I find that under my root directory, there are some directories that have the same inode number:
$ ls -aid */ .*/ 2 home/ 2 tmp/ 2 usr/ 2 var/ 2 ./ 2 ../ 1 sys/ 1 proc/
I only know that the directories’ names are kept in the parent directory, and their data is kept in the inode of the directories themselves.
I’m confused here.
This is what I think when I trace the pathname /home/user1.
- First I get into the inode 2 which is the root directory which contains the directory lists.
- Then I find the name home paired with inode 2.
- So I go back to the disk to find inode 2?
- And I get the name user1 here?
Answers:
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Method 1
They’re on different devices.
If we look at the output of stat, we can also see the device the file is on:
# stat / | grep Inode Device: 801h/2049d Inode: 2 Links: 24 # stat /opt | grep Inode Device: 803h/2051d Inode: 2 Links: 5
So those two are on separate devices/filesystems. Inode numbers are only unique within a filesystem so there is nothing unusual here. On ext2/3/4 inode 2 is also always the root directory, so we know they are the roots of their respective filesystems.
The combination of device number + inode is likely to be unique over the whole system. (There are filesystems that don’t have inodes in the traditional sense, but I think they still have to fake some sort of a unique identifier in their place anyway.)
The device numbers there appear to be the same as those shown on the device nodes, so /dev/sda1 holds the filesystem where / is on:
# ls -l /dev/sda1 brw-rw---- 1 root disk 8, 1 Sep 21 10:45 /dev/sda1
Method 2
The inode number of any given file is unique to the filesystem, but not necessarily unique to all filesystems mounted on a given host. When you have multiple filesystems, you will see duplicate inode numbers between filesystems, this is normal.
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