Introduction
There are two types of file links in Linux: hard links and symbolic links (soft links).
Hard link - this is simply an alternative file name that points to the same data on the hard drive. In practice, all hard links to a single file have the same weight because each of them points to exactly the same blocks of data.
Symbolic link (symbolic link or soft link) - is a separate file that contains the path to the file or directory to which the symbolic link refers. It is more flexible than a hard link, but depends on the existence of the original file.
If the above explanations seem unclear, try the commands below.
Example
Hard links
First, let's create a test file test1.txt, containing the text "abc":
echo abc > test1.txt
To create a hard link called test2.txt, issue the command:
ln test1.txt test2.txt
The file was not copied, but only acquired a new name pointing to the same area in memory. Now both names are equivalent. Removing the original name will not result in data loss as there is still a hard link called test2.txt pointing to this data.
So let's remove the original name test1.txt:
rm test1.txt
Using the cat command we will display the data from the test2.txt file:
cat test2.txt
The result, of course, is the text "abc". To find out how many hard links a given file has, you can run the ls -l command on one of its names:
ls -l test1.txt
Result:
-rw-r--r-- 2 runner21 runner21 4 Jan 14 12:46 test1.txt
The number 2 indicates that there are two hard links. Of course, they can be created in different places. To find all the places where they are located, run the command on one of the names (no matter whether it is test1.txt or test2.txt):
find / -samefile test1.txt
where / is the starting point of the search (root directory). You can customize this path to narrow down your search, e.g. to the /home directory:
find /home -samefile test1.txt
The result will be all paths specifying the same file.
Symbolic links
Let's create a test file test1.txt containing the text "abc":
echo abc > test1.txt
To create a symbolic link, issue the command:
ln -s test1.txt test2.txt
From now on, test2.txt points to test1.txt, but the two files are not equivalent. The test2.txt file is only an indication of what is visible when we execute the ls command:
ls -l test2.txt
The result is:
-rw-r--r-- 1 runner1 runner1 4 Jan 14 12:46 test2.txt -> test1.txt
The number specifying hard links has not changed, but we have received an explicit indication of what file the name test2.txt points to.
Warning: deleting the test1.txt file will result in data loss!
So if we delete test1.txt:
rm test1.txt
then test2.txt symbolic link will still exist, but will point to a non-existent file
cat test2.txt
as a result we will receive a message:
cat: test2.txt: No such file or directory
What's more interesting, if we now create a test1.txt file again with different contents but the same location:
echo cde > test1.txt
then test2.txt will now point to it (because the symbolic link has not changed):
cat test2.txt
The result is the text "cde".
If we want to find all symbolic links of the test1.txt file, we must issue the command:
find / -type l -name test1.txt
where / is the starting point of the search (root directory), and l specifies the search for a symbolic link. You can customize this path to narrow down your search, e.g. to the /home directory:
find /home -type l -name test1.txt
Summary
It is worth noting that:
- Hard links can only point to another file, while symbolic links can point to files or directories
- Hard links can point to the same file on the same file system, while symbolic links can point to files and directories that are located on different file systems, partitions, or even remote locations!
Good luck!
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