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-# 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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-
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-
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-With `log.SetFormatter(&log.JSONFormatter{})`, for easy parsing by logstash
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-or Splunk:
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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-#### Case-sensitivity
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-
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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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-
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-#### Example
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-
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-The simplest way to use Logrus is simply the package-level exported logger:
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-
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-```go
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-package main
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-
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-import (
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- log "github.com/sirupsen/logrus"
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-)
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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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-
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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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-
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-```go
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-package main
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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-```go
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-package main
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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-#### Fields
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-
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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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-
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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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-
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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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-
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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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-
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-#### Default Fields
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-
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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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-
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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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-
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-#### Hooks
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-
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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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-
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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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-
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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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-
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-func init() {
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-
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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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-
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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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-
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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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-
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-
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-#### Level logging
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-
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-Logrus has six logging levels: Debug, Info, Warning, Error, Fatal and Panic.
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-
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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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-
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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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-
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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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-
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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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-
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-#### Entries
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-
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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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-
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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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-
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-#### Environments
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-
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-Logrus has no notion of environment.
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-
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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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-
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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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-
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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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-
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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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-
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-#### Formatters
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-
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-The built-in logging formatters are:
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-
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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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-
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-Third party logging formatters:
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-
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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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-* [`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.
|
|
|
|
-* [`zalgo`](https://github.com/aybabtme/logzalgo). Invoking the P͉̫o̳̼̊w̖͈̰͎e̬͔̭͂r͚̼̹̲ ̫͓͉̳͈ō̠͕͖̚f̝͍̠ ͕̲̞͖͑Z̖̫̤̫ͪa͉̬͈̗l͖͎g̳̥o̰̥̅!̣͔̲̻͊̄ ̙̘̦̹̦.
|
|
|
|
-
|
|
|
|
-You can define your formatter by implementing the `Formatter` interface,
|
|
|
|
-requiring a `Format` method. `Format` takes an `*Entry`. `entry.Data` is a
|
|
|
|
-`Fields` type (`map[string]interface{}`) with all your fields as well as the
|
|
|
|
-default ones (see Entries section above):
|
|
|
|
-
|
|
|
|
-```go
|
|
|
|
-type MyJSONFormatter struct {
|
|
|
|
-}
|
|
|
|
-
|
|
|
|
-log.SetFormatter(new(MyJSONFormatter))
|
|
|
|
-
|
|
|
|
-func (f *MyJSONFormatter) Format(entry *Entry) ([]byte, error) {
|
|
|
|
- // Note this doesn't include Time, Level and Message which are available on
|
|
|
|
- // the Entry. Consult `godoc` on information about those fields or read the
|
|
|
|
- // source of the official loggers.
|
|
|
|
- serialized, err := json.Marshal(entry.Data)
|
|
|
|
- if err != nil {
|
|
|
|
- return nil, fmt.Errorf("Failed to marshal fields to JSON, %v", err)
|
|
|
|
- }
|
|
|
|
- return append(serialized, '\n'), nil
|
|
|
|
-}
|
|
|
|
-```
|
|
|
|
-
|
|
|
|
-#### Logger as an `io.Writer`
|
|
|
|
-
|
|
|
|
-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.
|
|
|
|
-
|
|
|
|
-```go
|
|
|
|
-w := logger.Writer()
|
|
|
|
-defer w.Close()
|
|
|
|
-
|
|
|
|
-srv := http.Server{
|
|
|
|
- // create a stdlib log.Logger that writes to
|
|
|
|
- // logrus.Logger.
|
|
|
|
- ErrorLog: log.New(w, "", 0),
|
|
|
|
-}
|
|
|
|
-```
|
|
|
|
-
|
|
|
|
-Each line written to that writer will be printed the usual way, using formatters
|
|
|
|
-and hooks. The level for those entries is `info`.
|
|
|
|
-
|
|
|
|
-This means that we can override the standard library logger easily:
|
|
|
|
-
|
|
|
|
-```go
|
|
|
|
-logger := logrus.New()
|
|
|
|
-logger.Formatter = &logrus.JSONFormatter{}
|
|
|
|
-
|
|
|
|
-// Use logrus for standard log output
|
|
|
|
-// Note that `log` here references stdlib's log
|
|
|
|
-// Not logrus imported under the name `log`.
