Category: Linux

How to Migrate CentOS 8 to AlmaLinux
CentOS 8 is reaching its End of Life in December 2021. If you are using CentOS 8, you may need to consider migrating to other operating systems.

Other alternatives for CentOS 8 are AlmaLinux, Rocky Linux, and Oracle Linux. All of these are free and are based on RHEL 8.

AlmaLinux is released a migration script

https://github.com/AlmaLinux/almalinux-deploy

This script allows you to convert CentOS 8 to AlmaLinux.

WARNING: Make sure you take a full system backup before migrating.

Before migrating, make sure your system is up to date.
```
dnf update
```
If you get error, Error: Failed to download metadata for repo ‘appstream’, run
```
sed -i -e "s|mirrorlist=|#mirrorlist=|g" /etc/yum.repos.d/CentOS-*
sed -i -e "s|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g" /etc/yum.repos.d/CentOS-*
dnf update
```
Reboot the server
```
reboot
```
Once the server is back online, we can run the AlmaLinux migration script to start the migration.
```
curl -O https://raw.githubusercontent.com/AlmaLinux/almalinux-deploy/master/almalinux-deploy.sh
bash almalinux-deploy.sh
```
After the migration is complete, run
```
dnf distro-sync -y
```
Now you need to reboot the server
```
reboot
```
October 10, 2021

How to find out what service is using a certain port?

To find out which service or program using a port on a Linux machine, you can use the command

fuser -vn tcp PORT_HERE

Example

root@sok-01:~# fuser -vn tcp 80
                     USER        PID ACCESS COMMAND
80/tcp:              root       1144 F.... nginx
                     boby       1145 F.... nginx
                     boby       1146 F.... nginx
                     boby       1147 F.... nginx
                     boby       1148 F.... nginx
root@sok-01:~#

In this case, TCP port 80 is used by a process with PID 1144, that is Nginx. This process has multiple subprocesses with PID 1145, 1146, 1147, and 1148.

You can also use

root@sok-01:~# fuser 80/tcp
80/tcp:               1144  1145  1146  1147  1148
root@sok-01:~#

This just lists all process IDs. You can find the process by looking at the result of “ps aux” command and finding the process with the above process ids.

Using netstat

Another method is to use “netstat -lntp” command

root@sok-01:~# netstat -lntp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      913/cupsd           
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      1144/nginx: master  
tcp        0      0 127.0.0.1:5982          0.0.0.0:*               LISTEN      22719/VBoxHeadless  
tcp        0      0 0.0.0.0:7070            0.0.0.0:*               LISTEN      1036/anydesk        
tcp        0      0 127.0.0.1:7878          0.0.0.0:*               LISTEN      2969/ssh            
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      1118/mysqld         
tcp        0      0 127.0.0.1:2222          0.0.0.0:*               LISTEN      22719/VBoxHeadless  
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      1/init              
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1144/nginx: master  
tcp        0      0 10.42.0.1:53            0.0.0.0:*               LISTEN      26291/dnsmasq       
tcp        0      0 192.168.122.1:53        0.0.0.0:*               LISTEN      1532/dnsmasq        
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      856/systemd-resolve 
tcp6       0      0 ::1:631                 :::*                    LISTEN      913/cupsd           
tcp6       0      0 ::1:7878                :::*                    LISTEN      2969/ssh            
tcp6       0      0 :::5900                 :::*                    LISTEN      22719/VBoxHeadless  
tcp6       0      0 :::111                  :::*                    LISTEN      1/init              
root@sok-01:~#

This lists all listening ports. The last column shows PID/Program name. To find a specific port, you can use grep

root@sok-01:~# netstat -lntp | grep 80
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1144/nginx: master  
root@sok-01:~#

In the above command, we find which program uses port 80.

October 2, 2021

linux software installation
October 2, 2021

Install Thin web server

Thin is a Ruby web server that can handle high levels of concurrency.

Install it with

gem install thin

root@server70 [/home/redmine]# gem install thin
Building native extensions.  This could take a while...
Building native extensions.  This could take a while...
Successfully installed eventmachine-0.12.10
Successfully installed daemons-1.1.2
Successfully installed thin-1.2.11
3 gems installed
Installing ri documentation for eventmachine-0.12.10...
Installing ri documentation for daemons-1.1.2...
Installing ri documentation for thin-1.2.11...
Installing RDoc documentation for eventmachine-0.12.10...
Could not find main page README
Could not find main page README
Could not find main page README
Could not find main page README
Installing RDoc documentation for daemons-1.1.2...
Installing RDoc documentation for thin-1.2.11...
root@server70 [/home/redmine]#

Installing thin on Ubuntu

You can install thin web server on Ubuntu/Debian using

apt install thin

October 2, 2021

How to host static site using pm2
PM2 is a process manager for node.js applications. You can use PM2 to host static websites.

