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Rotate Log Files

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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. Both server logs and audit logs may be rotated with the logRotate command, either together or independently.

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 mongosh:

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

If auditing is enabled, you can specify 1 to logRotate (instead of server) to rotate both the server and audit logs at the same time, if desired. The audit log will be rotated in the same fashion as the server log, according to the --logRotate setting.

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 mongosh:

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