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MySQL Error Log

Server errors, warnings, startup/shutdown messages, and diagnostic information

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Quick Facts

Default Path (Linux)
/var/log/mysql/error.log
Docker
stderr
Default Format
text
JSON Native
Yes (since 8.0.4)
Rotation
manual or logrotate

Log Example

Default format: Default Text Format

Example Log Entrylog
2025-12-20T14:32:18.123456Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.

Structure:

timestamp thread_id [severity] [error_code] message

Paths by Platform

Debian / Ubuntu
/var/log/mysql/error.log
RHEL / CentOS
/var/log/mysqld.log

Available Formats

Default Text Format

Default

Example:

2025-12-20T14:32:18.123456Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.

Structure:

timestamp thread_id [severity] [error_code] message

JSON Format

Native
Config Required

Available since version 8.0.4

Example:

{"timestamp":"2025-12-20T14:32:18.123456Z","thread":0,"severity":"Warning","error_code":"MY-010068","subsystem":"Server","message":"CA certificate ca.pem is self signed."}

Structure:

JSON object with structured fields

Fields Reference

FieldTypeDescriptionExample
timestamp
datetime
When the event occurred2025-12-20T14:32:18.123456Z
thread
integer
Thread ID0
severity
string
Error severity levelWarning
error_code
string
MySQL error codeMY-010068
subsystem
string
Server subsystemServer
message
string
Error messageCA certificate ca.pem is self signed.

Parsing Patterns

Grok Patterns

text:

%{TIMESTAMP_ISO8601:timestamp}Z %{NUMBER:thread} \[%{WORD:severity}\] \[%{DATA:error_code}\] \[%{WORD:subsystem}\] %{GREEDYDATA:message}

Collector Configurations

logstashruby
1filter {
2  grok {
3    match => { "message" => "%{TIMESTAMP_ISO8601:timestamp}Z %{NUMBER:thread} \[%{WORD:severity}\] \[%{DATA:error_code}\] \[%{WORD:subsystem}\] %{GREEDYDATA:mysql_message}" }
4  }
5}

Configuration

Enable Logging

Error log is enabled by default; configure path and format

/etc/mysql/mysql.conf.d/mysqld.cnf
[mysqld]
log_error = /var/log/mysql/error.log
log_error_verbosity = 2  # 1=errors, 2=+warnings, 3=+notes

Enable Json

Enable JSON error logging (MySQL 8.0.4+)

[mysqld]
log_error = /var/log/mysql/error.log
log_error_services = 'log_filter_internal; log_sink_json'

Log Rotation

Tool: logrotate | Config: /etc/logrotate.d/mysql

/etc/logrotate.d/mysql
/var/log/mysql/error.log {
    daily
    rotate 7
    missingok
    create 640 mysql adm
    compress
    sharedscripts
    postrotate
        mysqladmin --defaults-file=/etc/mysql/debian.cnf flush-logs error
    endscript
}

Use Cases

Startup issues

Track server initialization problems

severity
message

Replication errors

Monitor replication health

error_code
message

Troubleshooting

Tested On

v8.4.0 on Ubuntu 24.04
mysql_dba - 2025-12-10
Last updated: 2025-12-10 by mysql_dba
2 contributors134 upvotes
Validated

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