What is difference b/w soft link and mount partition

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dieu
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What is difference b/w soft link and mount partition

Unread postby dieu » Thu Mar 16, 2017 7:35 pm

Hello,

I think it must be a difference b/w soft link vs. mount partitions under IRIX 6.5

I have problem with socket connection at runtime. Wonder if this caused by the way I make soft link instead of mount partitions.

Working system has mount /san to /vol5/san, /ste mount to /vol1/ste
Since I'm lazy, i copy san to /home/san, copy /ste to /home/ste
make softlink to /san -> /home/san, softlink to /ste -> /home/ste and mount /home
so, other SGIs can see the same /home
Then i got socket connection problem at runtime.

any explanation will appreciate.

thanks,

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foetz
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Re: What is difference b/w soft link and mount partition

Unread postby foetz » Fri Mar 17, 2017 4:39 am

if you want other machines to use your locally mounted stuff you have to export it.
add /san and /ste to your nfs exports and set the permissions accordingly.

dieu
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Re: What is difference b/w soft link and mount partition

Unread postby dieu » Fri Mar 17, 2017 9:32 am

foet,

Other machines can see and use if i make soft links /san -> /home/san and /ste -> /home/ste
and only mount /home -> /vol0/disk1example

my question is what are differences between using soft links vs. mount partitions ?

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kjaer
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Re: What is difference b/w soft link and mount partition

Unread postby kjaer » Fri Mar 17, 2017 11:28 am

pretty sure an nfs export can't implicitly cross a filesystem boundary. this is a security measure.
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josehill
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Re: What is difference b/w soft link and mount partition

Unread postby josehill » Fri Mar 17, 2017 1:03 pm

Correct.
kjaer wrote:pretty sure an nfs export can't implicitly cross a filesystem boundary. this is a security measure.

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Re: What is difference b/w soft link and mount partition

Unread postby duck » Sat Mar 18, 2017 3:16 am

I sense much confusion in the questioneer. My apologies if this seems patronising, but it seems like these concepts could use a bit of a firming up.

A link is a file that points to the same data as another file in a given file system. The files are exactly the same, except for there being two of them. Since the link and the file are the same, the file cannot be of another filesystem as the link. Sometimes these are called hard links.

A symbolic link (soft as I think you call them) is a file that points to the path of another file or even a directory. This file is NOT the same as the other file, it merely points to the other file. Because of this it can point to anything, even itself (which doesn't make any sense, but there you go). Some operating systems allow wildcards in the path it points to so that the link may dynamically change depending on e.g. who opens it.

Filesystems are the logical structure of files and directories on a storage medium, these may be on a partition, an entire disk or in a file in another filesystem. It's the organisation of data on a medium.

Mounting is the act of attaching the filesystem (wherever it is) to a path in a directory structure. (IRIX does not, as far as I know, support mounting files.)

On unix and unix-like systems, there is only ever one directory structure, and to access files on another filesystem than the root filesystem that was mounted when the system started (nfs, memory filesystem, whatever) you mount these filesystems to a path in the directory structure. The contents of the filesystem the become part of the directory structure until you unmount it.

NFS acts as a filesystem. The server part provides a means for sharing the directory structure and files of a filesystem (not the filesystem itself!) to NFS clients, that in turn have the ability to emulate a filesystem but the structure and data is actually fetched from the server.

Thus you are able to mount these like filesystems but across the network.

NFS doesn't need to know about links, it just exports them like any other file. (hard) links are exactly the same as any other file it exports and thus work just like normal. Symbolic links on the other hand point to a path and thus is dependent on the layout of the client directory structure (if symbolic links are supported).

So a symbolic link that points outside the filesystem that has been exported via NFS, would still work on the client system that mounts it, but you couldn't access the data from the file on the server because the path points to a location in the client's directory structure as the symbolic link is being resolved on the client machine.

I hope that reduces the confusion?
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Re: What is difference b/w soft link and mount partition

Unread postby dieu » Tue Mar 21, 2017 4:32 pm

Thank you 'duck'. It helps and I like it.


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