Does standard module log do rotation

[ljh]

Hi forum,

I’m trying to use the standard log module to save log entries to file.

1. Does it support rotation? For example: mylog1.txt, mylog2.txt, mylog3.txt, …, and each file is 10M in size. In my code snippet, it is writing to a single log file and the file is already 3.1G.

2. Does it support log levels, like: log.info, log.error, …?

Thanks

package main

import (
	"log"
	"os"
)

func main() {
	var logfilename = "/Users/ljh/Documents/helloGo/mylog.txt"
	log.SetFlags(log.LstdFlags | log.Lshortfile)
	var logfile, err = os.OpenFile(logfilename, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
	if err != nil {
		log.Fatalf("OpenFile: %v", err)
	}
	defer logfile.Close()
	log.SetOutput(logfile)

	// for {
		log.Println("Hello World")
		//...
	//}
}

[NobbZ (Norbert Melzer)]

@ljh

Does it support rotation? For example: mylog1.txt, mylog2.txt, mylog3.txt, …, and each file is 10M in size. In my code snippet, it is writing to a single log file and the file is already 3.1G.

No, and should be dealt with by external tooling, those are battle tested… Best known examples are logrotated and systemd.

@ljh

Does it support log levels, like: log.info, log.error, …?

Kind of. It supports a common and a fatal log level.

If your requirements demand for more, then you need to find another logger. As I always have been a fan of JSON logging, I use zap whenever I need logging in a go project.

[ljh]

Thanks Norbert,

How is zap compared to glog which is under the golang directory.

[ljh]

I come up with some code using glog like the following. glog uses the standard log module. It seems that glog supports log rotation defaultly without change any settings.

package main

import (
	"flag"
	"github.com/golang/glog" //glog
	"os"
	"path"
	"path/filepath"
	"strings"
)

func main() {
	defer glog.Flush()
	flag.Parse()

	if strings.TrimSpace(flag.Lookup("log_dir").Value.String()) == "" {
		exe, _ := os.Executable()
		flag.Set("log_dir", path.Join(filepath.Dir(exe), "logs"))
	}
	flag.Set("alsologtostderr", "true")
	glog.Infof("log_dir: %s", flag.Lookup("log_dir").Value)

	glog.Infof("Info 日志: %s", "some info")
	glog.Warningf("Warning 日志: %s", "some warning")
	glog.Errorf("Error 日志: %s", "some error")
	// glog.Fatalf("Fatal 日志: %s", "some fatal")  // terminates the program

	// $ go build . && ./hello -log_dir="./logs" -v 4
	glog.V(1).Infof("V1 日志: %s", "some info")
	glog.V(2).Infof("V2 日志: %s", "some info")
	glog.V(3).Infof("V3 日志: %s", "some info")
	glog.V(4).Infof("V4 日志: %s", "some info")
}

/*
$ ls logs
hello.ERROR
hello.INFO
hello.Mac-mini.ljh.log.ERROR.20220402-231029.9073
hello.Mac-mini.ljh.log.INFO.20220402-231029.9073
hello.Mac-mini.ljh.log.WARNING.20220402-231029.9073
hello.WARNING
$
$ cat logs/hello.INFO
Log file created at: 2022/04/02 23:10:29
Running on machine: Mac-mini
Binary: Built with gc go1.18 for darwin/amd64
Log line format: [IWEF]mmdd hh:mm:ss.uuuuuu threadid file:line] msg
I0402 23:10:29.729131    9073 hello.go:22] log_dir: /Users/ljh/Documents/helloGo/logs
I0402 23:10:29.729662    9073 hello.go:24] Info 日志: some info
W0402 23:10:29.729674    9073 hello.go:25] Warning 日志: some warning
E0402 23:10:29.729936    9073 hello.go:26] Error 日志: some error
I0402 23:10:29.730170    9073 hello.go:30] V1 日志: some info
I0402 23:10:29.730180    9073 hello.go:31] V2 日志: some info
I0402 23:10:29.730185    9073 hello.go:32] V3 日志: some info
I0402 23:10:29.730190    9073 hello.go:33] V4 日志: some info
$
*/

[NobbZ (Norbert Melzer)]

Glog doesn’t seem to do JSON logging.