When running a program Ubuntu server with XFCE, I get the error
ubuntu@ubuntu:~$ ~/Downloads/grab-song-master/check-media-players.sh /home/ubuntu/Downloads/grab-song-master/check-media-players.sh: 3: qdbus: not found ubuntu@ubuntu:~$
The error is fixed by installing qbus
apt-get install qdbus
On CentOS, you need to install qdbus-qt5 package
yum install qdbus-qt5
On OVH VPS running AlmaLinux 8, IPv4 IP address gets dropped. I have to connect to the server using KVM feature available in OVH control panel.
I checked IP of the server with the command
ip a
It did hot show any IPv4 IP address. I checked the network configuration file
vi /etc/sysconfig/network-scripts/ifcfg-eth0
That had the following content
BOOTPROTO=dhcp DEFROUTE=yes DEVICE=eth0 DHCLIENT_SET_DEFAULT_ROUTE=yes HWADDR=fa:16:3e:6b:a6:1a IPV6ADDR=2607:5300:201:3100::952/56 IPV6INIT=yes IPV6_AUTOCONF=no IPV6_DEFAULTGW=2607:5300:201:3100::1 IPV6_FORCE_ACCEPT_RA=no MTU=1500 ONBOOT=yes TYPE=Ethernet USERCTL=no
To make the IP static, I made the following changes.
Find
BOOTPROTO=dhcp
Replace with
BOOTPROTO=static
Also added following 2 entry
IPADDR=144.217.13.76 GATEWAY=144.217.12.1
144.217.13.76 is the IP address of the VPS.
144.217.12.1 is the gateway used on the VPS, found using “ip route” or “route -n” command.
[root@vps-eb960963 network-scripts]# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 144.217.12.1 0.0.0.0 UG 0 0 0 eth0 144.217.12.1 0.0.0.0 255.255.255.255 UH 0 0 0 eth0 [root@vps-eb960963 network-scripts]#
Create a static route file
vi /etc/sysconfig/network-scripts/route-eth0
Add
144.217.12.1 dev eth0 default via 144.217.12.1 dev eth0
Here 144.217.12.1 is the gateway IP address found in the above step.
See IP
You can convert your remote VPS or Dedicated Server running CentOS 8 to Rocky Linux easily by running the following commands.
Install wget and tmux packages.
dnf install wget tmux
Next, start a tmux session, so in case you get disconnected from the remote server, you can connect back
tmux
Now download migration script
wget https://raw.githubusercontent.com/rocky-linux/rocky-tools/main/migrate2rocky/migrate2rocky.sh
Now verify your system can be converted with command
bash migrate2rocky.sh -V
If all is good, you can convert CentOS 8 to Rocky Linux with the command
bash migrate2rocky.sh -r
To list the content of jks keystore file used by tomcat web server, run command
keytool -list -keystore FILE.jks
It will ask Keystore password. Once you enter the password, it will list the contents of the file.
In the above keystore, there are 5 certificates with names inter, root1, root2, ssl_tomcat2, and tomcat.
To get detailed information on the certificates, use the command
keytool -list -v -keystore FILE.jks
See keytool
The keytool command is a key and certificate management utility. It enables users to administer their own public/private key pairs and associated certificates for use in self-authentication (where a user authenticates themselves to other users and services) or data integrity and authentication services, by using digital signatures. The keytool command also enables users to cache the public keys (in the form of certificates) of their communicating peers.
A certificate is a digitally signed statement from one entity (person, company, and so on), which says that the public key (and some other information) of some other entity has a particular value. When data is digitally signed, the signature can be verified to check the data integrity and authenticity. Integrity means that the data hasn’t been modified or tampered with, and authenticity means that the data comes from the individual who claims to have created and signed it.
The keytool command also enables users to administer secret keys and passphrases used in symmetric encryption and decryption (Data Encryption Standard). It can also display other security-related information.
The keytool command stores the keys and certificates in a keystone.
List contents of jks keystore file
Extracting SSL certificate from the Java Keystore (JKS)
To view the contents of tar.gz file, run
tar tf FILE.tar.gz
-f, --file=ARCHIVE use archive file or device ARCHIVE -t, --list list the contents of an archive
To install the Zabbix agent on Ubuntu, run the command
apt install zabbix-agent
To autostart, Zabbix agent on boot, enable it with
systemctl enable zabbix-agent
To manage Zabbix, use commands
systemctl stop zabbix-agent systemctl start zabbix-agent systemctl restart zabbix-agent
To see Zabbix listening port
netstat -lntp | grep zabbix
Edit file
vi /etc/zabbix/zabbix_agentd.conf
Find
Server=127.0.0.1
Replace with
Server=127.0.0.1,IP_OF_ZABBIX_SERVER_HERE
Restart zabbix agent
systemctl restart zabbix-agent
After the Zabbix agent is installed, you need to add the sevrer in your Zabbix installation.
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
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.
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.