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So I had been considering that partition is like a separate section of space. Recently, I decided to experiment with partitions and found a flaw in my understanding. Some examples refer to a case where one should make 3 partitions:

  1. / = root, 32GiB
  2. /boot = boot, 1GiB
  3. /home = home, 100% = 200GiB

Now it gets somewhat confusing to me - since I suppose that the / is the main container and other containers are children of the former one, why child containers, like, /home (200GiB) actually exceed the limits of / which has only 32GiB?

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    /home is not a child of / (ie., it is not contained within it) unless you do not create a separate partition for it, in which case you would need to make / large enough to contain it.
    – jasonwryan
    May 28, 2016 at 20:58
  • For reference, here is an example of a guide which suggests making distinct root and home partitions.
    – Louis Maddox
    Nov 13, 2021 at 10:42

3 Answers 3

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You are confusing filesystem (organization) semantics with partition (storage) semantics.

Linux filesystem hierarchy is like a single giant tree with a stem (/) , branches ( /boot, /home, /bin, /usr, /var ) and sub-branches ( /usr/bin, /var/log ...). This metaphor is equivalent of the parents, children and grandchildren.

All these symbols/names in the filesystem represent points on the tree where storage space, like a partition , usb, external drive etc. can be hung ("mounted").

If you hang/mount some storage space only onto the stem of the tree (/) , then all the branches, and subranches of the stem (/boot,/home,/usr/bin) have to be contained within that storage space.

However if , after mounting the first storage space onto the stem (/), you then proceed to mount some additional storage space (e.g. another partition) onto one of the branches (e.g. /home) , then this second mounted storage is added to the total storage under the filesystem, but can only be accessed through its mountpoint (e.g. /home) on the filesystem. This second storage mounted on /home is in ADDITION to that mounted on the (/). All other branches of the / (like /boot, /usr, /var etc) will still have to be contained with the first mounted storage !

So / , /boot, /home, and others are simply access points on the filesystem. When you mount some storage onto any of those points (e.g. /), all the children and grandchildren of that point are automatically contained within this storage space UNTIL you mount some additional storage on one of its children or grandchildren.

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Partitions do not contain other partitions.

Every partition that you use has a mounting point. The main (root) partition, needs to be automatically mounted on / during boot, and then other partitions can be mounted in any existing location you chose.

One important thing to note is that mounting a partition somewhere will hide what is already present at that same location of the partition it is mounted on. So if you write files in /boot before mounting it, those files will not be available once /boot gets mounted.

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The root (/) is the main container, and it contains all of your system. Partitions are just pieces of the hard drives, containing a file system.

Now, the root has nothing to do with the other file systems, you have to 'mount' them first. That way you bind a directory to a partition. So the 'home' directory in your file system would redirect to partition you mounted it. Note that the root itself is mount to a partition.

The partitions are not contained in each other, you just connect one with another by mounting them.

You can see in your /etc/fstab which partitions you have, and where they are mounted.

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