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	"title": "12 Critical Linux Log Files You Must be Monitoring -",
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	"plain_text": "12 Critical Linux Log Files You Must be Monitoring -\r\nBy Marcel\r\nPublished: 2020-04-19 · Archived: 2026-04-05 19:41:18 UTC\r\n12 Critical Linux Log Files You Must be Monitoring\r\nLog files are the records that Linux stores for administrators to keep track and monitor important events about the\r\nserver, kernel, services, and applications running on it. In this post, we’ll go over the top Linux log files server\r\nadministrators should monitor.\r\nContent Recently Updated: Originally posted on Sep 15th, 2015\r\nWhat are Linux log files\r\nLog files are a set of records that Linux maintains for the administrators to keep track of important events. They\r\ncontain messages about the server, including the kernel, services and applications running on it. \r\nLinux provides a centralized repository of log files that can be located under the  /var/log directory.\r\nThe log files generated in a Linux environment can typically be classified into four different categories:\r\nApplication Logs\r\nEvent Logs\r\nService Logs\r\nSystem Logs\r\nWhy monitor Linux log files\r\nLog monitoring is an integral part of any server administrator’s responsibility.\r\nBy monitoring Linux log files, you can gain detailed insight on server performance, security, error messages and\r\nunderlying issues by. If you want to take a proactive vs. a reactive approach to server management, regular log file\r\nanalysis is 100% required.\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 1 of 10\n\nIn short, log files allow you to anticipate upcoming issues before they actually occur. \r\nWhich Linux log files to monitor\r\nMonitoring and analyzing all of them can be a challenging task.\r\nThe sheer volume of logs can sometimes make it frustrating just to drill down and find the right file that contains\r\nthe desired information.\r\nTo make it a little easier for you, we will introduce you to some of the most critical Linux log files that you must\r\nbe monitoring.\r\nNote: Please note that this is not an all-inclusive list - but just a subset of the important log files that matter the\r\nmost. The more you can handle, the better it is for the health of your server. Listed below are the bare minimum\r\nthat you must monitor without fail\r\n/var/log/messages\r\nWhat’s logged here?:\r\nThis log file contains generic system activity logs.\r\nIt is mainly used to store informational and non-critical system messages.\r\nIn Debian-based systems,  /var/log/syslog directory serves the same purpose.\r\nHow can I use these logs?:\r\nHere you can track non-kernel boot errors, application-related service errors and the messages that are\r\nlogged during system startup.\r\nThis is the first log file that the Linux administrators should check if something goes wrong.\r\nFor example, you are facing some issues with the sound card. To check if something went wrong during the\r\nsystem startup process, you can have a look at the messages stored in this log file. \r\n/var/log/auth.log\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 2 of 10\n\nWhat’s logged here?\r\nAll authentication related events in Debian and Ubuntu server are logged here.\r\nIf you’re looking for anything involving the user authorization mechanism, you can find it in this log file.\r\nHow can I use these logs?:\r\nSuspect that there might have been a security breach in your server? Notice a suspicious javascript file where it\r\nshouldn’t be? If so, then find this log file asap!\r\nInvestigate failed login attempts\r\nInvestigate brute-force attacks and other vulnerabilities related to user authorization mechanism.\r\nWhat’s logged here?\r\nRedHat and CentOS based systems use this log file instead of /var/log/auth.log. \r\nIt is mainly used to track the usage of authorization systems.\r\nIt stores all security related messages including authentication failures.\r\nIt also tracks sudo logins, SSH logins and other errors logged by system security services daemon.\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 3 of 10\n\nHow can I use these logs?:\r\nAll user authentication events are logged here.\r\nThis log file can provide detailed insight about unauthorized or failed login attempts\r\nCan be very useful to detect possible hacking attempts.\r\nIt also stores information about successful logins and tracks the activities of valid users.\r\nWhat’s logged here?\r\nThe system initialization script, /etc/init.d/bootmisc.sh, sends all bootup messages to this log file\r\nThis is the repository of booting related information and messages logged during system startup process.\r\nHow can I use these logs?:\r\nYou should analyze this log file to investigate issues related to improper shutdown, unplanned reboots or\r\nbooting failures.\r\nCan also be useful to determine the duration of system downtime caused by an unexpected shutdown.\r\ndmesg\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 4 of 10\n\nWhat’s logged here?\r\nThis log file contains Kernel ring buffer messages.\r\nInformation related to hardware devices and their drivers are logged here.\r\nAs the kernel detects physical hardware devices associated with the server during the booting process, it\r\ncaptures the device status, hardware errors and other generic messages.\r\nHow can I use these logs?:\r\nThis log file is useful for dedicated server customers mostly.\r\nIf a certain hardware is functioning improperly or not getting detected, then you can rely on this log file to\r\ntroubleshoot the issue.\r\nOr, you can purchase a managed server from us and we’ll monitor it for you.\r\nWhat’s logged here?