What is inode ?
Each inode provides a unique identifier for each file and directory on the filesystem. When a file is created, it is assigned an inode number, which is unique within the filesystem. This allows the system to manage files by their inode numbers rather than by their names, which can be changed or duplicated across different directories
inodes stores the metadata about the file inode points to. inode will store metadata regarding the file size, permissions, user/group, location on hard disk, date/time etc.
inode doesn’t store the actual file.
Check inode details:
We can get details about the inode using “stat” system call. whenever we run long listing ls -l, the command is looping and making calls to the kernel and showing the output in the shell output.
manojkumar@n36-186-058:~$ ls -li /home | grep manoj
393576 lrwxrwxrwx 1 root root 23 Apr 1 16:11 manojkumar -> /data00/home/manojkumar
manojkumar@n36-186-058:~$ stat /home/manojkumar
File: /home/manojkumar -> /data00/home/manojkumar
Size: 23 Blocks: 0 IO Block: 4096 symbolic link
Device: 801h/2049d Inode: 393576 Links: 1
Access: (0777/lrwxrwxrwx) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2024-04-04 09:00:37.885311862 +0000
Modify: 2024-04-01 16:11:23.073950202 +0000
Change: 2024-04-01 16:11:23.073950202 +0000
Birth: -
inodes count
since total number of inodes are per partition, we can get details of free and used inodes with below command:
manojkumar@n36-186-058:~$ df -hi
Filesystem Inodes IUsed IFree IUse% Mounted on
udev 1.9M 362 1.9M 1% /dev
tmpfs 1.9M 591 1.9M 1% /run
/dev/sda1 7.5M 121K 7.4M 2% /
tmpfs 1.9M 2 1.9M 1% /dev/shm
tmpfs 1.9M 2 1.9M 1% /run/lock
tmpfs 1.9M 16 1.9M 1% /sys/fs/cgroup
tmpfs 1.9M 2 1.9M 1% /.syskrbonly
tmpfs 1.9M 13 1.9M 1% /run/user/0
/dev/sdb 32M 124K 32M 1% /data00
tmpfs 1.9M 13 1.9M 1% /run/user/1000
tmpfs 1.9M 11 1.9M 1% /run/user/2000
tmpfs 1.9M 11 1.9M 1% /run/user/1001Hard links
Suppose we have a file1.txt and we create a hard link to file.txt and name it as hardlink.txt. In this case, both file.txt and hardlink.txt points to same inode. so both are pointing to same space in the partition.
Below is the example:
manojkumar@n36-186-058:~$ ln file1.txt hardlink.txt
manojkumar@n36-186-058:~$ ls -ltr
total 8
-rw-r--r-- 2 manojkumar manojkumar 13 Apr 4 10:12 hardlink.txt
-rw-r--r-- 2 manojkumar manojkumar 13 Apr 4 10:12 file1.txt
manojkumar@n36-186-058:~$ stat file1.txt
File: file1.txt
Size: 13 Blocks: 8 IO Block: 4096 regular file
Device: 810h/2064d Inode: 11796490 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 1001/manojkumar) Gid: ( 1001/manojkumar)
Access: 2024-04-04 10:12:38.329800291 +0000
Modify: 2024-04-04 10:12:38.329800291 +0000
Change: 2024-04-04 10:12:50.937932823 +0000
Birth: -
manojkumar@n36-186-058:~$ stat hardlink.txt
File: hardlink.txt
Size: 13 Blocks: 8 IO Block: 4096 regular file
Device: 810h/2064d Inode: 11796490 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 1001/manojkumar) Gid: ( 1001/manojkumar)
Access: 2024-04-04 10:12:38.329800291 +0000
Modify: 2024-04-04 10:12:38.329800291 +0000
Change: 2024-04-04 10:12:50.937932823 +0000
Birth: -
manojkumar@n36-186-058:~$
if I change file1.txt, both files will see same change:
manojkumar@n36-186-058:~$ cat hardlink.txt
regular file
manojkumar@n36-186-058:~$ cat file1.txt
regular file
manojkumar@n36-186-058:~$ vim file1.txt
manojkumar@n36-186-058:~$
manojkumar@n36-186-058:~$
manojkumar@n36-186-058:~$ cat file1.txt
regular file but hardlink too
manojkumar@n36-186-058:~$ cat hardlink.txt
regular file but hardlink too
manojkumar@n36-186-058:~$Every file is a hard link. When a file is created, there is one hard link to that file.
Soft links/symlinks/symbolic links
soft link points to the file instead of same inode or space in the partition. soft link and actual file will have different inodes. soft links is similar as file shortcut in windows
manojkumar@n36-186-058:~$ ln -s file1.txt softlink.txt
manojkumar@n36-186-058:~$ ls -l
total 8
-rw-r--r-- 2 manojkumar manojkumar 30 Apr 4 10:16 file1.txt
-rw-r--r-- 2 manojkumar manojkumar 30 Apr 4 10:16 hardlink.txt
lrwxrwxrwx 1 manojkumar manojkumar 9 Apr 4 10:18 softlink.txt -> file1.txt
manojkumar@n36-186-058:~$ stat file1.txt
File: file1.txt
Size: 30 Blocks: 8 IO Block: 4096 regular file
Device: 810h/2064d Inode: 11796490 Links: 2
Access: (0644/-rw-r--r--) Uid: ( 1001/manojkumar) Gid: ( 1001/manojkumar)
Access: 2024-04-04 10:16:23.206164110 +0000
Modify: 2024-04-04 10:16:18.059110006 +0000
Change: 2024-04-04 10:16:18.063110048 +0000
Birth: -
manojkumar@n36-186-058:~$ stat softlink.txt
File: softlink.txt -> file1.txt
Size: 9 Blocks: 0 IO Block: 4096 symbolic link
Device: 810h/2064d Inode: 11796488 Links: 1
Access: (0777/lrwxrwxrwx) Uid: ( 1001/manojkumar) Gid: ( 1001/manojkumar)
Access: 2024-04-04 10:18:20.186393761 +0000
Modify: 2024-04-04 10:18:14.896338155 +0000
Change: 2024-04-04 10:18:14.896338155 +0000
Birth: -