creating a link file for lvm commands

[223848]

Hi All,

              In my Unix box i created a link file which is pointing to /usr/sbin/lvdisplay

# ln -s /usr/sbin/lvdisplay /tmp/test

# ll | grep -i test
lrwxrwxrwx   1 root       sys             19 Sep  5 06:32 test -> /usr/sbin/lvdisplay

# ./test
test: Error, "test" is not a valid LVM command.

I created a hard link also, but then also i got the same error.

Then i tried to linka file to the path of hostname...

# ln -s /usr/bin/hostname /tmp/new
[rx260-01]/tmp

After this when i executed /tmp/new i got the hostname

# /tmp/new
rx260-01

The Unix verision is 11.23.

Can  you please tell me why its behaving like this..

[Dennis Handly]

>In my HP-UX box I created a link file which is pointing to /usr/sbin/lvdisplay

Why do that?  Don't.  What does "ll -i /usr/sbin/lvdisplay" show?

>Can you please tell me why its behaving like this?

Only the obvious, most likely there are multiple commands all hardlinked to one executable and the wrong name falls off the switch to the error case.

[223848]

Hi,

     Thanks for the reply

# ll -i /usr/sbin/lvdisplay
   518 -r-sr-xr-x  33 root       sys        1329404 Mar 17  2008 /usr/sbin/lvdisplay
[rx260-01]/tmp
#

[Dennis Handly]

># ll -i /usr/sbin/lvdisplay
>   518 -r-sr-xr-x  33 root  /usr/sbin/lvdisplay

As I suspected, there are 33 different commands in that one executable.

[James R. Ferguson]

Hi:

There are 33 different hard links to the executable.  As Dennis said, this is a classic way of offering one executable that when it runs, evaluates the *name* by which it was called to decide what functionality to invoke.  The LVM commands have long used this paradigm.

Regards!

...JRF...

[223848]

Hi All,

     Thank for the update, but sorry i  didn t understand by   "There are 33 different hard links to the executable"...

Can you please  explain me ......

Thanks

Laiju

[James R. Ferguson]

---

@223848 wrote:

     Thank for the update, but sorry i  didn t understand by   "There are 33 different hard links to the executable"...

---

Review the manpages for 'ls(1)' to appreciate what it is that the output you posted says.

Do you understand what a hard-link is?  The LVM binaries are hard-links to a common piece of code.

http://en.wikipedia.org/wiki/Hard_link

Hard links differ from soft (symbolic links) so be sure to understand what they are:

http://en.wikipedia.org/wiki/Symbolic_link

Regards!

...JRF...

[Dennis Handly]

>"There are 33 different hard links to the executable".

>>   518 -r-sr-xr-x  33 root  /usr/sbin/lvdisplay

33 is the (hard) link count.  If you look for inode with value of 518, you should find them all:

find /usr/sbin -inum 518 -exec ll -i +

[223848]

Hi All,

      Thanks a lot for the information

What i understood is..

I checked and found that all lv and vg related commands have same inode that means,, eventhough we are using the diffenret commands  its executing a common script..

As we can wee 33 hardlinks are there ,

Eventhough if im creating an additional soft link or hard link with a new name ( in our scenario /tmp/test)  then also when im executing with the new link (/tmp/test) , it will cehck whether i used any of the above 33 names ..

Whether my concept is clear .....

Regards

Laiju.

[Dennis Handly]

>even though we are using the different commands, it's executing a common script.

This isn't a script, it's a binary executable.

(Though the same trick can be used for scripts.)

[223848]

Hi Dennis and James,

                     Thanks a lot for your kind time for teaching  me :)

Regards

Laiju