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Navigating the log files

 


Often you may find yourselves in the middle of searching for a keyword in your log files.  On the linux environment , you will easily find by using the command 

        grep 'your keyword' filename.log

Sometime you may want to know what happens before and after the occurrence of your keyword. 

In the example below I tried to look for an exception using grep command.



The output alone is not really helpful to identify the problem that I'm looking for. We need to understand what happened before and after the exception that occurred.


The first step is to get the line number of the first occurrence of this error.

Let's use the command with grep -n command



We can now see the line numbers; 2449 and 2515.

The next step is to find out the content of the log few lines adjacent to line 2449 in this example.

The following command gives the desired result that is connect of the log file between the lines shown in the example below.


sed -n '2440,2460 {  p; }' < nohup.out




This output helps us identifying the root cause of error which is, in this case, "sftp connection" error. There are alternate ways to find similar solution such as using awk, tail, head etc.

example: head -n 2450 nohup.out | tail -10




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