What is the difference between a symbolic link and a hard link

Question

Recently I was asked this during a job interview  I was honest and said I knew how a symbolic link behaves and how to create one  but do not understand the use of a hard link and how it differs from a symbolic one

User · Answer

Soft Link   soft or symbolic is more of a short cut to the original file    if you delete the original the shortcut fails and if you only delete the short cut nothing happens to the original   Soft link Syntax  ln -s   Pathof Target file  link  Output   link - gt    Target file  Proof  readlink  link  Also in ls  -l  link output you will see the first letter in lrwxrwxrwx as l which is indication that the file is a soft link   Deleting the link  unlink  link    Note  If you wish  your softlink can work even after moving it somewhere else from the current dir  Make sure you give absolute path and not relative path while creating a soft link  i e  starting from  root user Target file and not   Target file   Hard Link   Hard link is more of a mirror copy or multiple paths to the same file  Do something to file1 and it appears in file 2  Deleting one still keeps the other ok   The inode or file  is only deleted when all the  hard links or all the paths to the  same file inode has been deleted   Once a hard link has been made the link has the inode of the original file  Deleting renaming or moving the original file will not affect the hard link as it links to the underlying inode  Any changes to the data on the inode is reflected in all files that refer to that inode   Hard Link syntax  ln   Target file   link  Output  A file with name link will be created with the same inode number as of Targetfile   Proof  ls -i   link   Target file   check their inodes   Deleting the link  rm  -f  link  Delete the link just like a normal file    Note  Symbolic links can span file systems as they are simply the name of another file  Whereas hard links are only valid within the same File System   Symbolic links have some features hard links are missing    Hard link point to the file content  while Soft link points to the file name  while size of hard link is the size of the content while soft link is having the file name size  Hard links share the same inode  Soft links do not  Hard links can t cross file systems  Soft links do  you know immediately where a symbolic link points to while with hard links  you need to explore the whole file system to find files sharing the same inode     find   -inum 517333    home bobbin sync sh  root synchro   hard-links cannot point to directories    The hard links have two limitations    The directories cannot be hard linked  Linux does not permit this to maintain the acyclic tree structure of directories  A hard link cannot be created across filesystems  Both the files must be on the same filesystems  because different filesystems have different independent inode tables  two files on different filesystems  but with same inode number will be different

User · Answer

From MSDN   Symbolic link     A symbolic link is a file-system object that points to another file system object  The object being pointed to is called the target       Symbolic links are transparent to users  the links appear as normal   files or directories  and can be acted upon by the user or application   in exactly the same manner       Symbolic links are designed to aid in migration and application   compatibility with UNIX operating systems  Microsoft has implemented   its symbolic links to function just like UNIX links       Symbolic links can either be absolute or relative links  Absolute   links are links that specify each portion of the path name  relative   links are determined relative to where relative   link specifiers are in   a specified path   An example of Absolute Symbolic Link  X   C  alpha beta absLink gamma file  Link   absLink  maps to    machineB share  Modified Path     machineB share gamma file    An example of Relative Symbolic Links  X  C  alpha beta link gamma file Link   link  maps to        theta  Modified Path   C  alpha beta       theta gamma file  Final Path   C  theta gamma file    Hard link     A hard link is the file system representation of a file by which   more than one path references a single file in the same volume    To create a hard link in windows  navigate to where link is to be created and enter this command   mklink  H Link name target path   Note that you can delete hard links any order  regardless of the order in which they were created  Also  hard links can not be created when   references are in different local drives references include network drive  In other words  one of the references is a network drive hard link to be created is in the same path as the target   Junction  NTFS supports another link type called junction  MSDN defines it as follows      A junction  also called a soft link  differs from a hard link in that the storage objects it references are separate directories  and a junction can link directories located on different local volumes on the same computer  Otherwise  junctions operate identically to hard links     The bolded parts in hard link section and junction section show the basic difference between the two   Command to create a junction in windows  navigate to where link is to be created and then enter   mklink  J link name target path

User · Answer

Symbolic links link to a path name  This can be anywhere in a system s file tree  and doesn t even have to exist when the link is created  The target path can be relative or absolute   Hard links are additional pointers to an inode  meaning they can exist only on the same volume as the target  Additional hard links to a file are indistinguishable from the  original  name used to reference a file

User · Answer

I add on Nick s question  when are hard links useful or necessary  The only application that comes to my mind  in which symbolic links wouldn t do the job  is providing a copy of a system file in a chrooted environment

