feat: Add Victor's outputs and screenshots for Linux problem set

chapters/devopsLinuxCommands.tex

@@ -10,13 +10,22 @@
 \section{Purpose}
 This chapter records a set of Linux shell commands run in the authors' working
 user directories, and the solutions to the accompanying problem set.
-Terminal input and output are copied directly from the shell, so each listing is
-a record of an actual execution and serves as \gls{evidence} for this chapter.
+The setup figures reproduce Payton's terminal session. Section~\ref{Section:LinuxEvidence}
+adds Victor's actual problem-set execution screenshots as \gls{evidence}.
+The command answers in Section~\ref{Section:LinuxSolutions} describe solutions;
+where Victor used a different command, the difference is identified rather than
+presented as an execution of the exact answer shown.
 
 \section{Environment}
 \index{Linux!environment}
-The commands were run as the unprivileged user \texttt{payton} on Ubuntu~24.04
-under the \gls{wsl} on the author's workstation, in a \texttt{bash} shell.
+The setup figures were recorded by Payton as user \texttt{payton} on
+Ubuntu~24.04 under \gls{wsl}, in a \texttt{bash} shell.
+Victor independently performed the setup and problem set on September 27, 2026,
+as user \texttt{victor} on host \texttt{Victori7}, running Ubuntu~24.04.3 LTS
+under WSL~2. His working directory was \texttt{/home/victor/lx-test}.
+The session was recorded with \texttt{script}; its original transcript is retained
+with the evidence files. Normal commands ran without elevated privileges;
+\texttt{sudo} was used for the append-only attribute in Q20.
 
 \section{Working Directory Setup}
 \index{Linux!working directory setup}
@@ -35,8 +44,8 @@ and Figure~{\ref{Figure:LxTestFiles}} shows the resulting file contents.
 \item \texttt{printf "\ldots" > \textit{file}} writes the string to a file,
       turning each \texttt{\textbackslash n} into a newline. The \texttt{>}
       redirection creates the file or overwrites it if it already exists.
-      \texttt{printf} is used instead of \texttt{echo} because it handles escape
-      sequences the same way in every shell.
+      \texttt{printf} is used instead of \texttt{echo} for predictable formatting of these strings and newlines, avoiding
+      shell-dependent behavior of \texttt{echo}.
 \item \texttt{dd} with \texttt{if=/dev/zero}, \texttt{of=blob.bin},
       \texttt{bs=1K}, and \texttt{count=48} copies $48$ blocks of
       $1\,\mathrm{KiB}$ from \texttt{/dev/zero}, producing a file of
@@ -66,7 +75,8 @@ Figure~\ref{Figure:LxTestDirectories} confirms each step of the setup:
       points to \texttt{src/file1.txt}.
 \item \textbf{Timestamp:} \texttt{old.txt} is empty and shows the modified timestamp (\texttt{Jan~2~2024}).
 \item \textbf{Directories:} \texttt{archive}, \texttt{tmp}, and
-      \texttt{src/lib} report \texttt{total 0}, confirming they exist and are empty.
+      \texttt{src/lib} show no entries in the \texttt{ls -lA} listing, confirming they are empty
+      (\texttt{total 0} alone would not prove this).
 \item \textbf{Permissions:} New files are \texttt{rw-r--r--} ($644$) and new
       directories are \texttt{rwxr-xr-x} ($755$).
 \end{itemize}
@@ -155,7 +165,9 @@ two three four five
 \label{Figure:LxTestFiles}
 \end{figure}
 
+\clearpage
 \section{Problem Set Solutions}
+\label{Section:LinuxSolutions}
 \index{Linux!problem set}
 
