350 lines
12 KiB
Markdown
350 lines
12 KiB
Markdown
# Logrus <img src="http://i.imgur.com/hTeVwmJ.png" width="40" height="40" alt=":walrus:" class="emoji" title=":walrus:"/> [](https://travis-ci.org/Sirupsen/logrus) [][godoc]
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Logrus is a structured logger for Go (golang), completely API compatible with
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the standard library logger. [Godoc][godoc]. **Please note the Logrus API is not
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yet stable (pre 1.0). Logrus itself is completely stable and has been used in
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many large deployments. The core API is unlikely to change much but please
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version control your Logrus to make sure you aren't fetching latest `master` on
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every build.**
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Nicely color-coded in development (when a TTY is attached, otherwise just
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plain text):
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With `log.Formatter = new(logrus.JSONFormatter)`, for easy parsing by logstash
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or Splunk:
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```json
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{"animal":"walrus","level":"info","msg":"A group of walrus emerges from the
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ocean","size":10,"time":"2014-03-10 19:57:38.562264131 -0400 EDT"}
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{"level":"warning","msg":"The group's number increased tremendously!",
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"number":122,"omg":true,"time":"2014-03-10 19:57:38.562471297 -0400 EDT"}
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{"animal":"walrus","level":"info","msg":"A giant walrus appears!",
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"size":10,"time":"2014-03-10 19:57:38.562500591 -0400 EDT"}
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{"animal":"walrus","level":"info","msg":"Tremendously sized cow enters the ocean.",
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"size":9,"time":"2014-03-10 19:57:38.562527896 -0400 EDT"}
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{"level":"fatal","msg":"The ice breaks!","number":100,"omg":true,
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"time":"2014-03-10 19:57:38.562543128 -0400 EDT"}
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```
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With the default `log.Formatter = new(logrus.TextFormatter)` when a TTY is not
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attached, the output is compatible with the
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[logfmt](http://godoc.org/github.com/kr/logfmt) format:
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```text
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time="2015-03-26T01:27:38-04:00" level=debug msg="Started observing beach" animal=walrus number=8
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time="2015-03-26T01:27:38-04:00" level=info msg="A group of walrus emerges from the ocean" animal=walrus size=10
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time="2015-03-26T01:27:38-04:00" level=warning msg="The group's number increased tremendously!" number=122 omg=true
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time="2015-03-26T01:27:38-04:00" level=debug msg="Temperature changes" temperature=-4
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time="2015-03-26T01:27:38-04:00" level=panic msg="It's over 9000!" animal=orca size=9009
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time="2015-03-26T01:27:38-04:00" level=fatal msg="The ice breaks!" err=&{0x2082280c0 map[animal:orca size:9009] 2015-03-26 01:27:38.441574009 -0400 EDT panic It's over 9000!} number=100 omg=true
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exit status 1
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```
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#### Example
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The simplest way to use Logrus is simply the package-level exported logger:
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```go
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package main
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import (
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log "github.com/Sirupsen/logrus"
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)
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func main() {
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log.WithFields(log.Fields{
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"animal": "walrus",
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}).Info("A walrus appears")
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}
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```
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Note that it's completely api-compatible with the stdlib logger, so you can
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replace your `log` imports everywhere with `log "github.com/Sirupsen/logrus"`
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and you'll now have the flexibility of Logrus. You can customize it all you
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want:
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```go
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package main
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import (
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"os"
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log "github.com/Sirupsen/logrus"
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"github.com/Sirupsen/logrus/hooks/airbrake"
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)
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func init() {
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// Log as JSON instead of the default ASCII formatter.
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log.SetFormatter(&log.JSONFormatter{})
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// Use the Airbrake hook to report errors that have Error severity or above to
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// an exception tracker. You can create custom hooks, see the Hooks section.
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log.AddHook(airbrake.NewHook("https://example.com", "xyz", "development"))
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// Output to stderr instead of stdout, could also be a file.
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log.SetOutput(os.Stderr)
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// Only log the warning severity or above.
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log.SetLevel(log.WarnLevel)
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}
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func main() {
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log.WithFields(log.Fields{
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"animal": "walrus",
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"size": 10,
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}).Info("A group of walrus emerges from the ocean")
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log.WithFields(log.Fields{
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"omg": true,
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"number": 122,
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}).Warn("The group's number increased tremendously!")
