Moving a subdirectory to another filesystem using symbolic links

Another way of expanding a filesystem is to use space located in another filesystem. This can be accomplished using symbolic links. For example, if you are running out of space on the root filesystem for an application data files directory, you can use space located on a secondary filesystem. As far as the application is concerned, the files will still appear to reside in the root filesystem.

The procedure described here moves a subdirectory to another filesystem and creates a symbolic link using this example:

Subdirectory name:	subdir
Original location (path) of subdir tree:	/usr
New location (path) of subdir tree:	/d1

1. Suspend operations on your system and bring it down to single-user mode.

2. Make a backup of your system, and verify the backup to make certain it is valid.

3. Manually mount the secondary filesystem(s).
   
   mount /dev/d1 /d1

4. Get current permissions of /usr/subdir:
   
   ls -ld /usr/subdir

5. Create the new subdirectory in /d1:
   
   mkdir /d1/subdir

6. Change destination directory owner, group, permissions to match the original source:
   
   chown owner /d1/subdir
   chgrp group /d1/subdir
   chmod permissions /d1/subdir

7. Copy /usr/subdir to /d1/subdir using these commands:
   
   cd /usr/subdir
   find . -depth -print | cpio -pdmv /d1/subdir

   ---

   NOTE: cpio(C) is used instead of a copy command to better retain permissions.

   ---

8. Verify that the copy is successful:
   
   dircmp /usr/subdir /d1/subdir | tee /tmp/dirlog

9. Create the symbolic link:
   
   ln -s /d1/subdir /usr/subdir

you see the symbolic link that references the /d1/subdir directory. To see the physical directory entry itself, with its owner, group and permission information, include the -L option:

ls -ldL /usr/subdir

See also:

• cpio(C)

• mkdir(C)

• ln(C)