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Nagios NRPE Error: service/protocol combination not in /etc/services: nrpe/tcp

It had been awhile since I have installed NRPE or Nagios Remote Plugin Executor running through xinetd so once I thought I had everything configured I attempted to restart xinetd but NRPE was not working properly. Below I describe the error in more detail along with how I resolved the issue. In the below example the server was running CentOS Linux.

NRPE Service Protocol Combination Error Via /var/log/messages:

Dec 20 10:28:46 dev1 xinetd[29359]: service/protocol combination not in /etc/services: nrpe/tcp
Dec 20 10:28:46 dev1 xinetd[29359]: xinetd Version 2.3.14 started with libwrap loadavg labeled-networking options compiled in.
Dec 20 10:28:46 dev1 xinetd[29359]: Started working: 0 available services
Dec 20 10:29:52 dev1 xinetd[29359]: Exiting...

The output above was seen in the messages log file located in /var/log. That is always a great place to look when troubleshooting issues on Linux servers. Luckily the error made me quickly realize what I had forgotten to configure which was to add the NRPE port to /etc/services. To do this open the services file, which is located in the /etc/ directory, in your favorite text editor. Scroll down until you get to the proper place to enter port 5666, which is the NRPE port, and add the below line to the services file.

NRPE Service Port And Protocol Addition To /etc/services:

nrpe            5666/tcp                        # NRPE

Once added save the file and restart xinetd using the init.d script which would be something like “/etc/init.d/xinetd restart”. This should resolve the problem with NRPE. The output below shows the services before and after NRPE in the /etc/services file after you have added NRPE.

Linux /etc/services Sample Output After NRPE Addition:

netmon          2606/tcp        ospf6d          # Dell Netmon
netmon          2606/udp                        # Dell Netmon
dict            2628/tcp                        # RFC 2229
dict            2628/udp                        # RFC 2229
corbaloc        2809/tcp                        # CORBA naming service locator
icpv2           3130/tcp                        # Internet Cache Protocol V2 (Squid)
icpv2           3130/udp                        # Internet Cache Protocol V2 (Squid)
mysql           3306/tcp                        # MySQL
mysql           3306/udp                        # MySQL
trnsprntproxy   3346/tcp                        # Trnsprnt Proxy
trnsprntproxy   3346/udp                        # Trnsprnt Proxy
pxe             4011/udp                        # PXE server
fud             4201/udp                        # Cyrus IMAP FUD Daemon
rwhois          4321/tcp                        # Remote Who Is
rwhois          4321/udp                        # Remote Who Is
krb524          4444/tcp                        # Kerberos 5 to 4 ticket xlator
krb524          4444/udp                        # Kerberos 5 to 4 ticket xlator
rfe             5002/tcp                        # Radio Free Ethernet
rfe             5002/udp                        # Actually uses UDP only
cfengine        5308/tcp                        # CFengine
cfengine        5308/udp                        # CFengine
nrpe            5666/tcp                        # NRPE
cvsup           5999/tcp        CVSup           # CVSup file transfer/John Polstra/FreeBSD
cvsup           5999/udp        CVSup           # CVSup file transfer/John Polstra/FreeBSD
x11             6000/tcp        X               # the X Window System
afs3-fileserver 7000/tcp                        # file server itself
afs3-fileserver 7000/udp                        # file server itself
afs3-callback   7001/tcp                        # callbacks to cache managers
afs3-callback   7001/udp                        # callbacks to cache managers
afs3-prserver   7002/tcp                        # users & groups database
afs3-prserver   7002/udp                        # users & groups database
afs3-vlserver   7003/tcp                        # volume location database
afs3-vlserver   7003/udp                        # volume location database
afs3-kaserver   7004/tcp                        # AFS/Kerberos authentication service
afs3-kaserver   7004/udp                        # AFS/Kerberos authentication service
afs3-volser     7005/tcp                        # volume managment server
afs3-volser     7005/udp                        # volume managment server
afs3-errors     7006/tcp                        # error interpretation service
afs3-errors     7006/udp                        # error interpretation service
afs3-bos        7007/tcp                        # basic overseer process
afs3-bos        7007/udp                        # basic overseer process
afs3-update     7008/tcp                        # server-to-server updater
afs3-update     7008/udp                        # server-to-server updater
afs3-rmtsys     7009/tcp                        # remote cache manager service
afs3-rmtsys     7009/udp                        # remote cache manager service
sd              9876/tcp                        # Session Director

If you run into further issues with NRPE, which is also known as Nagios Remote Plugin Executor,¬†don’t hesitate to ask the questions on QD Engage.

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