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log.WithFields(log.Fields{
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"omg": true,
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"number": 100,
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}).Fatal("The ice breaks!")
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// A common pattern is to re-use fields between logging statements by re-using
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// the logrus.Entry returned from WithFields()
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contextLogger := log.WithFields(log.Fields{
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"common": "this is a common field",
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"other": "I also should be logged always",
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})
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contextLogger.Info("I'll be logged with common and other field")
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contextLogger.Info("Me too")
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}
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```
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For more advanced usage such as logging to multiple locations from the same
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application, you can also create an instance of the `logrus` Logger:
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```go
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package main
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import (
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"github.com/Sirupsen/logrus"
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)
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// Create a new instance of the logger. You can have any number of instances.
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var log = logrus.New()
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func main() {
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// The API for setting attributes is a little different than the package level
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// exported logger. See Godoc.
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log.Out = os.Stderr
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log.WithFields(logrus.Fields{
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"animal": "walrus",
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"size": 10,
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}).Info("A group of walrus emerges from the ocean")
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}
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```
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#### Fields
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Logrus encourages careful, structured logging though logging fields instead of
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long, unparseable error messages. For example, instead of: `log.Fatalf("Failed
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to send event %s to topic %s with key %d")`, you should log the much more
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discoverable:
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```go
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log.WithFields(log.Fields{
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"event": event,
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"topic": topic,
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"key": key,
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}).Fatal("Failed to send event")
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```
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We've found this API forces you to think about logging in a way that produces
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much more useful logging messages. We've been in countless situations where just
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a single added field to a log statement that was already there would've saved us
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hours. The `WithFields` call is optional.
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In general, with Logrus using any of the `printf`-family functions should be
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seen as a hint you should add a field, however, you can still use the
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`printf`-family functions with Logrus.
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#### Hooks
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You can add hooks for logging levels. For example to send errors to an exception
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tracking service on `Error`, `Fatal` and `Panic`, info to StatsD or log to
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multiple places simultaneously, e.g. syslog.
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Logrus comes with [built-in hooks](hooks/). Add those, or your custom hook, in
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`init`:
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```go
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import (
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log "github.com/Sirupsen/logrus"
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"github.com/Sirupsen/logrus/hooks/airbrake"
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"github.com/Sirupsen/logrus/hooks/syslog"
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"log/syslog"
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)
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func init() {
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log.AddHook(airbrake.NewHook("https://example.com", "xyz", "development"))
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hook, err := logrus_syslog.NewSyslogHook("udp", "localhost:514", syslog.LOG_INFO, "")
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if err != nil {
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log.Error("Unable to connect to local syslog daemon")
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} else {
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log.AddHook(hook)
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}
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}
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```
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| Hook | Description |
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| ----- | ----------- |
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| [Airbrake](https://github.com/Sirupsen/logrus/blob/master/hooks/airbrake/airbrake.go) | Send errors to an exception tracking service compatible with the Airbrake API. Uses [`airbrake-go`](https://github.com/tobi/airbrake-go) behind the scenes. |
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| [Papertrail](https://github.com/Sirupsen/logrus/blob/master/hooks/papertrail/papertrail.go) | Send errors to the Papertrail hosted logging service via UDP. |
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| [Syslog](https://github.com/Sirupsen/logrus/blob/master/hooks/syslog/syslog.go) | Send errors to remote syslog server. Uses standard library `log/syslog` behind the scenes. |
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| [BugSnag](https://github.com/Sirupsen/logrus/blob/master/hooks/bugsnag/bugsnag.go) | Send errors to the Bugsnag exception tracking service. |
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| [Hiprus](https://github.com/nubo/hiprus) | Send errors to a channel in hipchat. |
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| [Logrusly](https://github.com/sebest/logrusly) | Send logs to [Loggly](https://www.loggly.com/) |
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| [Slackrus](https://github.com/johntdyer/slackrus) | Hook for Slack chat. |
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| [Journalhook](https://github.com/wercker/journalhook) | Hook for logging to `systemd-journald` |
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| [Graylog](https://github.com/gemnasium/logrus-hooks/tree/master/graylog) | Hook for logging to [Graylog](http://graylog2.org/) |
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#### Level logging
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Logrus has six logging levels: Debug, Info, Warning, Error, Fatal and Panic.
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```go
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log.Debug("Useful debugging information.")
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log.Info("Something noteworthy happened!")
