1

On my Linux machine, I have the following file:

   drwxr-xr-x 2 jsgdr     Unix_31  4096 Dec  2 17:46 jsgdr 

How to change the permission 2 to 4 so that I will this:

   drwxr-xr-x 4 jsgdr     Unix_31  4096 Dec  2 17:46 jsgdr 
1

The 2 and 4 are not permissions, but a count of the number of hard links to the file. From the GNU documentation (the POSIX specification of ls specifies this, but this wording is clearer, IMHO):

‘-l’
‘--format=long’
‘--format=verbose’
In addition to the name of each file, print the file type, file mode bits, 
number of hard links, owner name, group name, size, and timestamp (see 
Formatting file timestamps), normally the modification time. Print question 
marks for information that cannot be determined.

For example:

$ touch a
$ ls -l
total 0
-rw-r--r-- 1 root root 0 Dec  2 21:48 a
$ ln a b
$ ls -l
total 0
-rw-r--r-- 2 root root 0 Dec  2 21:48 a
-rw-r--r-- 2 root root 0 Dec  2 21:48 b
$ ln a c
$ ls -l
total 0
-rw-r--r-- 3 root root 0 Dec  2 21:48 a
-rw-r--r-- 3 root root 0 Dec  2 21:48 b
-rw-r--r-- 3 root root 0 Dec  2 21:48 c

For a directory, the hard link count is related to the number of subdirectories. See Why does a new directory have a hard link count of 2 before anything is added to it? for more information.

1

The number you are talking about doesn't refer to the permissions.

mkdir demo
cd demo
ls -ld
drwxr-xr-x 2 root root 4096 Dec  2 10:21 .

So, the number 2 here refers to,

  • the entry for that directory in its parent directory;
  • the directory's own entry for .

However, if you want to see 4, you could see it when,

mkdir sub_demo{1,2}
ls -ld
drwxr-xr-x 4 root root 4096 Dec  2 10:23 .

As you could see, we are seeing the number 4 because we have 2 subdirectories that got created. So now 4 represents,

  • the entry for that directory in its parent directory;
  • the directory's own entry for .
  • the .. entries in the 2 sub-directories inside the directory.

You could find a detailed explanation from my other answer here.

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