Can you change what a symlink points to after it is created

Question

Does any operating system provide a mechanism  system call     not command line program  to change the pathname referenced by a symbolic link  symlink      other than by unlinking the old one and creating a new one   The POSIX standard does not   Solaris 10 does not   MacOS X 10 5  Leopard  does not   I m tolerably certain neither AIX nor HP-UX does either  Judging from this list of Linux system calls  Linux does not have such a system call either    Is there anything that does    I m expecting that the answer is  No       Since proving a negative is hard  let s reorganize the question   If you know that some  Unix-like  operating system not already listed has no system call for rewriting the value of a symlink  the string returned by readlink    without removing the old symlink and creating a new one  please add it     or them     in an answer

User · Answer

Yes  you can     ln -sfn source file or directory name softlink name

User · Answer

AFAIK  no  you can t  You have to remove it and recreate it  Actually  you can overwrite a symlink and thus update the pathname referenced by it     ln -s  bashrc test   ls -al test lrwxrwxrwx 1 pascal pascal 7 2009-09-23 17 12 test - gt   bashrc   ln -s  profile test ln  creating symbolic link  test   File exists   ln -s -f  profile test   ls -al test lrwxrwxrwx 1 pascal pascal 8 2009-09-23 17 12 test - gt   profile   EDIT  As the OP pointed out in a comment  using the --force option will make ln perform a system call to unlink   before symlink    Below  the output of strace on my linux box proving it     strace -o  tmp output txt ln -s -f  bash aliases test   grep -C3  unlink  tmp output txt  lstat64  test    st mode S IFLNK 0777  st size 7          0 stat64   bash aliases    st mode S IFREG 0644  st size 2043          0 symlink   bash aliases    test            -1 EEXIST  File exists  unlink  test                              0 symlink   bash aliases    test            0 close 0                                   0 close 1                                   0   So I guess the final answer is  no    EDIT  The following is copied from Arto Bendiken s answer over on unix stackexchange com  circa 2016   This can indeed be done atomically with rename 2   by first creating the new symlink under a temporary name and then cleanly overwriting the old symlink in one go  As the man page states      If newpath refers to a symbolic link the link will be overwritten    In the shell  you would do this with mv -T as follows     mkdir a b   ln -s a z   ln -s b z new   mv -T z new z   You can strace that last command to make sure it is indeed using rename 2  under the hood     strace mv -T z new z lstat64  z new    st mode S IFLNK 0777  st size 1          0 lstat64  z    st mode S IFLNK 0777  st size 1          0 rename  z new    z                        0   Note that in the above  both mv -T and strace are Linux-specific    On FreeBSD  use mv -h alternately   Editor s note  This is how Capistrano has done it for years now  ever since  2 15  See this pull request

User · Answer

Wouldn t unlinking it and creating the new one do the same thing in the end anyway

User · Answer

Technically  there s no built-in command to edit an existing symbolic link  It can be easily achieved with a few short commands    Here s a little bash zsh function I wrote to update an existing symbolic link     -----------------------------------------   Edit an existing symbolic link      1   Name of symbolic link to edit    2   Full destination path to update existing symlink with    ----------------------------------------- function edit-symlink          if   -z   1     then         echo  Name of symbolic link you would like to edit           read LINK     else         LINK   1      fi     LINKTMP   LINK-tmp      if   -z   2     then         echo  Full destination path to update existing symlink with           read DEST     else         DEST   2      fi     ln -s  DEST  LINKTMP     rm  LINK     mv  LINKTMP  LINK     printf  Updated  LINK to point to new destination - gt   DEST

User · Answer

Just a warning to the correct answers above   Using the -f   --force Method provides a risk to lose the file if you mix up source and target   mbucher server2   test  ls -la total 11448 drwxr-xr-x  2 mbucher www-data    4096 May 25 15 27   drwxr-xr-x 18 mbucher www-data    4096 May 25 15 13    -rw-r--r--  1 mbucher www-data 4109466 May 25 15 26 data tar gz -rw-r--r--  1 mbucher www-data 7582480 May 25 15 27 otherdata tar gz lrwxrwxrwx  1 mbucher www-data      11 May 25 15 26 thesymlink - gt  data tar gz mbucher server2   test   mbucher server2   test  ln -s -f thesymlink otherdata tar gz  mbucher server2   test   mbucher server2   test  ls -la total 4028 drwxr-xr-x  2 mbucher www-data    4096 May 25 15 28   drwxr-xr-x 18 mbucher www-data    4096 May 25 15 13    -rw-r--r--  1 mbucher www-data 4109466 May 25 15 26 data tar gz lrwxrwxrwx  1 mbucher www-data      10 May 25 15 28 otherdata tar gz - gt  thesymlink lrwxrwxrwx  1 mbucher www-data      11 May 25 15 26 thesymlink - gt  data tar gz   Of course this is intended  but usually mistakes occur  So  deleting and rebuilding the symlink is a bit more work but also a bit saver   mbucher server2   test  rm thesymlink  amp  amp  ln -s thesymlink otherdata tar gz  ln  creating symbolic link  otherdata tar gz   File exists   which at least keeps my file

User · Answer

It is not necessary to explicitly unlink the old symlink   You can do this   ln -s newtarget temp mv temp mylink    or use the equivalent symlink and rename calls    This is better than explicitly unlinking because rename is atomic  so you can be assured that the link will always point to either the old or new target   However this will not reuse the original inode   On some filesystems  the target of the symlink is stored in the inode itself  in place of the block list  if it is short enough  this is determined at the time it is created   Regarding the assertion that the actual owner and group are immaterial  symlink 7  on Linux says that there is a case where it is significant      The owner and group  of  an  existing  symbolic  link  can  be changed  using   lchown 2     The  only  time  that the ownership of a symbolic link matters is   when the link is being removed or renamed in a directory that has the sticky   bit set  see stat 2         The  last  access  and  last modification timestamps of a symbolic link can be   changed using utimensat 2  or lutimes 3        On Linux  the permissions of a symbolic link are not used in any operations    the  permissions  are always 0777  read  write  and execute for all user   categories   and can t be changed

User · Answer

Just in case it helps  there is a way to edit a symlink with midnight commander  mc   The menu command is  in French on my mc interface    Fichier     diter le lien symbolique   which may be translated to   File   Edit symbolic link   The shortcut is C-x C-s  Maybe it internally uses the ln --force command  I don t know   Now  I m trying to find a way to edit a whole lot of symlinks at once  that s how I arrived here

[unix] Can you change what a symlink points to after it is created?

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