What happens to a symbolic link when the original file is replaced?
I have update software in /opt/minergate-cli. I've renamed the directory minergate-cli to minergate-old with an mv command, then installed a newer version of the software giving the same directory name.
Assuming I had an old program and now a new program by the same name, that being "minergate" what happens to any symbolic links pointing to the program minergate?
Are they pointing to the original program living in minergate-old, or did the link move to the new program minergate.cli?
2 Answers
Summary
Symlinks do not follow the files to which they point. If you have
link_file -> original_fileand you domv original_file original_file.backupthelink_filewill be brokenIf you recreate original filename ( which is what OP did ) the symlink will work again
If you have to make
link_file -> original_file.backup, you have to deletelink_fileand create it again, pointing to new filename
Answer
What happens to symlink if we rename a file ?
Once you move a file to which symlink points, symlink is broken aka dangling symlink. You have to delete it and create new one if you want to point to the new filename.
For example, let's create a symlink to file:
$ ln -s testfile.txt mysymlink
$ ls -l mysymlink
lrwxrwxrwx 1 adm adm 12 Dec 8 13:28 mysymlink -> testfile.txtNow let's rename the file. You will see symlink still points to the pathname that no longer exists (which is important, file exists, pathname - does not):
$ mv testfile.txt testfile.txt.bak
$ ls -l mysymlink
lrwxrwxrwx 1 xie xie 12 Dec 8 13:28 mysymlink -> testfile.txt
$ cat mysymlink
cat: mysymlink: No such file or directoryHow to fix a broken symlink ?
If you can rename file to original pathname, the symlink will start working.
$ mv testfile.txt.bak testfile.txt $ cat mysymlink one two three
If renaming is not an option and you may not rename the file, create a new symlink and delete the old one.
# break the symlink
$ mv testfile.txt testfile.txt.bak
$ cat mysymlink
cat: mysymlink: No such file or directory
# remove the old symlink
$ rm mysymlink
# create symlink with same filename but pointing to new pathname
$ ln -s testfile.txt.bak mysymlink
$ cat mysymlink
one two threeOP question: Did the link move to the new program
minergate.cli?
If the symlink target /opt/minergate-cli has been re-created when new version of application was installed, the symlink will point to new file. If the new file has different filename, then symlink will be broken. Symlinks do not follow filename if filename was moved, as in OP's example when they did mv /opt/minergate-cli /opt/minergate.old , so symlink will still keep pointing to /opt/minergate-cli regardless if that file exists or not.
See also
6A symlink just holds the name of the file that it points to. (hint, do ls -l symlink and note its file size). If you delete the target file, but then create a new file with the same name, the symlink will happily keep working, referring to the new file contents:
$ echo "first file" > file
$ ln -s file symlink
$ ls -l symlink
lrwxrwxrwx 1 jackman jackman 4 Oct 23 23:33 symlink -> file
# ...........................^=size ...................^^^^ target is 4 chars
$ cat symlink
first file
$ mv file file.old
$ echo "this is the second" > file
$ cat symlink
this is the secondYou may be think about a "hard" link, which refers to the target file's inode:
$ echo "first line" > file
$ ln file hardlink
$ ls -li hardlink file
1078415 -rw-r--r-- 2 jackman jackman 11 Oct 23 23:38 file
1078415 -rw-r--r-- 2 jackman jackman 11 Oct 23 23:38 hardlink
$ cat hardlink
first line
$ mv file file.old
$ echo "this is the new contents" > file
$ cat hardlink
first line
$ ls -li hardlink file file.old
1059446 -rw-r--r-- 1 jackman jackman 25 Oct 23 23:39 file
1078415 -rw-r--r-- 2 jackman jackman 11 Oct 23 23:38 file.old
1078415 -rw-r--r-- 2 jackman jackman 11 Oct 23 23:38 hardlinkhere hardlink is the same file as the original file file.
