Zabbix: solve memory monitoring issue inside LXC containers

Zabbix-agent (NOT zabbix-agent2) has some problems with memory collecting from cgroups limited containers.
If you are using Proxmox, you know what I mean: The available memory is collected wrongly without calculating buffers and cache memory.

Note: This issue only affects zabbix-agent and has been fixed in zabbix-agent2.

Zabbix have bug report, but it seems that no one don’t want to fix it soon.
So let’s fix it together byself.

First we need to create new user parameter for zabbix, I used ct.memory.size name similarly built-in vm.memory.size parameter, but with my own single line script.

Please be sure that you have newest version of free tool, 3.3.10 and higher, because old one have different output format.

$ free -V
free from procps-ng 3.3.10

Edit /etc/zabbix/zabbix_agentd.d/zabbix_container.conf:

NOTE: Depending on the OS that you are working with, the path could change.

Please verify in /etc/zabbix/zabbix_agentd.conf the "include" path.

Example With Debian 12

  cat /etc/zabbix/zabbix_agentd.conf | grep ^Include
  Include=/etc/zabbix/zabbix_agentd.conf.d/*.conf

This is the path to add the new user parameter.

  ls /etc/zabbix/zabbix_agentd.conf.d/
  zabbix_container.conf 

Add user parameter for retrieve memory information:

UserParameter=ct.memory.size[*],free -b | awk '$ 1 == "Mem:" {total=$ 2; used=($ 3+$ 5); pused=(($ 3+$ 5)*100/$ 2); free=$ 4; pfree=($ 4*100/$ 2); shared=$ 5; buffers=$ 6; cache=$ 6; available=($ 6+$ 7); pavailable=(($ 6+$ 7)*100/$ 2); if("$1" == "") {printf("%.0f", total )} else {printf("%.0f", $1 "" )} }'

Add another one for retrieve swap information:

UserParameter=ct.swap.size[*],free -b | awk '$ 1 == "Swap:" {total=$ 2; used=$ 3; free=$ 4; pfree=($ 4*100/$ 2); pused=($ 3*100/$ 2); if("$1" == "") {printf("%.0f", free )} else {printf("%.0f", $1 "" )} }'

Add another one for retrieve right CPU load information:

UserParameter=ct.cpu.load[*],uptime | awk -F'[, ]+' '{avg1=$(NF-2); avg5=$(NF-1); avg15=$(NF)}{print $2/'$(nproc)'}'

Or just download and copy my zabbix_container.conf.

It will provide you support for next parameters:

ct.memory.size[total]
ct.memory.size[free]
ct.memory.size[buffers]
ct.memory.size[cached]
ct.memory.size[shared]
ct.memory.size[used]
ct.memory.size[pused]
ct.memory.size[available]
ct.memory.size[pavailable]
ct.swap.size[total]
ct.swap.size[free]
ct.swap.size[shared]
ct.swap.size[used]
ct.swap.size[pused]
ct.swap.size[available]
ct.swap.size[pavailable]
ct.cpu.load[percpu,avg1]
ct.cpu.load[percpu,avg5]
ct.cpu.load[percpu,avg15]

Don’t forget to restart zabbix-agent.service after

Ok, now we can check is our parameter working from zabbix server:

$ zabbix_get -s <container_ip> -k ct.memory.size[available]
1709940736

Ok it’s working.

Now let’s configure zabbix for use them. In Zabbix Interface:

Go Configuration → Templtes

• Make full copy “Template OS Linux” to “Template Linux Container”
• Open “Template Linux Container” → Items
• Replace all vm.memory.size items to ct.memory.size.
• Replace all system.swap.size items to ct.swap.size:
  You also need to remove commas in key filed here. Example:
  replace system.swap.size[,free] to ct.swap.size[free]
• Replace all system.cpu.load[percpu,*] items to ct.cpu.load[percpu,*].

Or just download and import my zabbix template.

Next, go to the Configuration → Hosts

• Unlink and clear “Template OS Linux” from your hosts
• Attach “Template Linux Container”

Wait some time and check the graphics:

Job is done!