User · Answer

Hard link Vs Soft link can be easily explained by this image

User · Answer

Underneath the file system  files are represented by inodes   Or is it multiple inodes   Not sure    A file in the file system is basically a link to an inode  A hard link  then  just creates another file with a link to the same underlying inode   When you delete a file  it removes one link to the underlying inode  The inode is only deleted  or deletable over-writable  when all links to the inode have been deleted   A symbolic link is a link to another name in the file system   Once a hard link has been made the link is to the inode  Deleting  renaming  or moving the original file will not affect the hard link as it links to the underlying inode  Any changes to the data on the inode is reflected in all files that refer to that inode   Note  Hard links are only valid within the same File System  Symbolic links can span file systems as they are simply the name of another file

User · Answer

Adding to all the above answers  the difference in finding the hardlink and softlink file can be understood as below   I have a file f6 in my current directory  as well as a directory named t2   File named f1 and   t2 f2 are symbolic links to f6   File named f7 and   t2 f8 are hard links of f6   To find soft as well as hard link we can use     find -L   -samefile f6    gt    f1  gt    f6  gt    f7  gt    t2 f2  gt    t2 f8   To find only hardlink we can use     find   -xdev -samefile f6   gt    f6  gt    f7  gt    t2 f8   Since hardlinks can be created on the same file system  we can search all the hardlinks without -L option used  with -xdev option  in the same file-system mount-point  It saves the unnecessary search into different mount points    So searching the hardlink is somewhat faster then searching the softlinks Please rectify if I am wrong or not clear

User · Answer

Also    Read performance of hard links is better than symbolic links  micro-performance  Symbolic links can be copied  version-controlled    etc  In another words  they are an actual file  On the other end  a hard link is something at a slightly lower level and you will find that compared to symbolic links  there are less tools that provide means for working with the hard links as hard links and not as normal files

User · Answer

IN this answer when i say a file i mean the location in memory  All the data that is saved is stored in memory using a data structure called inodes Every inode has a inodenumber The inode number is used to access the inode All the hard links to a file may have different names but share the same inode number Since all the hard links have the same inodenumber which inturn access the same inode  all of them point to the same physical memory   A symbolic link is a special kind of file Since it is also a file it will have a file name and an inode number As said above the inode number acceses an inode which points to data Now what makes a symbolic link special is that the inodenumbers in symbolic links  access those inodes which point to  a path  to another file More specifically the inode number in symbolic link acceses those inodes who point to another hard link   when we are moving copying deleting a file in GUI we are playing with the hardlinks of the file not the physical memory when we delete a file we are deleting the hardlink of the file  we are not wiping out the physical memory If all the hardlinks to file are deleted then it will not be possible to access the data stored although it may still be present in memory

User · Answer

I would point you to Wikipedia    Symbolic link Hard link   A few points    Symlinks  unlike hard links  can cross filesystems  most of the time   Symlinks can point to directories  Hard links point to a file and enable you to refer to the same file with more than one name  As long as there is at least one link  the data is still available

User · Answer

Hard link Vs Soft link can be easily explained by this image

User · Answer

What you think of as an ordinary  file  is actually two separate things  The data of a file  and a directory entry  When you create a hard link for a file  you actually create a second directory entry which refers to the same data  Both directory entries have the exact same functionality  each one can be used to open the file to read it  So you don t really have  a file plus a hard link   you have  file data with two directory entries   What you think of as deleting a file actually deletes a directory entry  and when the last directory entry for the data is deleted  then the data itself is deleted as well  For ordinary files that have only one directory entry  deleting the directory entry will delete the data as always   While a file is opened  the OS creates a temporary link to the file  so even when you delete all directory entries  the data stays but disappears as soon as you close the file     As an example  create a file A txt  a hard link B txt  and delete A txt  When you created A txt  some data was created  and a directory entry A txt  When you created the hard link  another directory entry B txt was created  pointing to the exact same data  When you delete A txt  you still have all the data and a single directory entry B txt  exactly as if you had create a file B txt in the first place    A soft link is just an  almost  ordinary file  except that it doesn t contain data  but the path of another directory entry  If you delete the file that the soft link refers to  then the soft link will contain a path that doesn t point to a directory entry anymore  it is broken  If you delete the soft link  it s like deleting any other file  the file it points to is unaffected

User · Answer

Hard links are useful when the original file is getting moved around   For example  moving a file from  bin to  usr bin or to  usr local bin   Any symlink to the file in  bin would be broken by this  but a hardlink  being a link directly to the inode for the file  wouldn t care   Hard links may take less disk space as they only take up a directory entry  whereas a symlink needs its own inode to store the name it points to   Hard links also take less time to resolve - symlinks can point to other symlinks that are in symlinked directories   And some of these could be on NFS or other high-latency file systems  and so could result in network traffic to resolve   Hard links  being always on the same file system  are always resolved in a single look-up  and never involve network latency  if it s a hardlink on an NFS filesystem  the NFS server would do the resolution  and it would be invisible to the client system    Sometimes this is important   Not for me  but I can imagine high-performance systems where this might be important   I also think things like mmap 2  and even open 2  use the same functionality as hardlinks to keep a file s inode active so that even if the file gets unlink 2 ed  the inode remains to allow the process continued access  and only once the process closes it does the file really go away   This allows for much safer temporary files  if you can get the open and unlink to happen atomically  which there may be a POSIX API for that I m not remembering  then you really have a safe temporary file  where you can read write your data without anyone being able to access it   Well  that was true before  proc gave everyone the ability to look at your file descriptors  but that s another story   Speaking of which  recovering a file that is open in process A  but unlinked on the file system revolves around using hardlinks to recreate the inode links so the file doesn t go away when the process which has it open closes it or goes away

