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getLog

getLog is an administrative command that returns the most recent 1024 logged mongod events. getLog does not read log data from the mongod log file. It instead reads data from a RAM cache of logged mongod events. To run getLog, use the db.adminCommand() method.

Starting in MongoDB 4.4, getLog returns log data in escaped Relaxed Extended JSON v2.0 format. Previously, log data was returned as plaintext.

Syntax

The getLog command has the following syntax:

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db.adminCommand( { getLog: <value> } )

Command Fields

The possible values for getLog are:

Output

If specified *, then the command returns a document with the names of the other acceptable values.

Otherwise, the command returns a document that includes the following fields:

  • totalLinesWritten field that contains the number of log events
  • log field that contains an array of log events
  • A db.adminCommand() response document, containing status and timestamp information.

Behavior

Line Truncation

Starting in MongoDB 4.2, getLog truncates any event that contains more than 1024 characters. In earlier versions, getLog truncates after 512 characters.

Character Escaping

Starting in MongoDB 4.4, getLog returns log data in escaped Relaxed Extended JSON v2.0 format, using the following escape sequences to render log output as valid JSON:

Character Represented Escape Sequence
Quotation Mark (") \"
Backslash (\) \\
Backspace (0x08) \b
Formfeed (0x0C) \f
Newline (0x0A) \n
Carriage return (0x0D) \r
Horizontal tab (0x09) \t

Control characters not listed above are escaped with \uXXXX where “XXXX” is the unicode codepoint in hexadecimal. Bytes with invalid UTF-8 encoding are replaced with the unicode replacement character represented by \ufffd.

Filtering

Within mongosh

getLog output can be filtered to make results more readable or to match on specific criteria.

The following operation prints just the log field (which contains the array of all recent log events), and removes character escaping from each log message:

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db.adminCommand( { getLog:'global'} ).log.forEach(x => {print(x)})

This operation presents getLog output in the same format as the MongoDB log file.

Note

getLog only shows the most recent 1024 logged mongod events, and is not a replacement for the MongoDB log file.

Outside mongosh with jq

When working with MongoDB structured logging, the third-party jq command-line utility is a useful tool that allows for easy pretty-printing of log entries, and powerful key-based matching and filtering.

jq is an open-source JSON parser, and is available for Linux, Windows, and macOS.

To use jq with getLog output, you must use the --eval option to mongosh. The following operation uses jq to filter on the REPL component to present only those log messages associated with replication:

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mongosh --quiet --eval "db.adminCommand( { getLog:'global'} ).log.forEach(x => {print(x)})" | jq -c '. | select(.c=="REPL")'

Be sure to provide any necessary connection-specific parameters to mongosh as needed, such as --host or --port.

See Parsing Structured Log Messages for more examples of filtering log output using jq. The jq syntax presented in each linked example can be used with the above mongo --eval operation with minor adjustment. For example, the following syntax adapts the linked “Counting Unique Messages” example for use with getLog:

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mongosh --quiet --eval "db.adminCommand( { getLog:'global'} ).log.forEach(x => {print(x)})" | jq -r ".msg" | sort | uniq -c | sort -rn | head -10

Examples

Retrieve Available Log Filters

The following operation, run from mongosh, returns the available log filters for passing to getLog:

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db.adminCommand( { getLog: "*" } )

The operation returns the following document:

{ "names" : [ "global", "startupWarnings" ], "ok" : 1 }

Retrieve Recent Events from Log

The following operation, run from mongosh, retrieves the most recent global events for the mongod:

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db.adminCommand( { getLog : "global" } )

The operation returns a document similar to the following:

