How to Recover Linux Grub Boot Loader

Normally, the order of installation should be first windows then linux so that the grub boot loader is installed and recognizes the windows partition too.

At my job i had to do it the other way around: we had a system with Centos 7 linux and we needed to install Windows to make this machine we useful either to rigging either to production staff.

I inserted the windows dvd and made a new partition in the unallocated space then install.

When i restarted the machine the linux boot loader had disappeared so i was googling how to recover it. Truth is it's pretty simple and after a really few minor mistakes i managed to make it work:

We need first to enter in RESCUE mode with a linux installation dvd/cd.

The system will be most probably mounted in /mnt/sysimage so we make the

chroot /mnt/sysimage

after that we do:

/sbin/grub2-install /dev/sda

to make grub recognize our windows entry just type:

sudo grub2-mkconfig > /dev/null

If everything went well the windows loader entry has been detected, all we need now is to save it to the grub.cfg:

grub2-mkconfig -o /boot/grub2/grub.cfg

Restart and voilà, we have our boot loader back with our windows O.S. entry!!!

Shortcut in Linux

How to create a shortcut in linux that executes a shell script

1. We create the shortcut.

Typically it's a ".desktop" ascii file with these entries although it can have more:

[Desktop Entry]
Type=Application
Encoding=UTF-8
Name=Sample Application Name
Comment=A sample application
Exec=application
Icon=application.png
Terminal=false

- The Name specifies the name of the launcher.
- Exec is the most important line as it specifies which script to launch and how it would be launched. We will leave this field blank til we have the shell script written
- Icon we set the path of the app's icon if available.
- Terminal specifies whether the app needs a terminal to run.

2. We create the shell script.

#!/bin/bash

. ~/.bashrc
PATH=$PATH:/srv/XXXX/XXXX/final_directory;
export PATH
cd /srv/projects/myproject

[some commands executing applications]

The first line is a comment indicating which shell will execute the script, in this case BASH.

The second line is a line that loads all the basrc file extensions

Then we perform some tasks such as adding another value to the system environment variable path and export that new entry.

We change our current directory and finally we call some commands that will launch our application.

3. We link the Exec command of the desktop file to the script

Note: if we have successfully coded our script it should work from the command line writing:

sh <ourscriptname>.sh

In our case an example of launching the shell script from our desktop file by double-clicking is

Exec=gnome-terminal -x bash -c "sh /path/to/thescript/scriptname.sh;bash"

Another linux tip: when we try to open a file sometimes we dont get to choose the right program even selecting "open with other programs". The trick to making appear the application in that list is editing as root its corresponding ".desktop" file normally placed in /usr/shared/applications/<name>.desktop and in the "command" or "Exec" field write at the end of the command the following: "<previous_commands><blank space>%U"

We save... and that should do the trick!!!