User · Answer

I add on Nick s question  when are hard links useful or necessary  The only application that comes to my mind  in which symbolic links wouldn t do the job  is providing a copy of a system file in a chrooted environment

User · Answer

Hard links are useful when the original file is getting moved around   For example  moving a file from  bin to  usr bin or to  usr local bin   Any symlink to the file in  bin would be broken by this  but a hardlink  being a link directly to the inode for the file  wouldn t care   Hard links may take less disk space as they only take up a directory entry  whereas a symlink needs its own inode to store the name it points to   Hard links also take less time to resolve - symlinks can point to other symlinks that are in symlinked directories   And some of these could be on NFS or other high-latency file systems  and so could result in network traffic to resolve   Hard links  being always on the same file system  are always resolved in a single look-up  and never involve network latency  if it s a hardlink on an NFS filesystem  the NFS server would do the resolution  and it would be invisible to the client system    Sometimes this is important   Not for me  but I can imagine high-performance systems where this might be important   I also think things like mmap 2  and even open 2  use the same functionality as hardlinks to keep a file s inode active so that even if the file gets unlink 2 ed  the inode remains to allow the process continued access  and only once the process closes it does the file really go away   This allows for much safer temporary files  if you can get the open and unlink to happen atomically  which there may be a POSIX API for that I m not remembering  then you really have a safe temporary file  where you can read write your data without anyone being able to access it   Well  that was true before  proc gave everyone the ability to look at your file descriptors  but that s another story   Speaking of which  recovering a file that is open in process A  but unlinked on the file system revolves around using hardlinks to recreate the inode links so the file doesn t go away when the process which has it open closes it or goes away

User · Answer

Hard links are very useful when doing incremental backups  See rsnapshot  for example  The idea is to do copy using hard links    copy backup number n to n   1 copy backup n - 1 to n     copy backup 0 to backup 1 update backup 0 with any changed files    The new backup will not take up any extra space apart from any changes you ve made  since all the incremental backups will point to the same set of inodes for files which haven t changed

User · Answer

A directory entry is link a structrue   struct dentry      ino t ino      char  name 256       the ino is the number of inode  the name is the file name  inode structure maybe like   struct inode        link t nlink                 for example you creat a file  1  the directory entry maybe like   struct dentry       ino t ino     such as 15         char  name 256       1          the inode struct maybe like      struct inode     inode number 15             link t nlink     nlink   1                         then you create a hard link may be  100   the directory entry maybe like     struct dentry       ino t ino     15         char  name 256      100          the inode struct maybe like      struct inode     inode numebr 15             link t nlink     nlink   2                         then you create a symbolic link may be  200  to file 1  the directory entry maybe like     struct dentry          ino t ino     such as 16            char  name 256       200           the inode struct maybe like      struct inode     inode number 15              link t nlink     nlink   2                           struct inode     inode number 16             link t nlink     nlink   1                          the data of inode 16 maybe  1 or 1

User · Answer

My two cents on usage   Soft links may be used to shorten long path names  i e    ln -s  long folder name on long path file txt  short file txt   Changes made to  short file txt will be applied on the original file   Hard links may be used to move around big files     ls -lh  myapp dev  total 10G -rw-r--r-- 2 root root 10G May 22 12 09 application bin   ln  myapp dev application bin  myapp prd application bin  Instant copy to different folder  and original file  on  myapp dev  may be moved or deleted  without touching the file on  myapp prd

