News Group Posts

init 1 doesn't unmount filesystems

From: Bela Lubkin <belal@sco.com>
Subject: Re: adding second SCSI drive
Date: Fri, 22 Nov 2002 08:22:51 GMT
References: <8913f8d8.0211212046.3064fde@posting.google.com>
<H5yrFA.4Cu@bokonon.stevedunn.ca> 

Stephen M. Dunn wrote:

[a new hard drive has been added, defined as /u, and old /u data copied
over to it -- old /u being a directory of the very full root filesystem]

>    Bring the system up, make sure the filesystem mounted properly
> (use mount to check), make sure the app works.  Reboot into
> single-user mode and toast the contents of /u to free up space on
> your first hard drive; leave the /u directory itself in place,
> because you need it there in order to mount your new filesystem.

At that "toast the contents of /u" step... be careful!

Stephen says "Reboot into single-user mode".  In part, he means "make
sure your shiny new /u is not mounted".  Rebooting will generally ensure
that, but there are ways you could prevent it.  Also, some readers may
have a mental shorthand for "reboot into single-user mode", where they
instead run `init 1` or `init S`.  Those commands take you into
single-user mode with non-root filesystems still mounted.

If the new /u was still mounted, "toast the contents of /u" would blow
away the new copy.  That alone wouldn't be catastrophic, since the
underlying /u directory (on the root filesystem) would still be there,
as would the good verified backup you made.  But -- in the ensuing
confusion, the root copy might get damaged; and 10% of the readers will
do this without making a good backup, no matter how hard you urge...

So, the idea is:

  make good verified backups

  tell the kernel about the new drive

  mount it somewhere (not /u)

  copy the contents of /u onto it

  unmount it (whether by rebooting or whatever)

  double-check that /u is now just a directory on the root filesystem

    [you can run `df -v / /u`; the "Filesystem" column in the output
     shows the device names corresponding to each directory; for
     instance:

       $ df -v / /etc
       Mount Dir  Filesystem              blocks      used      free   %used
       /          /dev/root             13880000   6445536   7434464    47%
       /etc       /dev/root             13880000   6445536   7434464    47%

       $ df -v / /u
       Mount Dir  Filesystem              blocks      used      free   %used
       /          /dev/root             13880000   6445536   7434464    47%
       /u         /dev/u                71649900  44609306  27040594    63%

     Notice that / and /etc have the same device node and stats --
     they're on the same filesystem.  / and /u are on different
     filesystems.]

  delete the contents of /u

  make sure a /u directory exists in the root filesystem, is empty, and
  has permissions 755

  mount the new drive onto /u

>Bela<
 

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