 \subsection{Navigation and File Operations}
@@ -164,26 +176,44 @@ two three four five
 \begin{lstlisting}[style=cmd]
 $ pwd
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{pwd} prints only the current directory; Victor's result was \texttt{/home/victor/lx-test}.
+
 \item List all entries in the current directory, one per line, including dotfiles.
 \begin{lstlisting}[style=cmd]
 $ ls -1a
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-1} places each entry on a separate line; \texttt{-a} includes dotfiles and the \texttt{.} and \texttt{..} entries.
+
 \item Copy \texttt{src/file1.txt} to \texttt{tmp/} only if \texttt{tmp} exists; do it verbosely.
 \begin{lstlisting}[style=cmd]
 $ [ -d tmp ] && cp -v src/file1.txt tmp/
 \end{lstlisting}
+\nopagebreak[4]
+The directory test prevents copying when \texttt{tmp} is absent; \texttt{-v} reports the source and destination. Victor's output confirms the copy.
+
 \item Move \texttt{old.txt} into \texttt{archive/} and keep its original timestamp.
 \begin{lstlisting}[style=cmd]
 $ mv old.txt archive/
 \end{lstlisting}
+\nopagebreak[4]
+Moving within this working tree preserves the file's modification time. Victor verified that the timestamp remained January 2, 2024 at 03:04 local time.
+
 \item Create a new empty file \texttt{notes.md} only if it doesn't already exist.
 \begin{lstlisting}[style=cmd]
 $ [ -e notes.md ] || touch notes.md
 \end{lstlisting}
+\nopagebreak[4]
+The existence test avoids touching an existing file. Victor used the equivalent conditional \texttt{if} form and verified that the newly created file was zero bytes.
+
 \item Show disk usage (human-readable) for the \texttt{src} directory only (not total FS).
 \begin{lstlisting}[style=cmd]
 $ du -sh src
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-s} reports one directory total and \texttt{-h} uses readable units. Victor observed \texttt{16K}; allocated disk usage includes directory storage and is not simply text length.
+
 \end{enumerate}
 
 \subsection{Viewing and Searching}
@@ -192,26 +222,44 @@ $ du -sh src
 \begin{lstlisting}[style=cmd]
 $ cat -n sys.log
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{cat -n} numbers displayed lines. Victor used \texttt{nl -ba}, which also numbered all four lines in this file.
+
 \item Show only the lines in \texttt{sys.log} that contain \texttt{ERROR} (case-sensitive).
 \begin{lstlisting}[style=cmd]
 $ grep 'ERROR' sys.log
 \end{lstlisting}
+\nopagebreak[4]
+Without \texttt{-i}, matching is case-sensitive. The result was \texttt{ERROR fan fail}.
+
 \item Count how many distinct words appear in \texttt{words.txt} (case-insensitive).
 \begin{lstlisting}[style=cmd]
 $ tr '[:upper:]' '[:lower:]' < words.txt | sort -u | wc -l
 \end{lstlisting}
+\nopagebreak[4]
+Each input line contains one word. Lowercasing before sorting and deduplication treats \texttt{Gamma} and \texttt{gamma} as one value; the resulting count was three.
+
 \item From \texttt{words.txt}, show lines that start with \texttt{g} or \texttt{G}.
 \begin{lstlisting}[style=cmd]
 $ grep '^[gG]' words.txt
 \end{lstlisting}
+\nopagebreak[4]
+The anchor \texttt{\^{}} restricts the match to the start of the line, and \texttt{[gG]} accepts either case. The two matches were \texttt{Gamma} and \texttt{gamma}.
+
 \item Display the first 2 lines of \texttt{people.csv} without using an editor.
 \begin{lstlisting}[style=cmd]
 $ head -n 2 people.csv
 \end{lstlisting}
+\nopagebreak[4]
+The first two lines are the header and the first data row: \texttt{id,name,dept} and \texttt{1,Ada,EE}.
+
 \item Show the last 3 lines of \texttt{sys.log} and keep following if the file grows.
 \begin{lstlisting}[style=cmd]
 $ tail -n 3 -f sys.log
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-n 3} selects the last three lines; \texttt{-f} keeps following. Victor captured the initial three lines, then stopped following with Ctrl+C. No later appended-line test is claimed.
+
 \end{enumerate}
 
 \subsection{Text Processing}
@@ -220,18 +268,30 @@ $ tail -n 3 -f sys.log
 \begin{lstlisting}[style=cmd]
 $ tail -n +2 people.csv | cut -d, -f2
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{tail} skips the header and \texttt{cut} selects the comma-separated second field. Victor's equivalent \texttt{awk} command returned Ada, Linus, Grace, and Dennis.
+
 \item Sort \texttt{words.txt} case-insensitively and remove duplicates.
 \begin{lstlisting}[style=cmd]
 $ sort -fu words.txt
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-f} ignores case during comparison and \texttt{-u} removes duplicates. Victor's output was alpha, beta, and Gamma; the retained spelling need not be lowercased.
+
 \item Replace every \texttt{three} with \texttt{3} in all files under \texttt{src/} in-place, creating \texttt{.bak} backups.
 \begin{lstlisting}[style=cmd]
-$ find src -type f -name '*.txt' -exec sed -i.bak 's/three/3/g' {} +
+$ find src/ -type f ! -name '*.bak' -exec sed -i.bak 's/three/3/g' {} +
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{find} visits regular files recursively, excluding existing backups; \texttt{sed}'s \texttt{g} replaces every occurrence on each line. The original files are saved with the \texttt{.bak} suffix. Victor verified both edited content and original backups. Run once to avoid replacing the original backups on a later run.
+
 \item Print the number of lines, words, and bytes for every \texttt{*.txt} file in \texttt{src/}.
 \begin{lstlisting}[style=cmd]
 $ wc src/*.txt
 \end{lstlisting}
+\nopagebreak[4]
+By default, \texttt{wc} reports lines, words, and bytes. After Q15, Victor observed \texttt{1 4 15} and \texttt{1 4 16}, totaling \texttt{2 8 31}. Backup filenames do not match \texttt{*.txt}.
+
 \end{enumerate}
 
