In order to list all logical volumes (LVM) in Linux you can issue the below command:

$ lvscan
  ACTIVE            '/dev/mysql-vg/swap_1' [31.88 GiB] inherit
  ACTIVE            '/dev/mysql-vg/root' [27.94 GiB] inherit
  ACTIVE            '/dev/mysql-vg/var' [833.64 GiB] inherit

#linux #lvscan #lvm #logical_volume

Python Microservices Developement

#python #ebook #epub #pdf #microservice #flask

How to configure a Delayed Replica Set Member?

Let's assume that our member is third in the array of replica members:

cfg = rs.conf()
 cfg.members[2].priority = 0
 cfg.members[2].hidden = true
 cfg.members[2].slaveDelay = 3600
 rs.reconfig(cfg)

The priority is set to 0 (preventing to be elected as primary).

The hidden to true in order to hide the node from clients querying the database.

And finally slaveDelay to number of seconds that we want it to get behind of Primary Node.

The use case for this is to have a replication that is used for analytical purposes or used for backup and so on.

#mongodb #mongo #replica #replication #primary #delayed_replica_set #slaveDelay

IMPORTANT:
The length of the secondary members[n].slaveDelay must fit within the window of the oplog. If the oplog is shorter than the members[n].slaveDelay window, the delayed member cannot successfully replicate operations.

How to add self-signed certificates to replica set nodes?

https://medium.com/@rossbulat/deploy-a-3-node-mongodb-3-6-replica-set-with-x-509-authentication-self-signed-certificates-d539fda94db4

#mongo #mongodb #ssl #self_signed #openssl

In order to see how much time your mongoDB slave is behind the primary node:

rs0:SECONDARY> db.printSlaveReplicationInfo()
 source: mongo.mongo.com:27017
     syncedTo: Mon Nov 12 2018 06:33:40 GMT+0000 (UTC)
     -4 secs (0 hrs) behind the primary

#mongodb #mongo #slave #printSlaveReplicationInfo #replica #replication

How to check MongoDB replication lag in Icinga2 and get notified when it is over 15 seconds?

We assume here that you have a replica set in place. First download the python script for our nagios plugin:

cd /usr/lib/nagios/plugins
 git clone git://github.com/mzupan/nagios-plugin-mongodb.git

Now the Icinga2 part. You first need to create a command for replication lag check:

cd /etc/icinga2/conf.d/commands

Create a new file replication_lag.conf:

object CheckCommand "check_replication_lag" {
     import "plugin-check-command"
     command = [ PluginDir + "/nagios-plugin-mongodb/check_mongodb.py", "-A", "replication_lag" ]
     arguments = {
         "-H" = "$mongo_host$"
         "-P" = "$mongo_port$"
     }
 }

Create a new file in services folder called replication_lag.conf:

apply Service for (display_name => config in host.vars.replication) {
     import "generic-service"
     check_command = "check_replication_lag"
     vars += config
     assign where host.vars.replication
 }

This service gets enabled where it finds replication in host config. Now in secondary mongoDB hosts configuration add the below part:

vars.replication["Secondary DB"] = {
     mongo_host = "slave.example.com"
     mongo_port = 27017
 }

#sysadmin #icinga2 #mongodb #replication #replication_lag #nagios_plugin

Read more about the nagios mongodb plugin here:

https://github.com/mzupan/nagios-plugin-mongodb

Why Axigen Mail Server log gives the error of Unable to perform STARTTLS and how to solve it?

Axigen by default initiate a TLS connection with the target mail server. When the target mail server does not accept TLS, Axigen will mark the mail message as Relay error with the error of Unable to perform STARTTLS.

It is suggest to leave this behaviour as is, but in case there is an exception that you want to send mail to that mail server you need to ignore TLS for the target. In order to do so login to Axigen webadmin interface and:

1- Navigate to Security & Filtering -> Acceptance & Routing -> Advanced Settings

2- Click the Add Acceptance / Routing Rule button

3- Write a suggestive name for the rule like disable_tls_example_com

4- In the Conditions section add the following two conditions:
- Recipient -> Domain -> add the condition -> select 'Is' from the combo box -> write Name_of_the_domain (example.com) in the combo box.
- Delivery -> Relaying mail -> click add the condition

5- Select at the top of the Conditions section For incoming messages that match -> ALL of the conditions below (instead of the default `ANY of the conditions below`)

6- in the Actions section select Settings -> Allow StartTLS -> add the action. DO NOT tick the check-box next to Allow StartTLS.

