Too many binary log files are in the disk.
the number of log files keep 14~16 as below. (normally 14)
mysql-bin-changelog.028255 134223043
mysql-bin-changelog.028256 134228506
mysql-bin-changelog.028257 134220246
mysql-bin-changelog.028258 134236483
mysql-bin-changelog.028259 134219139
mysql-bin-changelog.028260 134224849
mysql-bin-changelog.028261 134219266
mysql-bin-changelog.028262 134227092
mysql-bin-changelog.028263 16064294
mysql-bin-changelog.028264 134218994
mysql-bin-changelog.028265 134221078
mysql-bin-changelog.028266 134222337
mysql-bin-changelog.028267 134231770
mysql-bin-changelog.028268 134222330
mysql-bin-changelog.028269 119753944
I am pretty sure that the last tabs like '134227341' are from a global variable called max_binlog_size. but what makes the list keeps its size?
I did not set up this Maria DB, so I do not much about it. this is for RDS and MariaDB ver 10.x and no replication out there.
Suggest you set expire_logs_days to, say, 14. This would mean that any binlogs older than 14 days would be automatically deleted.
14 days should give you enough time to notice that a Slave is broken and fix it before losing the binlogs that it needs.
If you have not slaves and you don't use binlogs for backup, then set it to 1.
(There are other approaches, but this is reasonably simple.)