Category Archives: Linux

Posts that cover information that I have learned and have posted, all related to Linux.

morse-1 code

Cron Driven Morse Code Time Sounder

Linux, Projects, , , , ,

My goal was to make a new hourly chime,something with a bit of intelligence to it than just the same tone every hour. It was actually one of those random things that runs through your head when laying in bed trying to get in a mood to sleep.

A bit of history

Typically I have been using a preexisting system sound on a Linux PC to annunciate that it is the top of the hour. This helps to keep track of how long I am on the computer, time to take a break maybe. It also makes me away of the time, in case I am in the zone with coding or whatnot and need to be aware of how time flies. Once you have this, you kind of look for it, even when you are in the room doing something other than computer work.

Up to now this is what I typically had in my crontab…

00 09-23 * * * aplay /usr/share/sounds/fLight__2.0/stereo/Message.wav

I restrict the hours down, just so the thing doesn’t wake me at night if I forget to turn off the PC.

Festival

Years ago I used Festival, the text to speech program and made it annunciate the time. This works OK as long as you are at the PC. If you are away from it a bit, you don’t always pick up what the machine generated voice is saying. Morse Code has an advantage over voice, in that the tones are easy to pick up, even when faint. I have a ham license and have experienced this first hand. So that was my line of thinking with using Morse to give me the time at the top of the hour. It would be easy to not only know that it is the top of the hour but, I can tell what hour it is easily with Morse code. Plus it seemed like a fun twist. I have even thought of putting something like this on my Pi which runs 24/7 in my office. In our living room we have a bird clock, that has different bird sounds for each hour and that has been pretty useful at times, so that got me going on this whole hourly chime adventure years ago.

I was initially inclined to make my own tones but, a brief search found Stephen C. Phillips site and his Morse Code Translator. Using it I was able to create a more code “hour” sound file from 0-23, that plays the correct sounding for every hour.

It is possible to take any sound files and label them 0-23.wav and get other types of sounds to chime at the top of the hour. Birds songs, train whistles, nature sounds, the possibilities are endless.

How it works

Using the Morse Code Translator, I was able to create a series of Morse Code translations from 0-23, in WAV file format. The WAV files get put in a directory, morse-code-audio under my home folder and the following script gets called in place of the line shown above in my crontab….

#!/bin/bash

sounddir=/home/erick/morse-code-audio

# Grab the Hours off of the date.

hour=$(date +"%H")

#Call the correct file based off of the hour
 aplay $sounddir/$hour.wav

WAV Files for the Morse Code Time Sounder

I put the 0-23.wav files online, as a tar.gz.

morse-code-audio.tar

Compression, Signal Processing, Information Theory and Cryptography

Uncompressed the 24 WAV files in the tar file are a total of 348K , it is interesting just how compressible single frequency tones are. All of them compress down to a 2.8K tar.gz. I had to check twice, I thought I was missing a bunch of files. But it stands to reason when one thinks of a single frequency turned on and off slowly, has very little bandwidth. Provided the keying is shaped in a way so that it is not a pure sine wave modulated by a square wave, the pulses have to be shaped the corners rounded off to get the bandwidth below 100Hz. Thinking of Fourier transform, a tone left on from infinity has a bandwidth of zero. A digital signal, pulse shaped, on and off keying at 20WPM code is going to have a real narrow bandwidth, therefore highly compressible. The opposite extreme, white noise, would not be compressed down at all by gzip or any of the fancier types of compression. White noise is random, equally distributed across the spectrum, hence incompressible. But it makes for a hell of an encryption key for that very reason. The worlds of signal processing and cryptography do come together in interesting ways!

Resources

Stephen C Phillips has an excellent website and blog that covers a lot of technical topics among with the Morse Code Translator is an example. He also covers Python code and the Raspberry Pi for example.

http://blog.scphillips.com/

The featured image is from this site and it is an interesting read…

https://www.raspberrypi.org/learning/morse-code-virtual-radio/worksheet/

Samba and Linux Mint

Linux, Server, ,

In my original post on Samba I covered a lot of basics. Recently I learned a bit more using Linux Mint. In Mint Samba is already loaded in the process of installing the OS. I remembered that I had to add all the computers to the same workgroup to get Linux and Windows to play together. But I couldn’t get two Mint machines to work via Samba. Name resolution was the issue.