User · Answer

From MSDN   Symbolic link     A symbolic link is a file-system object that points to another file system object  The object being pointed to is called the target       Symbolic links are transparent to users  the links appear as normal   files or directories  and can be acted upon by the user or application   in exactly the same manner       Symbolic links are designed to aid in migration and application   compatibility with UNIX operating systems  Microsoft has implemented   its symbolic links to function just like UNIX links       Symbolic links can either be absolute or relative links  Absolute   links are links that specify each portion of the path name  relative   links are determined relative to where relative   link specifiers are in   a specified path   An example of Absolute Symbolic Link  X   C  alpha beta absLink gamma file  Link   absLink  maps to    machineB share  Modified Path     machineB share gamma file    An example of Relative Symbolic Links  X  C  alpha beta link gamma file Link   link  maps to        theta  Modified Path   C  alpha beta       theta gamma file  Final Path   C  theta gamma file    Hard link     A hard link is the file system representation of a file by which   more than one path references a single file in the same volume    To create a hard link in windows  navigate to where link is to be created and enter this command   mklink  H Link name target path   Note that you can delete hard links any order  regardless of the order in which they were created  Also  hard links can not be created when   references are in different local drives references include network drive  In other words  one of the references is a network drive hard link to be created is in the same path as the target   Junction  NTFS supports another link type called junction  MSDN defines it as follows      A junction  also called a soft link  differs from a hard link in that the storage objects it references are separate directories  and a junction can link directories located on different local volumes on the same computer  Otherwise  junctions operate identically to hard links     The bolded parts in hard link section and junction section show the basic difference between the two   Command to create a junction in windows  navigate to where link is to be created and then enter   mklink  J link name target path

User · Answer

I would point you to Wikipedia    Symbolic link Hard link   A few points    Symlinks  unlike hard links  can cross filesystems  most of the time   Symlinks can point to directories  Hard links point to a file and enable you to refer to the same file with more than one name  As long as there is at least one link  the data is still available

User · Answer

As the saying goes  a picture is worth a thousand words  Here is how I visualize it     Here is how we get to that picture    Create a name myfile txt in the file system that points to a new inode  which contains the metadata for the file and points to the blocks of data that contain its contents  i e  the text  Hello  World       echo  Hello  World    gt  myfile txt  Create a hard link my-hard-link to the file myfile txt  which means  create a file that should point to the same inode that myfile txt points to      ln myfile txt my-hard-link  Create a soft link my-soft-link to the file myfile txt  which means  create a file that should point to the file myfile txt      ln -s myfile txt my-soft-link    Look what will now happen if myfile txt is deleted  or moved   my-hard-link still points to the same contents  and is thus unaffected  whereas my-soft-link now points to nothing  Other answers discuss the pros cons of each

User · Answer

Simply   Hard link   is just add new name to a file  that s mean   a file can have many name in the same time  all name are equal to each other  no one preferred  Hard link is not mean to copy the all contents of file and make new file is not that  it just create an alternative name to be known     Symbolic link  symlink    is a file pointer to another file  if the symbolic link points to an existing file which is later deleted  the symbolic link continues to point to the same file name even though the name no longer names any file

User · Answer

Underneath the file system  files are represented by inodes   Or is it multiple inodes   Not sure    A file in the file system is basically a link to an inode  A hard link  then  just creates another file with a link to the same underlying inode   When you delete a file  it removes one link to the underlying inode  The inode is only deleted  or deletable over-writable  when all links to the inode have been deleted   A symbolic link is a link to another name in the file system   Once a hard link has been made the link is to the inode  Deleting  renaming  or moving the original file will not affect the hard link as it links to the underlying inode  Any changes to the data on the inode is reflected in all files that refer to that inode   Note  Hard links are only valid within the same File System  Symbolic links can span file systems as they are simply the name of another file

User · Answer

As the saying goes  a picture is worth a thousand words  Here is how I visualize it     Here is how we get to that picture    Create a name myfile txt in the file system that points to a new inode  which contains the metadata for the file and points to the blocks of data that contain its contents  i e  the text  Hello  World       echo  Hello  World    gt  myfile txt  Create a hard link my-hard-link to the file myfile txt  which means  create a file that should point to the same inode that myfile txt points to      ln myfile txt my-hard-link  Create a soft link my-soft-link to the file myfile txt  which means  create a file that should point to the file myfile txt      ln -s myfile txt my-soft-link    Look what will now happen if myfile txt is deleted  or moved   my-hard-link still points to the same contents  and is thus unaffected  whereas my-soft-link now points to nothing  Other answers discuss the pros cons of each

User · Answer

IN this answer when i say a file i mean the location in memory  All the data that is saved is stored in memory using a data structure called inodes Every inode has a inodenumber The inode number is used to access the inode All the hard links to a file may have different names but share the same inode number Since all the hard links have the same inodenumber which inturn access the same inode  all of them point to the same physical memory   A symbolic link is a special kind of file Since it is also a file it will have a file name and an inode number As said above the inode number acceses an inode which points to data Now what makes a symbolic link special is that the inodenumbers in symbolic links  access those inodes which point to  a path  to another file More specifically the inode number in symbolic link acceses those inodes who point to another hard link   when we are moving copying deleting a file in GUI we are playing with the hardlinks of the file not the physical memory when we delete a file we are deleting the hardlink of the file  we are not wiping out the physical memory If all the hardlinks to file are deleted then it will not be possible to access the data stored although it may still be present in memory

