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嘿!为你的应用创建滚动日志吧?

等你归去来 2019-02-01 14:44:00 阅读数:300 评论数:0 点赞数:0 收藏数:0

一般作为服务端的应用,必须要有相应的日志,否则问题怎么排查呢?

而日志怎么打印,也是一个技术活。不然java中也不会存在N多厂商争相提供日志框架了!

而日志滚动则往往也是刚需,毕竟没人能保证日志的量及可阅读性。日志滚动实现主要有两个大方向:

1.  让应用服务自行打印,打印到哪里也完全由应用决定!

2. 借助第三方的工具进行日志打印,这种一般要借助于控制台或者agent!

3. 让日志框架提供日志滚动功能,自行管理日志;这样做有个好处就是,应用自带,无需外部处理。坏处就是要完全依赖该应用,会影响该应用的性能,且如果该应用存在bug,则功能就不敢保证了。(稍后我会以logback的日志滚动说明)

4. 借助第三方的工具进行日志滚动;这样做的好处是滚动功能更独立,对代码无入侵,即使真的有问题,大不了把它干掉也没关系;另外,第三方工具不会因为应用本身的bug而导致滚动异常,从而保证了有足够的排查依据。(稍后我会以cronolog进行讲解滚动实现);

  

具体日志滚动实现

1. 使用应用打印的方式:如logback的rollingpolicy,则自带滚动日志功能!但是坑多!

1.1. 首先我们看下日志滚动的配置:(在 logback.xml 配置)

 <!--输出到文件-->
<appender name="file" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${log_path}/api.ln.log</file>
<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy" >
<fileNamePattern>${log_path}/api.%d{yyyy-MM-dd_HH}.log</fileNamePattern>
<!-- keep 10 days' worth of history capped at 8GB total size -->
<maxHistory>10</maxHistory>
<totalSizeCap>8GB</totalSizeCap>
</rollingPolicy>
<encoder>
<pattern>%d{MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>

这里配置以时间为滚动标准,每小时滚动一次!最大保留10天日志,总共大小不超过8G。我们后面来看下他的效果!

1.2. 看下滚动代码!

首先,日志滚动会有相应的线程一直在跑(不管是应用实现还是第三方实现都是这样,否则怎么随时检测滚动时机呢)!

  在 EventPlayer中,有个play方法,此时会决断是否是 EndEvent, 如果是的话就会调用后台线程生成!

 // ch.qos.logback.core.joran.spi.EventPlayer
public void play(List<SaxEvent> aSaxEventList) {
eventList = aSaxEventList;
SaxEvent se;
for (currentIndex = 0; currentIndex < eventList.size(); currentIndex++) {
se = eventList.get(currentIndex);
if (se instanceof StartEvent) {
interpreter.startElement((StartEvent) se);
// invoke fireInPlay after startElement processing
 interpreter.getInterpretationContext().fireInPlay(se);
}
if (se instanceof BodyEvent) {
// invoke fireInPlay before characters processing
 interpreter.getInterpretationContext().fireInPlay(se);
interpreter.characters((BodyEvent) se);
}
// rollingPollicy 在此处调唤醒
if (se instanceof EndEvent) {
// invoke fireInPlay before endElement processing
 interpreter.getInterpretationContext().fireInPlay(se);
interpreter.endElement((EndEvent) se);
}
}
}

然后,几经转换,就到了Interpreter 了,这里会做一个死循环,一直在监听!

 // ch.qos.logback.core.joran.spi.Interpreter
private void callEndAction(List<Action> applicableActionList, String tagName) {
if (applicableActionList == null) {
return;
}
// logger.debug("About to call end actions on node: [" + localName + "]");
Iterator<Action> i = applicableActionList.iterator();
while (i.hasNext()) {
Action action = i.next();
// now let us invoke the end method of the action. We catch and report
// any eventual exceptions
try {
action.end(interpretationContext, tagName);
} catch (ActionException ae) {
// at this point endAction, there is no point in skipping children as
// they have been already processed
cai.addError("ActionException in Action for tag [" + tagName + "]", ae);
} catch (RuntimeException e) {
// no point in setting skip
cai.addError("RuntimeException in Action for tag [" + tagName + "]", e);
}
}
}

最后,就会调用 RollingPolicy 的start()了,这里是 TimeBasedRollingPollicy .

