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Imaging the next simple file structure within the /home/user/ directory: 

/home/user 
       |--dir0 
           |--dir1
               |--file1

My current directory is 'dir1' and I remove the directory from inside with the following command:

rm -r ../dir1

After that (and not getting any errors on the terminal), the working directory still is the same and when using the command pwd the output is:

user@ubuntu:~/dir0/dir1$ pwd
/home/user/dir0/dir1
user@ubuntu:~/dir0/dir1$

Why would the OS return that the working directory is 'dir1' if that was already removed from the filesystem?

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4 Answers 4

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7

I think pwd you run was a bash shell built-in. It just printed out the path it held in memory without looking up the file system.

$ type pwd
pwd is a shell builtin
$ /bin/pwd
/bin/pwd: couldn't find directory entry in '..' with matching i-node
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  • @Fabby I'm correct. See the source of pwd_builtin(). It just prints the content of the_current_working_directory.
    – yaegashi
    Jul 31, 2015 at 16:01
  • Looked at the source code and it seems you're right... What do you want me to do? Delete my answer?
    – Fabby
    Jul 31, 2015 at 16:08
  • 2
    This answer (yaegashi’s answer, aboutpwd being a shelll builtin) is the correct answer to the question, but Fabby’s answer and unxnut’s answer (inode doesn’t get fully deleted until it’s no longer in use) also have some truth to them.  If you do ls -lai before the rm and ls -ldi after the rm, you’ll see that the current directory (the directory formerly known by the name dir1) still exists, with the same inode number, but with a link count of 0 and a size of 0 (and, accordingly, with no contents).  … (Cont’d)
    – G-Man Says 'Reinstate Monica'
    Jul 31, 2015 at 17:36
  • 2
    (Cont’d) …  Also, if you do df -i . before and after the rm, you’ll see that IUsed (the used inode count) goes down by n, where n is the number of files in dir1.  After you cd out of the directory, df -i shows that IUsed has dropped by one more, since the directory inode has finally been deallocated.
    – G-Man Says 'Reinstate Monica'
    Jul 31, 2015 at 17:37
  • @G-Man: as yaegashi is not responding: what's your opinion about this: Should I delete my answer so his moves to the top? (or edit his and include mine?) (or: shudder include his in mine?)
    – Fabby
    Jul 31, 2015 at 19:36
7

Why can you continue viewing a movie although it's been deleted?

Because the file descriptor might be gone, but the inode is still there! And only when the inode gets deleted, is the file gone forever!

So in your case: when you cd to / and all files in that tree are closed will the inodes be recycled and will the directory be gone forever¹...

Remember: this is not Windows, this is a professional OS!

;-)

¹Unless it gets undeleted before it gets recycled.

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2

The OS doesn't return that the working directory is 'dir1', the shell does. The shell keeps track of the current working directory, and the 'pwd' command you're running is a command built into the shell. The shell is not aware of the fact that your 'rm' command removed the directory.

$ type pwd
pwd is a shell builtin

Try running /bin/pwd instead:

$ /bin/pwd
/bin/pwd: couldn't find directory in .. with matching i-node
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The file (directory) is open. When you do rm it, the OS marks it as deleted without actually deleting it. In case you try to do cd into this directory from another shell instance, you will be denied the permission. After you cd out of this directory, the directory will actually get deleted.

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