User · Answer

Adding to all the above answers  the difference in finding the hardlink and softlink file can be understood as below   I have a file f6 in my current directory  as well as a directory named t2   File named f1 and   t2 f2 are symbolic links to f6   File named f7 and   t2 f8 are hard links of f6   To find soft as well as hard link we can use     find -L   -samefile f6    gt    f1  gt    f6  gt    f7  gt    t2 f2  gt    t2 f8   To find only hardlink we can use     find   -xdev -samefile f6   gt    f6  gt    f7  gt    t2 f8   Since hardlinks can be created on the same file system  we can search all the hardlinks without -L option used  with -xdev option  in the same file-system mount-point  It saves the unnecessary search into different mount points    So searching the hardlink is somewhat faster then searching the softlinks Please rectify if I am wrong or not clear

User · Answer

What you think of as an ordinary  file  is actually two separate things  The data of a file  and a directory entry  When you create a hard link for a file  you actually create a second directory entry which refers to the same data  Both directory entries have the exact same functionality  each one can be used to open the file to read it  So you don t really have  a file plus a hard link   you have  file data with two directory entries   What you think of as deleting a file actually deletes a directory entry  and when the last directory entry for the data is deleted  then the data itself is deleted as well  For ordinary files that have only one directory entry  deleting the directory entry will delete the data as always   While a file is opened  the OS creates a temporary link to the file  so even when you delete all directory entries  the data stays but disappears as soon as you close the file     As an example  create a file A txt  a hard link B txt  and delete A txt  When you created A txt  some data was created  and a directory entry A txt  When you created the hard link  another directory entry B txt was created  pointing to the exact same data  When you delete A txt  you still have all the data and a single directory entry B txt  exactly as if you had create a file B txt in the first place    A soft link is just an  almost  ordinary file  except that it doesn t contain data  but the path of another directory entry  If you delete the file that the soft link refers to  then the soft link will contain a path that doesn t point to a directory entry anymore  it is broken  If you delete the soft link  it s like deleting any other file  the file it points to is unaffected

User · Answer

Hard links are very useful when doing incremental backups  See rsnapshot  for example  The idea is to do copy using hard links    copy backup number n to n   1 copy backup n - 1 to n     copy backup 0 to backup 1 update backup 0 with any changed files    The new backup will not take up any extra space apart from any changes you ve made  since all the incremental backups will point to the same set of inodes for files which haven t changed

User · Answer

A directory entry is link a structrue   struct dentry      ino t ino      char  name 256       the ino is the number of inode  the name is the file name  inode structure maybe like   struct inode        link t nlink                 for example you creat a file  1  the directory entry maybe like   struct dentry       ino t ino     such as 15         char  name 256       1          the inode struct maybe like      struct inode     inode number 15             link t nlink     nlink   1                         then you create a hard link may be  100   the directory entry maybe like     struct dentry       ino t ino     15         char  name 256      100          the inode struct maybe like      struct inode     inode numebr 15             link t nlink     nlink   2                         then you create a symbolic link may be  200  to file 1  the directory entry maybe like     struct dentry          ino t ino     such as 16            char  name 256       200           the inode struct maybe like      struct inode     inode number 15              link t nlink     nlink   2                           struct inode     inode number 16             link t nlink     nlink   1                          the data of inode 16 maybe  1 or 1

User · Answer

Hard links are useful when the original file is getting moved around   For example  moving a file from  bin to  usr bin or to  usr local bin   Any symlink to the file in  bin would be broken by this  but a hardlink  being a link directly to the inode for the file  wouldn t care   Hard links may take less disk space as they only take up a directory entry  whereas a symlink needs its own inode to store the name it points to   Hard links also take less time to resolve - symlinks can point to other symlinks that are in symlinked directories   And some of these could be on NFS or other high-latency file systems  and so could result in network traffic to resolve   Hard links  being always on the same file system  are always resolved in a single look-up  and never involve network latency  if it s a hardlink on an NFS filesystem  the NFS server would do the resolution  and it would be invisible to the client system    Sometimes this is important   Not for me  but I can imagine high-performance systems where this might be important   I also think things like mmap 2  and even open 2  use the same functionality as hardlinks to keep a file s inode active so that even if the file gets unlink 2 ed  the inode remains to allow the process continued access  and only once the process closes it does the file really go away   This allows for much safer temporary files  if you can get the open and unlink to happen atomically  which there may be a POSIX API for that I m not remembering  then you really have a safe temporary file  where you can read write your data without anyone being able to access it   Well  that was true before  proc gave everyone the ability to look at your file descriptors  but that s another story   Speaking of which  recovering a file that is open in process A  but unlinked on the file system revolves around using hardlinks to recreate the inode links so the file doesn t go away when the process which has it open closes it or goes away