 // ch.qos.logback.core.rolling.TimeBasedRollingPolicy
public void start() {
// set the LR for our utility object
renameUtil.setContext(this.context);
// find out period from the filename pattern
if (fileNamePatternStr != null) {
fileNamePattern = new FileNamePattern(fileNamePatternStr, this.context);
determineCompressionMode();
} else {
addWarn(FNP_NOT_SET);
addWarn(CoreConstants.SEE_FNP_NOT_SET);
throw new IllegalStateException(FNP_NOT_SET + CoreConstants.SEE_FNP_NOT_SET);
}
compressor = new Compressor(compressionMode);
compressor.setContext(context);
// wcs : without compression suffix
fileNamePatternWithoutCompSuffix = new FileNamePattern(Compressor.computeFileNameStrWithoutCompSuffix(fileNamePatternStr, compressionMode), this.context);
addInfo("Will use the pattern " + fileNamePatternWithoutCompSuffix + " for the active file");
if (compressionMode == CompressionMode.ZIP) {
String zipEntryFileNamePatternStr = transformFileNamePattern2ZipEntry(fileNamePatternStr);
zipEntryFileNamePattern = new FileNamePattern(zipEntryFileNamePatternStr, context);
}
// 默认会使用 DefaultTimeBasedFileNamingAndTriggeringPolicy 进行滚动
if (timeBasedFileNamingAndTriggeringPolicy == null) {
timeBasedFileNamingAndTriggeringPolicy = new DefaultTimeBasedFileNamingAndTriggeringPolicy<E>();
}
timeBasedFileNamingAndTriggeringPolicy.setContext(context);
timeBasedFileNamingAndTriggeringPolicy.setTimeBasedRollingPolicy(this);
timeBasedFileNamingAndTriggeringPolicy.start();
if (!timeBasedFileNamingAndTriggeringPolicy.isStarted()) {
addWarn("Subcomponent did not start. TimeBasedRollingPolicy will not start.");
return;
}
// the maxHistory property is given to TimeBasedRollingPolicy instead of to
// the TimeBasedFileNamingAndTriggeringPolicy. This makes it more convenient
// for the user at the cost of inconsistency here.
if (maxHistory != UNBOUND_HISTORY) {
archiveRemover = timeBasedFileNamingAndTriggeringPolicy.getArchiveRemover();
archiveRemover.setMaxHistory(maxHistory);
archiveRemover.setTotalSizeCap(totalSizeCap.getSize());
if (cleanHistoryOnStart) {
addInfo("Cleaning on start up");
Date now = new Date(timeBasedFileNamingAndTriggeringPolicy.getCurrentTime());
cleanUpFuture = archiveRemover.cleanAsynchronously(now);
}
} else if (!isUnboundedTotalSizeCap()) {
addWarn("'maxHistory' is not set, ignoring 'totalSizeCap' option with value ["+totalSizeCap+"]");
}
// 调用父类start(), 设置启动标识,不允许多次调用初始化
super.start();
}
// DefaultTimeBasedFileNamingAndTriggeringPolicy 的实现,设置类功能主要还是调用 TimeBasedFileNamingAndTriggeringPolicy 的方法,而其自身,则是处理一些异常情况,以及开启一个 Remover, 供具体的实现调用
 @Override
public void start() {
super.start();
if (!super.isErrorFree())
return;
if(tbrp.fileNamePattern.hasIntegerTokenCOnverter()) {
addError("Filename pattern ["+tbrp.fileNamePattern+"] contains an integer token converter, i.e. %i, INCOMPATIBLE with this configuration. Remove it.");
return;
}
archiveRemover = new TimeBasedArchiveRemover(tbrp.fileNamePattern, rc);
archiveRemover.setContext(context);
started = true;
}
// TimeBasedFileNamingAndTriggeringPolicy, 则实际处理日志的滚动逻辑了
public void start() {
DateTokenConverter<Object> dtc = tbrp.fileNamePattern.getPrimaryDateTokenConverter();
if (dtc == null) {
throw new IllegalStateException("FileNamePattern [" + tbrp.fileNamePattern.getPattern() + "] does not contain a valid DateToken");
}
if (dtc.getTimeZone() != null) {
rc = new RollingCalendar(dtc.getDatePattern(), dtc.getTimeZone(), Locale.getDefault());
} else {
rc = new RollingCalendar(dtc.getDatePattern());
}
addInfo("The date pattern is '" + dtc.getDatePattern() + "' from file name pattern '" + tbrp.fileNamePattern.getPattern() + "'.");
rc.printPeriodicity(this);
if (!rc.isCollisionFree()) {
addError("The date format in FileNamePattern will result in collisions in the names of archived log files.");
addError(CoreConstants.MORE_INFO_PREFIX + COLLIDING_DATE_FORMAT_URL);
withErrors();
return;
}
setDateInCurrentPeriod(new Date(getCurrentTime()));
if (tbrp.getParentsRawFileProperty() != null) {
File currentFile = new File(tbrp.getParentsRawFileProperty());
if (currentFile.exists() && currentFile.canRead()) {
setDateInCurrentPeriod(new Date(currentFile.lastModified()));
}
}
addInfo("Setting initial period to " + dateInCurrentPeriod);
computeNextCheck();
}

