Explaining Soft Link And Hard Link In Linux With Examples
Soft and Hard
links in Unix/Linux
A link in UNIX is a pointer to a file. Like pointers in
any programming languages, links in UNIX are pointers pointing to a file or a
directory. Creating links is a kind of shortcuts to access a file. Links allow
more than one file name to refer to the same file, elsewhere.
There are two
types of links :
1.
Soft Link or
Symbolic links
2.
Hard Links
These links
behave differently when the source of the link (what is being linked to) is
moved or removed. Symbolic links are not updated (they merely contain a string
which is the path name of its target); hard links always refer to the source,
even if moved or removed.
For example, if
we have a file a.txt. If we create a hard link to the file and then delete the
file, we can still access the file using hard link. But if we create a soft
link of the file and then delete the file, we can’t access the file through
soft link and soft link becomes dangling. Basically hard link increases
reference count of a location while soft links work as a shortcut (like in
Windows)
1. Hard Links
Each hard linked file is assigned the same Inode value as the original,
therefore they reference the same physical file location. Hard links more
flexible and remain linked even if the original or linked files are moved
throughout the file system, although hard links are unable to cross different
file systems.
·
ls -l command
shows all the links with the link column shows number of links.
·
Links have
actual file contents
·
Removing any
link, just reduces the link count, but doesn’t affect other links.
·
Even if we
change the filename of the original file then also the hard links properly
work.
·
We cannot create
a hard link for a directory to avoid recursive loops.
·
If original file
is removed then the link will still show the content of the file.
·
The size of any
of the hard link file is same as the original file and if we change the content
in any of the hard links then size of all hard link files are updated.
·
The disadvantage
of hard links is that it cannot be created for files on different file systems
and it cannot be created for special files or directories.
·
Command to
create a hard link is:
$
ln [original filename] [link name]
·
2. Soft Links
·
A soft link is
similar to the file shortcut feature which is used in Windows Operating systems.
Each soft linked file contains a separate Inode value that points to the
original file. As similar to hard links, any changes to the data in either file
is reflected in the other. Soft links can be linked across different file
systems, although if the original file is deleted or moved, the soft linked
file will not work correctly (called hanging link).
·
ls -l command
shows all links with first column value l? and the link points to original
file.
·
Soft Link
contains the path for original file and not the contents.
·
Removing soft
link doesn’t affect anything but removing original file, the link becomes
“dangling” link which points to nonexistent file.
·
A soft link can
link to a directory.
·
Size of a soft
link is equal to the name of the file for which the soft link is created. E.g
If name of file is file1 then size of it’s soft link will be 5 bytes which is
equal to size of name of original file.
·
If we change the
name of the original file then all the soft links for that file become dangling
i.e. they are worthless now.
·
Link across file
systems: If you want to link files across the file systems, you can only use
symlinks/soft links.
·
Command to
create a Soft link is:
$
ln -s [original filename] [link name]
