[PLUG] MythTV: WHYY/PBS frequency finally changed

[JP Vossen via plug <plug@lists.phillylinux.org>]

For anyone still using OTA for MythTV or similar, the local Philly 
WHYY/PBS frequency finally changed in the last few days (circa 2020-07-03?).

This was scheduled at least twice and didn't happen 
(http://tvanswers.com/whenResultsZip.asp), so I forgot about it until I 
just noticed 2 shows failed to record.

My MythTV process to fix it turned out to be really simple...I thought. 
Then, of course, it broke, since it's MythTV and that's what it does. 
My symptoms after the rescan were schedule (EPG) and upcoming recordings 
were empty and `mythfilldatabase --dd-grab-all` = "No channels are 
configured to use grabber" which means that the "xmltvid" fields got lost.

To make a long story shorter, what I *should* have done was:
```
$ cd (to whatever user)
$ /usr/share/mythtv/mythconverg_backup.pl --backup_xmltvids --directory .
```

GUI: Applications > System > MythTV Backend Setup (will CLOSE Myth Server!)
	[*] 6. Channel Editor
		Use [DELETE] to delete all channels
		Channel Scan (can take forever)
	Answer "no" to running "mythfilldatabase"

```
$ /usr/share/mythtv/mythconverg_restore.pl --restore_xmltvids 
--directory . --filename mythtv_xmltvid_backup-20200708013025.sql  # 
change file name!
$ sudo systemctl restart mythtv-backend.service
$ sleep 2m ; mythfilldatabase --dd-grab-all
```

Of course I didn't know about `mythconverg_backup.pl` and while I do 
have `mysqldump` backups of everything, it was...everything and I wasn't 
sure what a full restore of that would do.

The manual way to fix missing xmltvid fields is to open (in my case):
1. The SchedulesDirect lineup report: 
https://www.schedulesdirect.org/lineups/report/PC%3A19426
2. The MythWeb Channel Info: 
http://mythtv-be-01.jpsdomain.org/mythweb/settings/tv/channels
3. Lots of painful copy & paste between them

But then I found https://www.mythtv.org/wiki/Database_Backup_and_Restore
Esp.: 
https://www.mythtv.org/wiki/Database_Backup_and_Restore#Restore_xmltvids_after_a_channel_scan

The restore after you break it can't help if you didn't do the backup 
before you broke it, but my MythTV server is a VM and I was smart enough 
to snapshot it.  So I only had to save my state, restore my snapshot, 
grab the backup and copy it elsewhere, revert my state, copy the file 
back and restore it.  Bang, everything was happy again.

Why the xmltvid fields got nuked in the first place...well, it's MythTV, 
why ask why?

Hopefully this will be useful to someone else,
JP
--  -------------------------------------------------------------------
JP Vossen, CISSP | http://www.jpsdomain.org/ | http://bashcookbook.com/
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