Enforce module load in CRUX

At the moment, my Linux (CRUX 3.5) does not load a kernel module for the my mainboard monitoring chipset. The mainboard is GigaByte GA-M68MT-S2 and the chip is Nuvoton NCT6775F. I need data from that chip for Conky or LM Sensors. To ensure it's available I've modified the /etc/rc.modules file, by adding

modprobe nct6775

Debugging of Ansible and Molecule

As I descrbided in this article additional Ansible options are passed at the end of molecule command. This can be use to increase verbosity of Ansible:

molecule converge -- -vvvv

Molecule own debug information can be printed to the standard output with *--debug** option, but it has be specify without molecule command. For example:

molecule --debug converge

Of course, both can be mixed togther:

molecule --debug converge -- -vvvv

edsn: Elite Dangerous Star Neighborhood

 Description

Virtual, for ever I was fascinating with maps of our star neighbourhood. Just like the one from European Southern Observatory website. Recently, I've enjoyed playing Elite Dangerous. I enjoy it even more, because it works perfectly fine on Linux (with Proton).  One of the great thing about Elite is freedom to roam between stars and visit, so many star neighbourhoods. 

The amount of stars is breathtaking. It's hard to visualize the ones which are close to the system you are in. So, I wrote a small Python script to get data from edsm and prepare them to be visualized with GNUplot.

Examples

Sol

Home, sweet home.

These are the commands to produce the SVG output after loading script and data into Gnuplot.

set term svg size 1600,1200
set view 45, 290, 1.25, 1.5
set output 'sol-r15.svg'; replot

Achenar

 I didn't know that the space around Achenar is so empty (OK. I don't have permit yet).

These are the commands to produce the SVG output after loading script and data into Gnuplot.

set term svg size 1600,1200
set view 45, 275, 1.25, 1.5
set output 'achenar-r15.svg'; replot

Kernel module info

A few commands to help in checking and adjusting kernel module options: 

1. Display information about kernel module, including all options
   
   modinfo $KERNEL_MODULE
   
   
2. Display information about current value for each option
   
   for i (/sys/module/$KERNEL_MODULE/parameters/*) {\
     echo $(basename $i);\
     cat $i\
   }
   
   
3. Change kernel module option without restart (temporary)
   
   echo "$NEW_VALUE" > /sys/module/$KERNEL_MODULE/parameters/$OPTION
   
   
4. Load module with an option set to value
   insmod $PATH_TO_MODULE/$KERNEL_MODULE.ko\ $OPTION1=$VALUE1 \
   $OPTION2=$VALUE2
   
   
5. Ensure kernel module option is set during boot up with grub
1. Open /etc/default/grub
2. Add/edit following line
   GRUB_CMDLINE_LINUX='$KERNEL_MODULE.$OPTION=$VALUE'
   

Of course $KERNEL_MODULE, as well as all other strings with "$" at the beginning, has to be replaced by appropriate value.

In CRUX /etc/default/grub does not exist, so it has to be created.

 Useful links

• https://www.cyberciti.biz/tips/how-to-display-or-show-information-about-a-linux-kernel-module-or-drivers.html
• https://devarea.com/linux-kernel-development-kernel-module-parameters/
• https://www.howtoforge.com/tutorial/kernel-boot-parameter-edit/
• https://www.linuxsecrets.com/1455-adding-kernel-boot-parameters-using-grub-on-linux
  

Shell script to setup system with new kernel

 

This is a small script helping in setting up a new kernel. It copies files from the Linux kernel source directory and builds the matching initramfs file.

 

#!/bin/sh
#
set -x
if [ $(dirname $PWD) != '/usr/src' ]
then
	echo ""
	echo "Please change directory to a one with Linux kernel sources"
	exit 1
fi

version=$(basename $PWD |awk -F\- '{print $2}')


ls boot/vmlinuz-${version}-* 2> /dev/null && \
	build=$(ls -1 /boot/vmlinuz-${version}-*| sort -n | awk -F\- '{print $3}') || \
	build=1

release=${version}-${build}
cp System.map /boot/System.map-${release}
cp arch/x86/boot/bzImage /boot/vmlinuz-${release}
mkinitrd /boot/initramfs-${release}.img ${version}

grub-mkconfig > /boot/grub/grub.cfg

Molecule and extra variables for Ansible

Imagine that you want to use Molecule to test an Ansible role with a not default value. That's just one off test, so adjusting molecule configuration in the converge.yml (or similar) file is not required. It's not very prominent in documentation, but you can pass Ansible variables after "--" (minus, minus) in the molecule commend. For example:

molecule converge -- -e "role_new_var=true"