I kept getting a “Failed to Retrieve Share List from Server” error. I was able to move files from a Mint machine to the Windows machine and then to the other Mint machine. The only thing I had to do is open up permissions on the folder to let Samba write to it. I used the Public folder under the /home/user directory. I would think that adding Samba to my user group would also work, I have checked into this and this is the answer I find…

http://unix.stackexchange.com/questions/206309/how-to-create-a-samba-share-that-is-writable-from-windows-without-777-permission

 

I did install Winbind thinking that it might help out. Windows machine can see Public folder, go into it and read and write with 777 permissions on it.

winbind is a component of the Samba suite of programs that solves the unified logon problem. Winbind uses a UNIX implementation of Microsoft RPC calls, Pluggable Authentication Modules (PAMs), and the name service switch (NSS) to allow Windows NT domain users to appear and operate as UNIX users on a UNIX machine.

https://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/winbind.html

 

I started with this post which got me sort of there…

Samba Basic – Lesson 1: Samba Simply

https://community.linuxmint.com/tutorial/view/672

 

Name Resolution with Samba

http://www.oreilly.com/openbook/samba/book/ch07_03.html

How to Fix ‘Failed to Retrieve Share List from Server’ in Ubuntu 12.04 / 11.10 when File Sharing with Windows

How to Fix ‘Failed to Retrieve Share List from Server’ in Ubuntu 12.04 / 11.10 when File Sharing with Windows

 

Using mount with bind to access usb drive via vsFTP

Info Links, Linux, Raspberry Pi, Raspberry Pi Server, Server, , , , , ,

I have a USB stick plugged into my Raspberry Pi for external storage, mostly to put music on for the Sockso Music Server to get at. But I wanted to use it a bit more for generic storage. FTP is great, you can get to it from any machine and the command line for it is the same on Win or Linux. So I can walk up to any machine, not have to install a thing and reach into a folder with FTP.

For instance, I have an infected Windows Machine, I don’t dare stick a USB stick in it. Instead I go to the command line, ftp to the Raspberry Pi and grab the tools I need from there.

The Issue

The issue was that I tried to symlink from the ftp directory to the USB drive. vsFTP will not follow symlinks for security reasons.

The Solution

Mount the directory you want under the FTP directory using bind. /media/sda is the USB stick mount point and the whole thing gets mounted under the FTP dir using…

sudo mount --bind /media/sda/ /home/ftpuser/usb-drive/

Resources

FTP on Raspberry Pi. An easy way to make shared folders

Alternatives to FTP

https://radu.cotescu.com/vsftpd-and-symbolic-links/

avconv replaces ffmpeg for Video/Audio Conversion

Linux, Raspberry Pi, Time Lapse Photography, , , , , , , ,

Recently I wanted to convert an AVI file to an m4v on Linux Mint 17.3. I tried to use ffmpeg, it’s not there. I can’t isntall it…hmmm. So I did some digging, it has been replaced by avconv. To get avconv….

sudo apt-get install libav-tools

To use

Online, I read that there are some syntax differences between ffmpeg and avconv, so I was reluctant to just symlink pointing ffmpeg to avconv and have scripts break.

But I did a quick test taking a good guess…

avconv -i timelapse-wx-station-4-08-to-7-12-2016.avi timelapse-wx-station-4-08-to-7-12-2016.m4v

…and, it worked. Got me a much smaller file than the AVI and worked it’s magic in a short minute or two.

Video of Weather Station from April 8,2016 to July 12,2016

This was what I was testing out with the conversion. Video taken by using fswebcam to gather a still shot of my weather station once per hour on the Raspberry Pi. Once per day the shots are rolled up into an AVI video and stored in a tmp folder which is mounted in RAM. Well the RAM folder does fill up after a while and I copied the file off and saved it on my desktop. This video shows the weather changing from spring to summer.

