System Commands · Quiz 1 · May 2025

**1. Compare what is stored:** A hard link is another directory entry for the same inode and data. A symbolic link is a separate object storing a target pathname. **2. Apply the consequences:** Hard links do not copy file contents and normally cannot span filesystems. Symbolic links can name targets across filesystems and can point to directories. **Answer: B — A hard link is essentially another name for the same file data (inode), while a .** A: **Incorrect:** Hard links share existing data rather than copying it. B: **Correct:** It correctly states shared identity versus a stored pathname. C: **Incorrect:** This reverses the cross-filesystem distinction. D: **Incorrect:** Hard links are generally restricted for directories; symbolic links can target directories or regular files.

**1. Select the prefix:** head -n 7 config.txt prints the first seven lines. **2. Select the suffix:** tail -n 3 config.txt prints the final three lines. These are the two commands in A. **Answer: A — head -n 7 config.txt and tail -n 3 config.txt.** A: **Correct:** head and tail implement the two requested selections. B: **Incorrect:** These are not valid cat first/last selection options. C: **Incorrect:** less is a pager; the listed invocations do not implement the two bounded outputs. D: **Incorrect:** The proposed display options are not the standard text-selection commands.

**1. Match the assigned ports:** SSH uses 22 (C), HTTP uses 80 (A), SMTP uses 25 (B), and HTTPS uses 443 (D). **Answer: B — 1-C, 2-A, 3-B, 4-D.** A: **Incorrect:** It mismatches SSH, HTTP and SMTP. B: **Correct:** All four port-service mappings agree. C: **Incorrect:** Each mapping assigns the wrong service. D: **Incorrect:** It assigns the wrong service to each port.

**1. Start with reachability:** An SSH timeout can arise before authentication because of a disconnected or unreachable host. ping 192.168.1.50 provides an initial basic network probe. **2. Interpret cautiously:** A reply supports host reachability; no reply is not conclusive because ICMP may be filtered. If needed, next check routing, firewalls and the SSH port. **Answer: B — Check basic reachability with ping 192.168.1.50.** A: **Incorrect:** Changing text editors does not repair a network timeout. B: **Correct:** It is a simple first reachability check. C: **Incorrect:** A crashed SSH service is only one possibility and has not been established. D: **Incorrect:** There is no evidence that SSH is listening on a web port.

**1. Perform the Vim edit:** 1G moves to the first line, dd removes that whole line, and :wq saves and exits. **2. Perform the nano edit:** Alt+\ moves to the file beginning; Ctrl+K cuts the current line. Ctrl+O, Enter saves, then Ctrl+X exits. **Answer: A — Vim 1G, dd, :wq; nano beginning, cut line, save, exit.** A: **Correct:** Both editors navigate to the first line, remove it and save before exiting. B: **Incorrect:** D does not remove the whole line including its newline, and the nano sequence is incorrect. C: **Incorrect:** x deletes a character rather than an entire line, and the nano sequence is incorrect. D: **Incorrect:** The listed quit-without-saving operations discard the requested edit.

**1. Connect the streams:** In command1 | command2, the shell connects command1’s standard output to command2’s standard input. **2. Distinguish execution control:** A pipe carries data; it does not mean “run only if the first command succeeds” or “run only if data appears.” **Answer: D — stdout of command1 becomes stdin of command2.** A: **Incorrect:** Sequential execution is the role of a list separator, not the defining pipe behaviour. B: **Incorrect:** A plain pipe does not redirect stderr. C: **Incorrect:** The second command starts even if the first produces no data. D: **Correct:** It correctly identifies stdout-to-stdin data flow.

**1. Require verification success:** && starts create_report only after verify_data returns zero. **2. Save only the report output:** > final_report.txt belongs to create_report and overwrites its output file when that branch runs. On verification failure the report command and its redirection are skipped. **Answer: C — verify_data && create_report > final_report.txt.** A: **Incorrect:** ; runs the report regardless of verification success. B: **Incorrect:** || runs the report after failure. C: **Correct:** It gates creation on success and overwrites the requested output file. D: **Incorrect:** A pipe supplies data and does not condition execution on a successful status.

**1. Separate the producer streams:** generate_raw_data 2> raw_data_errors.log captures only the producer’s stderr with truncation. **2. Pipe the remaining stdout:** | process_stream sends raw data into the processor. Its stdout remains on the terminal because it is not redirected. **Answer: A — generate_raw_data 2> raw_data_errors.log | process_stream.** A: **Correct:** It logs the producer’s stderr while piping its stdout into processing. B: **Incorrect:** It logs the processor’s stderr rather than the producer’s. C: **Incorrect:** It redirects stdout into a file named process_stream instead of running a pipeline. D: **Incorrect:** |& combines producer stderr with the data stream, rather than separately logging it.