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log.Warn("You should probably take a look at this.")
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log.Error("Something failed but I'm not quitting.")
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// Calls os.Exit(1) after logging
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log.Fatal("Bye.")
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// Calls panic() after logging
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log.Panic("I'm bailing.")
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```
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You can set the logging level on a `Logger`, then it will only log entries with
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that severity or anything above it:
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```go
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// Will log anything that is info or above (warn, error, fatal, panic). Default.
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log.SetLevel(log.InfoLevel)
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```
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It may be useful to set `log.Level = logrus.DebugLevel` in a debug or verbose
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environment if your application has that.
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#### Entries
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Besides the fields added with `WithField` or `WithFields` some fields are
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automatically added to all logging events:
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1. `time`. The timestamp when the entry was created.
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2. `msg`. The logging message passed to `{Info,Warn,Error,Fatal,Panic}` after
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the `AddFields` call. E.g. `Failed to send event.`
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3. `level`. The logging level. E.g. `info`.
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#### Environments
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Logrus has no notion of environment.
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If you wish for hooks and formatters to only be used in specific environments,
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you should handle that yourself. For example, if your application has a global
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variable `Environment`, which is a string representation of the environment you
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could do:
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```go
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import (
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log "github.com/Sirupsen/logrus"
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)
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init() {
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// do something here to set environment depending on an environment variable
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// or command-line flag
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if Environment == "production" {
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log.SetFormatter(logrus.JSONFormatter)
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} else {
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// The TextFormatter is default, you don't actually have to do this.
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log.SetFormatter(logrus.TextFormatter)
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}
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}
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```
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This configuration is how `logrus` was intended to be used, but JSON in
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production is mostly only useful if you do log aggregation with tools like
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Splunk or Logstash.
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#### Formatters
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The built-in logging formatters are:
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* `logrus.TextFormatter`. Logs the event in colors if stdout is a tty, otherwise
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without colors.
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* *Note:* to force colored output when there is no TTY, set the `ForceColors`
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field to `true`. To force no colored output even if there is a TTY set the
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`DisableColors` field to `true`
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* `logrus.JSONFormatter`. Logs fields as JSON.
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* `logrus_logstash.LogstashFormatter`. Logs fields as Logstash Events (http://logstash.net).
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```go
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logrus.SetFormatter(&logrus_logstash.LogstashFormatter{Type: “application_name"})
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```
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Third party logging formatters:
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* [`zalgo`](https://github.com/aybabtme/logzalgo): invoking the P͉̫o̳̼̊w̖͈̰͎e̬͔̭͂r͚̼̹̲ ̫͓͉̳͈ō̠͕͖̚f̝͍̠ ͕̲̞͖͑Z̖̫̤̫ͪa͉̬͈̗l͖͎g̳̥o̰̥̅!̣͔̲̻͊̄ ̙̘̦̹̦.
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You can define your formatter by implementing the `Formatter` interface,
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requiring a `Format` method. `Format` takes an `*Entry`. `entry.Data` is a
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`Fields` type (`map[string]interface{}`) with all your fields as well as the
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default ones (see Entries section above):
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```go
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type MyJSONFormatter struct {
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}
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log.SetFormatter(new(MyJSONFormatter))
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func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
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// Note this doesn't include Time, Level and Message which are available on
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// the Entry. Consult `godoc` on information about those fields or read the
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// source of the official loggers.
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serialized, err := json.Marshal(entry.Data)
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if err != nil {
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return nil, fmt.Errorf("Failed to marshal fields to JSON, %v", err)
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}
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return append(serialized, '\n'), nil
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}
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```
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#### Logger as an `io.Writer`
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Logrus can be transormed into an `io.Writer`. That writer is the end of an `io.Pipe` and it is your responsibility to close it.
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```go
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w := logger.Writer()
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defer w.Close()
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srv := http.Server{
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// create a stdlib log.Logger that writes to
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// logrus.Logger.
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ErrorLog: log.New(w, "", 0),
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}
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```
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Each line written to that writer will be printed the usual way, using formatters
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and hooks. The level for those entries is `info`.
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#### Rotation
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Log rotation is not provided with Logrus. Log rotation should be done by an
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external program (like `logrotate(8)`) that can compress and delete old log
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entries. It should not be a feature of the application-level logger.
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[godoc]: https://godoc.org/github.com/Sirupsen/logrus
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