how to show grub boot menu in lubuntu

Problem:

I want to reboot lubuntu in Recovery mode (Advanced options for Ubuntu > Recovery Mode). Problem: grub boot menu doesn’t appears when reboot my computer and I can’t see or choose any option.

Solution:

To solve it, you can edit grub settings to show the menu.

Step by step:

Use nano to edit the configuration file in the Terminal. Type:
```
sudo nano /etc/default/grub
```
find and edit these lines: GRUB_HIDDEN_TIMEOUT=0 or GRUB_TIMEOUT_STYLE=hidden. Add # at the start of this line to commment it out. They should be:
```
#GRUB_HIDDEN_TIMEOUT=0
```
or
```
#GRUB_TIMEOUT_STYLE=hidden
```
Save the changes and exit nano.
In the Terminal, type:
```
sudo update-grub
```

Source:

https://askubuntu.com/questions/668049/grub-menu-at-boot-time-holding-shift-not-working https://help.ubuntu.com/community/Grub2/Setup