I have 2 imacs in different states. Both have LR 5. I have been working with my LR5 on iMac #1 in State#1 and have my catalog and photos working fine (they are on my HD. When I came to State#2, I copied my data to my external drive and copied and pasted it into iMac#2 HD. Everything works fine. However, I'm running out of space on my HD and want to run LR5 from my external. When I open it,, all of my files have ? on them (apparently can't find the pictures. I had dragged my HD LR5 folder to the trash (but did not empty it). If I drag it out of the trash back to the Picture folder on my HD, I can get it to work by opening it on the external. The problem is that I need to get the LR5 folder out of my Picture folder on my HD to free up space. I've done alot of checking and I know that this is supposed to work ok if you keep the folder on the external and not need to have it on the HD.. The bottom line here is that I need to get LR5 to work from my external drive and get the LR5 folder off my HD to free up space. Help would be appreciated. Also, I have never done a back up. I always just hit the Skip until next time, but that is another issue.
When you copy the catalog file and folders to the external HD and then pasted to computer 2, Lightroom now does not know where the photos are. You have to reconnect them in Lightroom, which should be simple enough. Follow these directions: Adobe Lightroom - Find moved or missing files and folders
Also, I have never done a back up. I always just hit the Skip until next time, but that is another issue.
Since you brought up the topic, I consider you to be living dangerously and taking extreme and unnecessary risks. In my opinion, you need to make regular and automated backups of your catalog file AND your photos, immediately, no excuses. If tomorrow you drop your computer, or something else happens to render the catalog file or photos unreadable, then what are you going to do? Your edits and other catalog information are lost.