|
|
|
|
-log.SetOutput(logger.Writer())
|
|
|
|
-```
|
|
|
|
-
|
|
|
|
-#### Rotation
|
|
|
|
-
|
|
|
|
-Log rotation is not provided with Logrus. Log rotation should be done by an
|
|
|
|
-external program (like `logrotate(8)`) that can compress and delete old log
|
|
|
|
-entries. It should not be a feature of the application-level logger.
|
|
|
|
-
|
|
|
|
-#### Tools
|
|
|
|
-
|
|
|
|
-| Tool | Description |
|
|
|
|
-| ---- | ----------- |
|
|
|
|
-|[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.|
|
|
|
|
-|[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) |
|
|
|
|
-
|
|
|
|
-#### Testing
|
|
|
|
-
|
|
|
|
-Logrus has a built in facility for asserting the presence of log messages. This is implemented through the `test` hook and provides:
|
|
|
|
-
|
|
|
|
-* decorators for existing logger (`test.NewLocal` and `test.NewGlobal`) which basically just add the `test` hook
|
|
|
|
-* a test logger (`test.NewNullLogger`) that just records log messages (and does not output any):
|
|
|
|
-
|
|
|
|
-```go
|
|
|
|
-import(
|
|
|
|
- "github.com/sirupsen/logrus"
|
|
|
|
- "github.com/sirupsen/logrus/hooks/test"
|
|
|
|
- "github.com/stretchr/testify/assert"
|
|
|
|
- "testing"
|
|
|
|
-)
|
|
|
|
-
|
|
|
|
-func TestSomething(t*testing.T){
|
|
|
|
- logger, hook := test.NewNullLogger()
|
|
|
|
- logger.Error("Helloerror")
|
|
|
|
-
|
|
|
|
- assert.Equal(t, 1, len(hook.Entries))
|
|
|
|
- assert.Equal(t, logrus.ErrorLevel, hook.LastEntry().Level)
|
|
|
|
- assert.Equal(t, "Helloerror", hook.LastEntry().Message)
|
|
|
|
-
|
|
|
|
- hook.Reset()
|
|
|
|
- assert.Nil(t, hook.LastEntry())
|
|
|
|
-}
|
|
|
|
-```
|
|
|
|
-
|
|
|
|
-#### Fatal handlers
|
|
|
|
-
|
|
|
|
-Logrus can register one or more functions that will be called when any `fatal`
|
|
|
|
-level message is logged. The registered handlers will be executed before
|
|
|
|
-logrus performs a `os.Exit(1)`. This behavior may be helpful if callers need
|
|
|
|
-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.
|
|
|
|
-
|
|
|
|
-```
|
|
|
|
-...
|
|
|
|
-handler := func() {
|
|
|
|
- // gracefully shutdown something...
|
|
|
|
-}
|
|
|
|
-logrus.RegisterExitHandler(handler)
|
|
|
|
-...
|
|
|
|
-```
|
|
|
|
-
|
|
|
|
-#### Thread safety
|
|
|
|
-
|
|
|
|
-By default, Logger is protected by a mutex for concurrent writes. The mutex is held when calling hooks and writing logs.
|
|
|
|
-If you are sure such locking is not needed, you can call logger.SetNoLock() to disable the locking.
|
|
|
|
-
|
|
|
|
-Situation when locking is not needed includes:
|
|
|
|
-
|
|
|
|
-* You have no hooks registered, or hooks calling is already thread-safe.
|
|
|
|
-
|
|
|
|
-* Writing to logger.Out is already thread-safe, for example:
|
|
|
|
-
|
|
|
|
- 1) logger.Out is protected by locks.
|
|
|
|
-
|
|
|
|
- 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)
|
|
|
|
-
|
|
|
|
- (Refer to http://www.notthewizard.com/2014/06/17/are-files-appends-really-atomic/)
|
|
|