System Boot Initialization

Systemd services handle boot and shutdown processes. Create service files in /etc/systemd/system/:

[Unit]
Description=Custom Startup Service
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/startup-script.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Enable with: systemctl enable custom-service.service

User Session Initialization

User-level systemd services operate in ~/.config/systemd/user/:

[Unit]
Description=User Session Service

[Service]
Type=simple
ExecStart=/home/user/.local/bin/session-init

[Install]
WantedBy=default.target

Enable with: systemctl --user enable user-service.service

Shell Configuration Files

Bash executes scripts during shell initialization:

• /etc/profile: System-wide login shell configuration
• ~/.bash_profile: User-specific login shell configuration
• ~/.bashrc: User-specific non-login shell configuration

Example .bashrc addition:

# Launch terminal multiplexer on shell start
if command -v tmux >/dev/null 2>&1 && [ -z "$TMUX" ]; then
    exec tmux new-session -A -s main
fi

X11 Session Management

Xorg startup files execute before window manager initialization:

• ~/.xprofile: User-sepcific X session startup
• /etc/xprofile: System-wide X session startup

Example .xprofile:

# Set keyboard layout
setxkbmap -layout us -variant intl

# Configure display settings
xrandr --output HDMI-1 --auto --right-of eDP-1

Desktop Environment Autostart

XDG Autostart specification defines .desktop files in:

• ~/.config/autostart/: User-specific autostart entries
• /etc/xdg/autostart/: System-wide autostart entries

Example ~/.config/autostart/syncthing.desktop:

[Desktop Entry]
Type=Application
Name=Syncthing
Exec=syncthing -no-browser
Hidden=false
NoDisplay=false
X-GNOME-Autostart-enabled=true

Window Manager Configuration

Window managers often include startup commands in configuration files:

i3 window manager (~/.config/i3/config):

# Launch applications on window manager start
exec --no-startup-id nm-applet
exec --no-startup-id blueman-applet
exec --no-startup-id feh --bg-scale ~/wallpaper.jpg

Event-Driven Automation

Udev Device Management

Create rules in /etc/udev/rules.d/ to trigger actions on device events:

# /etc/udev/rules.d/99-backup.rules
ACTION=="add", KERNEL=="sd[b-z][0-9]", RUN+="/usr/local/bin/backup-trigger.sh"

Systemd Timers

Create timer units for scheduled execution:

/etc/systemd/system/daily-backup.timer:

[Unit]
Description=Daily Backup Timer

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target

/etc/systemd/system/daily-backup.service:

[Unit]
Description=Daily Backup Service

[Service]
Type=oneshot
ExecStart=/usr/local/bin/backup-system.sh

Filesystem Monitoring

Incron monitors filesystem events and executes commands:

Configure with incrontab -e:

/home/user/documents IN_CREATE,IN_MODIFY /usr/local/bin/process-document.sh

Inotify Event Monitoring

Use inotify-tools for filesystem event monitoring:

# Monitor directory for changes
inotifywait -m -r -e create,modify,delete /path/to/directory | while read event; do
    echo "Filesystem event detected: $event"
    /usr/local/bin/handle-change.sh
done