All posts for the month October, 2021

my tty


Some facts about tty on my systems.
under my /dev/
tty tty0 ttyS0 : wsl, wsl2, native linux, ec2
pts/ptmx ptmx: wsl, wsl2, native linux, ec2
/pts/0: added in many cases: wsl1, wsl2, ssh, for native linux: open terminal windows in local gnome or xrdp session.
ttyUSB0: seen on native linux, when USB is connected, e.g. a debug board. the same debug board show up as ttyS0 for wsl1.

pts/0 connects to ptmx, while tty to Terminal Emulator like ctrlAltF1 and supported by kernel directly
gnome directly connects to keyboard. gnome logically is like ssh+sshd
sshd asks ptmx to create pts/0
$ tty output: /dev/pts/* on wsl2 ssh and many other cases, except on wsl1, it outputs /dev/tty*

by Rio Wing on October 24, 2021  •  Permalink
Posted in linux
Tagged , ,

Posted by Rio Wing on October 24, 2021

https://riowingwp.wordpress.com/2021/10/24/my-tty/

XSPF playlist


List.xspf playlist, XSPF: XML Shareable Playlist Format, can play part of a media fileļ¼Œe.g. one piece music of a concert audio file.
This playlist is Vlc.exe specific, because the extension is tied to vcl command line options.
It’s tested with VLCPortable.exe v 3.0.6 on Winidows 10, play first song 4 seconds and second 6 seconds
Copy paste the following into a file, e.g. list.xspf, and then open it with vlc.

<?xml version="1.0" encoding="UTF-8"?>
<playlist version="1" xmlns="http://xspf.org/ns/0/">
<trackList>
    <track>
    <location>file:///T:/Media/ZhuangLiYiXiaYao.mp3</location>
    <extension application="http://www.videolan.org/vlc/playlist/0"> 
        <vlc:option>start-time=6.000</vlc:option> 
        <vlc:option>stop-time=10.000</vlc:option> 
    </extension> 
    </track>
    <track>
    <location>file:///T:/Media/14Waltz.mp3</location> 
    <extension application="http://www.videolan.org/vlc/playlist/0"> 
        <vlc:option>start-time=2.000</vlc:option> 
        <vlc:option>stop-time=8.000</vlc:option> 
    </extension> 
    </track>
</trackList>
</playlist>

by Rio Wing on October 17, 2021  •  Permalink
Posted in video
Tagged

Posted by Rio Wing on October 17, 2021

https://riowingwp.wordpress.com/2021/10/17/xspf-playlist/

wifi6


wifi6 Official name: 802.11ax , while wifi5 is .11ac


How is it better than wifi5:
by increasing total throughput and reducing waste.


check version on Windows:
c:> devmgmt – network – wireless: Qualcomm Atheros QCA61x4A Wireless Network Adapter
QCA6174A is wifi5: 2×2 dual-band 802.11ac Wi-Fi with MU-MIMO and Bluetooth 5.0 radios in a single-chip solution.
This laptop is Lenovo Yoga 920 from 2018.

check version on router: Arris BGW210-700 from ATT, which is 802.11n = wifi4

Limitation: if only one device on the wifi, speed increases by on 1/3, so similar to wifi5
the gain comes from 1024-QAM


Advantages: help a lot when large number of devices on the AP.

1. less wait time to start: since single frame can be shared by users, so other users can start if frame not full.
OFDMA: orthogonal frequency division multiple access, doesn’t increase overall capacity, but scheduling only.
MU-MIMO: Multi-User Multiple-Input Multiple-Output. wifi6 do upstream too.
wifi 5 can only do downstream, no good for video meeting.

2 more total throughout:
8×8 means 8 antenna sending 8 receiving. wifi5 usually 4×4 can do 8×8 too.
1024-QAM each Long DFDM Symbol from 8bit to 10bit, little better

3. more power efficient because sleep when not transferring data.

Who needs it: large number of devices connecting to one AP
price: double wifi5, over $100.

by Rio Wing on October 10, 2021  •  Permalink
Posted in DevOps

Posted by Rio Wing on October 10, 2021

https://riowingwp.wordpress.com/2021/10/10/wifi6/

Manual email attachment


Attachment is done by MIME Multipurpose Internet Mail Extensions
Here is a SMTP DATA section, which is on the same level as RCPT TO.
Two attachment: one text file and one tiny .bmp file.
In DATA section, after “Subject:” and “Subject:”, instead of blank, we have “MIME-Version:”
followed by 4 “Content-Type:”, named 1 2 3 4.

  1. multipart/mixed; and set boundary
  2. text/plain; text message
  3. text/plain; text attachment
  4. image/bmp .bmp attachment encoded with Content-Transfer-Encoding: base64
    mime.eml tested with http://www.encryptomatic.com/viewer
    See screenshot mine.jpg
    download: http://riowing.net/p/wp/mime.eml
by Rio Wing on October 3, 2021  •  Permalink
Posted in DevOps

Posted by Rio Wing on October 3, 2021

https://riowingwp.wordpress.com/2021/10/03/manual-email-attachment/