How to reset root password in CentOS 7

Resetting admin password in CentOS 7 is different than of CentOS 6, as CentOS 7 utilized Grub 2 and has a different procedure to access Single User Mode. First, boot your system in Single User Mode to reset the root password by following the below tutorial:

Once done, now, you may first chroot the system:

chroot /sysroot

Now, you may reset the password using the following:

passwd root

You should be done. If you are using SELinux, then you need to relabel accordingly:

touch /.autorelabel

Then, exit chroot and reboot the system:

exit && reboot

You should be done now.

How to boot CentOS 7 in Single User Mode

Booting CentOS 7 in single user mode is total different than of CentOS 6 as it uses a different version of Grub. We will go step by step to boot into single user mode in CentOS 7.

  1. First, boot the screen and press an arrow key while the timer comes on this screen to stop the timer

    CentOS 7 Boot Screen

  2. Press ‘e’ on the selected default CentOS version. That will take you to the following screen

    CentOS 7 Boot Edit Screen

  3. These are grub commands that the bootloader is using to boot you to the system. Arrow down in this window to the line, that starts with linux16. Now take the right arrow on the keyboard to take your cursor to the word that says ‘ro’ as shown in the image

    Linux16 Command Boot

  4. Now replace ro with rw init=/sysroot/bin/sh as shown below

    CentOS 7 Boot Sysroot

  5. Now press Ctrl + x to start Single User Mode

    Boot in Single User Mode CentOS 7

You should be done now, you are on the single user mode console. If you would like to use the main system, you may chroot as the following:

chroot /sysroot

Now, if you are trying to reset the root password, after booting into the single user mode, you may follow the following to reset the root password:

How To Get Disk Serial Number in Megaraid


We can use smartctl to get the disk serial ID in case of disk replacement or crashes, with the following:

smartctl -a /dev/sdX

Where X is the device identifier like, for the first disk, this would be sda, second sdb etc. But in case the devices are behind the RAID, this command returns an error:

[[email protected] ~]# smartctl -a /dev/sda
smartctl 7.0 2018-12-30 r4883 [x86_64-linux-3.10.0-1127.el7.x86_64] (local build)
Copyright (C) 2002-18, Bruce Allen, Christian Franke,

Smartctl open device: /dev/sda failed: DELL or MegaRaid controller, please try adding '-d megaraid,N'

How to make this work?


To get the serial numbers behind the LSI MegaRAID, you would first need to find out the device ID using LSI Megaraid tools. A quick way to install LSI Megaraid tool is available here:

How to: Install LSI Command Line Tool

One you have installed the LSI Megaraid command line tools, now you may use the following command to identify your device:

/opt/MegaRAID/MegaCli/MegaCli64 -PDList -aAll | egrep 'Slot\ Number|Device\ Id|Inquiry\ Data|Raw|Firmware\ state' | sed 's/Slot/\nSlot/g'

This would output something like the following:

Slot Number: 1
Device Id: 11
Raw Size: 447.130 GB [0x37e436b0 Sectors]
Firmware state: Online, Spun Up
Inquiry Data: 50026B72822A7D3A    KINGSTON SEDC500R480G                   SCEKJ2.3

In this server, it has one disk, but you may have multiple disk with different ‘Firemware state’ and ‘Device Id’. To use smartmontools, you need to pick the ‘Device Id’, mentioned here, which is 11. Now you can run the following command to get the device details using smartctl:

smartctl -d megaraid,N -a /dev/sdX

Here, N is the device ID, and X is the device name, you may get the device name using df -h command or fdisk -l. For our case, this command would be like the following:

smartctl -d megaraid,11 -a /dev/sda

This would print a lot of information about your device, but if you are looking to identify the Serial Number only, you may run the following:

~ smartctl -d megaraid,11 -a /dev/sda|grep Serial
Serial Number:    50026B72822A7D3A

One thing to note, we can also get Serial number from the MegaCli tools Inquiry data, you may have already noticed:

[[email protected] ~]# /opt/MegaRAID/MegaCli/MegaCli64 -PDList -aAll | grep 'Inquiry Data'
Inquiry Data: 50026B72822A7D3A    KINGSTON SEDC500R480G                   SCEKJ2.3

Here, the first parameter in the return is the same as smartctl returns as Serial number, it’s because it’s the serial number that megacli gets/identifies as well.

