Category: Technology

Fedora — Disabling IPv6

Since it’s the third time I’ve had to do this so far this year, I’m going to write down how I disable IPv6 in Fedora. Add these lines to /etc/sysctl.conf

[lisa@server~]# grep ipv6 /etc/sysctl.conf
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=1

Then load the sysctl settings (sysctl -p) or reboot.

Without IPv6, if you do X-redirection, you may get an error indicating the redirection was refused. In journalctl, there’s an error “error: Failed to allocate internet-domain X11 display socket”. Evidently you’ve got to configure sshd to use IPv4 by setting “AddressFamily inet” in /etc/ssh/sshd_config

[lisa@server~/]# grep AddressFamily /etc/ssh/sshd_config
AddressFamily inet

 

MythTV Verbose Logging

In the process of troubleshooting UPNP/DLNA on our MythTV server, I learned that you can send logging verbosity settings while the server is running. Using the mythbackend binary with the –setverbose flag, you can specify logging level. For example:

mythbackend --setverbose http:debug,upnp:debug

What items can you set levels on? It’ll conveniently tell you — “all” or “none” override existing settings, everything else will update the current logging levels (i.e. if I’ve already got http and upnp in debug, I can use “–setverbose audio:debug” to add audio to the list of things in debug mode).

[mythuser@server /var/log/mythtv/]# mythbackend -v help
Verbose debug levels.
Accepts any combination (separated by comma) of:

all - ALL available debug output
audio - Audio related messages
channel - Channel related messages
chanscan - Channel Scanning messages
commflag - Commercial detection related messages
database - Display all SQL commands executed
decode - MPEG2Fix Decode messages
dsmcc - DSMCC carousel related messages
dvbcam - DVB CAM debugging messages
eit - EIT related messages
file - File and AutoExpire related messages
frame - MPEG2Fix frame messages
general - General info
gpu - GPU OpenGL driver messages
gpuaudio - GPU Audio Processing messages
gpuvideo - GPU video rendering messages
gui - GUI related messages
http - HTTP Server messages
idle - System idle messages
jobqueue - JobQueue related messages
libav - Enables libav debugging
media - Media Manager debugging messages
mheg - MHEG debugging messages
most - Most debug (nodatabase,notimestamp,noextra)
network - Network protocol related messages
none - NO debug output
osd - On-Screen Display related messages
playback - Playback related messages
process - MPEG2Fix processing messages
record - Recording related messages
refcount - Reference Count messages
rplxqueue - MPEG2Fix Replex Queue messages
schedule - Scheduling related messages
siparser - Siparser related messages
socket - socket debugging messages
system - External executable related messages
timestamp - Conditional data driven messages
upnp - UPnP debugging messages
vbi - VBI related messages
xmltv - xmltv output and related messages

To disable debugging, use “mythbackend –setverbose none”

Oracle Function – Keeping Null Records With LISTAGG

I have been using LISTAGG to group a bunch of records together to be presented in a single HTML table cell. Problem is LISTAGG doesn’t do anything with null field values. As such, the data doesn’t line up across columns. The three ID values have two string values, which basically get centered in the cell. You cannot tell which ID value goes to which name value.

By adding a concatenation to the LISTAGG value, something will be included in the result set even when the record value is null.

Voila — records line up and I can tell the first ID doesn’t have an associated string value.

Fedora – Why were my packets dropped?

We’ve been seeing dropped packets on one of our servers — that usually means more data is coming in than can be processed, but it’s nice to confirm rather than guess. The command “netstat -s” displays summary statistics that are nicely grouped into causes:

TcpExt:
16 invalid SYN cookies received
88 resets received for embryonic SYN_RECV sockets
18 packets pruned from receive queue because of socket buffer overrun
2321 ICMP packets dropped because they were out-of-window
838512 TCP sockets finished time wait in fast timer

Browser How-To: Using the Developer Console

The developer console will show client-side errors. You can also use it to interact with data on a web page (like the approaches I’ve published to exporting data from Teams). To display the developer console, use Ctrl+Shift+i

When you first display the console, you may want to clear the existing output – it’s difficult to correlate the errors to discrete actions you’ve taken on the website. Once the console is clear, perform the action again and watch for errors as you perform each individual operation.

Clearing console output on Firefox:

Clearing console output on Chrome:

 

Zap2XML 503 Error

We’ve been using zap2xml.pl to pull TV listings into our MythTV installation for years. Yesterday, we noticed there wasn’t much scheduled to record. When I went to investigate it today, I found that there weren’t listings past Thursday. Running the zap2xml script manually, I see a bunch of 503 Backend unavailable errors. Checked the URL and, yeah, that’s a legit error.

So I had to quickly switch to a different source for listings. I found a Github project that generates the XML file we need. The same mythfilldatabase command (/usr/bin/mythfilldatabase –file –sourceid 2 –xmlfile /tmp/listings.xml) pulled in the data without error. And, now that there are programs listed, MythTV plans to record things again.

Increasing message text size in Evolution

Evolution has the most microscopic text. Scott literally picks his computer up sometimes just so he can read the message. You get a lot of text on the screen … I guess. But it’s not really useful if you cannot read it.

(1) There’s a system-wide default font in KDE. Under the Fonts, there are setting for “small”, “toolbar”, “menu”, “window title” … they seem to default to 10 points (8 for small). That’s rather small on a high-resolution monitor.

(2) In Evolution, select Edit > Preferences
Select Mail Preferences from the left sidebar. Untick the box “Use the same fonts as other applications” and then pick a bigger font. This only changes the message text — the from/subject/date and folder structure are still using the system font.

Python — dis

Found a cool method for testing the efficiency of different approaches to a python expression — dis disassembles the call and prints the component steps. Here, we see that there’s not much functional difference between “not a=b” and “a != b”.