User · Answer

Underneath the file system  files are represented by inodes   Or is it multiple inodes   Not sure    A file in the file system is basically a link to an inode  A hard link  then  just creates another file with a link to the same underlying inode   When you delete a file  it removes one link to the underlying inode  The inode is only deleted  or deletable over-writable  when all links to the inode have been deleted   A symbolic link is a link to another name in the file system   Once a hard link has been made the link is to the inode  Deleting  renaming  or moving the original file will not affect the hard link as it links to the underlying inode  Any changes to the data on the inode is reflected in all files that refer to that inode   Note  Hard links are only valid within the same File System  Symbolic links can span file systems as they are simply the name of another file

User · Answer

Symbolic links link to a path name  This can be anywhere in a system s file tree  and doesn t even have to exist when the link is created  The target path can be relative or absolute   Hard links are additional pointers to an inode  meaning they can exist only on the same volume as the target  Additional hard links to a file are indistinguishable from the  original  name used to reference a file

User · Answer

I add on Nick s question  when are hard links useful or necessary  The only application that comes to my mind  in which symbolic links wouldn t do the job  is providing a copy of a system file in a chrooted environment

User · Answer

I just found an easy way to understand hard links in a common scenario  software install   One day I downloaded a software to folder Downloads for install  After I did sudo make install  some executables were cped to local bin folder  Here  cp creates hard link  I was happy with the software but soon realized that Downloads isn t a good place in the long run  So I mved the software folder to  source directory  Well  I can still run the software as before without worrying about any target link things  like in Windows  This means hard link finds inode directly and other files around

User · Answer

Underneath the file system  files are represented by inodes   Or is it multiple inodes   Not sure    A file in the file system is basically a link to an inode  A hard link  then  just creates another file with a link to the same underlying inode   When you delete a file  it removes one link to the underlying inode  The inode is only deleted  or deletable over-writable  when all links to the inode have been deleted   A symbolic link is a link to another name in the file system   Once a hard link has been made the link is to the inode  Deleting  renaming  or moving the original file will not affect the hard link as it links to the underlying inode  Any changes to the data on the inode is reflected in all files that refer to that inode   Note  Hard links are only valid within the same File System  Symbolic links can span file systems as they are simply the name of another file

User · Answer

A simple way to see the difference between a hard link and a symbolic link is through a simple example  A hard link to a file will point to the place where the file is stored  or the inode of that file  A symbolic link will point to the actual file itself   So if we have a file called  a  and create a hard link  b  and a symbolic link  c  which all refer to file  a     echo  111   gt  a ln a b ln -s a c   The output of  a    b   and  c  will be    cat a -- gt  111 cat b -- gt  111 cat c -- gt  111   Now let s remove file  a  and see what happens to the output of  a    b   and  c    rm a cat a -- gt  No such file or directory cat b -- gt  111 cat c -- gt  No such file or directory   So what happened    Because file  c  points to file  a  itself  if file  a  is deleted then file  c  will have nothing to point to  in fact it is also deleted    However  file  b  points to the place of storage  or the inode  of file  a   So if file  a  is deleted then it will no longer point to the inode  but because file  b  does  the inode will continue to store whatever contents belonged to  a  until no more hard links point to it anymore

User · Answer

Also    Read performance of hard links is better than symbolic links  micro-performance  Symbolic links can be copied  version-controlled    etc  In another words  they are an actual file  On the other end  a hard link is something at a slightly lower level and you will find that compared to symbolic links  there are less tools that provide means for working with the hard links as hard links and not as normal files

User · Answer

My two cents on usage   Soft links may be used to shorten long path names  i e    ln -s  long folder name on long path file txt  short file txt   Changes made to  short file txt will be applied on the original file   Hard links may be used to move around big files     ls -lh  myapp dev  total 10G -rw-r--r-- 2 root root 10G May 22 12 09 application bin   ln  myapp dev application bin  myapp prd application bin  Instant copy to different folder  and original file  on  myapp dev  may be moved or deleted  without touching the file on  myapp prd

User · Answer

I would point you to Wikipedia    Symbolic link Hard link   A few points    Symlinks  unlike hard links  can cross filesystems  most of the time   Symlinks can point to directories  Hard links point to a file and enable you to refer to the same file with more than one name  As long as there is at least one link  the data is still available

User · Answer

Hard links are very useful when doing incremental backups  See rsnapshot  for example  The idea is to do copy using hard links    copy backup number n to n   1 copy backup n - 1 to n     copy backup 0 to backup 1 update backup 0 with any changed files    The new backup will not take up any extra space apart from any changes you ve made  since all the incremental backups will point to the same set of inodes for files which haven t changed

User · Answer

I just found an easy way to understand hard links in a common scenario  software install  One day I downloaded a software to folder Downloads for install  After I did sudo make install  some executables were cped to local bin folder  Here  cp creates hard link  I was happy with the software but soon realized that Downloads isn t a good place in the long run  So I mved the software folder to source directory  Well  I can still run the software as before without worrying about any target link things  like in Windows  This means hard link finds inode directly and other files around

