Linux links and symbolic links

How to Create Hard and Symbolic Links in Linux

In Unix-like operating systems such as Linux, “everything is a file” and a file is fundamentally a link to an inode (a data structure that stores everything about a file apart from its name and actual content).

A hard link is a file that points to the same underlying inode, as another file. In case you delete one file, it removes one link to the underlying inode. Whereas a symbolic link (also known as soft link) is a link to another filename in the filesystem.

Another important difference between the two types of links is that hard links can only work within the same filesystem while symbolic links can go across different filesystems.

How to Create Hard Links in Linux

To create a hard links in Linux, we will use ln utility. For example, the following command creates a hard link named tp to the file topprocs.sh .

Create a Hard Link to File

Looking at the output above, using ls command, the new file is not indicated as a link, it is shown as a regular file. This implies that tp is just another regular executable file that points to the same underlying inode as topprocs.sh .

To make a hard link directly into a soft link, use the -P flag like this.

How to Create Symbolic Links in Linux

To create a symbolic links in Linux, we will use same ln utility with -s switch. For example, the following command creates a symbolic link named topps.sh to the file topprocs.sh .

Create a Symbolic Link to File

From the above output, you can see from the file permissions section that topps.sh is a link indicated by l: meaning it is a link to another filename.

If the symbolic link already exist, you may get an error, to force the operation (remove exiting symbolic link), use the -f option.

Forcefully Create Symbolic Link

To enable verbose mode, add the -v flag to prints the name of each linked file in the output.

Enable Verbose in Command Output

That’s It! Do check out these following related articles.

In this article, we’ve learned how to create hard and symbolic links in Linux. You can ask any question(s) or share your thoughts about this guide via the feedback form below.

If You Appreciate What We Do Here On TecMint, You Should Consider:

TecMint is the fastest growing and most trusted community site for any kind of Linux Articles, Guides and Books on the web. Millions of people visit TecMint! to search or browse the thousands of published articles available FREELY to all.

If you like what you are reading, please consider buying us a coffee ( or 2 ) as a token of appreciation.

We are thankful for your never ending support.

Источник

Symbolic Links in Unix/Linux

Different file systems in the UNIX/Linux universe allow a variety of entries such as regular files, directories, sockets, named pipes, and links. In this article I will explain to you what links are, which types of links exist, how to create a symbolic link, and how to detect broken symbolic links easily. Links allow you to have multiple entry points into a file-system, allowing you to have many less copies (sometimes only one) yet maintaining flexibility by having multiple ways to reach a given file.

Linking Entries

On the UNIX/Linux command line, the tool ln abbreviates the term link. It allows you to create an additional reference to a file, or directory. It does that by adding an additional name of an entry in the file allocation table of the file system. Having done that you can access the referenced file or directory with both the original name, and the new name, too. Think of a single person might be an employee, client and prospect.

The tool ln belongs to the list of essential software in Unix/Linux. On Debian GNU/Linux and Ubuntu it is part of the package coreutils .

Hardlinks vs Softlinks

There is a clear distinction between hardlinks, and softlinks. Softlinks are named symbolic links, too. There are quite a few differences between the two types as listed below:

Hard Links	Soft link (symbolic link)
Target must exist	Target may already exist, but does not have to
Allowed within file systems only	Allowed between different file systems
Links directly to the place the file is stored	Links to the entry in the file system table (node)
Removing the link means removing the whole file	Removing the link means removing the link to the node, not the file itself

How to Create Symbolic Links

Running the ln command without options creates a hardlink from source to destination. With the help of the option -s it creates a symbolic link, instead. -s is the short name of the option, whereas —symbolic is the longer name. The link will be created in the current directory of the filesystem at the moment it is created. Developers just use the term symlink. In general, call it as follows:

target is the file or directory to link to, and link_name is the name of the link that shall reference to the target. As an example, this call creates a symbolic link from link_to_python to /usr/bin/python :

Example 1: Creating a symbolic link

To see what ln does, a useful option is -v ( —verbose for the longer option). This gives you further information on the action.

Example 2: Creating a symbolic link with additional information

As you can see, the output of the command depicts the new link created.

Use Cases

First, a regular use case you may not have been aware of are two commonly used file system entries — . (the local directory) and .. (parent directory). These are implemented as symbolic links.

