mate.desktop ]] && { echo "mate"; return 0; }
        [[ -f /usr/share/xsessions/xfce.desktop ]] && { echo "xfce"; return 0; }
    fi

    echo "cinnamon"
}

enable_lightdm() {
    local user="$1"
    local dir="/etc/lightdm/lightdm.conf.d"
    local conf="${dir}/50-autologin.conf"

    mkdir -p "$dir"
    backup_file "$conf"

    printf "[Seat:*]\nautologin-user=%s\nautologin-user-timeout=0\n" "$user" > "$conf"
    chmod 0644 "$conf"
    echo "Configured LightDM autologin in: $conf"
}

enable_gdm3() {
    local user="$1"
    local conf="/etc/gdm3/custom.conf"

    [[ -f "$conf" ]] || die "Expected $conf to exist, but it does not."
    backup_file "$conf"

    local tmp
    tmp="$(mktemp)"

    awk -v user="$user" '
    BEGIN {
        in_daemon=0
        seen_daemon=0
        set_enable=0
        set_user=0
    }

    /^\[daemon\][[:space:]]*$/ {
        seen_daemon=1
        in_daemon=1
        print
        next
    }

    /^\[[^]]+\][[:space:]]*$/ {
        if (in_daemon==1) {
            if (set_enable==0) print "AutomaticLoginEnable=True"
            if (set_user==0)   print "AutomaticLogin=" user
            in_daemon=0
        }
        print
        next
    }

    {
        if (in_daemon==1) {
            if ($0 ~ /^[[:space:]]*AutomaticLoginEnable[[:space:]]*=/) { print "AutomaticLoginEnable=True"; set_enable=1; next }
            if ($0 ~ /^[[:space:]]*AutomaticLogin[[:space:]]*=/)       { print "AutomaticLogin=" user; set_user=1; next }
        }
        print
    }

    END {
        if (in_daemon==1) {
            if (set_enable==0) print "AutomaticLoginEnable=True"
            if (set_user==0)   print "AutomaticLogin=" user
        }
        if (seen_daemon==0) {
            print ""
            print "[daemon]"
            print "AutomaticLoginEnable=True"
            print "AutomaticLogin=" user
        }
    }' "$conf" >"$tmp"

    cat "$tmp" >"$conf"
    rm -f "$tmp"
    chmod 0644 "$conf"
    echo "Configured GDM3 autologin in: $conf"
}

enable_sddm() {
    local user="$1"
    local session="$2"
    local dir="/etc/sddm.conf.d"
    local conf="${dir}/99-autologin.conf"

    mkdir -p "$dir"
    backup_file "$conf"

    printf "[Autologin]\nUser=%s\nSession=%s\nRelogin=true\n" "$user" "$session" > "$conf"
    chmod 0644 "$conf"
    echo "Configured SDDM autologin in: $conf"
}

main() {
    local user
    user="$(guess_user "${1:-}")"
    id "$user" >/dev/null 2>&1 || die "User '$user' does not exist."

    local dm
    dm="$(detect_dm)"

    echo "Target user: $user"
    echo "Detected display manager: $dm"

    case "$dm" in
        lightdm) enable_lightdm "$user" ;;
        gdm3)    enable_gdm3 "$user" ;;
        sddm)
            local session
            session="$(choose_session)"
            echo "SDDM session: $session (override with: SESSION=... )"
            enable_sddm "$user" "$session"
            ;;
        *) die "Unsupported display manager: $dm" ;;
    esac

    echo "Done. Reboot to apply: sudo reboot"
}

main "$@"