 \subsection{Permissions and Ownership}
@@ -240,18 +300,31 @@ $ wc src/*.txt
 \begin{lstlisting}[style=cmd]
 $ chmod 700 tmp/
 \end{lstlisting}
+\nopagebreak[4]
+Mode \texttt{700} gives the owner read, write, and directory-search permissions, with none for group or others. Victor verified \texttt{drwx------}.
+
 \item Give group execute permission to \texttt{src/lib} recursively without touching others/owner bits.
 \begin{lstlisting}[style=cmd]
 $ chmod -R g+x src/lib
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{g+x} adds only group execute; \texttt{-R} applies recursively. Victor's before/after value remained \texttt{755} because group execute was already enabled.
+
 \item Show the numeric (octal) permissions of \texttt{src/file2.txt}.
 \begin{lstlisting}[style=cmd]
 $ stat -c '%a' src/file2.txt
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{\%a} requests octal permissions. Victor observed \texttt{644}: owner read/write, group and others read-only.
+
 \item Make \texttt{notes.md} append-only for the owner via file attributes (if supported).
 \begin{lstlisting}[style=cmd]
+$ chmod 600 notes.md
 $ sudo chattr +a notes.md
 \end{lstlisting}
+\nopagebreak[4]
+Mode \texttt{600} limits ordinary access to the owner. The \texttt{a} attribute separately makes the file append-only; it is a file attribute, not an owner-specific permission bit. Victor's filesystem supported it: \texttt{lsattr} showed \texttt{a}, and \texttt{stat} showed \texttt{600}.
+
 \end{enumerate}
 
 \subsection{Links and Find}
@@ -260,14 +333,23 @@ $ sudo chattr +a notes.md
 \begin{lstlisting}[style=cmd]
 $ [ -L link-to-file1 ] && readlink link-to-file1
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-L} checks the link itself and \texttt{readlink} prints its stored target. Victor confirmed \texttt{src/file1.txt}.
+
 \item Find all regular files under the current tree larger than 40~KiB.
 \begin{lstlisting}[style=cmd]
 $ find . -type f -size +40k
 \end{lstlisting}
+\nopagebreak[4]
+The size test selects regular files larger than 40 KiB. Victor used the equivalent byte threshold \texttt{+40960c}, printing \texttt{./blob.bin} with 49,152 bytes.
+
 \item Find files modified in the last 10 minutes under \texttt{tmp/} and print their sizes.
 \begin{lstlisting}[style=cmd]
 $ find tmp/ -type f -mmin -10 -printf '%p %s\n'
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-mmin -10} selects recent modifications; \texttt{\%s} prints bytes. Victor's command returned no matches because no regular file under \texttt{tmp/} met that time window.
+
 \end{enumerate}
 
 \subsection{Processes and Job Control}
@@ -276,18 +358,30 @@ $ find tmp/ -type f -mmin -10 -printf '%p %s\n'
 \begin{lstlisting}[style=cmd]
 $ pstree -p "$USER"
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{pstree -p} shows process relationships and PIDs for the specified user. Victor instead recorded his own processes with \texttt{ps -u} and \texttt{--forest}, exposing the shell, recording process, and child shell hierarchy.
+
 \item Start \texttt{sleep 120} in the background and show its PID.
 \begin{lstlisting}[style=cmd]
 $ sleep 120 & echo $!
 \end{lstlisting}
+\nopagebreak[4]
+The ampersand starts a background job; \texttt{\$!} is its PID. Victor captured and printed PID 2476 in his session; PIDs vary between executions.
+
 \item Send a TERM signal to all \texttt{sleep} processes owned by you (don't use \texttt{kill -9}).
 \begin{lstlisting}[style=cmd]
 $ pkill -TERM -u "$USER" -x sleep
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-u} restricts matches to the current user's processes and \texttt{-x} requires the exact name. Victor first checked for unrelated sleep processes, then terminated the test process. Waiting for it returned status 143 (128 + SIGTERM 15), and a final process search returned no matches.
+
 \item Show the top 5 processes by memory usage (one-shot, not interactive).
 \begin{lstlisting}[style=cmd]
 $ ps aux --sort=-%mem | head -n 6
 \end{lstlisting}
+\nopagebreak[4]
+Descending memory percentage puts the largest consumers first; six output lines include one header and five processes. Victor used descending resident-memory size (RSS in KiB) instead; his largest displayed process was \texttt{snapd} at 41,208 KiB.
+
 \end{enumerate}
 
