bug#18937: chmod ???? bug?

[Bob Proulx]

Plato wrote:
> After using chmod
>       chmod -R 644 /media/plato/mountedpartition/     (I see I forgot the * 
> at the end)

That is a problematic command regardless of the '*' at the end or
not.  If any of the arguments is a directory then it will set the
directory permission to 644 as specified.  But directories need the
'x' bit (execute permission) set as well.

The above command will remove the execute bit from
/media/plato/mountedpartition and then fail to search below it due to
permission problems.  It will then leave the directory in an unhappy
state.

>       ls -l
> listing has all entry's like these:
>       First a list like this of every file and folder
>               ls: cannot access /media/plato/mountedpartition/justafiile.txt: 
> Permission denied

That is correct when the execute permission is removed from a directory.

> When I do
>       sudo ls Files
> I get a listing of the contents of files as expected.

This is because file mode bits only apply to non-root access.  Root is
the superuser and always has permission regardless of the file mode
bits.  Root always has access regardless of permissions.

> Is this a bug?

No.  It is doing exactly what you told it to do.

Try this:

  ls -ld /media/plato/mountedpartition

The -d option will tell ls to show the argument itself instead of
showing the contents of the directory.  With that you will see
something like this mode bits: drw-r--r-- but directories need to have
the x bit there too like drwxrwxr-x typically.

> It was not my intention to get this. I do not know how to get it back to what 
> it was.
> I tried it on a single file with
>       chmod 644 justafile.txt
> but that did not solve it. Any ideas?

After removing the execute bit from the directory you simply must add
the execute bit back to the directory.  It will probably be enough to
do this using symbolic modes.

  chmod a+x /media/plato/mountedpartition

In the old numeric form, combined with your previous 644, this would
be similar to:

  chmod 755 /media/plato/mountedpartition

Do not use the -R option with numeric arguments such as 644 because
the numeric mode will be recursively applied across directories.  That
is almost never what you want.  If using the -R option it is safer to
use the symbolic modes such as go-w.

Since this is all expected behavior I am going to go ahead and close
this bug.  However please continue the discussion here in the bug
log.  Any replies are still seen and discussed by the group.

Bob