A bourne shell function to check for the presence of user namespace support in the linux kernel by calling the unshare command to set one up

check-user-namespace.sh

check-user-namespace () {
  if ! command -v unshare >/dev/null 2>&1; then
    echo "The unshare command is not available. Install the util-linux package to fix this." >&2
    return 2
  fi
  if unshare -U true >/dev/null 2>&1; then
    echo "User namespace support enabled"
    return 0
  else
    echo "User namespace support not enabled"
    return 1
  fi
}