topic how to create the softlink two mount points in Operating System - Linux

how to create the softlink two mount points

rajesh73 — Fri, 08 Feb 2013 10:27:58 GMT

example

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda5             19840892   2189396 16627356 12% /
/dev/sda6               980308     17652    912056   2% /swap
/dev/sda1               101086     11342     84525 12% /boot
tmpfs                   253588         0    253588   0% /dev/shm
/dev/sda3             19840924    176220 18640564   1% /data2
/dev/sda2             19840924    176204 18640580   1% /scratch
[root@testlinux ~]#

i want to create the softlink betweeb /stage directory to /scratch mount point

Requirment

when user upload the data in /stage directory that time data it will reflect to /scratch mount point.how to create the soft link.

Re: how to create the softlink two mount points

rajesh73 — Fri, 08 Feb 2013 10:40:47 GMT

one small input one folder in mount point another one is root directory

Re: how to create the softlink two mount points

rajesh73 — Fri, 08 Feb 2013 11:06:25 GMT

one more input in my production server /stage and /scratch different vg.

Re: how to create the softlink two mount points

Matti_Kurkela — Fri, 08 Feb 2013 15:58:08 GMT

If the uploaded filename is not known in advance, you must softlink the entire directory. To do that, you must move away (or unmount if necessary) the current /stage directory. With soft links, it does not matter if the link and target are in different filesystems or VGs.

# umount /stage #(if necessary)
# mv /stage /stage.old
# ln -s /scratch /stage

Re: how to create the softlink two mount points

rajesh73 — Fri, 08 Feb 2013 16:50:44 GMT

Hi Matti,

Thnaks for your reply.

#mv /stage /stage.oldf -what is the requirment of this command

#ln -s /scratch /stage - this will create the link file under the /stage or /scratch

one more doubt,

if i change any mount point name in fstab entry ,the same need to update /etc/mtab this is required or automatically update happen

Re: how to create the softlink two mount points

Matti_Kurkela — Sat, 09 Feb 2013 09:30:55 GMT

> #mv /stage /stage.oldf -what is the requirment of this command

You cannot have two things with the same name in the same directory, i.e. if there is a directory/mountpoint named /stage, there cannot be a softlink named /stage, and vice versa.

Filesystems can only be mounted on top of directories, so if /stage was a mountpoint, there will be a directory named /stage left after the "umount /stage" command. Before creating the softlink, this directory needs to be moved away or deleted.

If you run the "ln -s /scratch /stage" command while /stage already exists, one of two things happens:

if /stage is a file, you'll get an error, telling you that /stage already exists.
if /stage is a directory, the ln command assumes you meant "link /scratch into directory /stage using its original name", and so you'll get your softlink as /stage/scratch, which is not what you wanted.

The "ln" command works much like "cp", but without actually copying the data.

> if i change any mount point name in fstab entry ,the same need to update /etc/mtab

No, you should not normally edit /etc/mtab at all.

/etc/mtab is updated by the mount/umount commands: its purpose is to describe what is currently mounted.

In Linux, /proc/mounts offers much the same thing and it can even be used as a replacement of /etc/mtab, but in some situations the mount command stores some extra data in /etc/mtab which is not available through /proc/mounts (mainly when you're using the "user" mount option to allow non-root users to mount/unmount things).

The only times you might want to edit or replace /etc/mtab are:

when you've accidentally overwritten the current /etc/mtab, e.g. by restoring an old full backup of /etc that had a different configuration of mountpoints than what the system currently has, or
when you have manually mounted/unmounted other filesystems while the root filesystem has been in read-only mode, so the mount/umount commands failed to update /etc/mtab accordingly (e.g. because of a disk failure affecting the root filesystem), or
you are preparing to shut down the system that has a mounted filesystem that you know cannot be unmounted cleanly (e.g. because it is on a disk that has failed in a bad way, or on a NFS server that has been permanently shut down) and you want the system to just ignore the problem and shut down as quickly as possible.