ubuntu-swap-file-for-more-memory.sh

increase swap file size to 8Gb
ref. https://askubuntu.com/a/1075516/22308
```bash
sudo swapoff /swapfile  ; _='# make all swap off';
sudo rm -rf /swapfile   ; _='# remove the current';

_='#                                16*1024Mb=16384Mb      
sudo dd if=/dev/zero of=/swapfile bs=1M count=16384 ; _='# set swapfile size to 16Gb';
sudo dd if=/dev/zero of=/swapfile bs=1M count=8192  ; _='# set swapfile size to  8Gb';
sudo dd if=/dev/zero of=/swapfile bs=1M count=4096  ; _='# set swapfile size to  4Gb';
sudo dd if=/dev/zero of=/swapfile bs=1M count=2048  ; _='# set swapfile size to  2Gb';

sudo chmod 600 /swapfile;

sudo mkswap /swapfile  ; _='# format the file as swap';

sudo swapon /swapfile  ; _='# activate it';
sudo swapon -s         ; _='# view swap size';
```

turn on swap as it may turned off when reboot as discussed here https://askubuntu.com/q/1166170/22308
```bash

# open editor for crontab 
sudo crontab -e
    : add below lines
    # turn on swap file ref. https://superuser.com/a/586078/34893
    @reboot /sbin/swapon /swapfile
```