经过如上初始化动作之后,发现并没有启动相应的轮循线程,所以这个点也是超出简单的认知了,不管怎么样,我们还要继续的!我们先来看一下 RollingFileAppender 的 append() 逻辑吧,毕竟它才是log的接入口!

 // ch.qos.logback.core.ch.qos.logback.core.rolling.RollingFileAppender, 其接入口为: UnsynchronizedAppenderBase.doAppend()
// ch.qos.logback.core.OutputStreamAppender
 @Override
protected void append(E eventObject) {
if (!isStarted()) {
return;
}
// 调用 RollingFileAppender 实现
 subAppend(eventObject);
}
// ch.qos.logback.core.ch.qos.logback.core.rolling.RollingFileAppender
 @Override
protected void subAppend(E event) {
// The roll-over check must precede actual writing. This is the
// only correct behavior for time driven triggers.
// We need to synchronize on triggeringPolicy so that only one rollover
// occurs at a time
synchronized (triggeringPolicy) {
if (triggeringPolicy.isTriggeringEvent(currentlyActiveFile, event)) {
rollover();
}
}
super.subAppend(event);
}

其中,rollover()就是其滚动逻辑!

所以,看到了吧!这里的文件滚动,是依赖于外部写入的,原因是为了写入的线程安全,保证文件的完整性!

换句话说就是,如果在滚动的这个时机,如果有外部写入,那么,文件得以滚动,否则,不会主动滚动文件!如果外部一直没日志写入,就不会存在日志滚动!

我们先来看下滚动的条件吧: triggeringPolicy.isTriggeringEvent(currentlyActiveFile, event)

 // ch.qos.logback.core.rolling.DefaultTimeBasedFileNamingAndTriggeringPolicy
public boolean isTriggeringEvent(File activeFile, final E event) {
long time = getCurrentTime();
if (time >= nextCheck) {
Date dateOfElapsedPeriod = dateInCurrentPeriod;
addInfo("Elapsed period: " + dateOfElapsedPeriod);
elapsedPeriodsFileName = tbrp.fileNamePatternWithoutCompSuffix.convert(dateOfElapsedPeriod);
setDateInCurrentPeriod(time);
computeNextCheck();
return true;
} else {
return false;
}
}

如上判断,即将当前时间与需要滚动的时间做对,大于滚动时间则返回 true, 并计算出下次需要滚动的时间,备用!

