Directory – Why Can’t List File/Directory Relative to .. from a Symlink Directory

cd-commanddirectorylssymlink

I have a /usr/tomcat6/logs directory linked to /var/log/tomcat6.

When I changed directory to /usr/tomcat6/logs and try to ls files using a relative pathname ../conf/Catalina/localhost, a No such file or directory error occurs. However, cd ../conf/Catalina/localhost works.

See the following:

[root@fedora ~]# ll /usr/tomcat*
lrwxrwxrwx. 1 root root 21 Jun 17 15:00 /usr/tomcat6 -> apache-tomcat-6.0.32/
lrwxrwxrwx. 1 root root 21 Jun 17 13:03 /usr/tomcat7 -> apache-tomcat-7.0.16/
[root@fedora ~]# cd /usr/tomcat6
[root@fedora tomcat6]# ll logs
lrwxrwxrwx. 1 root root 16 Jun 17 14:51 logs -> /var/log/tomcat6
[root@fedora tomcat6]# cd logs
[root@fedora logs]# cd ../conf/Catalina/localhost
[root@fedora localhost]# pwd
/usr/tomcat6/conf/Catalina/localhost
[root@fedora localhost]# cd /usr/tomcat6/logs
[root@fedora logs]# ll ../conf/Catalina/localhost
ls: cannot access ../conf/Catalina/localhost: No such file or directory

How could this happened? Is it a bug or special behaviour of symbolic link?

Best Answer

It is special behavior of bash's cd builtin; the relative file behavior is the natural one. Once you follow a symbolic link, you are in the actual path of the target and the original path information is lost; but if you use bash or zsh to cd there then the shell remembers the original path and uses it in future relative cd commands. But not in relative filename references, because bash doesn't actually know if you intended a filename or something else.

If you look at the cd documentation in bash, you'll see there are -L and -P options which tell it whether to use "logical" (remembering the original path) or "physical" (using the filesystem's idea) paths.

If you need to have the "logical" behavior at all times, you need to use a --bind mount (on Linux; Solaris and other OSes call it "loopback" or other things) instead of a symlink.

Related Solutions

Make a symbolic link to a relative pathname

If you create a symbolic link to a relative path, it will store it as a relative symbolic link, not absolute like your example shows. This is generally a good thing. Absolute symbolic links don't work when the filesystem is mounted elsewhere.

The reason your example doesn't work is that it's relative to the parent directory of the symbolic link and not where ln is run.

You can do:

$ pwd
/home/beau
$ ln -s foo/bar.txt bar.txt
$ readlink -f /home/beau/bar.txt
/home/beau/foo/bar.txt

Or for that matters:

$ cd foo
$ ln -s foo/bar.txt ../bar.txt

It's important to realise that the first argument after ln -s is stored as the target of the symlink. It can be any arbitrary string (with the only restrictions that it can't be empty and can't contain the NUL character), but at the time the symlink is being used and resolved, that string is understood as a relative path to the parent directory of the symlink (when it doesn't start with /).

Replace symbolic link which linked to directory target

You want the -T option:

$ mkdir v1
$ ln -s v1 foo
$ ls -FlA | grep foo
lrwxrwxrwx 1 phil phil     2 2011-09-05 01:58 foo -> v1/
$ mkdir v2
$ ln -s -T -f v2 foo
$ ls -FlA | grep foo
lrwxrwxrwx 1 phil phil     2 2011-09-05 01:59 foo -> v2/

Best Answer

Related Solutions

Make a symbolic link to a relative pathname

Replace symbolic link which linked to directory target

Related Question