Symlink some folders in home directory

Question

I recently installed dual boot Windows 10 and Ubuntu 20.04 on a new machine. I followed a guide which suggested giving /home a 10GB partition and throwing the rest in /. I started putting all my documents and media files in /home and quickly ran out of space. In hindsight, I would not have given myself so little space on /home, but I am unwilling to reformat and start again.

A simple solution is to symlink specific subfolders /home/username/bigstuff out to a folder on the big partition, say /media/extra-space/username/bigstuff. A detailed way of doing this is outlined by Paul's answer in this question. This works fine, except the permissions seem to be such that I cannot do anything in /home/username/bigstuff without a sudo.

I have three questions, with the last one being the most important for me:

1. Is this solution appropriate, or would it make experienced users weep? Should I be using a different directory, perhaps simply /extra-space/username/bigstuff ?
2. I am misunderstanding something basic: if /home is a subdirectory of /, how can it be on a separate partition? (This is what got me in the first place.) (answered)
3. How can I avoid having to write sudo every time I want to execute a command in /home/username/bigstuff (which is really on /media/extra-space/username/bigstuff)? I've tried changing the permissions on /media/extra-space/username but was not successful.

Thanks in advance.

EDIT in response to comments:

The output of stat --format=%m /media/extra-space/username/bigstuff is /. The output of stat --file-system --format=%T /media/extra-space/username/bigstuff is ext2/ext3. I'm not sure how to identify the relevant line of output from mount. The output of ls -ld /media/extra/username/bigstuff is

drwxr-xr-x 4 root root 4096 Feb 13 16:26 /media/extra/username/bigstuff

If it helps, in System Monitor, I see the following File Systems:

Device      Directory  Type 
/dev/sdb7   /          ext4
/dev/sdb1   /boot/efi  vfat
/dev/sdb5   /home      ext4

To be clear, I get a permission denied for mkdir when in ~/username/bigstuff, but it does seem correctly symlinked because after doing sudo mkdir test, /media/extra/username/bigstuff/test appears.

Answer 1

To recap, I:

• Created a directory extra/username/bigstuff in /media, which is on the device /dev/sdb7
• Ran ln -s /media/extra/username/bigstuff /home/username/bigstuff
• After Kamil pointed out that bigstuff is owned by root, I ran sudo -R chown username:username bigstuff. I also ran sudo chmod +w bigstuff. Now, ls -ld /media/extra/username/bigstuff gives drwxrwxr-x 3 username username 4096 Feb 13 16:19 /media/extra/username/bigstuff

Then I started poking more and got confused because I could create directories and files in subdirectories of .../bigstuff, but not in /bigstuff. I also saw that the owner name/group of /media/extra/username was still root:root. I sudo chown'ed that and that resolved my issues (can now create directories in .../bigstuff).