Saturday, January 2, 2016
Vi Error 'E185: Cannot find color scheme 'morning' in freshly installed ubuntu 14.04.3
Copied all ~/.vim folder to newly installed ubuntu box. But vi is complaining on start up.
"E185: Cannot find color scheme 'morning'"
Because at default it's using vim.tiny.
qyang@ubuntu:~$ ll /etc/alternatives/vi
lrwxrwxrwx 1 root root 17 Dec 6 13:24 /etc/alternatives/vi -> /usr/bin/vim.tiny*
In old ubuntu box:
qyang@lgm-pc:~$ ll /etc/alternatives/vi
lrwxrwxrwx 1 root root 18 Jun 15 2015 /etc/alternatives/vi -> /usr/bin/vim.gnome
Installing vim-gnome fixed this issue. ($sudo apt-get install vim-gnome)
Thursday, December 31, 2015
Remote desktop to Ubuntu 14.04.3 via default Vino over only SSH port
[1] Using ubuntu 14.04.3 default vino desktop sharing (current session)
[2] One bug fix in early 14.04 vino
[3] SSH tunnelling
[4] command line to config and start vino
See wiki post for details.
vino-preferences on remote ubuntu machine:
vinagre remote desktop client settings on local fedora20 machine:
Final show. Enjoy!!
Thursday, December 10, 2015
Install Playonlinux from command line to accept the license by Tab -> Enter
This POST addressed how to accept license when clicking enter doesn't respond the OK display when installing playonlinux from command line.
Solution: button. Same like in windows.
Solution:
HitThat is it. So easy, just switching among buttons, to highlightkey, then hit to accept the license.
Ubuntu apt mirror access error.
http://askubuntu.com/questions/553765/failed-to-fetch-update-on-ubuntu-14-04-lts-trusty-tahr
This post addressed one issue I had tonight.
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/trusty-backports/Release.gpg Unable to connect to us.archive.ubuntu.com:http:
Solution
sudo rm /var/lib/apt/lists/* -vf sudo apt-get update
Or switch apt mirror from this link
http://askubuntu.com/questions/37753/how-can-i-get-apt-to-use-a-mirror-close-to-me-or-choose-a-faster-mirror
Friday, November 20, 2015
Cron and Anacron to schedule jobs in Linux
$crontab -e to edit
$crontab -l to list
$crontab -l -u username to list cron jobs of username
anacron
runs commands periodically. Unlike cron(8), it does not assume that the machine is running continuously. Hence, it can be used on machines that aren't running 24 hours a day, to control daily, weekly, and monthly jobs that are usually controlled by cron.qyang@lubuntu-laptop:~$ service anacron start
qyang@lubuntu-laptop:~$ service anacron status
● anacron.service - Run anacron jobs
Loaded: loaded (/lib/systemd/system/anacron.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2015-11-21 09:19:57 AEDT; 4s ago
Main PID: 10233 (anacron)
CGroup: /system.slice/anacron.service
└─10233 /usr/sbin/anacron -dsq
Nov 21 09:19:57 lubuntu-laptop systemd[1]: Started Run anacron jobs.
Nov 21 09:19:57 lubuntu-laptop systemd[1]: Starting Run anacron jobs...
Nov 21 09:19:57 lubuntu-laptop anacron[10233]: Anacron 2.3 started on 2015-11-21
Nov 21 09:19:57 lubuntu-laptop anacron[10233]: Will run job `cron.daily' in 5 min.
Nov 21 09:19:57 lubuntu-laptop anacron[10233]: Will run job `svnsyncPQAFW.daily' in 15 min.
Nov 21 09:19:57 lubuntu-laptop anacron[10233]: Jobs will be executed sequentially
cron
Sample of downloading data regularly using cron Changing crontabroot@trac ~# cat /etc/crontab # /etc/crontab: system-wide crontab # Unlike any other crontab you don't have to run the `crontab' # command to install the new version when you edit this file # and files in /etc/cron.d. These files also have username fields, # that none of the other crontabs do. SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin # m h dom mon dow user command 17 * * * * root cd / && run-parts --report /etc/cron.hourly 25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily ) 47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly ) 52 6 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly ) #25 6 * * * root test -x /usr/sbin/anacron || ( cd /root/AuctionResults && run-parts --report /root/AuctionResults) 00 12 * * 7 root test -x /usr/sbin/anacron || ( cd /root/AuctionResults && run-parts --report /root/AuctionResults) #Run any executable files,eg.runpython under nominated folder AuctionResults
root@trac ~# ls -al ~/AuctionResults total 852 drwxr-xr-x 2 root root 4096 Nov 15 12:00 . drwx------ 11 root root 4096 Sep 9 00:41 .. -rwxr-xr-x 1 root root 1105 Jul 14 13:48 file-retrieve-via-url.py -rwxr-xr-x 1 root root 39 Jun 9 22:43 runpython
qyang@lubuntu-laptop:~/Svn_Local_Personal/A_001_Notes$ locate cron |grep bin /usr/bin/crontab /usr/sbin/anacron /usr/sbin/cron
/etc/cron.daily/.placeholder /etc/cron.daily/0anacron /etc/cron.daily/apport /etc/cron.daily/apt /etc/cron.daily/bsdmainutils /etc/cron.daily/dpkg /etc/cron.daily/logrotate /etc/cron.daily/man-db /etc/cron.daily/mlocate /etc/cron.daily/ntp /etc/cron.daily/passwd /etc/cron.daily/popularity-contest /etc/cron.daily/update-notifier-common /etc/cron.hourly/.placeholder /etc/cron.monthly/.placeholder /etc/cron.monthly/0anacron /etc/cron.weekly/.placeholder /etc/cron.weekly/0anacron /etc/cron.weekly/fstrim /etc/cron.weekly/man-db /etc/cron.weekly/update-notifier-common /etc/default/anacron /etc/default/cron /etc/init/anacron.conf /etc/init/cron.conf /etc/init.d/anacron /etc/init.d/cron
Aliasing Automatic Gain Control and FFT
Aliasing
A filter chosen in anticipation of a certain sample frequency is called an anti-aliasing filter. Aliasing on wiki. A real anti-aliasing filter trades off between bandwidth andaliasing
Undersampling, which causes aliasing.
Without an anti-aliasing filter, frequencies higher than the Nyquist frequency will influence the samples in a way that is misinterpreted by the interpolation process. Ref
Without an anti-aliasing filter, frequencies higher than the Nyquist frequency will influence the samples in a way that is misinterpreted by the interpolation process. Ref
- Paper(pdf) from National Instruments on Aliasing and Sampling at Frequencies Above the Nyquist Frequency.
- Notes:
R (sampling rate) = 100MS/s fs (signal being sampled = 70MHz fN (the Nyquist frequency) = 50MHz fa (aliased frequency) = 30MHz The frequency of the aliased signal can be found from the following simple equation: fa = |R*n - fs|
Although sampling at twice the Nyquist frequency will ensure that you measure the correct frequency of your signal, it will not be sufficient to capture the shape of the waveform. If the shape of the waveform is desired, you should sample at a rate approximately 10 times the Nyquist theory.
If known input frequency range, then sample rate more than 2*InputFreqRange? will remove aliasing. However, real input signal could include signal frequency higher than wanted frequency range, these high frequency signal will cause aliasing at pre-designed smapling rate. (high freq signal and low freq signal end up with same sampling points at lower (than required) sampling rate.) That's the whole reason u need anti-aliasing filter in the front end to filter out unsupported high frequency signals.
Automatic gain control - (AGC)
Finite Impulse Response (FIR) filter
FFT
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