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I have a not-quite-folder not-quite-file on my file system. It is an AWS EC2 instance running Ubuntu 18.04.4 LTS.

I have a script that runs nightly that picks up a file (/ebsvol/dead-drop/sync) and moves it to (/ebsvol/dead-drop/sync) using Robo, which in turn is using Symfony's Filesystem rename() method (https://symfony.com/doc/current/components/filesystem.html#rename).

  const CANARY_PATH = '/ebsvol/dead-drop/sync';
  const CANARY_WORKING_PATH = '/ebsvol/dead-drop/~sync';
...
  $this->taskFilesystemStack()
    ->rename(self::CANARY_PATH, self::CANARY_WORKING_PATH)
    ->run();

Something is going awry in the script or with this code, though that's not really why I'm here. The result and cleanup is why I'm here. :)

The result is that the ~sync "file" is created, however it is actually... a hard link to /bin? This is where things get fishy. My ls -ial looks like this:

3276803 -rw-rw-r--  1 configbot configbot  125 Jul  4 00:30 '~sync'

So it's just a text file, so let's try cat...

$ cat ~sync
cat: /bin: Is a directory

Uhh, OK.

$ cd ~sync

...changes my prompt to /bin, and doing an ls, it's surely bin. Incidentally, ls -ial on my root volume shows that /bin is iNode 12.

This has happened to me once in the past, and I just did rm -rf ~sync which hosed my entire server and I had to rebuild. So I'm trying to avoid that.

How do I get rid of this weird ~sync file/folder/symlink/hardlink without trashing /bin?

Some additional info:

  • /ebsvol is a separate EBS volume than / (i.e. separate hard drives/partitions!)
  • I think if it's a hard link in some weird way, rm ~sync might work. But wouldn't it show identical iNode numbers?
  • I will take a snapshot of both volumes before I attempt anything. :)
chrisfromredfin
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1 Answers1

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It's a very bad idea to name a file beginning with a tilde if you intend to access it with a shell like bash. The reason being that it interprets the tilde as meaning that you want to access a user's home directory.

Thus, bash (and other shells) expand ~ to the current user's home directory, and expand ~sync to the home directory of the user named sync.

It turns out that your Ubuntu system has a system user named sync whose home directory is /bin. Thus when you try to access ~sync from the shell, it expands this to the user's home directory, and you start getting odd messages. And when you ran rm -rf ~sync the effect was rm -rf /bin, which pretty much trashes the system.

If you want to access the file itself, either quote it, or prefix it with something, such as its path:

$ cat ./~sync

You should also rework your code so that it does not create filenames that start with a tilde. This will save you and future you a lot of headaches later.

Michael Hampton
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  • Wow. Yes, this is all correct and amazing. I knew about ~ being home, but in 20 years I NEVER knew about ~. This seems like the perfect storm: a user named sync, me choosing sync for a filename, me choosing to code it to ~sync while working. All of it. Thank you thank you thank you! I will rework the code and filenames. – chrisfromredfin Jul 04 '20 at 14:28