To check a Linux kernel

 Quick tutor on how to get data about Linux kernel

# uname -r
3.10.0–1062.el7.x86_64

# cat /proc/version
Linux version 3.10.0–1062.el7.x86_64 (mockbuild@x86–040.build.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5–39) (GCC) ) #1 SMP Thu Jul 18 20:25:13 UTC 2019

# hostnamectl | grep Kernel
Kernel: Linux 3.10.0–1062.el7.x86_64

screen Linux command

 This command is useful in cases where you need to leave some command in the running state, our command history is significantly important

Check if a system already running screens

screen -ls

Create/run a new screen console:

screen -S <screen-in-name>

Re-attach the screen:

screen -r <screen-in-name>

Kill screen session

screen -XS <screen-in-name> quit

useful links:
https://quickref.me/screen

to check open ports in Linux

# netstat -nlptu

# ss -nlptu

# nmap -sTU localhost

# lsof -i

add a user to the Docker group

 if you got an error like this:

$ docker run hello-world
docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.39/containers/create: dial unix /var/run/docker.sock: connect: permission denied.

add a user to the Docker group then

$ sudo usermod -a -G docker $USER
$ mkdir “$HOME”/.docker
$ sudo chmod g+rwx “$HOME/.docker” -R
$ sudo chmod 666 /var/run/docker.sock

check threads or core in Linux

 HW details on Linux (kernel):

echo "Threads/core: $(nproc --all)"            

lscpu | grep CPU