mirror of https://github.com/docker/cli.git
496 lines
18 KiB
Markdown
496 lines
18 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) [](https://godoc.org/github.com/sirupsen/logrus)
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Logrus is a structured logger for Go (golang), completely API compatible with
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the standard library logger.
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**Seeing weird case-sensitive problems?** It's in the past been possible to
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import Logrus as both upper- and lower-case. Due to the Go package environment,
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this caused issues in the community and we needed a standard. Some environments
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experienced problems with the upper-case variant, so the lower-case was decided.
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Everything using `logrus` will need to use the lower-case:
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`github.com/sirupsen/logrus`. Any package that isn't, should be changed.
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To fix Glide, see [these
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comments](https://github.com/sirupsen/logrus/issues/553#issuecomment-306591437).
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For an in-depth explanation of the casing issue, see [this
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comment](https://github.com/sirupsen/logrus/issues/570#issuecomment-313933276).
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**Are you interested in assisting in maintaining Logrus?** Currently I have a
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lot of obligations, and I am unable to provide Logrus with the maintainership it
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needs. If you'd like to help, please reach out to me at `simon at author's
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username dot com`.
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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.SetFormatter(&log.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.SetFormatter(&log.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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```
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To ensure this behaviour even if a TTY is attached, set your formatter as follows:
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```go
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log.SetFormatter(&log.TextFormatter{
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DisableColors: true,
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FullTimestamp: true,
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})
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```
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#### Logging Method Name
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If you wish to add the calling method as a field, instruct the logger via:
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```go
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log.SetReportCaller(true)
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```
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This adds the caller as 'method' like so:
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```json
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{"animal":"penguin","level":"fatal","method":"github.com/sirupsen/arcticcreatures.migrate","msg":"a penguin swims by",
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"time":"2014-03-10 19:57:38.562543129 -0400 EDT"}
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```
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```text
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time="2015-03-26T01:27:38-04:00" level=fatal method=github.com/sirupsen/arcticcreatures.migrate msg="a penguin swims by" animal=penguin
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```
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Note that this does add measurable overhead - the cost will depend on the version of Go, but is
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between 20 and 40% in recent tests with 1.6 and 1.7. You can validate this in your
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environment via benchmarks:
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```
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go test -bench=.*CallerTracing
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```
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#### Case-sensitivity
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The organization's name was changed to lower-case--and this will not be changed
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back. If you are getting import conflicts due to case sensitivity, please use
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the lower-case import: `github.com/sirupsen/logrus`.
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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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)
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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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// Output to stdout instead of the default stderr
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// Can be any io.Writer, see below for File example
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log.SetOutput(os.Stdout)
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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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"os"
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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.Stdout
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// You could set this to any `io.Writer` such as a file
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// file, err := os.OpenFile("logrus.log", os.O_CREATE|os.O_WRONLY, 0666)
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// if err == nil {
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// log.Out = file
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// } else {
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// log.Info("Failed to log to file, using default stderr")
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// }
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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 through 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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#### Default Fields
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Often it's helpful to have fields _always_ attached to log statements in an
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application or parts of one. For example, you may want to always log the
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`request_id` and `user_ip` in the context of a request. Instead of writing
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`log.WithFields(log.Fields{"request_id": request_id, "user_ip": user_ip})` on
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every line, you can create a `logrus.Entry` to pass around instead:
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```go
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requestLogger := log.WithFields(log.Fields{"request_id": request_id, "user_ip": user_ip})
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requestLogger.Info("something happened on that request") # will log request_id and user_ip
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requestLogger.Warn("something not great happened")
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```
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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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"gopkg.in/gemnasium/logrus-airbrake-hook.v2" // the package is named "airbrake"
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logrus_syslog "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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// 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(123, "xyz", "production"))
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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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Note: Syslog hook also support connecting to local syslog (Ex. "/dev/log" or "/var/run/syslog" or "/var/run/log"). For the detail, please check the [syslog hook README](hooks/syslog/README.md).
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A list of currently known of service hook can be found in this wiki [page](https://github.com/sirupsen/logrus/wiki/Hooks)
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#### Level logging
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Logrus has seven logging levels: Trace, Debug, Info, Warning, Error, Fatal and Panic.
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```go
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log.Trace("Something very low level.")
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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(&log.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(&log.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`. For Windows, see
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[github.com/mattn/go-colorable](https://github.com/mattn/go-colorable).
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* When colors are enabled, levels are truncated to 4 characters by default. To disable
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truncation set the `DisableLevelTruncation` field to `true`.
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* All options are listed in the [generated docs](https://godoc.org/github.com/sirupsen/logrus#TextFormatter).