To host a static website, create a folder, and put your files inside.
```
mkdir /home/website
```
Let’s create a static file, say index.html
```
echo "Welcome" > /home/website/index.html
```
Now you can make the site live using the following pm2 command
```
pm2 serve /home/website 8082
```
Now the static site will be available at
```
http://localhost:8082
```
If you have a Single Page Application (SPA) like Angular, React, you can use the option –spa with pm2 command so all non-existent pages get routed to index.html internally.
```
pm2 serve --spa
```
October 1, 2021
dmidecode
dmidecode is a tool for dumping a computer’s DMI (SMBIOS ) table contents in a human-readable format. This table contains a description of the system’s hardware components, as well as other useful pieces of information such as serial numbers and BIOS revision. Thanks to this table, you can retrieve this information without having to probe for the actual hardware. While this is a good point in terms of report speed and safeness, this also makes the presented information possibly unreliable.

The DMI table doesn’t only describe what the system is currently made of, it also can report the possible evolutions (such as the fastest supported CPU or the maximal amount of memory supported).

SMBIOS stands for System Management BIOS, while DMI stands for Desktop Management Interface. Both standards are tightly related and developed by the DMTF (Desktop Management Task Force).

To see system details, run
```
dmidecode
```
How to find RAM details in Linux
September 14, 2021
How to find RAM details in Linux
To find RAM memory details (model number/manufacturer) in Linux, you can use the command
```
dmidecode --type 17
```
To show only model numbers, run
```
dmidecode --type 17 | grep "Part Number"
```
Once you find the Part Number, you can search in google for the part number to see more details about the RAM.

On Ubuntu/Debian, you can install dmidecode with the command
```
apt install -y dmidecode
```
On RHEL, CentOS, OracleLinux, you can use the command
```
yum install dmidecode
```
On newer RHEL systems, you can use dnf instead of yum.
September 13, 2021

How to Install Elasticsearch in Docker

To Install Elasticsearch with Docker, first, you need to install docker on your server with command

wget -qO- https://get.docker.com/ | sh

Docker images for Elasticsearch are available from

https://hub.docker.com/_/elasticsearch

You can see all available versions at

https://hub.docker.com/_/elasticsearch?tab=tags&page=1&ordering=last_updated

To create an elasticsearch container, run

docker run -p 9200:9200 -p 9300:9300 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:7.5.2

To run it in the background

docker run --name sok-elasticsearch --restart=unless-stopped \
 -d -p 9200:9200 -p 9300:9300 \
 -e "xpack.security.enabled=false" \
 -e "discovery.type=single-node" docker.elastic.co/elasticsearch/elasticsearch:7.5.2

To verify if ElasticSearch works, run

boby@sok-01:~$ curl localhost:9200
{
  "name" : "730d385743b3",
  "cluster_name" : "docker-cluster",
  "cluster_uuid" : "V9XDIPXZQt-Tfgcy8hoIDg",
  "version" : {
    "number" : "7.5.2",
    "build_flavor" : "default",
    "build_type" : "docker",
    "build_hash" : "8bec50e1e0ad29dad5653712cf3bb580cd1afcdf",
    "build_date" : "2020-01-15T12:11:52.313576Z",
    "build_snapshot" : false,
    "lucene_version" : "8.3.0",
    "minimum_wire_compatibility_version" : "6.8.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
  },
  "tagline" : "You Know, for Search"
}
boby@sok-01:~$

Back to Elasticsearch

September 7, 2021

How to find CPU of a Linux Server

To find CPU used on a Linux system, run command

cat /proc/cpuinfo

Example

boby@sok-01:~$ cat /proc/cpuinfo | grep -i "model name"
model name	: AMD Ryzen 3 2200G with Radeon Vega Graphics
model name	: AMD Ryzen 3 2200G with Radeon Vega Graphics
model name	: AMD Ryzen 3 2200G with Radeon Vega Graphics
model name	: AMD Ryzen 3 2200G with Radeon Vega Graphics
boby@sok-01:~$

September 4, 2021

How to Delete Website (Virtual Server) in Virtualmin
In the Virtualmin Hosting control panel, websites are called Virtual Server. To delete a website, click on the Virtualmin tab.

From the dropdown menu, select the website you need to delete.

On the left menu, click on “Disable and Delete’. Then click on “Delete Virtual Server” Link.
```
Virtualmin > Domain > Disable and Delete > Delete Virtial Server
```
It will ask for confirmation. Click on the red “Yes, Delete it” button to delete the website.

See Virtualmin
September 4, 2021
How to display /proc/*/environ file in separate lines?
environ is a file located in /proc/PID/environ, it shows environment variables for a process.

If you run “cat environ”, you will get a long string.

To make it readable, you can use sed command.
```
cat environ | sed -z 's/$/\n/'
cat cmdline | tr '\0' ' ' ; echo
```
Example
September 3, 2021

Watermark video using ffmpeg

To watermark video using FFmpeg, run

ffmpeg -i SOURCE.mp4 -vf "drawtext=text='WATERMARK_TEXT':x=10:y=H-th-10:fontsize=32:fontcolor=white:shadowcolor=black:shadowx=2:shadowy=2" OUT.mp4

In the above command replace

SOURCE.mp4 = file name of the video you need to watermark.
OUT.mp4 = file name for the watermarked video.
WATERMARK_TEXT =  Text you need to watermark on the video.

See ffmpeg

August 31, 2021