How to Access Redis over TLS/SSL

If you are trying to purchase Managed Redis Database, from companies like digitalocean, then, you would get access to those Redis servers, only over TLS/SSL support. Unfortunately, by default redis-cli does not ship with TLS support, hence, you need to either use Tunnel to access redis instance through redis-cli or use different tool for your purpose.

Access Your Redis Instance using Python

If you are developing your application using python, and using a managed redis database, then, you would have to make the redis connection over TLS/SSL. This can be done by setting the ‘SSL’ to True, in the Redis constructor. Here is an example:

import redis

r = redis.Redis(host='', port=25061, password='abcdhjnmjtxeupp', decode_responses=True, ssl=True)

As you can see, I have set the ssl to True at the end, to set the connection over TLS/SSL.

Access Your Redis from Command Line using Redli

If you want to have access to your redis instance through a command line tool, then using redli is my first line choice. Configuring stunnel with redis-cli is also possible, but it would be another topic of discussion here.

Let’s see, how can we install redli:

Redli is a tool developed by IBM with TLS/SSL support. It is written in Golang. You may download a version for Linux from the IBMCloud Github repo and start using it:

~ wget
~ tar -xvzf redli_0.4.4_linux_amd64.tar.gz
~ cp redli /usr/bin/
~ chmod +x /usr/bin/redli

Now, you may use redli to connect to your Redis database with TLS enabled as following:

redli --tls -h -p 25061 -a abcdhjnmjtxeupp

See how ‘–tls’ is enabled to access redis over TLS here. Hope this helps.

How to Uninstall Let’s Encrypt from Cpanel / WHM

To uninstall the Cpanel / WHM plugin for Let’s Encrypt, login to your SSH for root and run the following:


It might take sometime, once completed, it should remove let’s encrypt as a provider from your AutoSSL plugin.

How to Install Let’s Encrypt in Cpanel

Let’s Encrypt is a popular tool to use free SSL for your website. Cpanel comes with Sectigo free ssl service through requesting and pooling system. Although, you might feel interested in getting the SSL released immediately without a queue based approach, and would prefer to use Let’s Encrypt that’s why.

There are two ways, you may install Let’s Encrypt in Cpanel.

  1. Using Cpanel Plugin

First one would be using the plugin created by Cpanel. Login to your server as root:

ssh [email protected]_ip

Then, run the following to install Let’s Encrypt in your cpanel system


It might take a couple of minutes, then it should install Let’s Encrypt as a provider in AutoSSL.

Now, go to WHM >> Manage AutoSSL and select Let’s Encrypt as the provider instead of Sectigo Cpanel default. You need to check the Agreement rules under the Let’s Encrypt selection and you may create the account in Let’s Encrypt using the same tool.

Once done, your new SSLs would be issued using the Let’s Encrypt tool through Cpanel AutoSSL plugin.

2. Using FleetSSL

There is a 3rd party tool, existed before Cpanel provided a plugin for Let’s Encrypt. It’s FleetSSL. One key benefit of using FleetSSL is that, it allows the Cpanel end users to control issuing and renewing the SSL from Cpanel. One key cons of using FleetSSL is that, it is not free of charge, it comes with 30$ one time fees. But mainly hosting provider would not mind to use this as it is a nice addition for the end user feature set in a hosting provider’s point of view.

