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Date:      Wed, 20 Oct 1999 10:16:40 -0400 (EDT)
From:      Zhihui Zhang <zzhang@cs.binghamton.edu>
To:        Neil Blakey-Milner <nbm@mithrandr.moria.org>
Cc:        freebsd-hackers@FreeBSD.ORG
Subject:   Re: Update the name of a filesystem (more details)
Message-ID:  <Pine.GSO.3.96.991020101301.24319A-100000@sol.cs.binghamton.edu>
In-Reply-To: <19991019212032.A6058@mithrandr.moria.org>

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On Tue, 19 Oct 1999, Neil Blakey-Milner wrote:

> On Mon 1999-10-18 (15:46), Zhihui Zhang wrote:
> > I am trying to change the mount point of a mounted filesystem (from
> > /testme to /test) with the update option (-u): 
> 
> That's not how -u works.  From the man page:
> 
> -u      The -u flag indicates that the status of an already mounted file
>         system should be changed.  Any of the options discussed above
>         (the -o option) may be changed; also a file system can be changed
>         from read-only to read-write or vice versa.
> 
> > # mount /dev/wd0s2e /testme
> > # mount -u /dev/wd0s2e /test
> > mount: /dev/wd0s2e on /test: specified device does not match mounted
> > device
> 
> This is because, as stated above, you can only change the options of the
> mounted filesystem, not its mountpoint.
> 
> > Why it does not work (I know I can umount first without using the update
> > option)? Any help is appreciated. 
> 
> This (umount then mount) is the way to change mountpoint names.
> 

Thanks for your reply.  I have just found that it is possible to change
the device name of a mounted filesystem: 

# ls -al wd0s2e
brw-r-----  1 root  wheel    0, 0x00030004 Oct 11 15:02 wd0s2e
# cd /dev
# mknod testnode b  0 0x00030004
# ls -al testnode
brw-r--r--  1 root  wheel    0, 0x00030004 Oct 20 09:50 testnode
# mount /dev/wd0s2e /testme
# df
Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
/dev/wd0s1a     39647    22125    14351    61%    /
/dev/wd0s1f   1787726   965430   679278    59%    /usr
/dev/wd0s1e     19815     3459    14771    19%    /var
procfs              4        4        0   100%    /proc
/dev/wd0s2e   2109789   659537  1281469    34%    /testme
# mount -u /dev/testnode /testme
# df
Filesystem    1K-blocks     Used    Avail Capacity  Mounted on
/dev/wd0s1a       39647    22125    14351    61%    /
/dev/wd0s1f     1787726   965430   679278    59%    /usr
/dev/wd0s1e       19815     3460    14770    19%    /var
procfs                4        4        0   100%    /proc
/dev/testnode   2109789   659537  1281469    34%    /testme

I know this is not very useful.  But the source code allows it to happen.

-Zhihui



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