Now click SAVE CONFIGURATION button. Your're done and you should see something like below in your axigen log file:

Set recipient <[email protected]> state to SENT

#mailserver #axigen #TLS #STARTTLS

DevOps with Kubernetes
#devops #kubernetes

#ebook #pdf #epub #kubernetes #devops

How to create Microsoft Edge extension?

https://docs.microsoft.com/en-us/microsoft-edge/extensions/guides/creating-an-extension

#browser #microsoft #extension #edge #addon

How to add comma to end of multiple lines in VIM? Yeah, that's tricky boy :))))

1- First go to Visual Block mode by pressing ^v (CTRL+V)

2- Now select your mutiple lines by going down using down arrow button.

3- Go to end of line by pressing end command in your keyboard in linux and windows or if you're using MAC by pressing fn+right arrow.

4- Now press shift+A (It worked in MAC in linux we needn't that)

5- type comma

6- press ESC (wait one second or so)

Voila! We're done.

#vim #tricks #VB #visual_block

Cannot umount a busy driver.

If you haven't tried to force umount by -f try it:

umount -f /mnt/your-mounted-drive

Now in case using -f it still gives error. Try this:

apt-get install psmisc

Now user fuser command like below:

fuser -c /mnt/your-mounted-drive
 /mnt/your-mounted-drive/: 2510c 11086

It outputs the pid of the processes using this volume. The extra character at the end of pid will give some extra info. ( c in 2510c)

c - the process is using the file as its current working directory

m - the file is mapped with mmap

o - the process is using it as an open file

r - the file is the root directory of the process

t - the process is accessing the file as a text file

y - this file is the controlling terminal for the process

Kill these processes:

kill -9 2510 11086

Now umount it:

umount /mnt/your-mounted-drive

#umount #NFS #fuser #psmisc

You can use the below command to do it all:

fuser -ickv /mnt/your-mounted-drive

Where:
- parameter k kills the offending process,

- while v shows in advance the process and its user

- i asks you for confirmation.

NOTE: if some process resists, then try again with fuser -ickv -9

#linux #fuser #umount

Log rotatation in Linux is so handy as its name implies, it rotates log files. If you have a look at the /var/log path you can see
some compressed files some files which ends with .1

/var/log/my-app.log {
     weekly
     rotate 4
     compress
     delaycompress
     missingok
     notifempty
     create 644 root root
 }

The location of log rotation configs is in /etc/logrotate.d/. I have created a file in it with the config above.

Explanation of some parameters:
- weekly: weekly says that you want to Linux to rotate your log files weekly, you can also set daily, monthly, yearly.

- rotate 4: it says that how many rotated files should be kept, here I keep 4 rotated files (one month).

- compress: well you tell me what this parameter does.

- delaycompress: some programs do not close file handlers immediately, here we tell log rotate to delay the compression.

- missingok: don't return error if the log file is missing

OK, the list goes on. Take a look at the manual yourself and see its options.

#linux #logrotate #rotate

How to package Edge extension?

https://docs.microsoft.com/en-us/microsoft-edge/extensions/guides/packaging/using-manifoldjs-to-package-extensions

#microsoft #edge #extension #addon

How to create Safari Extension?

https://code.tutsplus.com/tutorials/how-to-create-a-safari-extension-from-scratch--net-15050

#apple #safari #extension #addon

Don't crack! I'd like to talk a little bit of Angular here rather than backend and those jargons :)

As you might know, Angular bind elements to component variables in order to update values. There is concept for data binding which is called Banana in a box and its form is like [()] (a banana in a box). This is a two-way binding mechanism. But why it is like that. Why a banana in a box? :)

In Angular to bind properties to your component variables use [] like below:

<img [src]="my_source_image" />

On the contrary in order to bind an event to an element you would use () as below:

<button (click)="doSomething()">

In two-way binding you do as below in reality:

<input [ngModel]="ctrl.name" (ngModelChange)="ctrl.name=$event">

NOTE: you bind name to ngModel and on model change you set event value on form control name: ctrl.name=$event.

This is why Angular uses `[()]. It binds both properties and events in one go like a magic.


#angular #bind #event_binding #two_way_binding #banana_in_a_box