Resources

http://askubuntu.com/questions/432542/is-ffmpeg-missing-from-the-official-repositories-in-14-04

 

Pentium 3 without holder and Pentium 4 chip

A look at a Pentium 3 at 500MHz and Pentium 4 at 3.0GHz

Linux, My Thoughts, , , , , , ,

Recently I gutted a few old PC’s. The physical difference between the Pentium 3 (P3) from 1999 and Pentium 4 (P4) from 2005 were stark. It made me think of the way computers have progressed in terms of performance and power usage.

Pentium 3

The Pentium 3 that I removed uses a Slot 1 connector. basically it sits on a board that gets inserted into a slot on the motherboard. The little daughter board reveals a bunch of support hardware once the black cover is removed. There are a couple of chips that look like they might be for the RAM Cache. Looking this up in Wikipedia confirms this thought, “The L2 cache is off-die and runs at 50% CPU speed.” It also states a TDP of 28W. No wonder it can get away with a small fan and heatsink.

https://en.wikipedia.org/wiki/List_of_Intel_Pentium_III_microprocessors#.22Katmai.22_.28250_nm.29

Back of Pentium 3 and 4
Back of Pentium 3 and 4

Pentium 4

On the other hand the P4 HT 630 is a LGA 775 type of socket, a bunch of balls on the bottom that make contact to the socket on the motherboard, 475 of them! This socket design was one of the last for the P4. The P4 is a Prescott 2M and has a TDP of 84W. Hence the big fan and heat sink.

https://en.wikipedia.org/wiki/List_of_Intel_Pentium_4_microprocessors

In contrast, a few years ahead in 2009, a more modern computer, with more processing power would have a processor that uses about 40-50W TDP. So heat-sinks and fans have gotten smaller. Along with the power supplies, I had a Dual Xeon Circa 2004 that had a 1000W power supply, it was fast for it’s time, but also a space heater when it was running hard.

Simple Benchmarks

Running a Pi Benchmark written in C, out to 256000 digits. Lower is better.

1999: Old P3 at 700 MHz Time: 13026 seconds TDP about 28W

2004: P4 at 2400 MHz Time: 3741 seconds TDP 84W

2009: Intel(R) Celeron(R) M CPU 520 @ 1.60GHz Time: 2747 seconds TDP 30W

2011: Intel(R) Core(TM) i3-2100 CPU @ 3.10GHz  Time: 986 seconds TDP 65W

 

P3 and P4 Heatsinks
P3 (left) and P4 (right) Heatsinks
P3 fan center, on top of P4 fan
P3 fan center, on top of P4 fan

 

 

Sockso Music Server on Linux

Linux, Server, , , , , ,

The Sockso Music Server is very functional and quite easy to set up in standalone or daemon mode. It is cross platform as it only depends on a Java runtime environment being installed on the target computer.

Recently I loaded it on my desktop which runs Lubuntu 14.04. I tested it out on the desktop before loading it onto my Ubuntu  server PC, which holds my music repository.

  • I will outline installing the Java run time environment needed to run Sockso on an Ubuntu machine
  • The Sockso install procedure
  • Getting it to run as a daemon
  • Getting it to find your music
  • At the bottom of the page I will have some links to resources that I followed and will provide information for running Sockso on other platforms.

The Sockso install procedure

It is not so much an install like compiling/installing, apt-get or adding a package. It is a simple old school download and drop files in a directory install.

  1. Download the Sockso zip file.  You can do steps 2 and 3 while waiting for  the download!
  2. Create /usr/share/sockso directory as root or via sudo so all files are set to root:root. ( sudo mkdir /usr/share/sockso )
  3. Create Sockso data directory /var/sockso as root or via sudo. ( sudo mkdir /var/sockso )  If sockso is terminated uncleanly, the files in this directory can get corrupted and it will need to be rebuilt
  4. Extract the files to /usr/share/sockso/ ( sudo unzip sockso-1.5.3.zip -d /usr/share/sockso/ ) I am not 100% on my unzip usage, so this command actually made a sockso-1.5.3 folder under /usr/share/sockso. Then I needed to use sudo mv .. to move all the files and dirs up one level.

