Logging in ZooKeeper

ZooKeeper records file system processes output and events in text logs. This information can be useful when diagnosing technical issues.

Each ZooKeeper component stores logs locally, on the host it occupies. The logs have the .log extension and are located in the /var/log/zookeeper/ directory. In the same directory, you can find .out files that contain component restart information.

The logs naming convention is zookeeper-<user>-<component>-<host>.log.

Where:

The ZooKeeper uses for logging SLF4J and Log4J frameworks.

You can search through the logs for a specific information, like error messages. To do this, connect to the host with the component whose logs you want to inspect, and use a grep command.

For example:

This command searches for messages containing the word error in the CLI log, located on the elenas-adh3.ru-central1.internal host. The i option allows you to ignore case distinctions. The -A3 -B1 options expand the output to one line before and three lines after the line containing the error.

The example output:

ZooKeeper supports the following logging levels (from least to most informative):

The Log4j loggers also accept logging level values: OFF — for switching off the logging, and ALL — for allowing all types of messages.

Enabling one level of logging will enable this level and all levels above it. For example, if you set the logging level to WARN, then only warnings, errors, and fatal messages would get into the log files, but not INFO, DEBUG, and TRACE.

You can configure logging settings for ZooKeeper via the log4j.properties configuration file located on each ZooKeeper server host at etc/zookeeper/conf/.

The log4j.properties file contains logger settings, appender settings, and other logging properties. The parameters you set for a logger influence what a program reports to the system. The parameters you set for the appenders influence the information from loggers that ends up in the log files or console.

The configuration file begins with root logger default properties. This logger processes all messages in ZooKeeper since it’s the only logger configured. The default settings are: INFO, CONSOLE, ROLLINGFILE. This means that messages below the INFO level are discarded and the rest of the messages will end up in both console and log files.

The default appenders are:

You can use appenders layout class to change the log messages format. The default pattern layout describes: message level, date, thread information, and caller information in addition to the message itself.

For more detailed information on Log4j architecture, see the Apache Logging Services documentation.

To edit log4j.properties on all hosts at once, use ADCM:

To change logging properties in the zookeeper-env.sh file via ADCM: