Not listening on port 10051 (was working until 1600 today)

[GRIFFCOMM]

Hi

We followed the instrcunres here to install "https://www.zabbix.com/download", this worked for about 4 weeks (until today 1600), we have a number of proxies outside all Active reporting in no issues, then 1600 today, no data....

After ALOT of testing, we notice the Ubuntu install (20.04) is not listening on port 10051 (run command "sudo lsof -i -P -n" shows its listening on port 10050, so why would this change all of a sudden? we have active proxies, which are trying to get in on port 10051 and were working fine.

So we edited /etc/zabbiz/zabbix_server.cont and put line "ListenPort=10051", saved rebooted, still not listening on port 10051, so how do we get this to work?

Was there an update that made this port redundant? do we have to change all local clients to port 10050 now? and why would this just change by itself 4 hours ago?

I am also seeing this in the Administration > Queue page:

• Connection to Zabbix server "localhost" refused. Possible reasons:
• 1. Incorrect server IP/DNS in the "zabbix.conf.php";
• 2. Security environment (for example, SELinux) is blocking the connection;
• 3. Zabbix server daemon not running;
• 4. Firewall is blocking TCP connection.
• Connection refused

I have no idea whats going on here, but really looks like the server config is screwed somehow....
As a minimal level what needs to be in the server_config.conf to make this work?


Many Thanks

UPDATE

We fixed it, so for anyone else who sees this....

We then noticed a small message on the footer of the Web GUI "Zabbix server not running... ", so we looked at the log file /var/log/zabbox/zabbix_server.log, and has the below entries

Found this line:
2586:20210114:213204.781 [file:dbconfig.c,line:98] __zbx_mem_realloc(): out of memory (requested 16 bytes)

and then

2585:20210114:213204.785 Zabbix Server stopped. Zabbix 5.2.3 (revision ae46273eae).

Turns out need to increase the CacheSize setting in the zabbix_server.conf file, ours was # out so we put CacheSize=1G (1Gig)... restarted the server, now working ok.

[william9157]

I am using Ubuntu 24.04 LTS server with PostgreSQL 17.
I have been having the above issue, "Not Listening on port 10051". I have rebuilt and reinstalled PostgreSQL several times along with the Zabbix installation. Progressed through all the fixes and still had the same issue. In the end I did two things. I used the fix in this post and increased the cache to 1G and edited the "pg_hba.conf" file as shown below:

# Database administrative login by Unix domain socket
local all postgres trust

# TYPE DATABASE USER ADDRESS METHOD

# "local" is for Unix domain socket connections only
local all all trust
# IPv4 local connections:
host all all 0.0.0.0/0 trust
#host all all 127.0.0.1/32 scram-sha-256
# IPv6 local connections:
host all all ::1/128 trust
This was the only change that opened the 10051 port. This I confirmed using nmap from a desktop to the Zabbix host.
I do not understand why this would not work with md5 or password but only with the trust setting and the network address set to any address (INADDR_ANY)?
If the network address is set 127.0.0.1/32 with md5 and trust I could not get port 10051 open. At present its working maybe not as secure as I would like but it is a private network.

[MRedbourne]

I am using Ubuntu 24.04 LTS server with PostgreSQL 17.
I have been having the above issue, "Not Listening on port 10051". I have rebuilt and reinstalled PostgreSQL several times along with the Zabbix installation. Progressed through all the fixes and still had the same issue. In the end I did two things. I used the fix in this post and increased the cache to 1G and edited the "pg_hba.conf" file as shown below:

# Database administrative login by Unix domain socket
local all postgres trust

# TYPE DATABASE USER ADDRESS METHOD

# "local" is for Unix domain socket connections only
local all all trust
# IPv4 local connections:
host all all 0.0.0.0/0 trust
#host all all 127.0.0.1/32 scram-sha-256
# IPv6 local connections:
host all all ::1/128 trust
This was the only change that opened the 10051 port. This I confirmed using nmap from a desktop to the Zabbix host.
I do not understand why this would not work with md5 or password but only with the trust setting and the network address set to any address (INADDR_ANY)?
If the network address is set 127.0.0.1/32 with md5 and trust I could not get port 10051 open. At present its working maybe not as secure as I would like but it is a private network.

Hey. I'm not a PG user for DBs (generally... I have one PG database that I'm forced to use). However, MD5 is *widely* understood to have a plethora of problems associated with security. Notably, it's exceptionally easy to crack MD5 hashes, and PG MD5 authentication is vulnerable to PTH (pass the hash) attacks. In your config, you specified this

#host all all 127.0.0.1/32 scram-sha-256

.
Was this the part not working for you? Zabbix may not support scram-sha-256 yet (MongoDB had an issue in 2023 for agent2). I wouldn't necessarily apply so many limitations to the hash encryption. Dump MD5 though.

Edit: Also check your ZBX Server logs... /var/log/zabbix_server.log for signs of it failing to authenticate.

[MaryamAfzal0]

It sounds like your Zabbix server stopped listening on port 10051 unexpectedly. A few things to check:

1. Verify Zabbix server status – Run sudo systemctl status zabbix-server to confirm it's running.
2. Check logs – Look at /var/log/zabbix/zabbix_server.log for errors.
3. Firewall & SELinux – Ensure ufw or iptables isn’t blocking port 10051, and check getenforce for SELinux status.
4. Reinstall Zabbix server – If an update caused this, try reinstalling or reconfiguring Zabbix.
5. Config check – Confirm ListenPort=10051 in /etc/zabbix/zabbix_server.conf, restart the service, and verify with netstat -tulnp | grep 10051.

If the issue persists, consider rolling back recent updates or checking package changes.

[cyber]

Hey. I'm not a PG user for DBs (generally... I have one PG database that I'm forced to use). However, MD5 is *widely* understood to have a plethora of problems associated with security. Notably, it's exceptionally easy to crack MD5 hashes, and PG MD5 authentication is vulnerable to PTH (pass the hash) attacks. In your config, you specified this

#host all all 127.0.0.1/32 scram-sha-256

.
Was this the part not working for you? Zabbix may not support scram-sha-256 yet (MongoDB had an issue in 2023 for agent2). I wouldn't necessarily apply so many limitations to the hash encryption. Dump MD5 though.

Edit: Also check your ZBX Server logs... /var/log/zabbix_server.log for signs of it failing to authenticate.

Zabbix has no issues with scram-sha-256 in PG... I think PG defaulted to that already in v15? So, if you want to use md5, you need to specifically force it, when setting passwd for user...

Only way I can see, that PG change fixes someones 10051 port listening, is, that after PG changes your server managed to start up (connect to DB) and start listening there... And most probably there was/is issue with user authentication. PG logs should show that also...