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[#]: subject: "How to Monitor Log Files in Real Time in Linux [Desktop and Server]"
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[#]: via: "https://www.debugpoint.com/2021/08/monitor-log-files-real-time/"
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[#]: author: "Arindam https://www.debugpoint.com/author/admin1/"
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[#]: collector: "lujun9972"
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[#]: translator: "geekpi"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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How to Monitor Log Files in Real Time in Linux [Desktop and Server]
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======
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This tutorial explains how you can monitor Linux log files (desktop,
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server or applications) in real time for diagnosis and troubleshooting
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purpose.Basic SyntaxUsage
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When you ran into problems in your Linux desktop, or server or any application, you first look into the respective log files. The log files are generally a stream of text and messages from applications with a timestamp attached to it. It helps you to narrow down specific instances and helps you find the cause of any problem. It can also help to get assistance from the web as well.
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In general, all log files are located in /var/log. This directory contains log files with extension .log for specific applications, services, and it also contains separate other directories which contains their log files.
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![log files in var-log][1]
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So, that said, if you want to monitor a bunch of log files Or, a specific one – here’s are some ways how you can do it.
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### Monitor Log Files in real time – Linux
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#### Using tail command
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Using the tail command is the most basic way of following a log file in real time. Specially, if you are in a server with only just a terminal, no GUI. This is very helpful.
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Examples:
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```
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tail /path/to/log/file
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```
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![Monitoring multiple log files via tail][2]
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Use the switch -f to follow the log file, which updates in real time. For example, if you want to follow syslog, you can use the following command.
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```
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tail -f /var/log/syslog
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```
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You can monitor multiple log files using a single command using –
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```
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tail -f /var/log/syslog /var/log/dmesg
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```
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If you want to monitor http or sftp or any server, you can also their respective log files in this command.
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Remember, above commands requires admin privileges.
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#### Using lnav (The Logfile Navigator)
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![lnav Running][3]
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The lnav is a nice utility which you can use to monitor log files in a more structured way with color coded messages. This is not installed by default in Linux systems. You can install it using the below command:
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```
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sudo apt install lnav (Ubuntu)
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sudo dnf install lnav (Fedora)
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```
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The good thing about lnav is, if you do not want to install it, you can just download its pre-compiled executable and run in anywhere. Even from a USB stick. No setup is required, plus loaded with features. Using lnav you can query the log files via SQL among other cool features which you can learn on it [official website][4].
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[][5]
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SEE ALSO: This App is An Advanced Log File Viewer - lnav
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Once installed, you can simply run lnav from terminal with admin privilege, and it will show all the logs from /var/log by default and start monitoring in real time.
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#### A note about journalctl of systemd
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All modern Linux distributions today use systemd, mostly. The systemd provides basic framework and components which runs Linux operating system in general. The systemd provides journal services via journalctl which helps to manage logs from all systemd services. You can also monitor respective systemd services and logs in real time using the following command.
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```
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journalctl -f
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```
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Here are some of the specific journalctl commands which you can use for several cases. You can combine these with -f switch above to start monitoring in real time.
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* To emergency system messages use
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```
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journalctl -p 0
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```
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* Show errors with explanations
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```
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journalctl -xb -p 3
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```
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* Use time controls to filter out
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```
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journalctl --since "2020-12-04 06:00:00"
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journalctl --since "2020-12-03" --until "2020-12-05 03:00:00"
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journalctl --since yesterday
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journalctl --since 09:00 --until "1 hour ago"
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```
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If you want to learn more about and want to find out details about journalctl – I have written a [guide here][6].
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### Closing Notes
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I hope these commands and tricks helps you find out the root cause of your problem/errors in your desktop or servers. For more details, you can always refer to the man pages and play around with various switches. Let me know using the comment box below, if you have any comments or what do you think about this article.
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Cheers.
