OPTIONS

Rotate Log Files

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 logrotation tools.

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:

use admin
db.runCommand( { logRotate : 1 } )
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

New in version 3.0.0.

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:

use admin
db.runCommand( { logRotate : 1 } )

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

Syslog Log Rotation

New in version 2.2.

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

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, as in the following:

kill -SIGUSR1 <mongod process id>