I discover a way to run second X server on top of primary with one of:
$ xinit ~/.fvwm/xinit -- `command -v Xnest` :1
$ xinit ~/.fvwm/xinit -- `command -v Xephyr` :1
How can I find which DISPLAY (here is :1) is free for use programmatically?
Preferred is solution from command line.
What limits for DISPALY value count (hardware/software)?
same limits as for port number ( it's 6000 + display if server is listening on TCP ). Try to bind to a port, if successful - consider it's free, release and start X server with DISPLAY= (port - 6000)
Related
I'm getting complaints from employees in the field that our site is slow. When I check it -- the speed is acceptable. They are all going through a proxy server that is not controlled by me.
I'd like to run a continuous ping to the proxy server, but I haven't found anything to do that.
How do I check the speed from my site to a proxy server?
You can set up a cronjob to ping a site of your choice, at the frequency you choose. Here I ping google.com every 15 minutes. I can adjust the number of times I ping with the flag -c count and the time between pings with -i interval. This time is in seconds, I can use shorter intervals if required, for example 0.5.
I then pipe to tail -n to only use the last line with the results. At this stage my output is as follows:
rtt min/avg/max/mdev = 12.771/17.448/23.203/4.022 ms
We then use awk to only take the 4th field and use tr to replace the slashes with commas. Finally we store the result in a CSV file.
Here is the whole line in crontab:.
*/15 * * * * ping -c 5 -i 1 google.com | tail -n 1 | awk '{ print $4 }' | tr "/" "," >> /home/john/pingLog.csv
It is important to run this as root. To do so we edit the crontab using sudo:
sudo crontab -e
The end result is a comma separated file that you can open in Excel or equivalent, or process as you wish.
As noted in the ping output the 4 figures are min/avg/max/mdev.
Here is a version for Windows. The result is not so refined as we had in the Linux version but we're still getting the essentiels. You could put it in a .bat file and run it with a planned task or put it directly in the planned task.
ping google.com | findstr Minimum >> TotalPings.txt
Which adds the following line every time it is run:
Minimum = 23ms, Maximum = 23ms, Moyenne = 23ms
You can change the server pinged to suit your needs.
I'm looking for a numerical value that represents the wifi signal strength on my Mac. Is there an easy command line tool that can continuously report wifi signal and/or dropped packet statistics?
So I made a function in z shell to easily find the wifi strength with a numerical value thanks to the help from someone at MoonPoint.com[1] who knows far more about the utility than I do.
To use it, just append this code to the bottom of ~/.zshrc. Next time you open the shell, just type in wifi to run the command once or wifi -l or wifi --loop to run it continuously.
path+="/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/"
wifi(){
if [[ -n $1 && (($1 == -l || --loop)) ]]; then
clear
while true; do
airport -I;
echo "Press Ctr+c to exit.";
sleep 1;
clear;
done
else
airport -I;
echo "\nPass -l or --loop for continous measurement"
fi
}
The output will look like this.
wifi
agrCtlRSSI: -76
agrExtRSSI: 0
agrCtlNoise: -94
agrExtNoise: 0
state: running
op mode: station
lastTxRate: 130
maxRate: 217
lastAssocStatus: 0
802.11 auth: open
link auth: wpa2-psk
BSSID:
SSID: ATTUYrDBxi
MCS: 1
guardInterval: 800
NSS: 2
channel: 60,80
Pass -l or --loop for continous measurement
agrCtlRSSI represents the signal strength and can be a value from -100 to 0. The closer it is to 0, the better. I still need to figure out what NIC IC is being used so I understand what power (dB) it translates to, but it's at least better than three little wifi bars when troubleshooting connection speed.
I have openwrt implementation on a TPLink WR902AC (pocket router)
I have a /etc/network/wireless configuration file with 10 sta configurations for connecting to AP all of which are active (option disabled '0')
This is to ensure that openwrt connects to any one of the APs configured.
Only the first 4 configured are attempted to be connected and the rest are simply ignored.
(if first 4 configured are not available the 5th one is being ignored)
I tried to identify the bottleneck.
Only first 4 wpa_supplicant instances are called as evident from these files in /tmp/run
./tmp/run/wpa_supplicant/wifi3
./tmp/run/wpa_supplicant/wifi1
./tmp/run/wpa_supplicant/wifi2
./tmp/run/wpa_supplicant/wifi0
When I disable the first one, the fifth one gets connected on reconnect with "wifi"
I tried to check the source code. I lost the track after ubus being called from wifi script.
This I believe is similar question to https://forum.openwrt.org/t/limit-on-the-number-of-wifi-ssids/63141
iw list on openwrt show me the limit.
valid interface combinations:
* #{ IBSS } <= 1, #{ managed, AP, mesh point, P2P-client, P2P-GO } <= 4,
total <= 4, #channels <= 1, STA/AP BI must match
I tried to use wpa_supplicant directly instead of depending on scripts.
wpa_supplicant -c /root/wifi0.conf -i wifi0 -s -B
wpa_supplicant -c /root/wifi1.conf -i wifi1 -s -B
wpa_supplicant -c /root/wifi2.conf -i wifi2 -s -B
wpa_supplicant -c /root/wifi3.conf -i wifi3 -s -B
wpa_supplicant -c /root/wifi4.conf -i wifi4 -s -B
wpa_supplicant -c /root/wifi5.conf -i wifi5 -s -B
This failed with "interface wifi4" not available error.
