#Grep linux command examples how to
#Grep linux command examples series

This method of log filtering with ‘journalctl’ can be very useful when it comes to the critical services that failed to load, and using this method we can filter exact time and date for specific entry within the log file. $ journalctl -since '' -until ' 21:50'Īs we can see the log files are shown from ‘’ until ‘’ until the exact time of 21:50.

We can also filter the logs at exact date and time, by using the following ‘ journalctl’ command in the format below. head -n5 – shows only the first five lines of the logs.5 days ago – show log files that are 5 days old.

The date specifications should be of the format “ 18:17:16“.

-since – Start showing entries newer than the specified date, or older than the specified date, respectively.

journalctl – query the systemd journal.

One of the easiest ways to filter log files based on their date range is by using the ‘ journalctl’ command, which is used for displaying logs from journald and systemd log services.įor instance, if we want to read logs that are two days old, we will use the following command: $ journalctl -since '5 days ago' | head -n5Īn explanation of the above command is the following: Filter Linux Logs Using Journalctl Command

#Grep linux command examples how to

Now that we know how to read the log files in combination with other commands, let us show how we can filter the results from log files based on their date entries using journalctl, awk, grep, and sed commands.

The head command shows the first ten lines of a file.

The | is a pipe character that allows us to combine two and more commands in one single command to get the desired result from a file in Linux.

The cat command allows us to read the file contents in Linux.

The sudo command allows us to execute commands and read the files that only a ‘ root’ user has access to.

Here’s an explanation of the above command: But when you want to filter data in an organized way based on time, then we use journalctl, awk, grep, and sed commands.įor instance, in order to read the ‘ boot.log.1‘ file, we can use the following cat command. Simply doing cat to read a log file is a kinda basic way to inspect a log file. If you are facing difficulty while systematically reading log files in Linux.

#Grep linux command examples series

These log files reside in a special directory called ‘ /var/log‘ and we can access it by using the following command: $ cd /var/logĪs we can see, there are various log files within the ‘ /var/log‘ directory and each of the log files contains a series of vital information that is useful when it comes to resolving critical service or system issues. Log files are nothing more than text files containing a series of information about the Linux kernel, boot process, logging to the machine, applications, system, and so on.īy reading them, we can resolve critical issues with our distribution such as a device that fails to load within dmesg, Xorg display server log, user log, and more.