UNIX for Dummies Questions & Answers

I try to understand the meaning of an inode. I wonder whether
I read somewhere that an inode stores info about the file, size... so changing the size might change the inode?

Btw, is there a difference in both features in different platforms? I'm on a mac, but would a linux system be much different?

Inodes are unique in the borders of a single filesystem. Inode number is a pointer to the structure that is containing all the information that you mentioned. The number itself does not contain them. So changing file's info in the inode structure doesn't need to change the inode number (and it is not happening).

There is a list of the fields held in an inode in "man inode".

Running a basic editor such as "vi" to change the contents of a file will change the inode number of that file. Try it.

Code:

ls -lisad filename
vi filename
ls -lisad filename

The point was made above but it is very important to understand that inode numbers are only unique within a filesystem. If you are searching for inodes using "find /filesystem -inum" always use the "-xdev" switch to confine your search to that filesystem.

Not always that is the case

Code:

[root@linux tt]# touch test
ls -li test
2818830 -rw-rw-r-- 1 root root 0 mar 21 12:19 test
[root@linux tt]# echo "aaaaa" >> test
[root@linux tt]# ls -li test
2818830 -rw-rw-r-- 1 root root 6 mar 21 12:20 test
[root@linux tt]# echo "bbbbb" >> test
[root@linux tt]# ls -li test
2818830 -rw-rw-r-- 1 root root 12 mar 21 12:20 test

So changing file contents does not necessarily mean changing the inode number.

@bartus11
Very good example. Overwriting the contents of a file does not change the inode number.
Simple file editors such as "vi" do change the inode number because of the need to preserve the original file up to the last minute in case you abandon the edit.