Could someone point me to the source where this hard limit is set?
Is there any way around this?
Thanks in advance.
Update:-
mt7601u based usb WiFi dongle was added to wr902ac and configured (as radio2)
This time only one is connected. If I have AP configured, sta doesn't even get connected.
so number of slots is limited. (ap counts as one slot and each sta is one slot)
The built-in 2.4 GHZ has 4 slots & 5 GHz has 8 slots.
The mt7601u based wifi has only 1 slot.
Probably there exists a usb dongle that has 8 slots. Could someone point me to the theory behind all this?
I am working on a robot and my goal is to plot the state of the robot.
For now, my workflow is this:
Launch the program
Redirect the output in a file (robot/bash): rosrun explo explo_node > states.txt
Send the file to my local machine (robot/bash): scp states.txt my_desktop:/home/user
Plot the states with octave (desktop/octave): plot_data('states.txt')
Is there a simple solution to have the data in "real time"? For the octave side. I think that I can with not so much difficulty read from a file as an input and plot the data when data is added.
The problem is how do I send the data to a file?
I am opened to other solutions than octave. The thing is that I need to have 2d plot with arrows for the orientation of the robot.
Here's an example of how you could send the data over the network (as Andy suggested) and plot as it is generated (i.e. realtime). I also think this approach is the most flexible / appropriate.
To demonstrate, I will use a bash script that generates an
pair every 10th of a second, for the
function, in the range
:
#!/bin/bash
# script: sin.sh
for i in `seq 0 0.01 31.4`;
do
printf "$i, `echo "s($i)" | bc -l`\n"
sleep 0.1
done
(Don't forget to make this script executable!)
Prepare the following octave script (requires the sockets package!):
% in visualiseRobotData.m
pkg load sockets
s = socket();
bind(s, 9000);
listen(s, 1);
c = accept(s);
figure; hold on;
while ! isempty (a = str2num (char (recv (c, inf))))
plot (a(:,1), a(:,2), '*'); drawnow;
end
hold off;
Now execute things in the following order:
Run the visualiseRobotData script from the octave terminal.
(Note: this will block until a connection is established)
From your bash terminal run: ./sin.sh | nc localhost 9000
And watch the datapoints get plotted as they come in from your sin.sh script.
It's a bit crude, but you can just reload the file in a loop. This one runs for 5 minutes:
for i = 1:300
load Test/sine.txt
plot (sine(:,1), sine(:,2))
sleep (1)
endfor
You can mount remote directory via sshfs:
sshfs user#remote:/path/to/remote_dir local_dir
so you wouldn't have to load remote file. If sshfs is not installed, install it. To unmount remote directory later, execute
fusermount -u local_dir
To get a robot's data from Octave, execute (Octave code)
system("ssh user#host 'cd remote_dir; rosrun explo explo_node > states.txt'")
%% then plot picture from the data in local_dir
%% that is defacto the directory on the remote server
My problem is that when I add a printer using the Printers and Scanners UI printing works, when I add the same printer using lpadmin it doesn't.
To Add it through the UI I did the following:
From Printers and Scanners I selected the IP tab.
Address: 10.20.30.40, Protocol HP Jetdirect - Socket, Queue left blank, Name: TEST_01, Location "Top Floor", Use -> Select software -> HP LaserJet P3010 Series
After doing this, the Printer works as expected.
This is a (segment from a) script containing my lpadmin command that doesn't work
SUBNET=socket://10.20.30.
TEST_01=40
PPD_DIR=/Library/Printers/PPDs/Contents/Resources
TEST_01_PPD="hp LaserJet P3010 Series.gz"
lpadmin -E -p TEST_01 -v $SUBNET$TEST_01 -P "$PPD_DIR/$TEST_01_PPD" -D "TEST_01" -L "Top Floor"
The printer appears correctly in the UI but shows as paused.
I did find a message in system.log that may or may not be relevant - I was using Notes to test the printer:
Notes[502]: Failed to connect (_delegate) outlet from (com_hp_psdriver_19_11_0_PDEView) to (com_hp_psdriver_19_11_0_PDEAccountingController): missing setter or instance variable
Notes[2198]: Printing failed because PMSessionEndDocumentNoDialog() returned -30871.
The reason I want to use a script is that there are 20 printers to add on each of 30 new Macs. The actual script uses a series of arrays with lpadmin in a for loop. Everything I have read says it should work. What am I missing?
I think -E specified before the printer name enables encryption, whereas specified after it Enables the printer - effectively "unpausing" it. Madness- I know!
Mad Apple Documentation - see second sentence
I think you want:
lpadmin -p TEST_01 -v $SUBNET$TEST_01 -P "$PPD_DIR/$TEST_01_PPD" -D "TEST_01" -L "Top Floor" -E
I don't have a direct answer, but I can suggest an alternate approach: set up all 20 printers by hand on one computer, then copy the /etc/cups directory from that one to the other 29.