install Zabbix agent on Centos 8

 get one of the Zabbix agent version

~]# wget https://repo.zabbix.com/zabbix/5.0/rhel/8/x86_64/zabbix-release-5.0-1.el8.noarch.rpm

add Zabbix repository to be able to install

~]# rpm -Uvh https://repo.zabbix.com/zabbix/5.0/rhel/8/x86_64/zabbix-release-5.0-1.el8.noarch.rpm

Retrieving https://repo.zabbix.com/zabbix/5.0/rhel/8/x86_64/zabbix-release-5.0-1.el8.noarch.rpm
warning: /var/tmp/rpm-tmp.Ankajf: Header V4 RSA/SHA512 Signature, key ID a14fe591: NOKEY
Verifying...                          ################################# [100%]
Preparing...                          ################################# [100%]
Updating / installing...
   1:zabbix-release-5.0-1.el8         ################################# [ 50%]
Cleaning up / removing...
   2:zabbix-release-5.0-1.el5         ################################# [100%]

~]# dnf clean all

install the Zabbix agent package

~]# dnf install zabbix-agent

start the Zabbix agent service and start it in boot

~]# systemctl enable --now zabbix-agent

Created symlink /etc/systemd/system/multi-user.target.wants/zabbix-agent.service → /usr/lib/systemd/system/zabbix-agent.service.
[root@cabinet ~]# systemctl status zabbix-agent
● zabbix-agent.service - Zabbix Agent
   Loaded: loaded (/usr/lib/systemd/system/zabbix-agent.service; enabled; vendor preset: disabled)
   Active: active (running) since Sun 2022-07-24 10:54:58 EEST; 19s ago
  Process: 2920207 ExecStart=/usr/sbin/zabbix_agentd -c $CONFFILE (code=exited, status=0/SUCCESS)
 Main PID: 2920209 (zabbix_agentd)
    Tasks: 6 (limit: 49468)
   Memory: 3.8M

install net-tool to run the netstat

~]# yum install net-tools

check listening ports

~]# netstat -nlptu
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
...
tcp        0      0 10.10.10.102:1500       0.0.0.0:*               LISTEN      ...

check firewall state:

~]# firewall-cmd --state
not running

if it’s running then stop and disable the firewall
! this option makes sense due to using the target host behind the other firewall or gateway, otherwise to tune the firewall in the proper way

~]# systemctl stop firewalld
~]# systemctl disable firewalld

if it’s not running then check access to port 10050 from another host:

~ # telnet 10.10.10.102 10050
Trying 10.10.10.102...
telnet: Unable to connect to remote host: No route to host

if it’s blocked then check iptables on the target host:

~]# iptables -S
...
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
...

add the open 10050 port rule to the iptables by command

 ~]# iptables -I INPUT 5 -p tcp -m tcp --dport 10050 -j ACCEPT

check the rule again

~]# iptables -S | grep 10050
-A INPUT -p tcp -m tcp --dport 10050 -j ACCEPT

and check the access from another host by telnet

~ # telnet 10.10.10.102 10050
Trying 10.10.10.102...
Connected to 10.10.10.102.
Escape character is '^]'.
Connection closed by foreign host.

return to the target host and save current iptables settings to backup iptables file and to the actual iptables config file (/etc/sysconfig/iptables)

# save actual working settings to backup file
~]# iptables-save > iptables_rules_20220724

# replace the actual iptables config file with actual working settings
~]# cp iptables_rules_20220724 /etc/sysconfig/iptables

# check expected record
~]# cat /etc/sysconfig/iptables | grep 10050
-A INPUT -p tcp -m tcp --dport 10050 -j ACCEPT

# or the rule could be added inside the /etc/sysconfig/iptables
# -A INPUT -p tcp -m tcp --dport 10050 -j ACCEPT

References links:
https://serverspace.io/support/help/install-configure-zabbix-agent-centos-8/
https://linuxize.com/post/how-to-configure-and-manage-firewall-on-centos-8/
https://linuxhint.com/disable-firewall-centos-8/
https://forums.centos.org/viewtopic.php?t=9059
https://upcloud.com/resources/tutorials/configure-iptables-centos