接下来,我们看下,具体的文件滚动实现!两个主逻辑: 1. 将文件更名滚动; 2. 重新创建一个新的目标文件,以使后续可以写入!

 /**
* Implemented by delegating most of the rollover work to a rolling policy.
*/
public void rollover() {
// 此处lock为 ReentrantLock, 即是互斥锁,只能一个线程可访问!
 lock.lock();
try {
// Note: This method needs to be synchronized because it needs exclusive
// access while it closes and then re-opens the target file.
//
// make sure to close the hereto active log file! Renaming under windows
// does not work for open files.
this.closeOutputStream();
attemptRollover();
attemptOpenFile();
} finally {
lock.unlock();
}
}
// 滚动文件逻辑,调用设置的 policy 实现进行滚动,此处我设置的是 TimeBasedRollingPolicy
private void attemptRollover() {
try {
rollingPolicy.rollover();
} catch (RolloverFailure rf) {
addWarn("RolloverFailure occurred. Deferring roll-over.");
// we failed to roll-over, let us not truncate and risk data loss
this.append = true;
}
}
// ch.qos.logback.core.rolling.TimeBasedRollingPolicy rollover
public void rollover() throws RolloverFailure {
// when rollover is called the elapsed period's file has
// been already closed. This is a working assumption of this method.

String elapsedPeriodsFileName = timeBasedFileNamingAndTriggeringPolicy.getElapsedPeriodsFileName();
String elapsedPeriodStem = FileFilterUtil.afterLastSlash(elapsedPeriodsFileName);
if (compressionMode == CompressionMode.NONE) {
if (getParentsRawFileProperty() != null) {
renameUtil.rename(getParentsRawFileProperty(), elapsedPeriodsFileName);
} // else { nothing to do if CompressionMode == NONE and parentsRawFileProperty == null }
} else {
if (getParentsRawFileProperty() == null) {
compressionFuture = compressor.asyncCompress(elapsedPeriodsFileName, elapsedPeriodsFileName, elapsedPeriodStem);
} else {
compressionFuture = renameRawAndAsyncCompress(elapsedPeriodsFileName, elapsedPeriodStem);
}
}
if (archiveRemover != null) {
Date now = new Date(timeBasedFileNamingAndTriggeringPolicy.getCurrentTime());
this.cleanUpFuture = archiveRemover.cleanAsynchronously(now);
}
}

TimeBasedRollingPolicy 的滚动方式为,重命名文件即可!即先获取外部设置的主写文件,然后根据新文件命名规则,生成一个新路径,然后重命名文件!重命名也是有些讲究的,有兴趣的同学可以查看下其重命名的实现!

 

// ch.qos.logback.core.rolling.helper.RenameUtil
/**
* A relatively robust file renaming method which in case of failure due to
* src and target being on different volumes, falls back onto
* renaming by copying.
*
* @param src
* @param target
* @throws RolloverFailure
*/
public void rename(String src, String target) throws RolloverFailure {
if (src.equals(target)) {
addWarn("Source and target files are the same [" + src + "]. Skipping.");
return;
}
File srcFile = new File(src);
if (srcFile.exists()) {
// 如果目录不存在,会先去创建目录,所以你可以滚动到其他地方,而目录位置则不用管(权限除外)
File targetFile = new File(target);
createMissingTargetDirsIfNecessary(targetFile);
addInfo("Renaming file [" + srcFile + "] to [" + targetFile + "]");
boolean result = srcFile.renameTo(targetFile);
// 对于直接重命名失败,则会再次尝试,如果在不同的分区,则会使用一次文件复制的方式进行一次重命名,具体做法是,先把文件copy到新地址,然后再将当前文件删除
if (!result) {
addWarn("Failed to rename file [" + srcFile + "] as [" + targetFile + "].");
Boolean areOnDifferentVolumes = areOnDifferentVolumes(srcFile, targetFile);
if (Boolean.TRUE.equals(areOnDifferentVolumes)) {
addWarn("Detected different file systems for source [" + src + "] and target [" + target + "]. Attempting rename by copying.");
renameByCopying(src, target);
return;
} else {
addWarn("Please consider leaving the [file] option of " + RollingFileAppender.class.getSimpleName() + " empty.");
addWarn("See also " + RENAMING_ERROR_URL);
}
}
} else {
throw new RolloverFailure("File [" + src + "] does not exist.");
}
}