You may check for details here:

Now, once you complete installing Let’s Encrypt SSL, you may now use Let’s Encrypt for different cpanel services like webmail/cpanel/whm/calenders/MTA services. You may check the following to know how to:

dial unix /tmp/padapter.usk: socket: too many open files

Error Definition

There are times, when your application may throw error like the following in Linux:

dial unix /tmp/padapter.usk: socket: too many open files

It could only contain the following, without relating the fast message:

socket: too many open files

How to Fix

This error appears because Linux file system puts a limit of amount of open files you may use at a time. It is calculated based on a variable system set is called ‘file-max’. File System also keeps a variable called ‘file-nr’ to count the number of file you have in usage. To quickly look at your usage, you may run the following:

[[email protected] ~]# cat /proc/sys/fs/file-nr
4512    0       265535

The first number is the amount of file descriptions in use in your linux system. Here the last number is your hard limit and the second number is your soft limit. The hard limit is your file-max. To know your file-max value, you may run the following:

[[email protected] ~]# cat /proc/sys/fs/file-max

As we see, the limit is set to 265535 and the usage is 4512. If the usage goes up for some reason, for example an infinite loop on the cache creation, you may run out of file system open limit and hit the error. To set the value fir file-max, we will take sysctl.conf in consideration.

First open sysctl.conf file with the following:

nano /etc/sysctl.conf

Add the following line and save:

fs.file-max = 524280

This will increase your open file limit to 524280. Now to reflect the change immediately, you need to run the following:

sysctl -p

You should be done now.

How To Find : If two different date ranges intersects

I was making a Odoo module today, it had a requirement to find the products that has offering within two ranges. Each of the product has different range for discounts/offers. It is sort of like the following:

For example, a shampoo discount starts from 01-06-2020 and ends at 20-06-2020, while another product like a soap discount starts from 10-06-2020 and ends at 22-06-2020. Now if I look for discounted credit notes to apply within a range, then we need to provide some time range, that these ranges intersect. For example, if I want to find discounts that were given within 02-06-2020 – 11 – 06 – 2020, then we should get both the discounts available here, as the discounts were still available for a day to the Soap and a few days for Shampoo. That means, we need to find if any of the given two ranges intersects with the ranges we have discounts for.

The easiest way to calculate this, is to check which date is max among the lower boundaries and which date is minimum in the lower boundaries. This should follow that the starting date would be less than or equal to the ending date, but never greater than the ending date. If greater than, then it does not intersect logically. In python, we can do this like the following:

# first we find all the vendor discounts, it has property start_date and end_date
vendor_discounts = self.env[''].search([])

# list to keep the vendor discount instances
vendor_discount_id_in_range = []

# from the form, we get date_from and date_to, where the dates intersect
for vendor_discount in vendor_discounts:
   # here is the logic to find intersects
    if max(self.date_from, vendor_discount.start_date) <= min(self.date_to, vendor_discount.end_date):

So, the logic going to be like the following:

if max(input_date_from, start_date_to_match) <= min(input_date_to, end_date_to_match)

How to Enable Logging in Odoo

There are two ways to see the Odoo Logs. One is rough and can be used to see the latest Odoo logs, it’s the Journal tools. You may do this using the following if your Odoo service is installed as odoo13 for example

journalctl -u odoo13

Note: If you are having trouble primarily in installing Odoo properly, you may check the following:

The other way, is the enable logging to a file. This has to be enabled from the odoo.conf file which is located under /etc/ folder. First we open the /etc/odoo.conf file:

nano /etc/odoo.conf

Now, search to see if you have a directive called ‘logfile’. If you don’t, you may add the following to /etc/odoo.conf:

logfile = /var/log/odoo13/odoo.log

If you already have the directive, but commented out, like this:

; logfile = /var/log/odoo13/odoo.log

You may remove the ‘;’ in front of the logfile directive and save the file. Now you may restart your Odoo instance to allow odoo log the information to the file /var/log/odoo13/odoo.log

systemctl restart odoo13

If the restart showing some errors, probably because it is failing to put permission to odoo13 folder. You may try the following:

mkdir /var/log/odoo13
chown -Rf odoo:odoo /var/log/odoo13
systemctl restart odoo13

How to Install Odoo 13 in CentOS 7

Odoo is currently one of the most popular tool for business purposes. It has a community edition, that allows managing ERP at very low cost. Odoo was previously known as OpenERP. Odoo requires to be installed on a dedicated server or VPS. Odoo 13 had come out on October, 2019. Odoo 14 hasn’t been released yet for production. I will have a straight forward how to on installing the latest Odoo 13 in CentOS 7.