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* `logrus.JSONFormatter`. Logs fields as JSON.
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* All options are listed in the [generated docs](https://godoc.org/github.com/sirupsen/logrus#JSONFormatter).
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Third party logging formatters:
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* [`FluentdFormatter`](https://github.com/joonix/log). Formats entries that can be parsed by Kubernetes and Google Container Engine.
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* [`GELF`](https://github.com/fabienm/go-logrus-formatters). Formats entries so they comply to Graylog's [GELF 1.1 specification](http://docs.graylog.org/en/2.4/pages/gelf.html).
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* [`logstash`](https://github.com/bshuster-repo/logrus-logstash-hook). Logs fields as [Logstash](http://logstash.net) Events.
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* [`prefixed`](https://github.com/x-cray/logrus-prefixed-formatter). Displays log entry source along with alternative layout.
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* [`zalgo`](https://github.com/aybabtme/logzalgo). Invoking the P͉̫o̳̼̊w̖͈̰͎e̬͔̭͂r͚̼̹̲ ̫͓͉̳͈ō̠͕͖̚f̝͍̠ ͕̲̞͖͑Z̖̫̤̫ͪa͉̬͈̗l͖͎g̳̥o̰̥̅!̣͔̲̻͊̄ ̙̘̦̹̦.
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* [`nested-logrus-formatter`](https://github.com/antonfisher/nested-logrus-formatter). Converts logrus fields to a nested structure.
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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 *MyJSONFormatter) 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 transformed 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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This means that we can override the standard library logger easily:
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```go
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logger := logrus.New()
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logger.Formatter = &logrus.JSONFormatter{}
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// Use logrus for standard log output
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// Note that `log` here references stdlib's log
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// Not logrus imported under the name `log`.
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log.SetOutput(logger.Writer())
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```
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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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#### Tools
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| Tool | Description |
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| ---- | ----------- |
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|[Logrus Mate](https://github.com/gogap/logrus_mate)|Logrus mate is a tool for Logrus to manage loggers, you can initial logger's level, hook and formatter by config file, the logger will generated with different config at different environment.|
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|[Logrus Viper Helper](https://github.com/heirko/go-contrib/tree/master/logrusHelper)|An Helper around Logrus to wrap with spf13/Viper to load configuration with fangs! And to simplify Logrus configuration use some behavior of [Logrus Mate](https://github.com/gogap/logrus_mate). [sample](https://github.com/heirko/iris-contrib/blob/master/middleware/logrus-logger/example) |
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#### Testing
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Logrus has a built in facility for asserting the presence of log messages. This is implemented through the `test` hook and provides:
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* decorators for existing logger (`test.NewLocal` and `test.NewGlobal`) which basically just add the `test` hook
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* a test logger (`test.NewNullLogger`) that just records log messages (and does not output any):
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```go
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import(
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"github.com/sirupsen/logrus"
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"github.com/sirupsen/logrus/hooks/test"
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"github.com/stretchr/testify/assert"
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"testing"
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)
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func TestSomething(t*testing.T){
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logger, hook := test.NewNullLogger()
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logger.Error("Helloerror")
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assert.Equal(t, 1, len(hook.Entries))
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assert.Equal(t, logrus.ErrorLevel, hook.LastEntry().Level)
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assert.Equal(t, "Helloerror", hook.LastEntry().Message)
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hook.Reset()
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assert.Nil(t, hook.LastEntry())
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}
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```
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#### Fatal handlers
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Logrus can register one or more functions that will be called when any `fatal`
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level message is logged. The registered handlers will be executed before
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logrus performs a `os.Exit(1)`. This behavior may be helpful if callers need
|
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to gracefully shutdown. Unlike a `panic("Something went wrong...")` call which can be intercepted with a deferred `recover` a call to `os.Exit(1)` can not be intercepted.
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```
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...
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handler := func() {
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// gracefully shutdown something...
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}
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logrus.RegisterExitHandler(handler)
|
|
...
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|
```
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#### Thread safety
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By default, Logger is protected by a mutex for concurrent writes. The mutex is held when calling hooks and writing logs.
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If you are sure such locking is not needed, you can call logger.SetNoLock() to disable the locking.
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Situation when locking is not needed includes:
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|
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* You have no hooks registered, or hooks calling is already thread-safe.
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|
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* Writing to logger.Out is already thread-safe, for example:
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1) logger.Out is protected by locks.
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|
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2) logger.Out is a os.File handler opened with `O_APPEND` flag, and every write is smaller than 4k. (This allow multi-thread/multi-process writing)
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(Refer to http://www.notthewizard.com/2014/06/17/are-files-appends-really-atomic/)
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