How to find a word in files spread over many subdirectories

Imagine that you need to try to find a word in hundreds files located in a plenty of subfolders. grep -Rc might be a good candidate, but it's going to print the list of all files and the word is in just a handful of them. To make the output better grep can be joined with awk (and in the example below with zsh). 

I needed to find an example of sqlcmd command usage in my Ansible roles collection. I used the power of ZSH globbing (a few other examples can be found here and in other places) to limit search to yml file only. ZSH "**" pattern is also a nice replacement to the grep "--recursive"option. In awk the "-F" flag replaces the standard delimiter with the ":" character and prints only lines with second field not equal to zero.

grep -c sqlcmd **/*.yml | awk -F":" ' ($2 != 0 ){print $0}'

Get Public IP address of Azure VM from shell on VM - part II

Last year I wrote a quick note with a method of getting Azure VM public address from the shell on VM. Recently I spent a bit more time to look at https://docs.microsoft.com/en-us/azure/virtual-machines/linux/instance-metadata-service and found more precise call to get IP address from the metadata url: 

curl -H Metadata:true \
 "http://169.254.169.254/metadata/instance/network/interface/0/ipv4/ipAddress/0/publicIpAddress?api-version=2017-08-01&format=text"

BTW. The same method allows to get a private IP address.

curl -H Metadata:true \
 "http://169.254.169.254/metadata/instance/network/interface/0/ipv4/ipAddress/0/privateIpAddress?api-version=2017-08-01&format=text"

Painful encounter with oversized Postgres (9.6)

I had not so nice encounter with an oversize PostgresDB. Somehow rather small DB ballooned to 256 GB (what was a partition size). I'm not PostgresDB expert. I can barely use it, but I've spent some time doing internet search and that might be useful for other (or for me in the future).

In the end I regained nearly 200 GB of space with simple command:

vacuum full

As it is suggested by this Stack Overflow question.

The key to find above suggestion was to understand that the problem was related to pg_toast table. I found that fact out using oid2name tool, which BTW in Ubuntu is in /usr/lib/postgresql/10/bin/.

/usr/lib/postgresql/10/bin/oid2name -H localhost -U postgres -d postgres -f 24806

From database "postgres":
  Filenode      Table Name
--------------------------
     24806  pg_toast_24729

I learnt about the tool from this document and learnt how to use from the man page.

It's also worth to remember that following query didn't help me. I think it's nice, so posting it here, anyway:

SELECT table_schema, 
    table_name, 
    pg_relation_filepath('"'||table_schema||'"."'||table_name||'"') 
FROM information_schema.tables 
WHERE 
    pg_relation_filepath('"'||table_schema||'"."'||table_name||'"') 
LIKE 'base/12404/248%';

The above query was built based on another good suggestion from Stack Overflow. This one shows all big tables.

SELECT
    table_schema,
    table_name,
    pg_relation_size('"'||table_schema||'"."'||table_name||'"')
FROM  information_schema.tables
ORDER BY 3
LIMIT 10

prt-get/pkgmk adjustments

If I'm ever going to lose my current Crux config. I need to remember, to adjust following files for Crux:

• /etc/prt-get.conf to ensure that scripts as executed:
  
  

  runscripts yes            # (no|yes)

  
  
  
• /etc/pkgmk.conf to ensure that md5sums are ignored:
  
  

  PKGMK_IGNORE_MD5SUM="yes"

  
  

Bash and Arrays

Short reminder for my 'extended memory' on how to deal with lists in bash.

To define:

• a list (an array): declare -a list
• a dictionary (an associative array): declare -A dict

To use an array in loop: for item in ${list[@]}

Now the best, at least for scripts testing:
To print a whole array: declare -p list (please note, no "$" before list name).


Found at https://www.tutorialkart.com/bash-shell-scripting/bash-array/