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* * *
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--------------------------------------------------------------------------------
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via: https://www.debugpoint.com/2021/08/monitor-log-files-real-time/
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作者：[Arindam][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.debugpoint.com/author/admin1/
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[b]: https://github.com/lujun9972
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[1]: https://www.debugpoint.com/blog/wp-content/uploads/2021/08/log-files-in-var-log-1024x312.jpeg
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[2]: https://www.debugpoint.com/blog/wp-content/uploads/2021/08/Monitoring-multiple-log-files-via-tail-1024x444.jpeg
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[3]: https://www.debugpoint.com/blog/wp-content/uploads/2021/08/lnav-Running-1024x447.jpeg
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[4]: https://lnav.org/features
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[5]: https://www.debugpoint.com/2016/11/advanced-log-file-viewer-lnav-ubuntu-linux/
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[6]: https://www.debugpoint.com/2020/12/systemd-journalctl/
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@ -0,0 +1,131 @@
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[#]: subject: "How to Monitor Log Files in Real Time in Linux [Desktop and Server]"
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[#]: via: "https://www.debugpoint.com/2021/08/monitor-log-files-real-time/"
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[#]: author: "Arindam https://www.debugpoint.com/author/admin1/"
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[#]: collector: "lujun9972"
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[#]: translator: "geekpi"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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如何在 Linux 中实时监控日志文件（桌面和服务器）
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======
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本教程解释了如何实时监控 Linux 日志文件（桌面、服务器或应用），以进行诊断和故障排除。
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当你在你的 Linux 桌面、服务器或任何应用中遇到问题时，你会首先查看各自的日志文件。日志文件通常是来自应用的文本和信息流，上面有一个时间戳。它可以帮助你缩小具体的实例，并帮助你找到任何问题的原因。它也可以帮助从网络上获得援助。
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一般来说，所有的日志文件都位于 /var/log 中。这个目录包含以 .log 为扩展名的特定应用、服务的日志文件，它还包含单独的其他目录，这些目录包含其日志文件。
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![log files in var-log][1]
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所以说，如果你想监控一堆日志文件或特定的日志文件。这里有一些你可以做到方法。
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### 实时监控 Linux 日志文件
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#### 使用 tail 命令
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使用 tail 命令是实时跟踪日志文件的最基本方法。特别是，如果你所在的服务器只有一个终端，没有 GUI。这是很有帮助的。
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比如：
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```
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tail /path/to/log/file
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```
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![Monitoring multiple log files via tail][2]
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使用开关 -f 来跟踪日志文件，它是实时更新的。例如，如果你想跟踪 syslog，你可以使用以下命令。
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```
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tail -f /var/log/syslog
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```
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你可以用一个命令监控多个日志文件，使用：
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```
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tail -f /var/log/syslog /var/log/dmesg
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```
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如果你想监控 http 或 sftp 或任何服务器，你也可以在这个命令中监控它们各自的日志文件。
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记住，上述命令需要管理员权限。
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#### 使用 lnav（日志文件浏览器）
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![lnav Running][3]
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lnav 是一个很好的工具，你可以用它来用彩色编码的信息以更有条理的方式监控日志文件。在 Linux 系统中，它不是默认安装的。你可以用下面的命令来安装它：
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```
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sudo apt install lnav (Ubuntu)
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sudo dnf install lnav (Fedora)
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```
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lnav 的好处是，如果你不想安装它，你可以直接下载其预编译的可执行文件，然后在任何地方运行。甚至从 U 盘上也可以。它不需要设置，而且有很多功能。使用 lnav，你可以通过 SQL 查询日志文件，以及其他很酷的功能，你可以在它的[官方网站][4]上了解。
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Once installed, you can simply run lnav from terminal with admin privilege, and it will show all the logs from /var/log by default and start monitoring in real time.
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#### 关于 systemd 的 journalctl 说明
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今天所有的现代 Linux 发行版大多使用 systemd。systemd 提供了运行 Linux 操作系统的基本框架和组件。systemd 通过 journalctl 提供日志服务，帮助管理所有 systemd 服务的日志。你还可以通过以下命令实时监控各个 systemd 服务和日志。
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```
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journalctl -f
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```
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下面是一些特定的 journalctl 命令，可以在一些情况下使用。你可以将这些命令与上面的 -f 开关结合起来，开始实时监控。
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* 对紧急系统信息，使用
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```
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journalctl -p 0
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```
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* 显示带有解释的错误
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```
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journalctl -xb -p 3
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```
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* 使用时间控制来过滤输出
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```
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journalctl --since "2020-12-04 06:00:00"
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journalctl --since "2020-12-03" --until "2020-12-05 03:00:00"
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journalctl --since yesterday
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journalctl --since 09:00 --until "1 hour ago"
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```
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如果你想了解更多关于 journalctl 的细节，我已经写了一个[指南][6]。
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### 结束语
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我希望这些命令和技巧能帮助你找出桌面或服务器问题/错误的根本原因。对于更多的细节，你可以随时参考手册，玩弄各种开关。如果你对这篇文章有什么意见或看法，请在下面的评论栏告诉我。
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干杯。
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* * *
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--------------------------------------------------------------------------------
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via: https://www.debugpoint.com/2021/08/monitor-log-files-real-time/
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作者：[Arindam][a]
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选题：[lujun9972][b]
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译者：[geekpi](https://github.com/geekpi)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.debugpoint.com/author/admin1/
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[b]: https://github.com/lujun9972
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[1]: https://www.debugpoint.com/blog/wp-content/uploads/2021/08/log-files-in-var-log-1024x312.jpeg
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[2]: https://www.debugpoint.com/blog/wp-content/uploads/2021/08/Monitoring-multiple-log-files-via-tail-1024x444.jpeg
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[3]: https://www.debugpoint.com/blog/wp-content/uploads/2021/08/lnav-Running-1024x447.jpeg
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[4]: https://lnav.org/features
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[6]: https://www.debugpoint.com/2020/12/systemd-journalctl/
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