 \subsection{Archiving and Compression}
@@ -296,14 +390,23 @@ $ ps aux --sort=-%mem | head -n 6
 \begin{lstlisting}[style=cmd]
 $ tar -czf src.tgz src/
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-c} creates, \texttt{-z} compresses with gzip, and \texttt{-f} names the archive. The relative \texttt{src/} operand stores relative member paths.
+
 \item List the contents of \texttt{src.tgz} without extracting.
 \begin{lstlisting}[style=cmd]
 $ tar -tzf src.tgz
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{-t} lists members without extraction. Victor's archive contained the two text files, their backups, and the \texttt{src/lib/} directory.
+
 \item Extract only \texttt{file2.txt} from \texttt{src.tgz} into \texttt{tmp/}.
 \begin{lstlisting}[style=cmd]
 $ tar -xzvf src.tgz -C tmp/ --strip-components=1 src/file2.txt
 \end{lstlisting}
+\nopagebreak[4]
+The named member limits extraction to one file, \texttt{-C} selects the destination, and stripping one path component produces \texttt{tmp/file2.txt}. Victor verified matching content with \texttt{cmp}.
+
 \end{enumerate}
 
 \subsection{Networking and System Information}
@@ -312,18 +415,30 @@ $ tar -xzvf src.tgz -C tmp/ --strip-components=1 src/file2.txt
 \begin{lstlisting}[style=cmd]
 $ ss -ltnp
 \end{lstlisting}
+\nopagebreak[4]
+The flags select listening TCP sockets, numeric addresses, and process details when permitted. Victor saw two loopback listeners on port 53; the process column was blank in his unprivileged invocation, so no associated PIDs are claimed.
+
 \item Print your default route (gateway) in a concise form.
 \begin{lstlisting}[style=cmd]
 $ ip route show default
 \end{lstlisting}
+\nopagebreak[4]
+Victor's default route used gateway \texttt{172.23.224.1} through \texttt{eth0}. This is a local environment result, not a fixed gateway for every machine.
+
 \item Display kernel name, release, and machine architecture.
 \begin{lstlisting}[style=cmd]
 $ uname -srm
 \end{lstlisting}
+\nopagebreak[4]
+The requested fields identify the kernel and architecture. Victor observed Linux, release \texttt{6.18.33.2-microsoft-standard-WSL2}, and \texttt{x86\_64}.
+
 \item Show the last 5 successful logins (or last sessions) on the system.
 \begin{lstlisting}[style=cmd]
 $ last -n 5
 \end{lstlisting}
+\nopagebreak[4]
+Victor's last five available records were reboot/system-boot sessions rather than individual user logins. The record type is retained as shown; no successful user authentications are inferred.
+
 \end{enumerate}
 
 \subsection{Packages and Services (Debian/Ubuntu)}
@@ -332,28 +447,133 @@ $ last -n 5
 \begin{lstlisting}[style=cmd]
 $ dpkg-query -W -f='${Version}\n' coreutils
 \end{lstlisting}
+\nopagebreak[4]
+The query reads installed-package metadata. Victor also printed the package name and observed \texttt{coreutils 9.4-3ubuntu6.3}.
+
 \item Search available packages whose names contain \texttt{ripgrep}.
 \begin{lstlisting}[style=cmd]
 $ apt-cache search --names-only ripgrep
 \end{lstlisting}
+\nopagebreak[4]
+The search checks package names in the local catalog. It found \texttt{ripgrep}; availability in the catalog does not establish that the package is installed.
+
 \item Check whether service \texttt{cron} is active and print its status line only.
 \begin{lstlisting}[style=cmd]
 $ systemctl status cron | grep 'Active:'
 \end{lstlisting}
+\nopagebreak[4]
+Filtering the detailed status selects its Active line. Victor used \texttt{systemctl is-active cron}, a concise active-state query, and recorded \texttt{active}.
+
 \end{enumerate}
 
