### View system distribution
```sh
$ cat /etc/*release
```

### Check memory state
```sh
$ free -mh
```

## Check system state
```sh
$ top
```

### View file system
```sh
$ df -h
```

### List system running process
```sh
$ ps aux
```
filter by keyword
```sh
$ ps aux | grep 
```

### List system listening port
```sh
$ netstat -tlnp
```

### Extract .tar.gz file
```sh
$ tar zxvf 
```

### Compress a file / folder to .tar.gz
```sh
$ tar zcvf 
.tar.gz 
```
If you are using absolute path for target file path, all sub-folder and files will added to output file. To avoid this, you may use the `-C` option to indicate the start point.
```sh
$ tar zcvf 
.tar.gz -C /var/www /var/www/html
```
The output file root folder will be start from `html` folder.