{"id":13857,"date":"2019-04-06T11:57:23","date_gmt":"2019-04-06T11:57:23","guid":{"rendered":"http:\/\/www.appservgrid.com\/paw92\/?p=13857"},"modified":"2019-04-06T11:57:23","modified_gmt":"2019-04-06T11:57:23","slug":"4-ways-to-watch-or-monitor-log-files-in-real-time","status":"publish","type":"post","link":"https:\/\/www.appservgrid.com\/paw92\/index.php\/2019\/04\/06\/4-ways-to-watch-or-monitor-log-files-in-real-time\/","title":{"rendered":"4 Ways to Watch or Monitor Log Files in Real Time"},"content":{"rendered":"

How can I see the content of a log file in real time in Linux? Well there are a lot of utilities out there that can help a user to output the content of a file while the file is changing or continuously updating. Some of the most known and heavily used utility to display a file content in real time in Linux is the\u00a0tail command<\/a>\u00a0(manage files effectively).<\/p>\n

Read Also<\/strong>:\u00a04 Good Open Source Log Monitoring and Management Tools for Linux<\/a><\/p>\n

1. tail Command \u2013 Monitor Logs in Real Time<\/h3>\n

As said,\u00a0tail command<\/strong>\u00a0is the most common solution to display a log file in real time. However, the command to display the file has two versions, as illustrated in the below examples.<\/p>\n

In the first example the command\u00a0tail<\/strong>\u00a0needs the\u00a0-f<\/code>\u00a0argument to follow the content of a file.<\/p>\n

