sudo: unable to write to /var/lib/sudo/ts/admin: No space left on device

I have installed a couple of packages that aren't Readynas specific that expect to be installed in the root partition, and the following is what I did.  As long as at least most of the files are installed in a separate directory and, more importantly, all data is placed within that directory or another application-specific one, this should work for you.  Note that in specific commands, I've used two spaces as a delimiter to make it clear there is a space.  They aren't necessary, but Linux doesn't care how many spaces you use.

Start by doing a normal install in the OS partition.  Note the name(s) of the new directories created.  I'm using plural here, but it's often just one.  You can run it to make sure it works, but if it creates a database or other large file(s), it's best to not let it do that.  Some time ago, I copied the following command from a Reddit post as a way of finding the newest directory:  find   .   -type d   -printf   '%T@ %p\n'   |  sort  -nr  |  head  -n  1.  Note that the final 1  is the number of directories to list, so you may want to increase it.

Create a mirror (copy all files and folders) of those directories in /apps.  While /apps appears to be at root, it's actually a mountpoint for /data/apps (assuming your main data volume is data).  If there are multiple directories involved, you may want to make your mirrors sub-directories of a main one you create in /apps.

Next, rename the directories in the OS partition and then create symlinks in their place using the original names.

Now, run the program.  If it works, you're almost done.  If it doesn't, go back and see what you missed.  Once it's running as expected, you can delete the renamed directories and you are done.

If the original install has symlinks within it, then there is more work to do changing them, but that will be too application-specific for me to cover here.

Once set up, this will typically also allow you to install updates without having to re-do all this.

So, in a hypothetical install with a single directory (with or without subdirectories):

Normal install creates /usr/local/myapp.

You create /apps/myapp  and copy all contents of /usr/local/myapp there (all in this one command):  cp  -r  /usr/local/myapp   /apps/myapp.

You rename /usr/local/myapp:  mv  /usr/local/myapp  /usr/local/myapp.old.

You create a symlink:  ln  -s  /apps/myapp  /usr/local/myapp.

Test the program.

If all is well, delete the original installation:  rm  -r  /usr/local/myapp.old.

Since you are messing around in the OS partition, double-check all commands before executing.  Writing them in a text file and then pasting from that is a good way to do that.  Plus, you can save the text file for use as a guide for the next install.

I suspect you don't need quite as much detail as I've given, but others who need it may read and try to follow this.