I use lightroom 5. Have always used the general automatic backup. I want to backup my catalog to an external backup drive. I go to file,, then export catalog and I get message that about 900 pictures will be exported. I have about 38000 pictures with key

Question

I am out of space on my desktop. I want to export my catalog to an external drive and then work off that external drive which has more storage. I have about 38000 pix, which have keywords etc that I want to be part of this export so I can work on groups of pictures, when necessary.
When I go to files, export catalog I get a message that about 1000 pics will be in the catalog to be exported. How might I get all the pics with keywords metadata and other vital info exported?

Answer 1

With due respect, you appear to have a fundamental lack of knowledge on how LR works.  The "pic" files are not in the catalogs.  They are separate.
The catalog has NOTHING in it but the adjustments you've made.  There are no "pics" in it at all.  The 38,000 photos exist separately.  So Exporting your catalog to another drive will do nothing to fix the crowded "desktop".  It only would move the list of adjustment to another location.
The reason that it Exports a catalog with only 1000 "pics" is because that is what you have somehow selected.  If you want to export a catalog for all the "pics", select all of them.  But, that won't make room on your "desktop".  You need to move the "pics".
To make room on your "desktop", you need to move the "pic" files themselves, not the catalog.  To do that may require an understanding of computer file structure.  In terms of how Lightroom ties your adjustments (recorded in the catalogs) you will have to use Lightroom itself to move the files.  You do that within the Library module and, to do it right, will require an understanding of operating system standard file structures.
To keep the adjustments (recorded in the catalogs) connected with the "pics" you need to plug in the external HDD, and WITHIN LIGHTROOM, create a files structure on the external HDD you are happy with.  Then, you can copy, cut and past or drag and drop from you "desktop" to the new file structure.  If you do it within LR, your adjustments will remain intact. 
It may be tempting to use your operating system programs, like Windows Explorer or the Mac equivalent to move the files, but that will fix the "desktop" space problem but you will loose all of you keywords, adjustments or whatever.
It is probably rude and impolite, but it amazes me that people trust their cherished photography to a program such as Lightroom without ever doing the homework to understand the underlying principles of operation. 
Good luck!  This can be terribly confusing.