You can use the "Disk Usage Analyser" to see what is using all of your drive space.

1. Open "Disk Usage Analyser" by searching for it in the Dash.


2. Click on your root (/) drive.


3. Wait for the graph at the right to stop displaying loading dots (it may take a while).


4. You can now review which files are taking up the most space (You can just close the 'Permission denied' error if it appears).


5. Hover your mouse over a sector to get the name of that folder and its size.

To delete the largest files/folders

After performing the above steps and with the file path to a larger file/folder which you want to delete, you can do the following:

• Only if the file is in your Home directory, you could just move it to an external hard drive (or delete it altogether if it's unimportant)


• If the file is not in your Home folder, you can take a guess at which package it belongs to and try apt-get uninstall to remove that package (if you don't need it)


• Anything else, please edit your question with the path to the file/folder which you'd like to delete. You should not randomly delete files which are not in your Home folder.

Mounting a separate partition on /usr

This would be my suggestion. Use the following instructions:

1. Install GParted using this command in a terminal:

   
   
   

   sudo apt-get install gparted
   
   



2. Open GParted by searching for it in the dash.


3. Locate a large partition (>100GB, I'd suggest sda5) of which is mostly unused (<50% used)


4. Shrink this partition by 10GB (or 10000MB)


5. Create a new logical ext4 partition taking up all of the free space.



6. Open a root Nautilus window (be careful with this)

   
   
   

   sudo -H nautilus
   
   



7. Copy the contents of the /usr folder (contents, not the folder itself) into the root of your new ext4 partition created above.



8. Execute this command in a terminal, replacing /dev/sda1 with the partition identifier of your new partition created above:

   
   
   

   sudo blkid | grep '/dev/sda1' | grep -Po 'UUID="[^"]+"'
   
   

   
   
   
   
   
   • Copy the complete output of this command (should be similar to this: UUID="X7X2X1X3-X573-4929-97XX-XX1514X31X7X")
   
   



9. Open the /etc/fstab file with this command:

   
   
   

   sudo -H gedit /etc/fstab
   
   




10. Paste in it the following on it's own line, substituting your copied text in where necessary:

    
    
    

    <PASTE_HERE>    /usr    ext4    errors=remount-ro 0       1
    
    



11. Reboot

The below steps are optional, but will delete redundant copies of the /usr folder still on your original / drive, freeing up space.

1. Boot into a LiveCD/USB.


2. Mount your original / drive in Nautilus, and take a note of where it's mounted to.



3. Open a root Nautilus window (be careful with this)

   
   
   

   sudo -H nautilus
   
   



4. Navigate to your original / drive (which you noted above)


5. Delete the contents of the /usr folder, not the folder itself but everything inside it.


6. Reboot.

Replies

Can the files outside the home directory not be copied to an external drive?

No, they can not. You should not manually delete (or move away) any files outside of your Home folder unless you (you yourself, not apt-get or similar) put them there.

Is having two mount point at the same logical partition possible?

No, that is not possible.