 

Install Java

On my server that runs headless I performed the following after I typed in java on the command line and it told me that it was missing. It usually resides at /usr/bin/java in a Debian/Ubuntu type of file system. If it is installed it will dump out a help file. Using the command which java will also tell you if it is installed…

The program 'java' can be found in the following packages:
 * default-jre
 * gcj-4.6-jre-headless
 * openjdk-6-jre-headless
 * gcj-4.5-jre-headless
 * openjdk-7-jre-headless
Try: sudo apt-get install <selected package>

I went for version 6 headless for starters. I am not sure what the difference between all the versions are, but version 6 worked for me.

erick@ubuntuserver:/tmp$ sudo apt-get install openjdk-6-jre-headless
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following extra packages will be installed:
  ca-certificates-java icedtea-6-jre-cacao icedtea-6-jre-jamvm java-common
  libnspr4 libnss3 libnss3-1d openjdk-6-jre-lib tzdata-java
Suggested packages:
  default-jre equivs libnss-mdns sun-java6-fonts ttf-dejavu-extra
  fonts-ipafont-gothic fonts-ipafont-mincho ttf-wqy-microhei ttf-wqy-zenhei
  ttf-indic-fonts-core ttf-telugu-fonts ttf-oriya-fonts ttf-kannada-fonts
  ttf-bengali-fonts
The following NEW packages will be installed:
  ca-certificates-java icedtea-6-jre-cacao icedtea-6-jre-jamvm java-common
  libnspr4 libnss3 libnss3-1d openjdk-6-jre-headless openjdk-6-jre-lib
  tzdata-java
0 upgraded, 10 newly installed, 0 to remove and 5 not upgraded.
Need to get 44.2 MB of archives.

 

…and so on as it installed.

Reading Java Version

If you already have java and want to view the version…

java -version

…will get you the version, such as listed on my desktop PC…

erick@Precision-WorkStation-530-MT:/var/sockso$ java -version
java version "1.7.0_91"
OpenJDK Runtime Environment (IcedTea 2.6.3) (7u91-2.6.3-0ubuntu0.14.04.1)
OpenJDK Client VM (build 24.91-b01, mixed mode, sharing)

Test run

Before making it run as a daemon I wanted to test drive it. So the following command will start it up…

sudo sh /usr/share/sockso/linux.sh --nogui --datadir /var/sockso

When you terminate it, try to shut it down clean via a sigterm when you kill the process. I have read that killing it uncleanly can screw up the data directory ( /var/sockso ). Then you have to empty the directory and rebuild it’s contents. I haven’t had it screw up the directory yet.

Running Sockso as a daemon

Running Sockso as a daemon is an advantage when you are running on a server. It will startup when the machine starts and the machine will take care of closing it down cleanly upon shutdown.

Perl script for running sockso as a daemon

After moving the Sockso files to the proper location there will be a Perl file at /usr/share/sockso/scripts/init.d/sockso

Copy the sockso run file written in perl from…

 /usr/share/sockso/scripts/init.d/sockso

…to…

/etc/init.d/sockso

…using…

sudo cp /usr/share/sockso/scripts/init.d/sockso /etc/init.d/sockso

 

Edit the file and change the directory at the top of the file to point to where sockso is installed ( /usr/share/sockso ).

Also make it executable.

sudo nano /etc/init.d/sockso


sudo chmod +x /etc/init.d/sockso

Now that it is in the init.d directory, the following should work…

sockso (start|stop|restart)

Remember to change the directory at the top of the sockso to point to the /usr/share/sockso dir.

 

Starting Sockso on boot

Follow the Steps 4,5,6 on this blog post…

https://samiux.wordpress.com/2009/07/17/howto-sockso-1-1-8-music-server-on-ubuntu-9-04-server/

I have a copy here as a PDF –> sockso-start-on-boot , just in case the link above disappears.

 

Sockso Command Prompt

Sockso comes with it’s own command prompt to administer it. help will list the commands. You can use the Sockso command line to add music to Sockso’s collections, add and delete users and perform other maintenance to it.

There is also a management webpage where you can perform the same functions as via the command line.

Finding Music

There is a command line mode for sockso where you can point it to certain directories to index music from.