{
      "totalLinesWritten" : <num>,
      "log" : [
              "{\"t\":{\"$date\":\"2020-05-19T19:10:48.871+00:00\"},\"s\":\"I\",  \"c\":\"STORAGE\",  \"id\":4615611, \"ctx\":\"initandlisten\",\"msg\":\"MongoDB starting\",\"attr\":{\"pid\":12345,\"port\":27001,\"dbPath\":\"/var/lib/mongo\",\"architecture\":\"64-bit\",\"host\":\"server1.example.com\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:48.871+00:00\"},\"s\":\"I\",  \"c\":\"CONTROL\",  \"id\":23403,   \"ctx\":\"initandlisten\",\"msg\":\"Build Info\",\"attr\":{\"buildInfo\":{\"version\":\"4.4.0\",\"gitVersion\":\"328c35e4b883540675fb4b626c53a08f74e43cf0\",\"openSSLVersion\":\"OpenSSL 1.1.1c FIPS  28 May 2019\",\"modules\":[],\"allocator\":\"tcmalloc\",\"environment\":{\"distmod\":\"rhel80\",\"distarch\":\"x86_64\",\"target_arch\":\"x86_64\"}}}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:48.871+00:00\"},\"s\":\"I\",  \"c\":\"CONTROL\",  \"id\":51765,   \"ctx\":\"initandlisten\",\"msg\":\"Operating System\",\"attr\":{\"os\":{\"name\":\"CentOS Linux release 8.0.1905 (Core) \",\"version\":\"Kernel 4.18.0-80.11.2.el8_0.x86_64\"}}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:48.871+00:00\"},\"s\":\"I\",  \"c\":\"CONTROL\",  \"id\":21951,   \"ctx\":\"initandlisten\",\"msg\":\"Options set by command line\",\"attr\":{\"options\":{\"config\":\"/etc/mongod.conf\",\"net\":{\"bindIp\":\"127.0.0.1\",\"port\":27001},\"processManagement\":{\"fork\":true,\"timeZoneInfo\":\"/usr/share/zoneinfo\"},\"replication\":{\"replSetName\":\"repl-shard1\"},\"sharding\":{\"clusterRole\":\"shardsvr\"},\"storage\":{\"dbPath\":\"/var/lib/mongo\",\"journal\":{\"enabled\":true},\"wiredTiger\":{\"engineConfig\":{\"cacheSizeGB\":0.1}}},\"systemLog\":{\"destination\":\"file\",\"logAppend\":true,\"path\":\"/var/log/mongodb/mongod.log\"}}}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:48.873+00:00\"},\"s\":\"I\",  \"c\":\"STORAGE\",  \"id\":22270,   \"ctx\":\"initandlisten\",\"msg\":\"Storage engine to use detected by data files\",\"attr\":{\"dbpath\":\"/var/lib/mongo\",\"storageEngine\":\"wiredTiger\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:48.873+00:00\"},\"s\":\"I\",  \"c\":\"STORAGE\",  \"id\":22315,   \"ctx\":\"initandlisten\",\"msg\":\"wiredtiger_open config\",\"attr\":{\"config\":\"create,cache_size=102M,session_max=33000,eviction=(threads_min=4,threads_max=4),config_base=false,statistics=(fast),log=(enabled=true,archive=true,path=journal,compressor=snappy),file_manager=(close_idle_time=100000,close_scan_interval=10,close_handle_minimum=250),statistics_log=(wait=0),verbose=[recovery_progress,checkpoint_progress,compact_progress],\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"CONNPOOL\", \"id\":22576,   \"ctx\":\"ReplicaSetMonitor-TaskExecutor\",\"msg\":\"Connecting\",\"attr\":{\"hostAndPort\":\"server1.example.com:27001\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"CONNPOOL\", \"id\":22576,   \"ctx\":\"ReplicaSetMonitor-TaskExecutor\",\"msg\":\"Connecting\",\"attr\":{\"hostAndPort\":\"server2.example.com:27001\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"CONNPOOL\", \"id\":22576,   \"ctx\":\"ReplicaSetMonitor-TaskExecutor\",\"msg\":\"Connecting\",\"attr\":{\"hostAndPort\":\"server3.example.com:27001\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"CONNPOOL\", \"id\":22576,   \"ctx\":\"ReplicaSetMonitor-TaskExecutor\",\"msg\":\"Connecting\",\"attr\":{\"hostAndPort\":\"server4.example.com:27001\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"CONNPOOL\", \"id\":22576,   \"ctx\":\"ReplicaSetMonitor-TaskExecutor\",\"msg\":\"Connecting\",\"attr\":{\"hostAndPort\":\"server5.example.com:27001\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"CONNPOOL\", \"id\":22576,   \"ctx\":\"ReplicaSetMonitor-TaskExecutor\",\"msg\":\"Connecting\",\"attr\":{\"hostAndPort\":\"server6.example.com:27001\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"NETWORK\",  \"id\":23015,   \"ctx\":\"listener\",\"msg\":\"Listening on\",\"attr\":{\"address\":\"/tmp/mongodb-27001.sock\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"NETWORK\",  \"id\":23015,   \"ctx\":\"listener\",\"msg\":\"Listening on\",\"attr\":{\"address\":\"127.0.0.1\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:10:58.877+00:00\"},\"s\":\"I\",  \"c\":\"NETWORK\",  \"id\":23016,   \"ctx\":\"listener\",\"msg\":\"Waiting for connections\",\"attr\":{\"port\":27001,\"ssl\":\"off\"}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:15:10.392+00:00\"},\"s\":\"I\",  \"c\":\"NETWORK\",  \"id\":22943,   \"ctx\":\"listener\",\"msg\":\"connection accepted\",\"attr\":{\"remote\":\"127.0.0.1:35724\",\"sessionId\":67,\"connectionCount\":30}}",
              "{\"t\":{\"$date\":\"2020-05-19T19:15:10.393+00:00\"},\"s\":\"I\",  \"c\":\"NETWORK\",  \"id\":51800,   \"ctx\":\"conn67\",\"msg\":\"client metadata\",\"attr\":{\"remote\":\"127.0.0.1:35724\",\"client\":\"conn67\",\"doc\":{\"application\":{\"name\":\"MongoDB Shell\"},\"driver\":{\"name\":\"MongoDB Internal Client\",\"version\":\"4.4.0\"},\"os\":{\"type\":\"Linux\",\"name\":\"CentOS Linux release 8.0.1905 (Core) \",\"architecture\":\"x86_64\",\"version\":\"Kernel 4.18.0-80.11.2.el8_0.x86_64\"}}}}"
      ],
      "ok" : 1,
      "$gleStats" : {
              "lastOpTime" : Timestamp(<ts>),
              "electionId" : ObjectId(<id>)
      },
      "lastCommittedOpTime" : Timestamp(<ts>),
      "$configServerState" : {
              "opTime" : {
                      "ts" : Timestamp(<ts>),
                      "t" : NumberLong(8)
               }
      },
      "$clusterTime" : {
              "clusterTime" : Timestamp(<ts>),
              "signature" : {
                      "hash" : BinData(<bin>),
                      "keyId" : NumberLong(0)
               }
      },
      "operationTime" : Timestamp(<ts>)
}
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