Question: I'm new in react-native.
I have run react native project on Ubuntu by using 'react-native run-android' command. And I got the error on emulator 
"Unable to load script from assets 'index.android.bundle'.Make sure your bundle is packaged correctly or you are running a package server."

Answer: 
It seems to be a problem in the newest version of React Native (0.46). Using the previous version seems to solve the problem `react-native init name --version react-native@0.45.1` and removes the error when running `react-native run-android`.

Edit: It is now fixed in version 0.46.1.
i'm using ubuntu 18.04 LTS ,react-native: 0.55.2. In my case here are few solutions for the problem .

1. in the terminal before you run npm run android type npm start. you might see an error
ERROR Metro Bundler can't listen on port 8081.
this occurs because there might be a process which is already running

Solution- type `sudo lsof -i :8081` 

you will see an output similar to this 

> 
> \*\*COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
> 
> 
> 
> ```
>  node    5670 tasif   17u  IPv6  80997      0t0  TCP *:tproxy (LISTEN)**
> 
> ```
> 
> 

type `kill -9 (PID number)`then `run npm android`.
2. if it still doesnt work type again npm start . you might see this error

E`RROR ENOSPC: no space left on device, watch'....../......./.....'`

solution :

$ `sudo sysctl fs.inotify.max_user_watches=524288`

$ `sudo sysctl -p`

then type `npm run android`.

please go to this link to see different solutions and more details <https://github.com/guard/listen/wiki/Increasing-the-amount-of-inotify-watchers#the-technical-details>
3. delete the emulator and build it again. kill the recent terminal and then build emulator and start again.