I have a directory and a symlink to it:

mkdir dir
ln -s dir dir_symlink

I want to replace the symlink with the directory and the directory with the symlink. Is there a way to do that atomically (or very fast)? The directory is large.

dir should now be a symlink to the dir_symlink directory (which is no longer a symlink, and contains the former contents of dir).

  • On any modern filesystem, a renaming is fast as it does not depend on the content / size of the directory / file. – xhienne Aug 3 '17 at 22:52
  • It isn't possible to do it atomically with user-level tools alone. (It's possible to do it “very fast” with three mv commands, of course.) It might be possible with a union mount. – Gilles Aug 3 '17 at 23:12

if I had to do this very often, I would write a little bash script like this:


echo "select symlink"
read -e -r symlink
echo "select directory"
read -e -r dir

var=$(echo "$dir" | sed 's/\///g')

rm "$symlink"
mv "$dir" "$symlink"
ln -s "$symlink" "$var"

the sed command removes the / that gets added when you use auto-complete for the input.
Note: it would remove all of them, also if you selected a directory tree.

You could tell sed to only match the end of line like this: sed 's/\/*$//g'

  • bash (and ksh and zsh) can remove a trailing slash (and only a trailing one) with ${dir%/} – dave_thompson_085 Aug 4 '17 at 4:36
  • thanks for this one @dave_thompson_085, should I update my answer? – nath Aug 4 '17 at 18:08

If the directories are on same filesystem mv is only renaming the directory and doesn't involve any copying. Just remove the old symlink, rename the directory using mv and create a new symlink.

  • 2
    This is not atomic, but it's the best you can do. – Celada Aug 3 '17 at 22:37
  • Updated the answer. On same filesystem, mv should be atomic as far as I know. – sebasth Aug 3 '17 at 22:45
  • 1
    There are two operations involved: mv + ln. They can't be both done atomically – xhienne Aug 3 '17 at 22:50
  • Of course, I don't think I have claimed such. – sebasth Aug 3 '17 at 22:50

It's worth noting that if this is on a macOS machine, the new APFS filesystem supports atomic swaps for just this type of scenario. Although the functionality doesn't seem to be built into a command such as mv, it is accessible with a little bit of Swift code (the C code is almost identical, but you can easily just paste this into the Swift REPL, which is easier):

import Foundation
renamex_np("/path/to/file/one", "/path/to/file/two", UInt32(RENAME_SWAP))

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