head

Summary

head is a versatile command-line utility that enables users to display the first few lines of a text file, by default it shows the first 10 lines. In case of incident response and cyber security, it is a useful tool to quickly analyze logs or configuration files while investigating potential security breaches or malware infections in a system.

Usage

The basic syntax of head command is as follows:

head [options] [file(s)]

Where options are flags that could be used to modify the output and [file(s)] are the input file(s) for which you want to display the first few lines.

Examples

• Display the first 10 lines of a file:

head myfile.txt

• You can change the number of lines to display using -n flag:

head -n 20 myfile.txt

• To display the first 5 lines of multiple files:

head -n 5 file1.txt file2.txt

• Another helpful flag is -q or --quiet, which avoids displaying file headers when viewing multiple files:

head -q -n 5 file1.txt file2.txt

Application in Incident Response

During an incident response, the head command helps to quickly analyze logs and files to identify potential malicious activity or errors. You can use head to peek into logs at the early stages of an investigation, and once you have gathered enough information, you can move on to more advanced tools to analyze the data in depth.

For example:

• Check the first 5 lines of the system log for any potential issues:

head -n 5 /var/log/syslog

• Analyze the beginning of a large log file without loading the entire file:

head -n 100 /var/log/large-log-file.log

In summary, the head command is a handy tool for preliminary analysis of log files that can save crucial time during an incident response. However, for more in-depth analysis, other tools and techniques should be employed.