\r\nThis is a very important log file as it contains information logged by the kernel.\r\nHow can I use these logs?:\r\nPerfect for troubleshooting kernel related errors and warnings.\r\nKernel logs can be helpful to troubleshoot a custom-built kernel.\r\nCan also come handy in debugging hardware and connectivity issues.\r\n/var/log/faillog\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 5 of 10\n\nWhat’s logged here?\r\nThis file contains information on failed login attempts.\r\nHow can I use these logs?:\r\nIt can be a useful log file to find out any attempted security breaches involving username/password hacking and\r\nbrute-force attacks.\r\ncron\r\nWhat’s logged here?\r\nThis log file records information on cron jobs.\r\nHow can I use these logs\r\nWhenever a cron job runs, this log file records all relevant information including successful execution and\r\nerror messages in case of failures.\r\nIf you’re having problems with your scheduled cron, you need to check out this log file.\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 6 of 10\n\nWhat’s logged here?\r\nIt contains the information that is logged when a new package is installed using the yum command.\r\nHow can I use these logs?:\r\nTrack the installation of system components and software packages.\r\nCheck the messages logged here to see whether a package was correctly installed or not.\r\nHelps you troubleshoot issues related to software installations.\r\nSuppose your server is behaving unusually and you suspect a recently installed software package to be the root\r\ncause for this issue. In such cases, you can check this log file to find out the packages that were installed recently\r\nand identify the malfunctioning program. \r\nmaillog or /var/log/mail.log\r\nWhat’s logged here?\r\nAll mail server related logs are stored here.\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 7 of 10\n\nHow can I use these logs?\r\nFind information about postfix, smtpd, MailScanner, SpamAssassain or any other email related services\r\nrunning on the mail server.\r\nTrack all the emails that were sent or received during a particular period\r\nInvestigate failed mail delivery issues.\r\nGet information about possible spamming attempts blocked by the mail server.\r\nTrace the origin of an incoming email by scrutinizing this log file.\r\nWhat’s logged here?\r\nThis directory contains the logs recorded by the Apache server.\r\nApache server logging information are stored in two different log files – error_log and access_log.\r\nHow can I use these logs?:\r\nThe error_log contains messages related to httpd errors such as memory issues and other system related\r\nerrors.\r\nThis is the place where Apache server writes events and error records encountered while processing httpd\r\nrequests.\r\nIf something goes wrong with the Apache webserver, check this log for diagnostic information.\r\nBesides the error-log file, Apache also maintains a separate list of access_log.\r\nAll access requests received over HTTP are stored in the access_log file.\r\nHelps you keep track of every page served and every file loaded by Apache.\r\nLogs the IP address and user ID of all clients that make connection requests to the server.\r\nStores information about the status of the access requests, – whether a response was sent successfully or\r\nthe request resulted in a failure.\r\n/var/log/mysqld.log or /var/log/mysql.log\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 8 of 10\n\nWhat’s logged here?\r\nAs the name suggests, this is the MySQL log file.\r\nAll debug, failure and success messages related to the [mysqld] and [mysqld_safe] daemon are logged to\r\nthis file.\r\nRedHat, CentOS and Fedora stores MySQL logs under  /var/log/mysqld.log, while Debian and Ubuntu\r\nmaintains the log in /var/log/mysql.log directory.\r\nHow can I use this log?\r\nUse this log to identify problems while starting, running, or stopping mysqld.\r\nGet information about client connections to the MySQL data directory\r\nYou can also setup ‘long_query_time’ parameter to log information about query locks and slow running\r\nqueries.\r\nFinal Takeaway\r\nWhile monitoring and analyzing all the log files generated by the system can be a difficult task, you can make use\r\nof a centralized log monitoring tool to simplify the process.\r\nSome of our customers take advantage of using  Nagios Log Server to manage their server logs. There are many\r\nopensource options available if that’s out of the budget. Needless to say though, monitoring Linux logs manually\r\nis hard.\r\nSo if you want to take a truly proactive approach to server management, investing in a centralized log collection\r\nand analysis platform which allows you to view log data in real-time and set up alerts to notify you when potential\r\nthreats arise.\r\nLinux\r\nSecurity\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 9 of 10\n\nCertified ethical hacker and security team leader on EuroVPS support desk. I keep bad stuff out.\r\n20 Ways to Secure Your Linux VPS so You Don’t Get Hacked\r\nLinux VPS servers have their advantages. In fact, Linux VPS are much more secure when compared to other\r\noperating system...\r\nHow to Prevent Annoying Spam Outbreaks in cPanel and Plesk Servers\r\nWe hate spam, you hate spam! We all hate spam! If you are using the cPanel or Plesk control panel, this post goes\r\nover a...\r\n10 Effective Ways to Secure your Windows Server from Technological Hooligans\r\nReady for some Windows server security tips and tricks? For all you security minded Windows Server users, we'll\r\ntalk abo...\r\nSource: https://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nhttps://www.eurovps.com/blog/important-linux-log-files-you-must-be-monitoring/\r\nPage 10 of 10",
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