Second, developers install several versions of a program to do their tests. The usage of symbolic links can become quite handy to reference to the current version that is tested, and keeps two or more instances of it available without much trouble.

Finding Dead Symbolic Links

What if you delete a file that has a symbolic link pointing to it? We refer to these links with a non-existent «target» as «dead» links. To detect such cases the find command is quite helpful. Therefor, the option -L , and the action -type l comes into play. The -L flag tells find to follow symbolic links, while -type l will only match symbolic links.

In Example 3 the current directory contains two files named auto and backup , as well as two symbolic links — data pointing to auto , and generic pointing to files . Unfortunately, the files file/directory does not exist.

Using the find command, we can examine the links and outputs their names in case the link target does not exist. In our case it is the symbolic link named generic pointing to files that does not exist.

Free eBook: Git Essentials

Check out our hands-on, practical guide to learning Git, with best-practices, industry-accepted standards, and included cheat sheet. Stop Googling Git commands and actually learn it!

Example 3: Detecting broken links using find

As an alternative, you may like the symlinks command. This is a non-default package available for both Debian GNU/Linux, and Ubuntu. With the two options -s and -v , symlinks detects the entries. As seen in Example 4 below, links without valid targets are classified as dangling.

Example 4: Detecting broken links using symlinks

Conclusion

The concept of symbolic links are no big mystery. Creating these references can simplify the use of software, and helps to test different versions of it on the same system. Keep in mind that the Linux Professional Institute (LPI) will ask you questions about it during certification for LPI1.

Acknowledgements

The author would like to thank Gerold Rupprecht for his support, and critics while preparing this article.

Источник

What is Symbolic Links in Linux? How to Create Symbolic Links?

What is Symbolic link in Linux and why is it used?

A symbolic link, also known as a symlink or a soft link, is a special type of file that simply points to another file or directory just like shortcuts in Windows. Creating symbolic link is like creating alias to an actual file.

If you try to access the symbolic link, you actually access the target file to which the symlink points to. Changes performed on the content of the link file changes the content of the actual target file.

If you use the ls command with option -l, this is what a symbolic link looks like:

In most Linux distributions, the links are displayed in a different color than the rest of the entries so that you can distinguish the links from the regular files and directories.

Soft Link displayed in different color

Symbolic links offer a convenient way to organize and share files. They provide quick access to long and confusing directory paths. They are heavily used in linking libraries in Linux.

Now that you know a little about the symbolic links, let’s see how to create them.

How to create a symbolic link in Linux

To create a symbolic link to target file from link name, you can use the ln command with -s option like this:

The -s option is important here. It determines that the link is soft link. If you don’t use it, it will create a hard link. I’ll explain the difference between soft links and hard links in a different article.

Things to keep in mind about symbolic links

Symbolic links could be confusing at times therefore you should keep note of a few things.

Changes made to link are reflected in the original file

That’s the whole purpose of the links after all. You access the target file by accessing the link. You can make changes to the target file through the links. Let’s see with example.

I have a file prog.py in newdir/test_dir. It has the following attributes:

Now, I’ll create a soft link to this file in my present directory:

Here are the attributes of the newly created link:

Notice the l (it’s L, not one) at the beginning of the line? If you are familiar with the file permissions in Linux, you would know that the ‘l’ signifies link and thus it tells you that this file is actually a link. To refresh your memory, – means file, and d means directory.

Now if I use this link to change the content or the attributes, the same will be reflected in the target file. For example, I am using touch command on the soft link and you’ll notice that it changes the timestamp of the target file.

Does it link to a file or a directory? You may not know!

How would you know if the link points to file or a directory? You cannot know that until you follow the path and access the target file itself.

You can create links to non-existent file or directory

Yes, that’s totally possible. This is why you should be careful while creating soft links in Linux. The target file to which you are linking doesn’t need to exist. You won’t get any error or warning for creating link to a file/directory that does not exist.

You’ll get error only when you try to access the target file, either through the link or on its own. The ls command will still work though.

The symbolic links are created with 777 permission but it means nothing

Did you notice the file permission on the symbolic link? The symlinks are always created with 777 permission (rwxrwxrwx). For regular file, this would mean that anyone can access the file. But that’s not the case for the links.

If the file permissions on the links were treated as it is, any user could create a symlink to a secure file and access it freely. That would be a major security issue. Thankfully, that doesn’t happen. Because the permission on the target files matter, not the permission on links.