$ sudo tail -f \/var\/log\/apache2\/access.log\r\n<\/pre>\n
\n
\"Monitor<\/a><\/p>\n
Monitor Apache Logs in Real Time<\/p>\n<\/div>\n
The second version of the command is actually a command itself:\u00a0tailf<\/strong>. You won\u2019t need to use the\u00a0-f<\/code>\u00a0switch because the command is built-in with the\u00a0-f<\/code>\u00a0argument.<\/p>\n
$ sudo tailf \/var\/log\/apache2\/access.log\r\n<\/pre>\n
\n
\"Real<\/a><\/p>\n
Real Time Apache Logs Monitoring<\/p>\n<\/div>\n
Usually, the log files are rotated frequently on a Linux server by the logrotate utility. To watch log files that get rotated on a daily base you can use the\u00a0-F<\/code>\u00a0flag to\u00a0tail command<\/strong>.<\/p>\n
Read Also<\/strong>:\u00a0How to Manage System Logs (Configure, Rotate and Import Into Database) in Linux<\/a><\/p>\n
The\u00a0tail -F<\/code>\u00a0will keep track if new log file being created and will start following the new file instead of the old file.<\/p>\n
$ sudo tail -F \/var\/log\/apache2\/access.log\r\n<\/pre>\n
However, by default,\u00a0tail command<\/strong>\u00a0will display the last\u00a010<\/strong>\u00a0lines of a file. For instance, if you want to watch in real time only the last two lines of the log file, use the\u00a0-n<\/code>\u00a0file combined with the\u00a0-f<\/code>\u00a0flag, as shown in the below example.<\/p>\n
$ sudo tail -n2 -f \/var\/log\/apache2\/access.log\r\n<\/pre>\n
\n
\"Watch<\/a><\/p>\n
Watch Last Two Lines of Logs<\/p>\n<\/div>\n
2. Multitail Command \u2013 Monitor Multiple Log Files in Real Time<\/h3>\n
Another interesting command to display log files in real time is\u00a0multitail command<\/a>. The name of the command implies that\u00a0multitail utility<\/strong>\u00a0can monitor and keep track of multiple files in real time. Multitail also lets you navigate back and forth in the monitored file.<\/p>\n
To install\u00a0mulitail utility<\/strong>\u00a0in Debian and RedHat based systems issue the below command.<\/p>\n
$ sudo apt install multitail   [On Debian & Ubuntu]\r\n$ sudo yum install multitail   [On RedHat & CentOS]\r\n$ sudo dnf install multitail   [On Fedora 22+ version]\r\n<\/pre>\n
To display the output of two log file simultaneous, execute the command as shown in the below example.<\/p>\n
$ sudo multitail \/var\/log\/apache2\/access.log \/var\/log\/apache2\/error.log\r\n<\/pre>\n
\n
\"Multitail<\/a><\/p>\n
Multitail Monitor Logs<\/p>\n<\/div>\n
3. lnav Command \u2013 Monitor Multiple Log Files in Real Time<\/h3>\n
Another interesting command, similar to\u00a0multitail command<\/strong>\u00a0is the\u00a0lnav command<\/a>.\u00a0Lnav utility<\/strong>\u00a0can also watch and follow multiple files and display their content in real time.<\/p>\n
To install lnav utility in Debian and RedHat based Linux distributions by issuing the below command.<\/p>\n
$ sudo apt install lnav   [On Debian & Ubuntu]\r\n$ sudo yum install lnav   [On RedHat & CentOS]\r\n$ sudo dnf install lnav   [On Fedora 22+ version]\r\n<\/pre>\n
Watch the content of two log files simultaneously by issuing the command as shown in the below example.<\/p>\n
$ sudo lnav \/var\/log\/apache2\/access.log \/var\/log\/apache2\/error.log\r\n<\/pre>\n
\n
\"lnav<\/a><\/p>\n
lnav \u2013 Real Time Logs Monitoring<\/p>\n<\/div>\n
4. less Command \u2013 Display Real Time Output of Log Files<\/h3>\n
Finally, you can display the live output of a file with\u00a0less command<\/a>\u00a0if you type\u00a0Shift+F<\/code>.<\/p>\n
As with\u00a0tail utility<\/strong>, pressing\u00a0Shift+F<\/code>\u00a0in a opened file in\u00a0less<\/strong>\u00a0will start following the end of the file. Alternatively, you can also start less with less\u00a0+F<\/code>\u00a0flag to enter to live watching of the file.<\/p>\n
$ sudo less +F  \/var\/log\/apache2\/access.log\r\n<\/pre>\n
\n
\"Watch<\/a><\/p>\n
Watch Logs Using Less Command<\/p>\n<\/div>\n
That\u2019s It! You may read these following articles on Log monitoring and management.<\/p>\n
    \n
  1. \n
      \n
    1. Manage Files Effectively using head, tail and cat Commands in Linux<\/a><\/li>\n
    2. How to Setup and Manage Log Rotation Using Logrotate in Linux<\/a><\/li>\n
    3. Petiti \u2013 An Open Source Log Analysis Tool for Linux SysAdmins<\/a><\/li>\n
    4. How to Query Audit Logs Using \u2018ausearch\u2019 Tool on CentOS\/RHEL<\/a><\/li>\n
    5. Manage Log Messages Under Systemd Using Journalctl [Comprehensive Guide]<\/a><\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
      In this article, we showed how to watch data being appended in log files in real-time on the terminal in Linux. You can ask any questions or share your thoughts concerning this guide via the comment form below.<\/p>\n
      Source<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
      How can I see the content of a log file in real time in Linux? Well there are a lot of utilities out there that can help a user to output the content of a file while the file is changing or continuously updating. Some of the most known and heavily used utility to display … <\/p>\n
      Continue reading “4 Ways to Watch or Monitor Log Files in Real Time”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-13857","post","type-post","status-publish","format-standard","hentry","category-linux"],"_links":{"self":[{"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/posts\/13857","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/comments?post=13857"}],"version-history":[{"count":1,"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/posts\/13857\/revisions"}],"predecessor-version":[{"id":13858,"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/posts\/13857\/revisions\/13858"}],"wp:attachment":[{"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/media?parent=13857"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/categories?post=13857"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.appservgrid.com\/paw92\/index.php\/wp-json\/wp\/v2\/tags?post=13857"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}