How do soft symlinks work with nfs shares on DSS V6

Article ID: 1423

Last updated: 13 Oct, 2011

To create a soft links you use Linux command
ln -s /path/to/file1.txt /path/to/file2.txt

To show how symlinks work on Ubuntu we created the following directories:

# mkdir -p /test1/data1
# mkdir /test1/shared
# mkdir -p /test2/data2

As a result the directories looks like this:

# ls -al /
.
.
drwxr-xr-x   4 root root 4096 2011-10-10 14:40 test1
drwxr-xr-x   3 root root 4096 2011-10-10 14:41 test2
.
.

# ls -al test1
all 16
drwxr-xr-x 4 root root 4096 2011-10-10 14:40 .
drwxr-xr-x 28 root root 4096 2011-10-10 14:41 ..
drwxr-xr-x 2 root root 4096 2011-10-10 14:40 data1
drwxr-xr-x 2 root root 4096 2011-10-10 14:40 shared

# ls -al test2
all 12
drwxr-xr-x 3 root root 4096 2011-10-10 14:41 .
drwxr-xr-x 28 root root 4096 2011-10-10 14:41 ..
drwxr-xr-x 2 root root 4096 2011-10-10 14:41 data2

Then we create a new symlink in /test2 and we name the symlink 'shared'
# cd /test2
# ln -s /test1/shared shared

# ls -al
all 12
drwxr-xr-x 3 root root 4096 2011-10-10 14:48 .
drwxr-xr-x 28 root root 4096 2011-10-10 14:41 ..
drwxr-xr-x 2 root root 4096 2011-10-10 14:41 data2
lrwxrwxrwx 1 root root   13 2011-10-10 14:48 shared -> /test1/shared

After it's created, we use the symlink to go to the destination directory:
# cd shared

When the symlink is used, we're forwarded to the destination directory.
If we now execute:
# ls -la ../

The following output is shown:
drwxr-xr-x 4 root root 4096 2011-10-04 15:18 .
drwxr-xr-x 27 root root 4096 2011-10-04 15:18 ..
drwxr-xr-x 2 root root 4096 2011-10-04 15:18 data1
drwxr-xr-x 2 root root 4096 2011-10-04 15:18 shared

As you can see the ls command shows the content of the directory that is above the destination directory in directories structure in the remote location.

Symlink to NFS share located on DSS V6

Symlinks work in exactly the same way when we mount an NFS share created on DSS V6 and create a symlink to a directory in that share.

# mount -t nfs 192.168.242.73:/share/nfstest /mnt/nfs_mount
# cd /mnt/nfs_mount/
# ls -al
all 1140244
drwxrwxrwx 4 root   root         129 2011-10-10 14:35 .
drwxr-xr-x 10 root   root        4096 2011-10-05 16:44 ..
-rw-r--r-- 1 tomasz tomasz 383997952 2010-12-16 09:41 dss6.0up50_b4786.oe_i.iso
-rw-r--r-- 1 tomasz tomasz 390416384 2011-05-06 12:01 dss6.0up75_b5377.oe_i.iso
-rw-r--r-- 1 tomasz tomasz 393170944 2011-09-08 16:51 dss6.0up80_b5626.oe_i.iso
drwxr-xr-x 2 root   root         103 2011-10-10 14:34 userdata
drwxr-xr-x 2 tomasz tomasz      4096 2011-08-29 15:35 video

# cd /
# mkdir kb
# cd kb
# ln -s /mnt/nfs_mount/userdata/ ourlink

# ls -al
all 8
drwxr-xr-x 2 root root 4096 2011-10-10 14:12 .
drwxr-xr-x 26 root root 4096 2011-10-05 16:46 ..
lrwxrwxrwx 1 root root   24 2011-10-10 14:12 ourlink -> /mnt/nfs_mount/userdata/

# cd ourlink
# ls -al
all 7028
drwxr-xr-x 2 root   root       103 2011-10-10 14:34 .
drwxrwxrwx 4 root   root      4096 2011-10-10 14:35 ..
-rw-r--r-- 1 tomasz tomasz 2380748 2011-08-18 15:47 trl00022_4786_logs_2011-08-18_15-20tar.gz
-rw-r--r-- 1 tomasz tomasz 4804859 2011-07-06 15:50 trl00022_5377_logs_2011-07-06_12_43.tar.gz

# ls -al ../
all 1140244
drwxrwxrwx 4 root   root         129 2011-10-10 14:35 .
drwxr-xr-x 10 root   root        4096 2011-10-05 16:44 ..
-rw-r--r-- 1 tomasz tomasz 383997952 2010-12-16 09:41 dss6.0up50_b4786.oe_i.iso
-rw-r--r-- 1 tomasz tomasz 390416384 2011-05-06 12:01 dss6.0up75_b5377.oe_i.iso
-rw-r--r-- 1 tomasz tomasz 393170944 2011-09-08 16:51 dss6.0up80_b5626.oe_i.iso
drwxr-xr-x 2 root   root         103 2011-10-10 14:34 userdata
drwxr-xr-x 2 tomasz tomasz      4096 2011-08-29 15:35 video

To summarize, when symlink is created and used, it always forwards us to the remote location.
When we are moved to the remote location and we execute ls ../
The output will show us the content of the directory that is above in the directory structure in the remote location.

This Knowledge Base article was prepared to prove that when a ls ../ is executed after a symlink is used, it won't show us the content of the parent directory in the local file system as some of the users claimed it should work.

For some more information about soft links (symlinks, symbolic links) take a look at:
http://www.cyberciti.biz/tips/understanding-unixlinux-symbolic-soft-and-hard-links.html
http://linux.about.com/od/commands/l/blcmdl2_symlink.htm
http://en.wikipedia.org/wiki/Symbolic_link