How to Set Up rsyslog and SSH Key Authentication on CentOS 8

Overview

The article demonstrates how to inspect a CentOS 8 system, configure rsyslog for remote logging, and set up SSH key‑based authentication between a client (IP 192.168.222.250) and a server (IP 192.168.222.251).

System Inspection

# cat /etc/redhat-release
CentOS Stream release 8
# uname -r
4.18.0-257.el8.x86_64
# dmesg | head -n 5
[    5.273545] XFS (dm-2): Starting recovery (logdev: internal)
[    5.323019] XFS (dm-2): Ending recovery (logdev: internal)
# tail -f /var/log/messages
Jul 19 16:39:01 lnh systemd-logind[976]: New session 1 of user root.

Two logging daemons run on the system:

syslogd : handles non‑kernel messages.

klogd : records kernel‑generated logs.

Checking Daemons

# ps aux | grep syslogd
root 1194 0.0 0.2 218472 5768 ? Ssl 16:37 0:00 /usr/sbin/rsyslogd -n
# ps aux | grep klogd
root 1362 0.0 0.0 12108 1080 pts/0 S+ 16:51 0:00 grep --color=auto klogd

Configuring the rsyslog Server

1. Clone the virtual machine as a full clone.

2. Define client and server IPs:

lnh (client)   192.168.222.250
xbz (server)   192.168.222.251

3. Edit /etc/rsyslog.conf on both hosts to enable remote logging (uncomment the four lines that forward logs).

4. Restart the service and disable the firewall:

# systemctl restart rsyslog.service
# systemctl stop firewalld.service
# setenforce 0

5. Verify that the server receives logs:

# tail -f /var/log/secure
Jul 19 17:02:19 lnh sshd[1012]: Server listening on :: port 22.
Jul 19 17:02:24 lnh sshd[1012]: Accepted password for root from 192.168.222.1 port 55495 ssh2

SSH Basics

The client (lnh) connects to the server (xbz) using:

# ssh [email protected] '/usr/sbin/ip a'

Host keys are stored in /etc/ssh/ (e.g., ssh_host_ecdsa_key, ssh_host_rsa_key.pub) and the client’s known hosts file ( ~/.ssh/known_hosts) records the server’s public key.

Generating and Deploying RSA Keys

On the client:

# ssh-keygen -t rsa
# ssh-copy-id [email protected]

The public key is copied to ~/.ssh/authorized_keys on the server. Afterward, password‑less login works:

# ssh [email protected]
Last login: Tue Jul 19 17:05:36 2022 from 192.168.222.1

The same steps are repeated in reverse to allow the server to log into the client.

Useful scp Options

-r

: recursive copy -p: preserve permissions -P: specify remote port -q: quiet mode -a: archive mode (preserves all attributes)