User · Answer

I add on Nick s question  when are hard links useful or necessary  The only application that comes to my mind  in which symbolic links wouldn t do the job  is providing a copy of a system file in a chrooted environment

User · Answer

Symbolic links give another name to a file  in a way similar to hard links  But a file can be deleted even if there are remaining symbolic links

User · Answer

A simple way to see the difference between a hard link and a symbolic link is through a simple example  A hard link to a file will point to the place where the file is stored  or the inode of that file  A symbolic link will point to the actual file itself   So if we have a file called  a  and create a hard link  b  and a symbolic link  c  which all refer to file  a     echo  111   gt  a ln a b ln -s a c   The output of  a    b   and  c  will be    cat a -- gt  111 cat b -- gt  111 cat c -- gt  111   Now let s remove file  a  and see what happens to the output of  a    b   and  c    rm a cat a -- gt  No such file or directory cat b -- gt  111 cat c -- gt  No such file or directory   So what happened    Because file  c  points to file  a  itself  if file  a  is deleted then file  c  will have nothing to point to  in fact it is also deleted    However  file  b  points to the place of storage  or the inode  of file  a   So if file  a  is deleted then it will no longer point to the inode  but because file  b  does  the inode will continue to store whatever contents belonged to  a  until no more hard links point to it anymore

User · Answer

Soft Link   soft or symbolic is more of a short cut to the original file    if you delete the original the shortcut fails and if you only delete the short cut nothing happens to the original   Soft link Syntax  ln -s   Pathof Target file  link  Output   link - gt    Target file  Proof  readlink  link  Also in ls  -l  link output you will see the first letter in lrwxrwxrwx as l which is indication that the file is a soft link   Deleting the link  unlink  link    Note  If you wish  your softlink can work even after moving it somewhere else from the current dir  Make sure you give absolute path and not relative path while creating a soft link  i e  starting from  root user Target file and not   Target file   Hard Link   Hard link is more of a mirror copy or multiple paths to the same file  Do something to file1 and it appears in file 2  Deleting one still keeps the other ok   The inode or file  is only deleted when all the  hard links or all the paths to the  same file inode has been deleted   Once a hard link has been made the link has the inode of the original file  Deleting renaming or moving the original file will not affect the hard link as it links to the underlying inode  Any changes to the data on the inode is reflected in all files that refer to that inode   Hard Link syntax  ln   Target file   link  Output  A file with name link will be created with the same inode number as of Targetfile   Proof  ls -i   link   Target file   check their inodes   Deleting the link  rm  -f  link  Delete the link just like a normal file    Note  Symbolic links can span file systems as they are simply the name of another file  Whereas hard links are only valid within the same File System   Symbolic links have some features hard links are missing    Hard link point to the file content  while Soft link points to the file name  while size of hard link is the size of the content while soft link is having the file name size  Hard links share the same inode  Soft links do not  Hard links can t cross file systems  Soft links do  you know immediately where a symbolic link points to while with hard links  you need to explore the whole file system to find files sharing the same inode     find   -inum 517333    home bobbin sync sh  root synchro   hard-links cannot point to directories    The hard links have two limitations    The directories cannot be hard linked  Linux does not permit this to maintain the acyclic tree structure of directories  A hard link cannot be created across filesystems  Both the files must be on the same filesystems  because different filesystems have different independent inode tables  two files on different filesystems  but with same inode number will be different

User · Answer

Symbolic links give another name to a file  in a way similar to hard links  But a file can be deleted even if there are remaining symbolic links

User · Answer

Hard links are very useful when doing incremental backups  See rsnapshot  for example  The idea is to do copy using hard links    copy backup number n to n   1 copy backup n - 1 to n     copy backup 0 to backup 1 update backup 0 with any changed files    The new backup will not take up any extra space apart from any changes you ve made  since all the incremental backups will point to the same set of inodes for files which haven t changed

User · Answer

I just found an easy way to understand hard links in a common scenario  software install   One day I downloaded a software to folder Downloads for install  After I did sudo make install  some executables were cped to local bin folder  Here  cp creates hard link  I was happy with the software but soon realized that Downloads isn t a good place in the long run  So I mved the software folder to  source directory  Well  I can still run the software as before without worrying about any target link things  like in Windows  This means hard link finds inode directly and other files around