Run sockso to bring up it’s command line. At it;s command line use coladd and then the path to the folder that your music is in to add it. It takes a while to do this, it is indexing it into a database so be patient. You can add multiple directories into it’s collections. If you add music to a directory in the collection, sockso will find it and add it. By default it scans directories in it’s collections every 30 minutes. I’ve tested it and it is pretty cool, dump in some music and a little while later, it’s there like magic.

coladd /home/username/Music

collist will list all the collections. coldel deletes collections.

colscan will force a scan for new collections that have been added.

Symbolic Links to Music Folder

The sockso coladd command has issues with spaces in directory names. What I have done is made a bunch of symbolic links using ln -s directory of music directory-of-music. This makes it easy to see where all the music is and sockso just has to deal with my Music directory and if I add or remove music it will figure it out on it’s own. I show an example below in the Raspberry Pi section.

Sockso on Raspberry Pi

I just ( April 2016 ) installed Sockso on my Raspberry Pi. I got the idea of sticking a USB stick into one of it’s open ports and dump my music repository on it. Them with sockso I can get to it whenever I want. Previously I had it set up on my main server that I have to use Wake on LAN to start up when I am not at home. Having Sockso on the Rasp Pi allows me to get at it instantly and saves energy by not having to run a full fledged server just to play music remotely.

Below is a tree of the Music directory that I created under my home directory. As can be seen there are symlinks without spaces that point to locations on the usb stick, mounted at /media/sda.

erick@raspberrypi ~/Music $ tree -L 1
.
├── main-collection -> /media/sda/music
└── renee-ipod-music -> /media/sda/Renee's iPod/iTunes_Control/Music/

The USB stick is formatted it’s default way that it came, FAT32. I use pmount /dev/sda1 /media/sda to mount it. In this was it is mounted not as root, it is mounted by my user, so all files are easily accessed by my own user, locally and remotely using NFS or SSHFS. In this way I can add and remove files easily.

 

 Users

In Sockso there is a concept of users. You can have multiple people logged in and have personalized settings. You can even authorize uploads by setting that option.

Adding users at the Sockso command line works similar to adding users in Linux.

useradd NAME PASS EMAIL ISADMIN 1/0     Adds a new user

Commands:
userlist                                Lists the users
useradd NAME PASS EMAIL ISADMIN 1/0     Adds a new user
userdel ID                              Deletes a user
useradmin ID ISADMIN 1/0                Sets a user to be admin/non-admin
useractive ID ISACTIVE (1/0)            Toggles users between being active or not
coladd PATH                             Adds a folder to the collection
coldel PATH                             Removes a folder from the collection
collist                                 Lists the folders in the collection
colscan DIR (optional)                  Start a collection scan
propset NAME VALUE                      Sets a property
propdel NAME                            Deletes a property
proplist FILTER                         Lists properties
version                                 Show version information
exit                                    Exit Sockso

 

Resources

Where to get Sockso, it’s official site

http://sockso.pu-gh.com/

This site is a bit dated but still helpful.

https://samiux.wordpress.com/2009/07/17/howto-sockso-1-1-8-music-server-on-ubuntu-9-04-server/

Sockso Read Me

Requirements
————

Sockso should come packaged with everything it needs to run,
all you have to do is have Java installed on your computer.
You can download the latest Java version for free from
the Sun website at: http://www.java.com

To run Sockso under Windows just double click “Run Sockso”.
Easy!

“Linux”
——-

If you’re running Linux or something similiar then you may
just be able to double click the “linux.sh” shell script.
If this doesn’t work for you then you can run this script
from a terminal with:

$> sh linux.sh

Feedback
——–

If you’ve used Sockso then I’d love to hear what you think, so
please send me some email at: rod(at symbol)pu-gh(dot)com

Running as daemon
—————–
Usage: sockso (start|stop|restart)

 

 

 

 

 

sSMTP Installing and Configuration and Use Tips

Linux, Raspberry Pi, Raspberry Pi Server, Server, , , , , , , , , ,

Recently I was looking at creating a method of sending a warning email when ever my house temperature went below a threshold. I remembered that sSMTP was a simple way to send automated emails and CRON emails. I have some simple notes on what I did.

