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Linux Links

Overview:

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.

Types of Links:

* Soft Link or Symbolic links
* Hard Links

Types of Files:

Symbol Type of File
- Normal file
d Directory
l Link file (shortcut)
b Block file (Harddisk, Floppy disk)
c Character file (Keyboard, Mouse)

Difference between soft link and hard link:

Soft Link Hard link
Size of link file is equal to no. of characters in the name of original file Size of both file is same
Can be created across the Partition Can't be created across the partition
Inode no. of source and link file is different Inode no. of both file is same
if original file is deleted, link is broken and data is lost If original file is deleted then also link will contain data
SHORTCUT FILE BACKUP FILE
ln -s <source> <linkname> ln <source> <linkname>

Working with Links:

  • Creating a soft link
    $ ln -s samplefile samplefile.slink
$ ln -s samplefile samplefile.slink
$ ls -l
total 0
drwxrwxrwx 1 root krishnaprasadkv 4096 May 27 14:45 sampledir
-rwxrwxrwx 1 root krishnaprasadkv  139 May 30 14:30 samplefile
lrwxrwxrwx 1 root root              10 May 30 15:14 samplefile.slink -> samplefile
  • Creating a Hard link
    $ ln testing testing.hlink
$ ln testing testing.hlink
$ ls -l
total 0
drwxrwxrwx 1 root krishnaprasadkv 4096 May 27 14:45 sampledir
-rwxrwxrwx 1 root krishnaprasadkv  139 May 30 14:30 samplefile
lrwxrwxrwx 1 root root              10 May 30 15:14 samplefile.slink -> samplefile
-rw-r--r-- 2 root root               0 May 30 15:16 testing
-rw-r--r-- 2 root root               0 May 30 15:16 testing.hlink
  • List help page of ln command with their option.
    $ ln --help
Usage: ln [OPTION]... [-T] TARGET LINK_NAME   (1st form)
  or:  ln [OPTION]... TARGET                  (2nd form)
  or:  ln [OPTION]... TARGET... DIRECTORY     (3rd form)
  or:  ln [OPTION]... -t DIRECTORY TARGET...  (4th form)
In the 1st form, create a link to TARGET with the name LINK_NAME.
In the 2nd form, create a link to TARGET in the current directory.
In the 3rd and 4th forms, create links to each TARGET in DIRECTORY.
Create hard links by default, symbolic links with --symbolic.
By default, each destination (name of new link) should not already exist.
When creating hard links, each TARGET must exist.  Symbolic links
can hold arbitrary text; if later resolved, a relative link is
interpreted in relation to its parent directory.

Mandatory arguments to long options are mandatory for short options too.
      --backup[=CONTROL]      make a backup of each existing destination file
  -b                          like --backup but does not accept an argument
  -d, -F, --directory         allow the superuser to attempt to hard link
                                directories (note: will probably fail due to
                                system restrictions, even for the superuser)
  -f, --force                 remove existing destination files
  -i, --interactive           prompt whether to remove destinations
  -L, --logical               dereference TARGETs that are symbolic links
  -n, --no-dereference        treat LINK_NAME as a normal file if
                                it is a symbolic link to a directory
  -P, --physical              make hard links directly to symbolic links
  -r, --relative              create symbolic links relative to link location
  -s, --symbolic              make symbolic links instead of hard links
  -S, --suffix=SUFFIX         override the usual backup suffix
  -t, --target-directory=DIRECTORY  specify the DIRECTORY in which to create
                                the links
  -T, --no-target-directory   treat LINK_NAME as a normal file always
  -v, --verbose               print name of each linked file
      --help     display this help and exit
      --version  output version information and exit

The backup suffix is '~', unless set with --suffix or SIMPLE_BACKUP_SUFFIX.
The version control method may be selected via the --backup option or through
the VERSION_CONTROL environment variable.  Here are the values:

  none, off       never make backups (even if --backup is given)
  numbered, t     make numbered backups
  existing, nil   numbered if numbered backups exist, simple otherwise
  simple, never   always make simple backups

Using -s ignores -L and -P.  Otherwise, the last option specified controls
behavior when a TARGET is a symbolic link, defaulting to -P.