在做完日志重命名的滚动后,还有一个可能的工作,就是删除过期的日志!这个工作由 archiveRemover 来做,即之前在 DefaultTimeBasedFileNamingAndTriggeringPolicy 中创建的实例! 会调用其 archiveRemover.cleanAsynchronously(now);

 public Future<?> cleanAsynchronously(Date now) {
ArhiveRemoverRunnable runnable = new ArhiveRemoverRunnable(now);
ExecutorService executorService = context.getScheduledExecutorService();
Future<?> future = executorService.submit(runnable);
return future;
}

在做删除过期日志时,会先获取一个 ExecutorService, 进行异步删除, 而这个 ExecutorService 默认开启 8 常驻线程,进行日志处理!

删除动作进行异步执行,从而避免影响业务执行!清理过程如下:

 public class ArhiveRemoverRunnable implements Runnable {
Date now;
ArhiveRemoverRunnable(Date now) {
this.now = now;
}
@Override
public void run() {
// 先清除当前文件,再根据设置的最大值,删除列表
 clean(now);
if (totalSizeCap != UNBOUNDED_TOTAL_SIZE_CAP && totalSizeCap > 0) {
capTotalSize(now);
}
}
}
public void clean(Date now) {
long nowInMillis = now.getTime();
// for a live appender periodsElapsed is expected to be 1
int periodsElapsed = computeElapsedPeriodsSinceLastClean(nowInMillis);
lastHeartBeat = nowInMillis;
if (periodsElapsed > 1) {
addInfo("Multiple periods, i.e. " + periodsElapsed + " periods, seem to have elapsed. This is expected at application start.");
}
for (int i = 0; i < periodsElapsed; i++) {
// 此处会根据 maxHistory 进行 -1 后清除文件,即: 只会清理 periodsElapsed 次历史日志
int offset = getPeriodOffsetForDeletionTarget() - i;
Date dateOfPeriodToClean = rc.getEndOfNextNthPeriod(now, offset);
cleanPeriod(dateOfPeriodToClean);
}
}
public void cleanPeriod(Date dateOfPeriodToClean) {
// 获取需要删除的文件列表,然后依次删除,如果文件夹内的文件全部被删除,则将文件夹删除
File[] matchingFileArray = getFilesInPeriod(dateOfPeriodToClean);
for (File f : matchingFileArray) {
addInfo("deleting " + f);
f.delete();
}
if (parentClean && matchingFileArray.length > 0) {
File parentDir = getParentDir(matchingFileArray[0]);
removeFolderIfEmpty(parentDir);
}
}
// 按规则匹配需要删除的文件
protected File[] getFilesInPeriod(Date dateOfPeriodToClean) {
String filenameToDelete = fileNamePattern.convert(dateOfPeriodToClean);
File file2Delete = new File(filenameToDelete);
if (fileExistsAndIsFile(file2Delete)) {
return new File[] { file2Delete };
} else {
return new File[0];
}
}
// 清理历史文件逻辑,注意要想清理历史文件,就一定要设置好 totalSizeCap, 否则,不会进行自动清理!
void capTotalSize(Date now) {
long totalSize = 0;
long totalRemoved = 0;
for (int offset = 0; offset < maxHistory; offset++) {
Date date = rc.getEndOfNextNthPeriod(now, -offset);
File[] matchingFileArray = getFilesInPeriod(date);
descendingSortByLastModified(matchingFileArray);
for (File f : matchingFileArray) {
long size = f.length();
if (totalSize + size > totalSizeCap) {
addInfo("Deleting [" + f + "]" + " of size " + new FileSize(size));
totalRemoved += size;
f.delete();
}
totalSize += size;
}
}
addInfo("Removed " + new FileSize(totalRemoved) + " of files");
}