Installation

Very easy, just use apt-get from the command line…

sudo apt-get install ssmtp

Configuring

The configuration file (/etc/ssmtp/ssmtp.conf) can be edited using any test editor you typically use.

 

Config at /etc/ssmtp/ssmtp.conf

Below is my config file with the critical info blocked out. Lines in Red are what I modded to get ssmtp working for me.

The key pieces to get it working for me at least were…

hostname = My ISP’s domain

root = my complete email that I use at the ISP

mailhub = I looked it up in Thunderbird, it is the smtp.myispsdomain.net part.

AuthUser=my complete email that I use at the ISP. It might be different for you. Years ago it used to be just the user name part of email without the domain.

AuthPass = The password that goes along with my email.

I commented out the defaults for the ones that existed in the code.

The config file is a bit ugly after I touched it but I was trying to get this up and running quick and didn’t clean it up. But, hey it works!

 

#
 # Config file for sSMTP sendmail
 #
 # The person who gets all mail for userids < 1000
 # Make this empty to disable rewriting.
 #root=postmaster  <--- comment out
 
# The place where the mail goes. The actual machine name is required no
 # MX records are consulted. Commonly mailhosts are named mail.domain.com
  #mailhub=mail <-- comment out
 
# Where will the mail seem to come from?
 #rewriteDomain=
# The full hostname
 #hostname=raspberrypi <--- I was testing and kill this, failed to work
 # hostname has to be the mail domain! Or else it complains about
  # the raspberrypi part! The STMP server at frontier does that is.
  hostname=myispdomain.net
# Are users allowed to set their own From: address?
 # YES - Allow the user to specify their own From: address
 # NO - Use the system generated From: address
 #FromLineOverride=YES <-- Commented out and set below, I was testing!
# New Code put here 11302015
  root=me@myispdomain.net
  mailhub=smtp.myispdomain.net
AuthUser=me@myispdomain.net
AuthPass=myemailpassword
FromLineOverride=YES
#UseSTARTTLS=YES <-- Tried this, I didn't need it for my ISP.

CRON Email

Once installed if you or root on the machine have any CRON jobs, you will start to get email from them. You can stop this by appending …

> /dev/null 2>&1

to the end of the commands that are being run by CRON. Which will cut back on the emails that you will receive.

 Testing

I installed mail utils to allow sending simple messages…

sudo apt-get install mailutils

Then I sent a message via the command line…

echo "Test" | mail -s "Test Subject" me@myispsdomain.net

…and I was able to see it work OK.

Send files via email

If you want to send files you have to install mpack.

sudo apt-get install mpack

 

Then you can send files to your email like this…

mpack -s "Test" /tmp/web/log.txt me@myispsdomain.net

 Command Line Usage

If you execute ssmtp with an email address it will let you create an email from the command line. Which is good for quick emails to for example remind yourself of something, or send a snippet of code to yourself. You edit the email in the form of the example below and hit Ctrl-D when done and then it will send out.
ssmtp recipient_email@example.com
The following is an example right off the command line. Note the one line of space after the Subject, this is a must have…
erick@raspberrypi ~ $ ssmtp me@myispdomain.net
To:me@myispdomain.net
From:me@myispdomain.net
Subject:This is a test of ssmtp from the command line!

Hello there this is a test of the ssmtp from the command line tool. It could be used to send a reminder or small snips of code. Use Ctrl-D when you are done.

It is called up by using ssmtp emailtosendto@domain.com

Bye,
Me

Example of Sending CPU Temp Warning Emails

When I am away from home I can infer if my house is running to cold, which may indicate a problem with the furnace. The Raspberry Pi is light loaded, usually just idling, so the CPU temperature tracks the room temperature, with an offset. When I am away, I set the house thermostat at 47 degrees F. If it drops below this value the CPU temperature of the Raspberry Pi will drop below 34 degrees Celsius. So I can just have it send me an email if this happens. Then I can double check a log that is created of the temperature reading to see what is going on. Also I run a webcam pointed at an actual thermometer for a sanity check, this is logged by using fswebcam to take an hourly snapshot. So I have my bases covered for the most part. Obviously if the power is out, I am in the dark about the temperature, because the whole thing is down! Solving that is a future project.

