The syslog server comes standard on CentOS/RHEL 7+ and is a system utility providing support for message logging. Support of both internet and unix domain sockets enables this utility to support both local and remote logging.  With a couple of configuration changes can become a central monitoring server. There are syntax changes pre CentOS/RHEL 7.4 and CentOS/RHEL 7.4+ for semanage and rsyslog.  This article will focus on a working installation for CentOS/RHEL 7.4+.

There are a couple ways of going about this.  The /etc/rsyslog.conf can be modified, but it is cleaner to add a new configuration file to /etc/rsyslog.d and that is the approach that will be taken for this article.

Rsyslog Server

Prerequisites

yum update -y
yum install policycoreutils-python firewalld rsyslog -y
systemctl enable --now firewalld rsyslog

Configuration

Rsyslog syntax has changed where the ~ has been replaced with the word stop.  The – minus sign is no longer needed.  If your rsyslogd will not start it is likely because you have used ~.  Change it to the word stop and restart the service.

This article will focus on udp/514; however, will show tcp/514 configurations too.

Selinux

Since CentOS/RHEL 7.4+, semanage requires the word port.

semanage port -a -t syslogd_port_t -p udp 514
#semanage port -a -t syslogd_port_t -p tcp 514

Firewall Rules

# firewall-cmd --permanent --add-port=514/tcp
firewall-cmd --permanent --add-port=514/udp
firewall-cmd --reload

Create Configuration File

There are many possibilities here.  This one works for testing purposes and can be modified any number of ways that best fits your given situation.

cat > /etc/rsyslog.d/10-remote.conf << EOF
# Provides UDP syslog reception
$ModLoad imudp
$UDPServerRun 514
$AllowedSender UDP, 192.168.1.0/24

# Provides TCP syslog reception
#$ModLoad imtcp
#$InputTCPServerRun 514
#$AllowedSender TCP, 192.168.1.0/24

$template RemoteStore, "/var/log/remote/%HOSTNAME%/%timegenerated:1:10:date-rfc3339%"
:source, !isequal, "localhost" ?RemoteStore
:source, isequal, "last" stop
EOF

Restart Service

systemctl restart rsyslog

Validation

Determine if rsyslogd is running and listening.

[root@c7rsyslog ~]# ss -tulpn | grep rsyslog
udp    UNCONN     0      0         *:514                   *:*                   users:(("rsyslogd",pid=1572,fd=3))
udp    UNCONN     0      0        :::514                  :::*                   users:(("rsyslogd",pid=1572,fd=4))

Rsyslog Client

Create Configuration File

Since the server is using udp/514 there is only one @ preceding the IP address. If there is a tcp/514 connection then use two @@.

echo '*.* @192.168.1.234:514' | tee -a /etc/rsyslog.d/99-rsyslog-client.conf
systemctl restart rsyslog

Validation

Determine if the client can access the rsyslogd server.

[root@idm~]# nmap -p 514 -sU -P0 192.168.1.234

Starting Nmap 6.40 ( http://nmap.org ) at 2019-10-05 09:35 EDT
Nmap scan report for 192.168.1.234
Host is up (0.00016s latency).
PORT    STATE         SERVICE
514/udp open|filtered syslog
MAC Address: 00:0C:29:B2:14:F6 (VMware)

Nmap done: 1 IP address (1 host up) scanned in 0.35 seconds

A test message may be sent to see if the rsyslog server picked it up.

logger "Test from logclient"

Results

Go back to the server to verify.  Note that the serves are listed.

Source(s)

• https://www.tecmint.com/create-centralized-log-server-with-rsyslog-in-centos-7/
• man rsyslogd
• https://linux.die.net/man/8/syslogd_selinux
• https://www.tutorialspoint.com/unix_commands/semanage.htm
• https://www.the-art-of-web.com/system/rsyslog-config/
• https://raymii.org/s/tutorials/Syslog_config_for_remote_logservers_for_syslog-ng_and_rsyslog_client_server.html