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Rotate Log Files

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  • Overview
  • Default Log Rotation Behavior
  • Log Rotation with --logRotate reopen
  • Syslog Log Rotation
  • Forcing a Log Rotation with SIGUSR1
  • Interaction with Audit Logs

Overview

When used with the --logpath option or systemLog.path setting, mongod and mongos instances report a live account of all activity and operations to a log file. When reporting activity data to a log file, by default, MongoDB only rotates logs in response to the logRotate command, or when the mongod or mongos process receives a SIGUSR1 signal from the operating system.

MongoDB's standard log rotation approach archives the current log file and starts a new one. To do this, the mongod or mongos instance renames the current log file by appending a UTC timestamp to the filename, in ISODate format. It then opens a new log file, closes the old log file, and sends all new log entries to the new log file.

You can also configure MongoDB to support the Linux/Unix logrotate utility by setting systemLog.logRotate or --logRotate to reopen. With reopen, mongod or mongos closes the log file, and then reopens a log file with the same name, expecting that another process renamed the file prior to rotation.

Finally, you can configure mongod to send log data to the syslog using the --syslog option. In this case, you can take advantage of alternate log rotation tools.

To rotate the log files, you must perform one of these steps:

  • Send a SIGUSR1 signal to the mongod or mongos process.

  • Run the MongoDB logRotate command.

  • Run the Linux/Unix logrotate utility.

See the examples later on this page.

Tip

See also:

For information on logging, see the Process Logging section.

Default Log Rotation Behavior

By default, MongoDB uses the --logRotate rename behavior. With rename, mongod or mongos renames the current log file by appending a UTC timestamp to the filename, opens a new log file, closes the old log file, and sends all new log entries to the new log file.

1

Start a mongod instance.

mongod -v --logpath /var/log/mongodb/server1.log

You can also explicitly specify --logRotate rename.

2

List the log files

In a separate terminal, list the matching files:

ls /var/log/mongodb/server1.log*

The results should include one log file, server1.log.

3

Rotate the log file.

Rotate the log file by issuing the logRotate command from the admin database in a mongo shell:

db.adminCommand( { logRotate : "server" } )

Note

You can't run this command on an arbiter for an authenticated replica set.

4

View the new log files

List the new log files to view the newly-created log:

ls /var/log/mongodb/server1.log*

There should be two log files listed: server1.log, which is the log file that mongod or mongos made when it reopened the log file, and server1.log.<timestamp>, the renamed original log file.

Rotating log files does not modify the "old" rotated log files. When you rotate a log, you rename the server1.log file to include the timestamp, and a new, empty server1.log file receives all new log input.

Log Rotation with --logRotate reopen

Log rotation with --logRotate reopen closes and opens the log file following the typical Linux/Unix log rotate behavior.

1

Start a mongod instance, specifying the reopen --logRotate behavior.

mongod -v --logpath /var/log/mongodb/server1.log --logRotate reopen --logappend

You must use the --logappend option with --logRotate reopen.

2

List the log files

In a separate terminal, list the matching files:

ls /var/log/mongodb/server1.log*

The results should include one log file, server1.log.

3

Rotate the log file.

Rotate the log file by issuing the logRotate command from the admin database in a mongo shell:

db.adminCommand( { logRotate : "server" } )

You should rename the log file using an external process, following the typical Linux/Unix log rotate behavior.

Syslog Log Rotation

With syslog log rotation, mongod sends log data to the syslog rather than writing it to a file.

Starting in version 4.2, MongoDB includes the component in its log messages to syslog.

1

Start a mongod instance with the --syslog option

mongod --syslog

Do not include --logpath. Since --syslog tells mongod to send log data to the syslog, specifying a --logpath will causes an error.

To specify the facility level used when logging messages to the syslog, use the --syslogFacility option or systemLog.syslogFacility configuration setting.

2

Rotate the log.

Store and rotate the log output using your systems default log rotation mechanism.

Forcing a Log Rotation with SIGUSR1

For Linux and Unix-based systems, you can use the SIGUSR1 signal to rotate the logs for a single process.

For example, if a running mongod instance has a process ID (PID) of 2200, the following command rotates the log file for that instance on Linux:

kill -SIGUSR1 2200

Interaction with Audit Logs

If auditing is enabled, the logRotate command also rotates the audit log.

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