Below is the snippet of code from a shell script that sits in /etc/cron.hourly that handles the warning emails that are sent to 2 addresses. variables mailaddr and mailaddr2.

temp is the CPU temperature in Celsius as an integer stripped using cut from the thermal_zone0 reading.

minimum and maximum are my temperature thresholds. I don’t care much about maximum but I have it set at 65 Deg. C. just in case.

# Read the temp and cut it to grab leftmost 2 characters, integer Temp
temp="`cat /sys/class/thermal/thermal_zone0/temp | cut -c1-2`"
#echo $temp

# Mail if about or below the limits
if (( $temp > $maximum )); then
   #echo "above"
   echo "Rasp Pi CPU Temp = $temp. " | mail -s "Rasp Pi HIGH CPU Temp > $maximum" $mailaddr
   echo "Rasp Pi CPU Temp = $temp. " | mail -s "Rasp Pi HIGH CPU Temp > $maximum" $mailaddr2

elif (( $temp < $minimum )); then
   #echo "below"
   echo "Rasp Pi CPU Temp = $temp. " | mail -s "Rasp Pi LOW CPU Temp < $minimum" $mailaddr
   echo "Rasp Pi CPU Temp = $temp. " | mail -s "Rasp Pi LOW CPU Temp < $minimum" $mailaddr2

fi

Boot Email

I want to know if an when the Raspberry Pi I run 24/7 ever reboots due to a power outage, so I have it send me an email. The line of code below handles it and is in the root crontab. I have it sleep for 180 seconds first, then send the email. This allows the cascaded routers which I have the Pi connected to and the cable modem, time to come on line.

@reboot sleep 180 && echo "Rasp Pi Rebooted" | mail -s "Rasp Pi Reboot!" me@myispsdomain.net

I also log boots in a file that I can view online, just to keep track in one record.

@reboot date >> /var/www/bootlog.txt

Keeping track of boots helps for instance if I am away from home and the power goes out. If I get the email that the Pi rebooted, I can check to see how long the power was down and what the temperature of the house is to see if all is well.

Every hour I take a time/date stamped webcam snapshot of a thermometer so I can just look to see how many are missing and have a rough estimate of how long the power was out and how cold the house got and verify that it is getting warmer because the furnace is on!

In the future I will connect a BME280 sensor to the Raspberry Pi that will be able to read ambient room temperature directly, along with humidity and barometric pressure. So I won’t have to infer the house temperature via the CPU temperature.

Resources

This is the page I used to configure ssmtp on the Rasp Pi.

http://www.raspberry-projects.com/pi/software_utilities/email/ssmtp-to-send-emails

Backgrounding in Linux

Linux, , , , , ,

Ctrl-Z + bg

I used to use the trick of hitting Ctrl-Z when a long running process in running in the terminal and then entering bg to background it.

nohup

But, I have a new favorite way to background using nohup. Lets say I am running a program like one that calculates pi called pi, for example. I can enter…

nohup pi &

…and it keeps the process running even if I kill the parent process, as in  the shell that I launched it from, by closing it. All of the output from the program winds up in the directory in a file called nohup.out.

Stopping the backgrounded program

If I really want to stop the program, I can do it via kill.

First find the process ID (PID) using…

ps aux | grep pi

…what I get is this…

erick 2315 89.5 0.6 10884 8116 pts/1 R+ 18:24 0:10 pi 10000000

The PID is the first number, in this case 2315. So I will use…

kill 2315

…and this process will be killed gracefully by sending a SIGTERM to ask the process to stop, just like a Ctrl-C would do from the command prompt.

Forcing a backgrounded program to stop

If a process won’t stop when you issue a plain kill (SIGTERM) you an send a sigspec, specifying the type of kill set to KILL to force it to quit…

kill -s KILL 2315

…will shut the program down immediately without saving to disc or whatever the program might do to clean up ( might not free up memory that was MALLOC’d for instance ) when it shuts down.

You can see the difference if you run a process in one terminal and use kill in another.

kill 2315 gives you…

erick@erick-laptop:~/pi$ pi 100000000
 Terminated

where

kill -s KILL 2315 gives you…

erick@erick-laptop:~/pi$ pi 100000000
 Killed

Users, Groups and Sudo

Linux, Raspberry Pi, , , , , ,

One thing that I did once I got my Raspberry Pi up and running is to add a user account, other than the pi account that is there by default. I have an erick account on my machines, so why not have one on the pi.

useradd

So under the default pi prompt I used the useradd command to add erick as a user. I figured that I would not login as pi and gave pi a strong password.

useradd -m erick

This will prompt for a password and make a user directory under homes by default. It also fills the directory with files and directories based on the /etc/skel directory.

Lots of Options for useradd

Usage: useradd [options] LOGIN

Options:
-b, –base-dir BASE_DIR       base directory for the home directory of the
new account
-c, –comment COMMENT         GECOS field of the new account
-d, –home-dir HOME_DIR       home directory of the new account
-D, –defaults                print or change default useradd configuration
-e, –expiredate EXPIRE_DATE  expiration date of the new account
-f, –inactive INACTIVE       password inactivity period of the new account
-g, –gid GROUP               name or ID of the primary group of the new
account
-G, –groups GROUPS           list of supplementary groups of the new
account
-h, –help                    display this help message and exit
-k, –skel SKEL_DIR           use this alternative skeleton directory
-K, –key KEY=VALUE           override /etc/login.defs defaults
-l, –no-log-init             do not add the user to the lastlog and
faillog databases
-m, –create-home             create the user’s home directory
-M, –no-create-home          do not create the user’s home directory
-N, –no-user-group           do not create a group with the same name as
the user
-o, –non-unique              allow to create users with duplicate
(non-unique) UID
-p, –password PASSWORD       encrypted password of the new account
-r, –system                  create a system account
-s, –shell SHELL             login shell of the new account
-u, –uid UID                 user ID of the new account
-U, –user-group              create a group with the same name as the user
-Z, –selinux-user SEUSER     use a specific SEUSER for the SELinux user mapping

 

Once I was able to log in under my new account, I tried setting up fswebcam to collect some timelapse video and then I had my first hitch. I needed to be part of the video group to run fswebcam.

id

The id command ran from the command line…

id username

…will list not only the user and group ID of the user UID and GID. But all of the groups that he user belongs to. It has the options -u, -g, -G. -u lists the UID alone, -g is the users GID alone and -G lists all the group ID’s that the user belongs to.

usermod

I was not part of the video group so I would have to add myself, but I was not part of the admin group either so I was not able to even run sudo.

So with a quick logout to the pi user, I was able to add myself to the admin group.

sudo usermod -a -G admin erick

The sudoers file

If you run sudo visudo, it will open the /etc/sudoers.tmp file. At the bottom of this file there is a line that explains that accounts added to the admin group are allowed to run sudo.

# Members of the admin group may gain root privileges
 %admin ALL=(ALL) ALL

Now that I can sudo from my own account, I can login back in as erick and run…

sudo usermod -a -G video erick

…to add myself to the video group. Now I was off and running with using fswebcam under my account.

NFS and Users

With users there is the notion of the name and then there is the numerical UID. NFS uses the numerical UID to map across machines. If you plan on using NFS on multiple machines, it pays to keep the UID’s lined up between them. For example, if you set up 2 Linux machines from scratch, there will be a user at UID 1000, that would be you, whatever you called it by name. The first user is at 1000. If you use NFS to mount a directory from one machine to another, no problem it all lines up. The user at UID 1000 is the same on both machines, permissions work out, files can be moved back and forth, no problems.

But if like with the example of the Raspberry Pi above. User pi is created on the NOOBS Disk when you load the Raspberian option. It is at UID 1000 and GID 1000. So if you add and other user for yourself, guess what it appears at UID 1001. Something to keep in mind when using NFS. You can use NFS in a way that will get around this using the methods laid out in the NFS post.

But it is much easier to try to keep all of the name and UID’s lined up from the beginning and not have to worry about the trickiness business. Even it means adding a user to the Raspberry Pi and then moving the UID of the pi user to some other UID and yourself to UID 1000, GID 1000 if that will line it up with your other machines on the network.