'ls' displays different results when in directory

Radikll · 05-07-2013, 06:13 PM

How can this ever happen?

Code:

jon@ben:~/Development/www$ ls -l ../random-checkout/
total 28
drwxrwxr-x 15 jon jon 4096 May  7 17:02 application
-rwxrwxr-x  1 jon jon 6357 May  7 17:02 index.php
-rwxrwxr-x  1 jon jon 2496 May  7 17:02 license.txt
-rw-rw-r--  1 jon jon  398 May  7 17:02 README.md
drwxrwxr-x  8 jon jon 4096 May  7 17:02 system
drwxrwxr-x 11 jon jon 4096 May  7 17:02 user_guide
jon@ben:~/Development/www$ cd ../random-checkout/
jon@ben:~/Development/random-checkout$ ls -l
total 20
drwxr-xr-x  6 jon jon 4096 May  7 17:45 auth_example
drwxr-xr-x 12 jon jon 4096 May  7 15:32 CodeIgniter-Ion-Auth
drwxrwxr-x 10 jon jon 4096 Mar 27 16:24 m3-stream-read-only
drwxrwxr-x  4 jon jon 4096 Apr  2 18:03 trunk
drwxrwxr-x  6 jon jon 4096 Mar 27 18:07 xuggle-read-only
jon@ben:~/Development/random-checkout$

I could not believe my eyes when I saw this! The directory somehow contains two different sets of files and folders at the same time!!

It happened when I ran this command.

Code:

jon@ben:~/Development/www$ mv auth_example ../random-checkout/
mv: cannot move `auth_example' to `../random-checkout/': Permission denied
jon@ben:~/Development/www$ sudo mv auth_example ../random-checkout/
[sudo] password for jon:

Trouble shooting info:

Code:

jon@ben:~/Development/random-checkout$ df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/sda1                 70G   34G   33G  51% /
udev                     3.9G  4.0K  3.9G   1% /dev
tmpfs                    1.6G  1.4M  1.6G   1% /run
none                     5.0M     0  5.0M   0% /run/lock
none                     3.9G  5.6M  3.9G   1% /run/shm
none                     100M     0  100M   0% /run/user
/home/jon/.Private        70G   34G   33G  51% /home/jon
...
jon@ben:~/Development/random-checkout$ sudo parted -l
Model: ATA ST9750420AS (scsi)
Disk /dev/sda: 750GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  76.0GB  76.0GB  primary  ext4         boot
...
jon@ben:~/Development/random-checkout$ uname -a
Linux ben 3.5.0-27-generic #46-Ubuntu SMP Mon Mar 25 19:58:17 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

I know I can just remove the directory and the problem will be solved, but I just really want to know why and how this happened. If you can't tell I know my way around linux and the command-line.

suicidaleggroll · 05-07-2013, 06:22 PM

Sounds like your PWD is inside a symlink.

Code:

ls ..

will print the results from the parent directory of the target of the symlink

Code:

cd ..; ls

will print the results from the parent directory of the symlink itself.

For example, take the following

Code:

$ mkdir -p dir1/dir2/dir3/dir4
$ cd dir1/dir2/dir3/dir4
$ ln -s ../../../dir2/ dir5
$ cd dir5
$ pwd
/home/user/dir1/dir2/dir3/dir4/dir5
$ ls -l ..
total 4
drwxrwxr-x 3 user user 4096 2013-05-07 17:19 dir2
$ cd ..; pwd; ls -l
/home/user/dir1/dir2/dir3/dir4
total 0
lrwxrwxrwx 1 user user 14 2013-05-07 17:20 dir5 -> ../../../dir2/
$

The contents of "ls -l .." is dir2, the contents of "cd ..; ls -l" is the dir5 symlink. Just a difference in how ls and cd handle ".." from inside a symlink.

Of course this begs the question, "why do cd and ls treat ".." differently when inside a symlink?" Which then begs the more philosophical question, "what is ".." when you're inside a symlink"?

Radikll · 05-07-2013, 07:31 PM

OH! yep that was it. Pretty odd (and confusing) that cd handles ".." differently from ls and mv. I'll have to keep that in mind.

Code:

jon@ben:~/Development/www$ ls /var
backups  cache  lib  local  lock  log  mail  opt  random-checkout  run  spool  tmp  www
jon@ben:~/Development/www$ ls ..
backups  cache  lib  local  lock  log  mail  opt  random-checkout  run  spool  tmp  www

Thanks for the solution!

edit:
They probably designed cd to be a special case, since it'd be really annoying to cd into a symlink and then have to use the absolute path to get back.

Code:

jon@ben:~/Development/www$ rm -rf ../random-checkout/
rm: cannot remove `../random-checkout': Permission denied
jon@ben:~/Development/www$ sudo rm -rf ../random-checkout/
[sudo] password for jon: 
jon@ben:~/Development/www$ ls ..
backups  cache  lib  local  lock  log  mail  opt  run  spool  tmp  www

rm functions like ls and mv.

rknichols · 05-07-2013, 08:58 PM

It is only the shell's cd builtin that, by default, follows back along any symlinks that were used to get to the CWD. Let's say that "/etc/somewhere" is actually a symlink to a directory "/opt/somepkg/etc/somewhere". If you had no reason to suspect that a symlink was involved, then doing "cd /etc/somewhere" and then "cd ..", you would expect to end up in "/etc", and that is what the cd builtin would do. Finding yourself instead in "/opt/somepkg/etc" would be quite a surprise.

You can make the shell's cd follow the physical directory structure by adding the "-P" option to the cd command. You can make that effective for future cd commands by setting the shell's "-P" option.

External commands, like rm and mv, have no way to know how you got to the CWD, so they have no choice but to follow the physical structure.