You may use the chmod command to change the permission on the link but it will change the permission of the linked file, not the link itself.

You can link to a link of a link aka chained symbolic link

You can make a symbolic link that points to another link and so on. This is called chained symbolic link. It’s better to avoid them as it creates more confusion.

Well, that’s it. I presume you have a better knowledge of the soft links now and you know how to create symbolic links in Linux. You may read about the symlinks command that can help you find broken symlinks in Linux and manage them easily.

If you have questions or suggestions, please leave a comment below.

Источник

How to: Linux / UNIX create soft link with ln command

Symbolic links can be made to directories as well as to files on different filesystems or different partitions.

Two types of links

• symbolic links (also known as “soft links” or “symlinks”): Refer to a symbolic path indicating the abstract location of another file.
• hard links : Refer to the specific location of physical data.

How do I create soft link / symbolic link under Unix and Linux?

Soft links are created with the ln command. For example, the following would create a soft link named link1 to a file named file1, both in the current directory
$ ln -s file1 link1
To verify new soft link run:
$ ls -l file1 link1
Sample outputs:

• No ads and tracking
• In-depth guides for developers and sysadmins at Opensourceflare✨
• Join my Patreon to support independent content creators and start reading latest guides:
  • How to set up Redis sentinel cluster on Ubuntu or Debian Linux
  • How To Set Up SSH Keys With YubiKey as two-factor authentication (U2F/FIDO2)
  • How to set up Mariadb Galera cluster on Ubuntu or Debian Linux
  • A podman tutorial for beginners – part I (run Linux containers without Docker and in daemonless mode)
  • How to protect Linux against rogue USB devices using USBGuard

Join Patreon ➔

From the above outputs it is clear that a symbolic link named ‘link1’ contains the name of the file named ‘file1’ to which it is linked.

How to use the ln command

So the syntax is as follows to create a symbolic link in Unix or Linux, at the shell prompt:
$ ln -s < source-filename >< symbolic-filename >

For example create a softlink for /webroot/home/httpd/test.com/index.php as /home/vivek/index.php, enter the following command:
$ ln -s /webroot/home/httpd/test.com/index.php /home/vivek/index.php
$ ls -l
Sample outputs:

You can now edit the soft link named /home/vivek/index.php and /webroot/home/httpd/test.com/index.php will get updated:
$ vi /home/vivek/index.php
Your actual file /webroot/home/httpd/test.com/index.php remains on disk even if you deleted the soft link /home/vivek/index.php using the rm command:
$ rm /home/vivek/index.php ## ##
## But original/actual file remains as it is ##
$ ls -l /webroot/home/httpd/test.com/index.php

Creating Symlink to a directory

The syntax remains same:
$ ln -s
For example, create a symbolic link from the /home/lighttpd/http/users/vivek/php/app/ directory to the /app/ directory you would run:
$ ln -s /home/lighttpd/http/users/vivek/php/app/ /app/
Now I can edit files using /app/
$ cd /app/
$ ls -l
$ vi config.php

How to overwrite symlinks/Soft link

Pass the -f to the ln command to overwrite links:
ln -f -s /path/to/my-cool-file.txt link.txt

How to delete or remove symlinks/soft links

Use the rm command to delete a file including symlinks:
rm my-link-name
unlink /app/
rm /home/vivek/index.php

Getting help about the ln command

Type the following ln command:
$ man ln
$ ln —help

ln command option	Description
—backup	make a backup of each existing destination file
-b	like —backup but does not accept an argument
-d	allow the superuser to attempt to hard link directories (note: will probably fail due to system restrictions, even for the superuser)
-f	remove existing destination files
-i	prompt whether to remove destinations
-L	dereference TARGETs that are symbolic links
-n	treat LINK_NAME as a normal file if it is a symbolic link to a directory
-P	make hard links directly to symbolic links
-r	create symbolic links relative to link location
-s	make symbolic links instead of hard links
-S	override the usual backup suffix
-t	specify the DIRECTORY in which to create the links
-T	treat LINK_NAME as a normal file always
-v	print name of each linked file
—help	display this help and exit
—version	output version information and exit

Conclusion

You learned how to create a symbolic link in Linux using the ln command by passing the -s option. See ln command man page here for more information.

🐧 Get the latest tutorials on Linux, Open Source & DevOps via

Источник