# Change the default target:
systemctl set-default graphical.target

# Switch target in real time:
systemctl isolate multi-user.target

# Create a custom service – /etc/systemd/system/myapp.service:
[Unit]  Description=My App  After=network.target
[Service]  ExecStart=/usr/bin/myapp  Restart=always
[Install]  WantedBy=multi-user.target

# Enable hook in /etc/mkinitcpio.conf:
HOOKS=(base udev autodetect modconf block myhook filesystems keyboard fsck)

# Rebuild initramfs after adding the hook:
mkinitcpio -P                   # all presets
mkinitcpio -p linux             # 'linux' preset only

#!/bin/sh
run_latehook() {
  # Solarized Dark inspired palette
  local palette=\
  "002b36 dc322f 859900 b58900 \
268bd2 d33682 2aa198 eee8d5 \
073642 cb4b16 586e75 657b83 \
839496 6c71c4 93a1a1 fdf6e3"
  local i=0 seqs=''
  for col in $palette; do
    seqs="${seqs}\033]P$(printf '%X' $i)${col}"
    i=$((i+1))
  done
  for tty in /dev/tty[0-6]; do
    [ -w "$tty" ] || continue
    printf "$seqs" > "$tty"
    printf "\033[H\033[J" > "$tty"
    [ -f /font.psf.gz ] &&
      setfont -C "$tty" /font.psf.gz
  done
}

#!/bin/bash
build() {
  add_runscript
  add_binary setfont
  add_binary printf
  # Find font
  local fp=$(find \
    /usr/share/kbd/consolefonts/ \
    -name 'ter-v28b*' | head -1)
  if [ -n "$fp" ]; then
    add_file "$fp" /font.psf.gz
  else
    echo 'WARNING: font missing!'
  fi
}
help() {
  cat <<EOF
Sets Solarized Dark palette
and loads Terminus 28px font
on all VTs during boot.
EOF
}

# Start plain X11:
startx               # reads ~/.xinitrc
xinit /usr/bin/openbox -- :0

# ~/.xinitrc example:
exec openbox-session

# Start a Wayland session (sway):
sway                 # from a plain TTY
dbus-launch --exit-with-session sway

# Wayland environment variables:
export XDG_SESSION_TYPE=wayland

# Replace the running WM with another one (X11):
openbox --replace &      # replace current WM with Openbox
i3 --replace &           # replace with i3
bspwm &                  # bspwm lacks --replace; force it:
pkill -x openbox && bspwm

# Check the current WM:
wmctrl -m               # requires: pacman -S wmctrl

# Install and enable SDDM:
pacman -S sddm
systemctl enable sddm.service
systemctl start sddm.service

# Switch DM (disable old one, enable new one):
systemctl disable lightdm.service
systemctl enable sddm.service

# Session files – where DM looks for sessions:
ls /usr/share/xsessions/        # X11 sessions
ls /usr/share/wayland-sessions/ # Wayland sessions

# Custom session ~/.dmrc (for some DMs):
[Desktop]
Session=i3

# Create a user:
useradd -m -G wheel,audio,video \
  -s /bin/bash john
passwd john

# Modify a user:
usermod -aG docker john  # add to group
usermod -s /bin/zsh john # change shell
userdel -r john          # remove with home

# Group management:
groupadd devs
groupmod -n developers devs
groupdel developers

# Inspection:
groups john          # user's groups
id john              # UID, GID, groups
cat /etc/passwd      # user list

chmod 755 script.sh        # rwxr-xr-x  (owner=rwx, group=rx, other=rx)
chmod u+x,g-w file         # symbolic: add x for owner, remove w for group
chmod -R 644 directory/    # recursive: rw-r--r-- for all files
chmod o-rwx secret.txt     # revoke all permissions for 'others'

# chown – change ownership:
chown john file.txt
chown john:devs file.txt
chown -R www-data:www-data /var/www

# Group only:
chgrp audio /dev/snd/*

# chattr – filesystem attributes:
chattr +i file.txt    # immutable (locked)
chattr -i file.txt    # remove immutable
chattr +a log.txt     # append-only
lsattr file.txt       # show attributes

# Works on ext2/3/4, btrfs