After upgrading (via mirror) from 13.37 to 14.0 to 14.1 to 14.1 current mozilla applications, for example, and Sendmail, complain that they cannot find libicule...so files. The applications will not run. How do I get missing library files of this kind (if they are, indeed, missing), and how install them?

icu4c, it is called
install it, you must
in 13.37, it was not

How did you upgrade? Did you use slackpkg or do it manually based on the UPGRADE instructions that come with slackware?

It sounds like you didn't do the step where new packages get installed (if you are using slackpkg it is slackpkg install-new). If you didn't do this you will need to go back and install the new packages for each version you upgraded through, and then upgrade again your target version so that all of the new packages you installed also get upgraded to their latest version. You should also make sure you remove the deleted packages. This can be facilitated by using "slackpkg clean-system", but be careful because it will propose deleting any non-slackware packages you may have installed so read the list carefully or blacklist your non-slackware packages.

Brian

In the Slackware Package Browser choose your release, the content mode, type the full name of the missing library in the Search field, click on the Search button, when the answers appear (this can take some time), download the package you want then install it with this command:

Thank you for your help. I installed libicule as suggested which worked at once, and I was able to use the same principle for the other missing libraries, but libsoup had to be got from Slackware Packages as also recommended. I was following the Slackware upgrade instructions, but I did neglect install-new (I had recently been using Debian, which doesn't have it), and, indeed, I used clean-system.

Now all works well, and I am grateful for your assistance -- but Sendmail says it has sent messages while also reporting a failure to deliver!