A security operations center (SOC) analyst observed an unusually high number of login failures on a particular database server. The analyst wants to gather supporting evidence before escalating the observation to management. Which of the following expressions will provide login failure data for 11/24/2015?

The objective is to gather the actual log entries ("supporting evidence") related to login failures for a specific date. The command grep 20151124 securitylog | grep "login" correctly performs this task in two stages. First, grep 20151124 securitylog filters the securitylog file for all lines containing the string for the correct date (November 24, 2015). Second, the output is piped (|) to grep "login", which further filters the results to show only the lines containing the term "login". This provides the analyst with all login-related events from that day, including the failures, which can then be reviewed as evidence.

A. The -c flag provides only a count of matching lines, not the actual log data needed for evidence.
B. This command searches for the incorrect date (20150124 is January 24) instead of the required November 24, 2015.
D. Similar to option A, the -c flag returns a numerical count instead of the log entries themselves.

1. GNU Grep 3.11 Manual, Section 2.1, "Command-line Options": The official documentation for grep specifies the function of the -c or --count option: "Suppress normal output; instead print a count of matching lines for each input file." This confirms that options A and D would not provide the evidentiary data required by the analyst.

2. MIT OpenCourseWare, 6.005 Software Construction, Spring 2016, "Reading 1: Static Checking": In the section on "Pipes and filters," the courseware explains the use of the pipe (|) operator to connect the output of one command to the input of another. It provides an example: ls | grep .java, which is analogous to the structure used in the question for filtering log data in stages. This validates the command's structure.

3. University of California, Berkeley, EECS Department, "CS 161: Computer Security, Fall 2020, Lab 0": This lab exercise instructs students on using command-line tools for security tasks. It demonstrates using grep to search for specific patterns in files and using pipes to combine commands for more complex filtering, which is the exact technique required to solve the problem posed in the question.