How to fix iTunes downloading IOS update but not installing? iTunes is currently downloading software for the iPad "iPad".


has been displayed for more than an hour.  (Second update at end.)

Where does iTunes save iOS updates? suggests that the update should be less than a gigabyte and should be put in ~/Library/iTunes/iPhone Software Updates—which is currently empty, owned by me, and writable.  UPDATE: There must be either another temporary location, or the 1440-byte packets were something else.  Because now (26 minutes later) that directory is 2.6 GB.

tcpdump -vv shows that I am fetching packets of 1440 bytes from ussea4-vip-bx-006.aaplimg.com.http at about 1.3 GB per hour.  And responding to each with a packet of length zero on the same port.  (No other packets are shown on any other port, which seems odd.)

lsof and sudo lsof have no output—what's up with that?

What is actually happening and what do I do about it?

Latest iTunes and MacOS; IOS 12.4.1

UPDATE TWO: The "iTunes is downloading and will install" went away with no diagnostics, and then iTunes told me that an update is available and do I want to download and install it?  (Same question I already answered.). iPad is still 12.4.1.  The download filename was iPad_64bit_TouchID_ASTC_13.1.1_17A854_Restore.ipsw which grew to 3585 MB and stopped.  Clicked update again and iTunes started a new file called iPad_64bit_TouchID_ASTC_13.1.1_17A854_Restore.ipsw.download  The .download was not there the previous time.

There were no other files in that directory during the previous attempt although there had been several attempts the day before.

Attempts to have the iPad update itself never got past "update requested" over a several-hour wait.  The following things failed to help:


turning WiFi off and on in the iPad
rebooting the router and iPad at the same time
shutting down anything possibly competing for bandwidth
plugging it into power.
shut down and restart
hard reset
resetting network
removing used apps to free up four gigabytes of storage (with thirty
already free)
looking for the update in "storage" to delete it (it wasn't there
asking iTunes to fix it in DFU mode


Five of these suggestions were found on several identical web pages, each finishing with the suggestion that I fix it by running their app.  Looked like all these apps were repackaging of the same thing, which reeks of malware or spyware.
I do not know whether this is general or something unique to me, but here's what seems to be happening here:


When iTunes is asked to update the iPad or iPhone, it downloads the update but doesn't install it.  Usually there are no diagnostics, but on one occasion there was an "error 4000" when the download completed.
After the download, putting the device in DFU mode and launching iTunes causes iTunes to install the downloaded update.
Trying to do DFU mode without doing the download first fails.


None of the "normal" update methods did anything, though they have worked on these devices on previous updates.