I installed netrunner in /dev/sda9, alongside with Mint which was already installed on another partition.
As netrunner couldn’t boot anymore, I decided to chroot to it from my Mint OS (boot Mint, mount /dev/sda9 and chroot to it) to see what’s in the logs.
To my surprise, I found that there is a “@” folder at the top of the partition 
see trace below
ychaouche#ychaouche-PC 15:32:45 /mnt $ sudo mount /dev/sda9 any/
ychaouche#ychaouche-PC 15:32:48 /mnt $ cd any/
ychaouche#ychaouche-PC 15:32:51 /mnt/any $ ls
total 0
drwxr-xr-x 1 root root 238 Jan 12 11:23 @
ychaouche#ychaouche-PC 15:32:52 /mnt/any $ cd @
ychaouche#ychaouche-PC 15:32:59 /mnt/any/@ $ ls
total 40K
lrwxrwxrwx 1 root root 7 Jan 12 11:00 bin -> usr/bin
drwxr-xr-x 1 root root 194 Jan 12 11:22 boot
drwxr-xr-x 1 root root 0 Jul 1 14:40 dev
drwxr-xr-x 1 root root 4.1K Jul 1 16:12 etc
drwxr-xr-x 1 root root 0 Jul 1 14:40 home
lrwxrwxrwx 1 root root 30 Jan 12 11:13 initrd.img -> boot/initrd.img-4.19.0-1-amd64
lrwxrwxrwx 1 root root 30 Jan 12 11:13 initrd.img.old -> boot/initrd.img-4.19.0-1-amd64
lrwxrwxrwx 1 root root 7 Jan 12 11:00 lib -> usr/lib
lrwxrwxrwx 1 root root 9 Jan 12 11:00 lib32 -> usr/lib32
lrwxrwxrwx 1 root root 9 Jan 12 11:00 lib64 -> usr/lib64
lrwxrwxrwx 1 root root 10 Jan 12 11:00 libx32 -> usr/libx32
drwxr-xr-x 1 root root 0 Jan 12 11:00 media
drwxr-xr-x 1 root root 32 Jul 1 16:06 mnt
drwxr-xr-x 1 root root 26 Jan 12 11:11 opt
drwxr-xr-x 1 root root 0 Jul 1 14:40 proc
drwx------ 1 root root 158 Jul 1 16:23 root
drwxr-xr-x 1 root root 0 Jul 1 14:40 run
lrwxrwxrwx 1 root root 8 Jan 12 11:00 sbin -> usr/sbin
drwxr-xr-x 1 root root 0 Jan 12 11:00 srv
drwxr-xr-x 1 root root 0 Jul 1 14:40 sys
drwxrwxrwt 1 root root 236 Jul 3 09:56 tmp
drwxr-xr-x 1 root root 116 Jan 12 10:58 usr
drwxr-xr-x 1 root root 90 Jan 12 11:19 var
lrwxrwxrwx 1 root root 27 Jan 12 11:13 vmlinuz -> boot/vmlinuz-4.19.0-1-amd64
lrwxrwxrwx 1 root root 27 Jan 12 11:13 vmlinuz.old -> boot/vmlinuz-4.19.0-1-amd64
ychaouche#ychaouche-PC 15:33:00 /mnt/any/@ $