# Useful shell command

* commands

```shell
// add a user to root group
$ visudo

# User privilege specification
root    ALL=(ALL:ALL) ALL
newuser ALL=(ALL:ALL)ALL

hold `ctrl` and press `x` to save and exit
```



* run as root

```shell
user@host$ sudo su -

// prompt will show root login
root@host$ 
```



* add a user to a group

```shell
// create docker group
$ sudo groupadd docker

// add current user to group
$ sudo usermod -aG docker ${USER}

// restart to take effect
```



* change file permission

```shell

// excecute, read, write
$ chmod 777 filename

//
```

## node version manager [nvm](https://github.com/nvm-sh/nvm)

* version manger for nodejs
* use nvm to avoid npm version conflict installation
* ubuntu 20.10 support node 12
* ubuntu 19.10 support node 10

```shell
// installation

$ curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.38.0/install.sh | bash

$ wget -qO- https://raw.githubusercontent.com/nvm-sh/nvm/v0.38.0/install.sh | bash

$ export NVM_DIR="$([ -z "${XDG_CONFIG_HOME-}" ] && printf %s "${HOME}/.nvm" || printf %s "${XDG_CONFIG_HOME}/nvm")"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm

// to install node version 10.10.0
$ nvm install 10.10.0

// remove node to solve conflicting version
$ sudo apt-get remove nodejs
$ sudo apt autoremove
```