[lug] strange filesystem behavior

Jeffrey S. Haemer jeffrey.haemer at gmail.com
Wed Apr 13 13:57:45 MDT 2016


It's because "ls" is a program, but "cd" is a builtin.  From the bash man

cd [-L|[-P [-e]] [-@]] [dir]
              Change  the  current  directory  to dir.  if dir is not
supplied, the value of the HOME shell variable is the default.  Any
              arguments following dir are ignored.  The variable CDPATH
defines the search path for the directory  containing  dir:  each  directory
              name  in  CDPATH  is  searched for dir.  Alternative
directory names in CDPATH are separated by a colon (:).  A null directory
name in
              CDPATH is the same as the current directory, i.e., ``.''.  If
dir begins with a slash (/), then CDPATH is  not  used.  The  -P  option
              causes  cd to use the physical directory structure by
resolving symbolic links while traversing dir and before processing
instances of
              .. in dir (see also the -P option to the set builtin
command); the -L option forces symbolic links to be  followed  by
 resolving  the
              link  after  processing  instances  of .. in dir.  If ..
appears in dir, it is processed by removing the immediately previous
              component from dir, back to a slash or the beginning of dir.
If the -e option is supplied with -P, and the current working  directory
              cannot be successfully determined after a successful
directory change, cd will return an unsuccessful status.  On systems that
              it, the -@ option presents the extended attributes associated
with a file as a directory.  An argument of - is  converted  to  $OLDPWD
              before  the  directory change is attempted.  If a non-empty
directory name from CDPATH is used, or if - is the first argument, and the
              directory change is successful, the absolute pathname of the
new working directory is written to  the  standard  output.   The  return
              value is true if the directory was successfully changed;
false otherwise.


set -P      If set, the shell does not resolve symbolic links when
executing commands such as cd that change the  current  working  direc‐
                tory.   It uses the physical directory structure instead.
By default, bash follows the logical chain of directories when per‐
                forming commands which change the current directory.


On Wed, Apr 13, 2016 at 1:28 PM, Davide Del Vento <
davide.del.vento at gmail.com> wrote:

> The point with syslinked directories is that if you have
> /foo/bar/baz
> which is a syslink to
> /whatever/the/heck
> and you cd into /foo/bar/baz, then when you do "cd .." or "ls .." in one
> case you go to /foo/bar/ in the other you go /whatever/the/ (forgot
> what-is-what)
> I noticed it pretty early when I encountered syslink'ed directories years
> ago, and never investigated further, just learnt to live with it.
> On Wed, Apr 13, 2016 at 1:17 PM, Michael Hirsch <mdhirsch at gmail.com>
> wrote:
>> Can anyone explain this?  The owners of this system use a lot of
>> symlinks to play weird games with their files.  For instance, in the
>> directory used below, /var/tmp/jobsched/jaws/conf the last entry,
>> conf, is actually a symlink into another filesystem entirely.  But I
>> still don't understand how this is possible.
>> Consider this:
>> bash-4.1$ pwd
>> /var/tmp/jobsched/jaws/conf
>> bash-4.1$ ls ../../../..
>> autosys_api  common  daemon         jaws.sh            jboss  log
>> sbin     sdk
>> batch        config  import_export  jaws.sh.vmoptions  lib    README
>> scripts  tools
>> bash-4.1$ cd ../../../..
>> bash-4.1$ ls
>> account  cvs    etscfg  lib    lost+found  mqm.client  phd        run
>>    VRTSat_lhc  yp
>> adm      db     ftp     local  lum         nis         preserve
>> spool   VRTSvcs     zapplets
>> cache    db2    games   lock   mail        openv       prodperim  tmp
>>  vx
>> crash    empty  gdm     log    mqm         opt         redhat     VRTSat
>> vxvm
>> So when I "ls ../../../.." ls sees a bunch of file, starting with
>> "autosys_api" and "common".  But if I cd to that directory ls sees a
>> completely different set of files.
>> I didn't think that symlinks and filesystems worked like this.  I
>> expected to see the same files in the two "ls" commands.
>> What is making this happen?  What am I missing.
>> Thanks,
>> Michael
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> _______________________________________________
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Jeffrey Haemer <jeffrey.haemer at gmail.com>
720-837-8908 [cell], http://seejeffrun.blogspot.com [blog],
http://www.youtube.com/user/goyishekop [vlog]
*פרייהייט? דאס איז יאַנג דינען וואָרט.*
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