Check a certificate

openssl x509 -in server.crt -text -noout

Check a key

openssl rsa -in server.key -check

Check a CSR

openssl req -text -noout -verify -in server.csr

Verify a certificate and key matches

openssl x509 -noout -modulus -in server.crt| openssl md5
openssl rsa -noout -modulus -in server.key| openssl md5
How to configure Linux to use Trackpoint Scrolling on Lenovo Thinkpads:

Just create a file '20-thinkpad.conf'
in /usr/share/X11/xorg.conf.d/

with content:

Section "InputClass"
     Identifier "Trackpoint Wheel Emulation"
     MatchProduct       "TPPS/2 IBM TrackPoint|DualPoint Stick|Synaptics Inc. Composite TouchPad / TrackPoint|ThinkPad USB Keyboard with TrackPoint|ThinkPad Compact USB Keyboard with TrackPoint|USB Trackpoint pointing device"
     MatchDevicePath    "/dev/input/event*"
     Option             "EmulateWheel"          "true"
     Option             "EmulateWheelButton"    "2"
     Option             "Emulate3Buttons"       "false"
     Option             "XAxisMapping"          "6 7"
     Option             "YAxisMapping"          "4 5"
 EndSection

restart mdm (for LinuxMint Cinnamon) or reboot.
Helps for system administration with systemd:

Control and manipulate services

systemctl
systemctl enable [servicename]
systemctl stop/start [servicename]
systemctl disable [servicename]

Remove services from systemd

systemctl stop [servicename]
systemctl disable [servicename]
rm /etc/systemd/system/[servicename]
systemctl daemon-reload
systemctl reset-failed
Some CentOS firewald syntax ...
firewall-cmd --help
firewall-cmd --get-active-zones
firewall-cmd --get-default-zone
firewall-cmd --get-zone-of-interface=eth0
firewall-cmd --permanent --zone=public --change-interface=eth0
firewall-cmd --get-zones
firewall-cmd --zone=public --list-sources
firewall-cmd --permanent --zone=public --add-service=http
firewall-cmd --permanent --zone=public --add-service=https
firewall-cmd --zone=public --permanent --add-port=6556/tcp
firewall-cmd --reload
firewall-cmd --list-ports --zone=public
firewall-cmd --zone=public --list-all
firewall-cmd --list-services

... work in progress ...