Count the number of logins from IP address 192.168.0.101. If you need to review login information from prior dates, you can check the wtmp-YYYYMMDD (or wtmp.) and btmp-YYYYMMDD (or btmp.) files in /var/log, which are the old archives of wtmp and btmp files, generated by logrotate.Ģ. Check how many times (and at what times) a particular user (e.g., gacanepa) logged on to the system between August 18 and September 17. Here are a few simple use cases of utmpdump.ġ. The last (eighth) field indicates the date and time when the record was created. If DNS resolution is not provided, the sixth and seventh fields will show identical information (the IP address of the remote system). The seventh field holds the IP address of the remote system (if the login is performed from the local host, this field will show 0.0.0.0). The sixth field holds the name of the remote host (if the login is performed from the local host, this field is blank, except for run-level messages, which will return the kernel version). The fifth field holds the main TTY or PTY (pseudo-terminal), if that information is available.
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The fourth field can be either empty or hold the user name, reboot, or runlevel. The third field can hold one of the following values: ~~ (indicating a runlevel change or a system reboot), bw (meaning a bootwait process), a digit (indicates a TTY number), or a character and a digit (meaning a pseudo-terminal). The first field shows a session identifier, while the second holds PID. To do the same with /var/log/wtmp: # utmpdump /var/log/wtmpĪnd finally with /var/log/btmp: # utmpdump /var/log/btmpĪs you can see, the output formats of three cases are identical, except for the fact that the records in the utmp and btmp are arranged chronologically, while in the wtmp, the order is reversed.Įach log line is formatted in multiple columns described as follows. In order to display the contents of /var/run/utmp, run the following command: # utmpdump /var/run/utmp
#Centos grep usage how to#
How to Use Utmpdump and Interpret its OutputĪs we mentioned earlier, these log files, as opposed to other logs most of us are familiar with (e.g., /var/log/messages, /var/log/cron, /var/log/maillog), are saved in binary file format, and thus we cannot use pagers such as less or more to view their contents. Besides, utmpdump can be used to modify utmp or wtmp, which can be useful if you want to fix any corrupted entries in the binary logs. The information gleaned from utmpdump is more comprehensive than the output of the tools mentioned earlier, and that's what makes it a nice utility for the job.
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This tool is available by default on stock CentOS 6 and 7. In this post I'll show you how to use utmpdump, a simple program from the sysvinit-tools package that can be used to dump these binary log files in text format for inspection. /var/log/btmp (which logs failed login attempts) is used by lastb utility to show the listing of last failed login attempts./var/log/wtmp (which stores the history of connections to the system) is used by last tool to show the listing of last logged-in users./var/run/utmp (which logs currently open sessions) is used by who and w tools to show who is currently logged on and what they are doing, and also by uptime to display system up time.On a CentOS system, user login history is stored in the following binary files: Also, examining reboot user's login activities can reveal system uptime and reboot history. For example, remote logins from unknown IP addresses or accounts being used outside working hours or during vacation leave should raise a red flag. In case of user management, examining user logon and logout logs (both failed and successful) can alert us about any potential security breaches or unauthorized use of our system. Keeping, maintaining and analyzing logs (i.e., accounts of events that have happened during a certain period of time or are currently happening) are among the most basic and essential tasks of a Linux system administrator.
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How to monitor user login history on CentOS with utmpdump