User · Answer

Some nice intuition that might help  using any Linux ish  console   Create two files     touch foo  touch bar   Enter some Data into them     echo  Cat   gt  foo   echo  Dog   gt  bar    Actually  I could have used echo in the first place  as it creates the files if they don t exist    but never mind that    And as expected    cat foo  cat bar Cat Dog   Let s create hard and soft links     ln foo foo-hard   ln -s bar bar-soft   Let s see what just happened     ls -l  foo foo-hard bar bar-soft - gt  bar   Changing the name of foo does not matter     mv foo foo-new   cat foo-hard Cat   foo-hard points to the inode  the contents  of the file - that wasn t changed     mv bar bar-new   ls bar-soft bar-soft   cat bar-soft   cat  bar-soft  No such file or directory   The contents of the file could not be found because the soft link points to the name  that was changed  and not to the contents    Likewise  If foo is deleted  foo-hard still holds the contents  if bar is deleted  bar-soft is just a link to a non-existing file

User · Answer

Symbolic links link to a path name  This can be anywhere in a system s file tree  and doesn t even have to exist when the link is created  The target path can be relative or absolute   Hard links are additional pointers to an inode  meaning they can exist only on the same volume as the target  Additional hard links to a file are indistinguishable from the  original  name used to reference a file

User · Answer

Symbolic links link to a path name  This can be anywhere in a system s file tree  and doesn t even have to exist when the link is created  The target path can be relative or absolute   Hard links are additional pointers to an inode  meaning they can exist only on the same volume as the target  Additional hard links to a file are indistinguishable from the  original  name used to reference a file

User · Answer

Hard links are useful when the original file is getting moved around   For example  moving a file from  bin to  usr bin or to  usr local bin   Any symlink to the file in  bin would be broken by this  but a hardlink  being a link directly to the inode for the file  wouldn t care   Hard links may take less disk space as they only take up a directory entry  whereas a symlink needs its own inode to store the name it points to   Hard links also take less time to resolve - symlinks can point to other symlinks that are in symlinked directories   And some of these could be on NFS or other high-latency file systems  and so could result in network traffic to resolve   Hard links  being always on the same file system  are always resolved in a single look-up  and never involve network latency  if it s a hardlink on an NFS filesystem  the NFS server would do the resolution  and it would be invisible to the client system    Sometimes this is important   Not for me  but I can imagine high-performance systems where this might be important   I also think things like mmap 2  and even open 2  use the same functionality as hardlinks to keep a file s inode active so that even if the file gets unlink 2 ed  the inode remains to allow the process continued access  and only once the process closes it does the file really go away   This allows for much safer temporary files  if you can get the open and unlink to happen atomically  which there may be a POSIX API for that I m not remembering  then you really have a safe temporary file  where you can read write your data without anyone being able to access it   Well  that was true before  proc gave everyone the ability to look at your file descriptors  but that s another story   Speaking of which  recovering a file that is open in process A  but unlinked on the file system revolves around using hardlinks to recreate the inode links so the file doesn t go away when the process which has it open closes it or goes away

User · Answer

I just found an easy way to understand hard links in a common scenario  software install  One day I downloaded a software to folder Downloads for install  After I did sudo make install  some executables were cped to local bin folder  Here  cp creates hard link  I was happy with the software but soon realized that Downloads isn t a good place in the long run  So I mved the software folder to source directory  Well  I can still run the software as before without worrying about any target link things  like in Windows  This means hard link finds inode directly and other files around

User · Answer

I would point you to Wikipedia    Symbolic link Hard link   A few points    Symlinks  unlike hard links  can cross filesystems  most of the time   Symlinks can point to directories  Hard links point to a file and enable you to refer to the same file with more than one name  As long as there is at least one link  the data is still available

User · Answer

Simply   Hard link   is just add new name to a file  that s mean   a file can have many name in the same time  all name are equal to each other  no one preferred  Hard link is not mean to copy the all contents of file and make new file is not that  it just create an alternative name to be known     Symbolic link  symlink    is a file pointer to another file  if the symbolic link points to an existing file which is later deleted  the symbolic link continues to point to the same file name even though the name no longer names any file

User · Answer

Some nice intuition that might help  using any Linux ish  console   Create two files     touch foo  touch bar   Enter some Data into them     echo  Cat   gt  foo   echo  Dog   gt  bar    Actually  I could have used echo in the first place  as it creates the files if they don t exist    but never mind that    And as expected    cat foo  cat bar Cat Dog   Let s create hard and soft links     ln foo foo-hard   ln -s bar bar-soft   Let s see what just happened     ls -l  foo foo-hard bar bar-soft - gt  bar   Changing the name of foo does not matter     mv foo foo-new   cat foo-hard Cat   foo-hard points to the inode  the contents  of the file - that wasn t changed     mv bar bar-new   ls bar-soft bar-soft   cat bar-soft   cat  bar-soft  No such file or directory   The contents of the file could not be found because the soft link points to the name  that was changed  and not to the contents    Likewise  If foo is deleted  foo-hard still holds the contents  if bar is deleted  bar-soft is just a link to a non-existing file

[unix] What is the difference between a symbolic link and a hard link?

Examples related to unix

Examples related to symlink

Examples related to hardlink