Mk_mysql plugin bug

professional_prutser · March 2, 2026, 1:15pm

CMK version: 2.4.0p22 raw
OS version: Debian Stable

Error message:

Output of “cmk-agent-ctl dump”: (If it is a problem with checks or plugins)

<<<mysql_ping>>>
[[/var/run/mysqld/mysqld2.sock]]
mariadb-admin: connect to server at 'localhost' failed
error: 'Can't connect to local server through socket '/var/run/mysqld/mysqld2.sock' (2)'
Check that mariadbd is running and that the socket: '/var/run/mysqld/mysqld2.sock' exists!
<<<mysql_ping>>>
[[/var/run/mysqld/mysqld3.sock]]
mariadb-admin: connect to server at 'localhost' failed
error: 'Can't connect to local server through socket '/var/run/mysqld/mysqld3.sock' (2)'
Check that mariadbd is running and that the socket: '/var/run/mysqld/mysqld3.sock' exists!

I found where these mysql2 and mysql3 sockets came from.

github.com/Checkmk/checkmk

agents/plugins/mk_mysql

62e116382


      
          if type mariadb-admin &>/dev/null; then
              MYSQL=mariadb
              MYSQLADMIN=mariadb-admin
          elif type mysqladmin &>/dev/null; then
              MYSQL=mysql
              MYSQLADMIN=mysqladmin
          else
              exit 0
          fi
          
          mysql_socket_string=$(grep -F -h socket "$MK_CONFDIR"/mysql{.local,}.cfg | sed -ne 's/.*socket=\([^ ]*\).*/\1/p')
          alias_string=$(grep -F -h alias "$MK_CONFDIR"/mysql{.local,}.cfg | sed -ne 's/.*aliases=\([^ ]*\).*/\1/p')
          
          if [ -z "$mysql_socket_string" ]; then
              mysql_socket_string=$(ps -fww -C mysqld | grep "socket" | sed -ne 's/.*socket=\([^ ]*\).*/\1/p')
          fi
          if [ -z "$mysql_socket_string" ]; then
              do_query "" ""
          else
              IFS=" " mapfile -t mysql_sockets <<<"$mysql_socket_string"
              IFS="," read -r -a aliases <<<"$alias_string"

But the plugin example config file does include:

github.com/Checkmk/checkmk

agents/cfg_examples/mysql.cfg

2ce6ace2e


      
          !include /etc/check_mk/mysql.local.cfg
          [check_mk]
          aliases=Alias1,Alias2
          
          # There is always one alias per socket which can also be empty
          # Example with three sockets, the second one has an empty alias:
          # [client]
          # user=monitoring
          # password="password"
          # socket=/var/run/mysqld/mysqld.sock
          # socket=/var/run/mysqld/mysqld2.sock
          # socket=/var/run/mysqld/mysqld3.sock
          
          # host=127.0.0.1
          # !include /etc/check_mk/mysql.local.cfg
          # [check_mk]
          # aliases=Alias1,,Alias3

The grep in mk_mysql should NEVER match a commented line.

looking at github, the grep was introduced in werk 15336 by @BenediktSeidl

Sara · March 3, 2026, 4:18pm

Hi @professional_prutser !
Thank you for reporting,
We were able to confirm this and I will create a ticket for a bug.

In the meantime, a colleague who helped me with confirming this, suggested to use sed -ne 's/[\w]*socket=\([^ ]*\).*/\1/p') as a workaround.

Thanks again!

professional_prutser · March 19, 2026, 9:31am

Not fixed in 2.4.0p23

Sara · March 19, 2026, 9:47am

Unfortunately, even though it has been reported, we cannot give any promises on when this will be fixed.
Please consider using the workaround in the meantime.

professional_prutser · March 20, 2026, 8:20am

Is not about the workaround. It’s about open source / community.

I put in time and effort to make CheckMK better. Why would i bother if checkmk can’t even fix this tiny, handed on a silver plate, bug? I would think a “community manager” would understand.

Or, in other words, why would i pay for checkmk, if this is how you handle free help? It works in two ways

Sara · March 20, 2026, 11:27am

Hello @professional_prutser ,

To keep the product stable, we don’t make changes without testing them thoroughly first. We have a set process to ensure that new updates don’t break other parts of the system.

We have logged your bug report and will review it alongside our other tasks. As the maintainers, we are ultimately responsible for the project’s quality and all final decisions.