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  • Feb 12 / 2018
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Linux

Execute cron on a specific day of the month (e.g. second monday)

How to execute a cron on a specific day of the week once in the month?

This could look simple as we could think that this line in cron would do the trick:

But this would not work as the ‘2’ for checking the Tuesday will come as a OR condition, and the command would be executed from day 8 to day 14 and on every Tuesday of the month.

As a workaround for that, you can use that command:

Here is the explanation of this cron line:

Doing this check will allow to verify first that we are on the second tuesday before to execute the command. Don’t forget to add a backslash before the ‘%’ character to escape it.

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  • Dec 21 / 2017
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Linux

Control services on Linux (systemV, systemd, initctl…)

On Linux, there’s many ways to control services that can run on your system. Here are the main and most known init systems that you can find on the common distros, depending on their version.

SystemV

That system is one of the oldest and one of the most common. Its init scripts are stored in /etc/init.d/

To list all the available services, you have to use that command:

To perform an action on one of those services, you will be using:

Upstart (initctl)

Upstart is a successor of SystemV scripts. It works asynchronously, and its scripts are stored in /etc/init/

To list all the available scripts, you have to use that command:

To perform an action on one of those services, you will be using:

SystemD

Its name SystemD means System Daemon. It manages daemons that can be running on a system. It’s a successor of upstart and allows a more flexible management for the services. Init scripts are stored in /etc/systemd/system/

To list all the available scripts, you have to use that command:

To perform an action on one of those services, you will be using:

SupervisorD

Finally, SupervisorD is a supervisor focusing mainly on the applications more than the system. It allows management of applications execution and control their life like you could do with system services.

To display all the applications managed by supervisord:

To control those processes, you will be using:

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  • Nov 21 / 2017
  • 0
Linux

Generate a CSR with openssl

Generate a CSR (Certificate Signing Request) on your server when you want to get a certificate from a certified provider is often a mandatory step, very easy to execute.

Here are the different steps to execute:

  1. Create a specific directory where you will put all your files
  2. Generate a private key of 2048 bits
  3. Now generate a CSR with openssl and with the private key you just generated

    Many information will be asked during the creation:
  4. You now have your CSR and your private key

It’s up to you to get your signed certificate from an official provider using those files.

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  • Nov 02 / 2017
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Linux

Change or remove password expiration for linux user

It can happen that you’re getting that message when trying to connect to your linux server:

The message is quite explicit and you need to update your password right now.

If you don’t want to update your password too many times, you can update the frequency of the expiration to 90 days for example:

Or you can completely disable the expiration by pushing the max value for expiration date to 99999 days:

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  • Oct 18 / 2017
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Linux

Update CA trusted root certificates on Linux server

If you’re getting many “unstrusted issuer” alerts in your app logs, it might be due to some CA trusted certificates outdated.
To fix that, just perform an update:

For Ubuntu/Debian

For CentOS/RedHat

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  • Oct 04 / 2017
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Linux

Write multiple lines to file in bash (script)

If you need to push multiple lines to one file through a bash script, you can simply use that syntax:

Tip: Be aware that if you’re using indentation, last line should not be indented (this would lead you to some errors).

If you want to add line instead of overwriting file (like we did in the previous example), just replace the “>” with “>>” after cat command.

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