Log in to your system and update

First step would be to login to your system and then update the system using yum.

ssh [email protected]_ip

You may check the CentOS version from the redhat release file using the following:

cat /etc/redhat-release

It should show you something like the following if you

CentOS Linux release 7.8.2003 (Core)

Now, you may try updating the system with yum

yum update -y

Once done, now install the EPEL repository as we need it to satisfy a couple of dependecies:

yum install epel-release

Install Python 3.6 packages and Odoo dependencies

We need Python 3.6 at least to run Odoo 13. Odoo 12 had support for Python 3.5, unfortunately, Odoo 13 doesn’t. We will use ‘Software Collection (scl)’ repository to install and use Python 3.6. To find the available Python versions in SCL, you may check the following:

SCL Repository for Python

Now, to install Python 3.6 using SCL, we first need to install the SCL repository for Centos:

yum install centos-release-scl

Once the SCL is loaded, now, you may install the python 3.6 using the following command:

yum install rh-python36

Once the Python is installed, now we will install several tools and packages for Odoo dependencies with the following command:

yum install git gcc nano wget nodejs-less libxslt-devel bzip2-devel openldap-devel libjpeg-devel freetype-devel

Create Odoo User

We now need to create a system user and group for Odoo and define a home directory to /opt/odoo

useradd -m -U -r -d  /opt/odoo -s /bin/bash odoo

You may use any username here, but remember to create the same username for the PostgreSQL as well.

Install PostgreSQL

CentOS base repository unfortunately, comes with Postgresql 9.2. But we want to use PostgreSQL 9.6 for our Odoo installation. You may check the available PostgreSQL for CentOS 7 using the following command:

yum list postgresql*

As by default CentOS 7 does not provide the PostgreSQL 9.6, we would use PostgreSQL official repository to download and install the 9.6 version.

First, we install the Postgres Yum Repository using the following command:

yum install

Now, you may install PostgreSQL 9.6 and related required packages using the following command:

yum install postgresql96 postgresql96-server postgresql96-contrib postgresql96-libs

Now, we need to initialize the postgres database and start it. You may do that using the following:

# Initialize the DB
/usr/pgsql-9.6/bin/postgresql96-setup initdb

# Start the database
systemctl start postgresql-9.6.service

Now you may enable Postgres to start when booting up using the systemctl enable command:

systemctl enable postgresql-9.6.service

Now, we need to create a database user for our Odoo installation. You may do that using the following:

su - postgres -c "createuser -s odoo"

Note: If you have created a different user for Odoo installation other than ‘odoo’ than you should change the username here as well.

Install Wkhtmltopdf

Wkhtmltopdf is a open source tool to make html in pdf format so that you may print pdf reports. This tool is used by Odoo and requires to be installed as dependency. CentOS 7 repository does not provide the latest version of this tool, and Odoo requires you to use the latest version. Hence, we require to download the latest version from the Wkhtmltopdf website and install it. To do that, you may first visit the page:

The page gives you the direct rpm download link for each version of CentOS/Ubuntu/Mac etc. Download the stable version for CentOS 7. At the time of writing, the URL for CentOS 7 x86_64 bit is the following:

You may install this using the following:

cd /opt/
yum localinstall wkhtmltox-0.12.6-1.centos7.x86_64.rpm

Install and Configure Odoo 13

If you have come all through here, that means you are done with the all dependency installations before starting to download Odoo 13 source code. We will download Odoo 13 from it’s Github repo and use virtualenv to create an isolated python environment to install this python software.