 \subsection{Bash and Scripting}
 \begin{enumerate}[label=\arabic*., leftmargin=*, resume]
-\item Write a one-liner that loops over \texttt{*.txt} in \texttt{src/} and prints each file's name and line count.
+\item Write a one-liner that loops over \texttt{*.txt} in \texttt{src/} and prints: : .
+\textbf{Assumption:} the intended output is each file's name and line count, since
+the supplied problem PDF displays an incomplete output format.
 \begin{lstlisting}[style=cmd]
 $ for f in src/*.txt; do echo "$f: $(wc -l < "$f")"; done
 \end{lstlisting}
+\nopagebreak[4]
+For the stated line-count assumption, \texttt{wc -l} counts each file's lines and the loop prefixes its name. Victor's captured command instead printed filename and contents under a different interpretation of the incomplete prompt; Figure~\ref{Figure:HW2-J} documents that alternative.
+
 \item Write a command that exports CSV rows where \texttt{dept == "CS"} to \texttt{cs.txt} (exclude header).
 \begin{lstlisting}[style=cmd]
 $ awk -F, 'NR>1 && $3=="CS"' people.csv > cs.txt
 \end{lstlisting}
+\nopagebreak[4]
+The field separator is a comma; \texttt{NR>1} skips the header and field three selects CS. Victor verified that \texttt{cs.txt} contained \texttt{2,Linus,CS} and \texttt{4,Dennis,CS}.
+
 \item Create a variable \texttt{X} with value 42, print it, then remove it from the environment.
 \begin{lstlisting}[style=cmd]
 $ export X=42; echo "$X"; unset X
 \end{lstlisting}
+\nopagebreak[4]
+\texttt{export} adds the variable to the shell's exported environment; \texttt{unset} removes it. Victor printed \texttt{X=42}, then verified its absence using \texttt{printenv}.
+
 \end{enumerate}
+
+\section{Problem Set Execution Evidence}
+\label{Section:LinuxEvidence}
+These screenshots were supplied by Victor from his recorded September 27th
+session. They show actual commands and outputs, grouped by problem-set section.
+They supplement Payton's setup figures. Captions identify the question ranges;
+the explanations above distinguish equivalent commands.
+Empty output is retained where it is the observed result.
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/03-section-a-q01-q06.png}
+\caption{Q1--Q6: navigation and file operations. The moved file retains its original modification time, and the new notes file is empty.}
+\label{Figure:HW2-A}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/04-section-b-q07-q12.png}
+\caption{Q7--Q12: viewing and searching. The final command remains in follow mode at capture; Victor subsequently stopped it with Ctrl+C.}
+\label{Figure:HW2-B}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/05-section-c-q13-q16.png}
+\caption{Q13--Q16: text processing. Original text is retained in the backups, while the edited files total 31 bytes.}
+\label{Figure:HW2-C}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/06-section-d-q17-q20.png}
+\caption{Q17--Q20: permissions and attributes. Group execute was already set; the append-only attribute and owner-only notes-file access are verified.}
+\label{Figure:HW2-D}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/07-section-e-q21-q23.png}
+\caption{Q21--Q23: links and file searches. The recent-modification search returns no matches.}
+\label{Figure:HW2-E}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/08-section-f-q24-precheck.png}
+\caption{Q24 and precheck: Victor records his process tree and confirms no existing user-owned sleep processes before the demonstration.}
+\label{Figure:HW2-F1}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/09-section-f-q25-q27.png}
+\caption{Q25--Q27: background process, SIGTERM, exit status 143, and the five largest processes by resident-memory usage.}
+\label{Figure:HW2-F2}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/10-section-g-q28-q30.png}
+\caption{Q28--Q30: archive creation, member listing, selected extraction, and successful content comparison.}
+\label{Figure:HW2-G}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/11-section-h-q31-q34.png}
+\caption{Q31--Q34: sockets, route, kernel, and boot-session history. The unprivileged socket listing contains no process details.}
+\label{Figure:HW2-H}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/12-section-i-q35-q37.png}
+\caption{Q35--Q37: installed coreutils version, available ripgrep package, and active cron state.}
+\label{Figure:HW2-I}
+\end{figure}
+
+\begin{figure}[H]
+\centering
+\includegraphics[width=\linewidth,height=0.77\textwidth,keepaspectratio]{figures/13-section-j-q38-q40.png}
+\caption{Q38--Q40: Victor uses the filename-and-contents interpretation for Q38, then verifies the CS export and removal of X from the environment.}
+\label{Figure:HW2-J}
+\end{figure}