以上就是一个删除过期日志的逻辑,主要有几个点:

1. 只会进行清理 maxHistory 个周期的日志,即只会倒推 n 个周期内的日志;
2. 只会清理文件大小大于 totalSizeCap 大小以后的文件;(这个文件强依赖文件列表的排序,这里的排序是根据最后修改时间来排的)
3. maxHistory 并非最大保留天数,不要相信坑货文档,它只是一个扫描周期而已,不过这个值在上一步清理时会处理一次!

还有个细节,咱们得再来看看:滚动时机,按天,按小时,按分钟?

 // 滚动时机判定
// ch.qos.logback.core.rolling.helper.RollingCalendar
public Date getEndOfNextNthPeriod(Date now, int periods) {
return innerGetEndOfNextNthPeriod(this, this.periodicityType, now, periods);
}
static private Date innerGetEndOfNextNthPeriod(Calendar cal, PeriodicityType periodicityType, Date now, int numPeriods) {
cal.setTime(now);
switch (periodicityType) {
case TOP_OF_MILLISECOND:
cal.add(Calendar.MILLISECOND, numPeriods);
break;
case TOP_OF_SECOND:
cal.set(Calendar.MILLISECOND, 0);
cal.add(Calendar.SECOND, numPeriods);
break;
case TOP_OF_MINUTE:
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.add(Calendar.MINUTE, numPeriods);
break;
case TOP_OF_HOUR:
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.add(Calendar.HOUR_OF_DAY, numPeriods);
break;
case TOP_OF_DAY:
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.add(Calendar.DATE, numPeriods);
break;
case TOP_OF_WEEK:
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.add(Calendar.WEEK_OF_YEAR, numPeriods);
break;
case TOP_OF_MONTH:
cal.set(Calendar.DATE, 1);
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.add(Calendar.MONTH, numPeriods);
break;
default:
throw new IllegalStateException("Unknown periodicity type.");
}
return cal.getTime();
}

可以看到其滚动的粒度: TOP_OF_MILLISECOND/TOP_OF_SECOND/TOP_OF_MINUTE/TOP_OF_HOUR/TOP_OF_DAY/TOP_OF_WEEK/TOP_OF_MONTH, 要说起来,粒度还是很细的哦!至于能不能真的有用,另说了!

总结下logback的滚动方式!

1. 在写入的时机进行滚动时机检查,合适则进行滚动;
2. 同步滚动操作,保证线程安全;
3. 使用重命名的方式进行滚动文件处理,如果失败会尝试一次不同分区的文件复制操作;
4. 删除过期日志有两个时机,一个是判断当前周期前 n 个周期文件,如果有则删除;
5. 对于设置了最大文件大小限制时,另外进行允许周期内的文件大小判定,超过大小后按修改时间最早删除;
6. 触发滚动时机后,进行异步删除,一般不影响业务;

第三方工具如: 经典版 cronolog, 时尚版 logrotate(麻烦)

cronolog 是一个很古老的日志滚动工具了(应该已经不维护了)。它可以接收应用的输出日志,然后按照规则进行日志存储,比如按照年月日时分秒来保存文件!

在网上其资料也已经不是很多了,很多人为了下载一个安装包也是绞尽脑汁啊!我也提供一个便捷安装包吧: 点此下载; 

其 github 项目地址: https://github.com/fordmason/cronolog , 你完全可以自己去下载一个完全的包,自己安装!

不过我还是要说一下其他两个安装方式:

1. 直接使用 yum 源安装;(好像是要安装 epel 源) (推荐)

yum install cronolog -y

2. 使用上面下载的包,直接解压即可

tar -zxvf cronolog-bin.tar.gz -C /

3. 使用网上别人提供的源码安装

hehe...

说了这么多,还不是为了使用,如何与应用结合?

其实只需要在你原来应用启动的后面再加上如下命令就可以了!