First, login as odoo from root:

su - odoo

Clone the Odoo source code from Github repository:

git clone --depth 1 --branch 13.0 /opt/odoo/odoo13

This will bring the Odoo 13 branch from the Odoo repository and put it inside the folder /opt/odoo/odoo13

Now, we need to enable software collections in order to access python binaries:

scl enable rh-python36 bash

Then we need to create a virtual environment to complete the installation:

cd /opt/odoo
python3 -m venv odoo13-venv

Now, you may activate the virtual environment you have just created:

source odoo13-venv/bin/activate

Now, we upgrade the pip and install the wheel library:

pip install --upgrade pip
pip3 install wheel

Once done, now we can using pip3 to install all the required Python modules from the requirements.txt file:

pip3 install -r odoo13/requirements.txt

Once the installation is complete, now we can deactivate the virtual environment and get back to the root user

deactivate && exit ; exit

If you think, you will create custom modules, you may now create it and give odoo the permission accordingly:

mkdir /opt/odoo/odoo13-custom-addons
chown odoo: /opt/odoo/odoo13-custom-addons

Now, we can fill up the odoo configuration file. First open the odoo.conf file:

nano /etc/odoo.conf

You may paste the following inside:

; This is the password that allows database operations:
admin_passwd = set_the_password_to_create_odoo_database
db_host = False
db_port = False
db_user = odoo
db_password = False
addons_path = /opt/odoo/odoo13/addons,/opt/odoo/odoo13-custom-addons
; You can enable log file with uncommenting the next line
; logfile = /var/log/odoo13/odoo.log

Please do not forget to change the password ‘set_the_password_to_create_odoo_database’ with a new strong password. This would be used to create Odoo databases from the login screen.

Create the systemd service file and start Odoo 13

Now, we will create a service file, to be able to start, stop and restart Odoo daemon. To do that, first create a service file using the following:

nano /etc/systemd/system/odoo13.service

and paste the following:

Requires=postgresql-9.6.service postgresql-9.6.service

ExecStart=/usr/bin/scl enable rh-python35 -- /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf


Now, save the file and exit.

Now, you need to reload the systemd daemon to be able to read the latest changes you have made to services. To do that, run:

systemctl daemon-reload

Finally, now we can start Odoo 13 instance using the following command:

systemctl start odoo13

If you are interested to check the status of the instance, you may do this:

systemctl status odoo13
[[email protected] ~]# systemctl status odoo13
● odoo13.service - Odoo13
   Loaded: loaded (/etc/systemd/system/odoo13.service; enabled; vendor preset: disabled)
   Active: active (running) since Sun 2020-09-13 08:26:46 EDT; 23h ago
 Main PID: 24502 (scl)
   CGroup: /system.slice/odoo13.service
           ├─24502 /usr/bin/scl enable rh-python36 -- /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf
           ├─24503 /bin/bash /var/tmp/sclSWH04z
           └─24507 /opt/odoo/odoo13-venv/bin/python3 /opt/odoo/odoo13/odoo-bin -c /etc/odoo.conf

It show green active running, if everything worked out. If you see no error, you may now enable Odoo to start during the boot:

systemctl enable odoo13

If you would like to see the logs, you may either use the journal tools like the following:

journalctl -u odoo13

or uncomment the following line to log the debugs in /etc/odoo.conf

logfile = /var/log/odoo13/odoo.log

After making any change to /etc/odoo.conf, do not forget the restart the Odoo13 instance using systemctl.

Test the Installation

You may now test the installation using http://your_server_ip:8069. If everything worked, it should come up. If it doesn’t, you may try stopping your ‘firewalld’ to see if firewall is blocking the port or not:

systemctl stop firewalld

At Mellowhost, we provide Odoo installation and configuration assistance for absolute free of charge. If you are willing to try out any of our VPS for Odoo, you may do so and talk with us through the Live chat or the ticket for Odoo assistance.

Furthermore, Good luck.