**1. Read the anchors:** ^A requires A at the start and Z$ requires Z at the end. **2. Read the middle:** .* means zero or more arbitrary non-newline characters within the line. Consequently AZ, ABZ and A123Z all match. **Answer: B — Starts with A, ends with Z, with any intervening characters.** A: **Incorrect:** The anchors require the whole line boundary positions, and * allows more than one middle character. B: **Correct:** It correctly describes the two anchors and variable-length middle. C: **Incorrect:** No alternation appears in the expression. D: **Incorrect:** AZ matches, but longer strings also match.

**1. Anchor the prefix:** ^ap requires lowercase ap at the start of a line. **2. Apply case-sensitive matching:** It prints apple, apricot and apply, but not banana or Apollo. **Answer: D — grep '^ap' data.txt.** A: **Incorrect:** ap* means a followed by zero or more p characters anywhere, so banana can match its a. B: **Incorrect:** $ap puts an end anchor before ap rather than anchoring the beginning. C: **Incorrect:** ap$ requires ap at the end of a line. D: **Correct:** ^ap directly expresses the requested starting prefix.

**1. Parse the ERE:** ^(Task|Project) ID: [0-9]+ requires Task or Project at the start, then the literal text and at least one digit. **2. Apply output redirection:** grep prints matching complete lines; > results.txt creates or truncates the destination and saves those lines. **Answer: A — Matching Task/Project ID lines overwrite results.txt.** **Convention note:** There is no final $ anchor, so additional text after the matched digits is allowed. A: **Correct:** It describes the anchored alternatives, digit repetition and overwrite. B: **Incorrect:** The match is anchored and + accepts more than one digit. C: **Incorrect:** > overwrites rather than appends. D: **Incorrect:** The alternatives allow either prefix; they do not require both.

**1. Open the destination:** With ordinary shell settings, > file1 opens an existing file with truncation, or creates a new file if it is absent and the directory permits it. **2. Distinguish append:** >> is the append operator. Standard > does not request interactive confirmation. **Answer: B, C — Existing content is overwritten; a missing file is created.** **Convention note:** This assumes successful permissions and ordinary clobber settings; set -C/noclobber can prevent overwriting an existing regular file. A: **Incorrect:** Appending is the role of >>, not >. B: **Correct:** An existing destination is normally truncated before execution. C: **Correct:** A missing destination can be created. D: **Incorrect:** The shell normally performs this redirection without confirmation.

**1. Decode ls -lai:** ls lists entries; -l requests long format, -a includes dot-prefixed entries, and -i adds inode numbers. **2. Interpret /usr/bin:** This standard directory primarily contains executable commands available to users. Thus A, D and E are correct. **Answer: A, D, E — A, D and E.** A: **Correct:** ls is the directory-listing utility. B: **Incorrect:** -l requests long format rather than short format. C: **Incorrect:** -a includes hidden entries rather than suppressing them. D: **Correct:** -i displays each entry’s inode number. E: **Correct:** /usr/bin primarily holds user commands/executables.

**1. Read the BRE interval:** [[:digit:]]\{3\} matches a run of three digits. The escaped braces are the correct basic-regex repetition syntax. **2. Apply substring matching:** With no ^ or $ anchors, 123,789,2345 and 111 all contain a three-digit run. The mixed strings 45a and b01 do not. Four lines match. **Answer: 4.**

**1. Create and copy with absolute paths:** A creates /home/user/Temp/Backup, copies Documents/report.txt there, and lists the destination. **2. Resolve C’s relative paths:** After cd Temp, mkdir Backup creates the same directory. ../Documents/report.txt refers back to the home-level Documents directory, so its copy and listing are also correct. **Answer: A, C — Command sets A and C.** A: **Correct:** Its absolute paths consistently identify the required source and destination. B: **Incorrect:** mk dir, copy and list are not the standard commands shown by the task. C: **Correct:** Its relative paths resolve correctly from Temp. D: **Incorrect:** newdir and move are not the required commands, and moving would not preserve the original as requested.

**1. Encode the target mode:** Owner rw gives \(4+2=6\); group r gives 4; others none gives 0. Thus chmod 640 is correct. **2. Check symbolic notation:** chmod u=rw,g=r,o= sets exactly the same permission categories. Both produce −rw-r-----. **Answer: B, D — chmod 640 or chmod u=rw,g=r,o=; −rw-r-----.** A: **Incorrect:** 750 grants owner/group execute permission and differs from the request. B: **Correct:** 640 produces exactly rw-r-----. C: **Incorrect:** 740 also grants owner execute permission, regardless of the claimed displayed string. D: **Correct:** The symbolic assignments exactly set owner rw, group r and others none.