$> | /usr/local/sbin/cronolog -S /var/logs/ai_ln.out /var/logs/ai.%Y-%m-%d-%H.out

完整的操作示例如下:

exec nohup java -jar /www/aproj\.jar 2>&1 | /usr/local/sbin/cronolog -S /var/logs/ai_ln.out /var/logs/ai.%Y-%m-%d-%H.out >> /dev/null &

如上命令是网上大部分人是这么写的,但是在某些情况下会有问题。比如我想远程启动这个服务的时候,就会一直拿不到结果!为啥?反正写成下面这个就完美了!即在 cronolog 之后,再加一个重定向输出 2>&1 。

exec nohup java -jar /www/aproj\.jar 2>&1 | /usr/local/sbin/cronolog -S /var/logs/ai_ln.out /var/logs/ai.%Y-%m-%d-%H.out >> /dev/null 2>&1 &

那么,这个工具和应用自己输出日志相比,有什么好处吗?它是怎么实现的呢?

好处前面已经说了,对代码无侵入,控制更灵活!

其实现原理为,接收一个标准的输入流,然后写入到相应文件即可!它不负责文件的删除,所以删除过期文件还得依赖另外的脚本!

其主体源码如下:

/* Loop, waiting for data on standard input */
for (;;)
{
/**
* Read a buffer's worth of log file data, exiting on errors
* or end of file.
*/
n_bytes_read = read(0, read_buf, sizeof read_buf);
if (n_bytes_read == 0)
{
exit(3);
}
if (errno == EINTR)
{
continue;
}
else if (n_bytes_read < 0)
{
exit(4);
}
time_now = time(NULL) + time_offset;
/**
* If the current period has finished and there is a log file
* open, close the log file
*/
if ((time_now >= next_period) && (log_fd >= 0))
{
close(log_fd);
log_fd = -1;
}
/**
* If there is no log file open then open a new one.
*/
if (log_fd < 0)
{
log_fd = new_log_file(template, linkname, linktype, prevlinkname,
periodicity, period_multiple, period_delay,
filename, sizeof (filename), time_now, &next_period);
}
DEBUG(("%s (%d): wrote message; next period starts at %s (%d) in %d secs\n",
timestamp(time_now), time_now,
timestamp(next_period), next_period,
next_period - time_now));
/**
* Write out the log data to the current log file.
*/
if (write(log_fd, read_buf, n_bytes_read) != n_bytes_read)
{
perror(filename);
exit(5);
}
}

大概操作就是:

1. cronolog 进程开启后,会一直死循环,除非遇到错误如应用关闭等;
2. 阻塞从标准输入读取信息,读取到后,再进行文件操作;
3. 每次读取内容后判断是否到达需要新滚动的周期,如果到了,就把原来的文件close掉,并重新创建一个用于写的文件;
4. 只管向打开的文件中写入缓冲内容即可;
5. 所有读入数据是基于管道操作的,简单实用;

看起来很简单啊!会不会有什么问题呢?应该不会吧,它可是经过时间考验的哦。越是简单的,往往越是可靠的!

看着上面代码,有同学肯定要说了,这么简单的代码谁不会啊,自己顺手就来一个shell搞定。 且不论你的shell写得是否可靠,但是你基于 shell, 别人是基于c的,恐怕不是一个量级的哦!

最后,还有个问题我们要处理下,那就是过期日志的清理问题?

这个简单的脚本是不会给你做了,或者说我没有发现它有这功能;所以,只能自己写脚本清理了!一行代码搞定!

 # vim clean_log.sh
find /var/logs/ai -mtime +8 -name "ai.*out" -exec rm -rf {} \;
# 然后在 crontab 中加入执行时机即可,一般一天一次!
0 0 * * * sh clean_log.sh

搞定!

以上,就是一些日志滚动的实现及原理解析了!是不是有一种豁然开朗的感觉?哈哈。。

事情其实并没有想像中的难!

 

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https://www.cnblogs.com/yougewe/p/10343855.html

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