System Commands · Quiz 1 · Sep 2025

**1. Follow the hard link:** ln data.txt hardlink_data creates another name for data.txt’s inode, without copying its data. **2. Follow the symbolic link:** ln -s creates softlink_data as a separate inode storing the path data.txt. Thus the two regular-file names share an inode and the symlink has its own. **Answer: A — data.txt and hardlink_data share an inode; softlink_data differs.** A: **Correct:** It correctly separates hard-link identity from symbolic-link storage. B: **Incorrect:** The symbolic link has a distinct inode. C: **Incorrect:** This reverses the two link types. D: **Incorrect:** The two hard-linked names share one inode.

**1. Decode the octal digits:** Read=4, write=2, execute=1. Mode 554 gives owner \(5=4+1\), group \(5=4+1\), others \(4\). **2. Translate to permissions:** Owner and group can read and execute; others can read. No category receives write permission. **Answer: B — Owner/group read and execute; others read.** A: **Incorrect:** The owner also has read, and the group has no write. B: **Correct:** It matches r-x r-x r--. C: **Incorrect:** The group has read rather than write. D: **Incorrect:** No category has write permission.

**1. Restrict the filename:** sales_[a-z].csv contains exactly one lowercase-letter position between sales_ and .csv. **2. Count results:** The shell expands that glob to the matching files; piping the ordinary ls listing to wc -l counts them. **Answer: D — ls /home/user/Data/sales_[a-z].csv | wc -l.** **Convention note:** This course-style counting pipeline assumes ordinary matching filenames and at least one match. A: **Incorrect:** * allows any number and type of intervening characters. B: **Incorrect:** ? allows any single character, including a digit. C: **Incorrect:** [a-z]? requires two intervening characters. D: **Correct:** [a-z] requires exactly one lowercase letter.

**1. Identify the network-status tool:** netstat displays socket and network-connection information, including local port numbers. Options such as -l and -n are used when specifically listing listening sockets numerically. **Answer: A — netstat.** **Convention note:** Bare netstat normally shows active sockets; netstat -lntu is a more specific command for listening TCP/UDP ports. A: **Correct:** It reports local network sockets and port information. B: **Incorrect:** whois retrieves registration information. C: **Incorrect:** Wireshark captures packets rather than directly listing local listening sockets. D: **Incorrect:** nslookup queries DNS.

**1. Replace throughout Vim:** :%s/Hello/Hi/g applies substitution to every line (%) and every occurrence per line (g); :wq writes and quits. **2. Replace throughout nano:** Ctrl+\ starts replacement. Enter Hello and Hi, choose A for all matches, then Ctrl+O, Enter writes the file and Ctrl+X exits. **Answer: B — Global substitution in Vim and Replace All in nano.** A: **Incorrect:** :s without a range operates on the current line only. B: **Correct:** It uses each editor’s global replacement workflow and saves the result. C: **Incorrect:** The search/overwrite and delete shortcuts do not perform an all-occurrences replacement. D: **Incorrect:** Deleting a line and inserting Hi does not preserve the rest of the file.

**1. Identify the streams:** Normal output is descriptor 1; error output is descriptor 2. **2. Redirect only errors:** ./deploy.sh 2> errors.txt sends descriptor 2 to the file while leaving descriptor 1 connected to the terminal. **Answer: C — ./deploy.sh 2> errors.txt.** A: **Incorrect:** > redirects normal output, contrary to the request. B: **Incorrect:** It discards normal output and does not save errors. C: **Correct:** It redirects only stderr and leaves stdout visible. D: **Incorrect:** &> redirects both streams into the file.

**1. Combine both inputs:** cat intro.txt summary.txt emits both files’ contents in sequence. **2. Sort and overwrite:** The pipe feeds their combined lines to sort; > full_report.txt saves the sorted result and truncates any previous content. **Answer: D — cat intro.txt summary.txt | sort > full_report.txt.** A: **Incorrect:** cat with a named summary.txt does not also consume the piped intro.txt stream. B: **Incorrect:** >> appends instead of overwriting. C: **Incorrect:** It saves only intro.txt and sends the second sorted stream to the terminal. D: **Correct:** It combines, sorts and overwrites the requested destination.

**1. Parse the counts:** In grep -E, [A-Za-z]{3} requires three letters and [0-9]{2} requires two following digits. **2. Apply the anchors:** ^ and $ require that exact five-character pattern to occupy the whole line, such as Abc12, with no prefix or suffix. **Answer: B — Exactly three letters followed by exactly two digits.** A: **Incorrect:** The digits must immediately follow the three letters and end the line. B: **Correct:** Exactly three letters followed by exactly two digits form the entire line. C: **Incorrect:** It also restricts the preceding three characters and total length. D: **Incorrect:** Both the order and exact counts are constrained.

**1. Encode both boundaries:** ^report anchors the prefix and \.txt$ anchors the literal extension at line end. **2. Allow intermediate text:** .* permits zero or more characters, so the pattern matches report1.txt, report123.txt and report.txt in the supplied file. **Answer: B — grep "^report.*\.txt$" /home/user/files/files.txt.** A: **Incorrect:** The escaped dot and following * repeat literal dots; they do not stand for arbitrary intervening text. B: **Correct:** It correctly anchors the prefix and literal suffix with an arbitrary middle. C: **Incorrect:** report* repeats only the preceding t and does not encode an arbitrary middle. D: **Incorrect:** It effectively limits the filename to report plus one character and txt, omitting valid longer names.

**1. Test extraction:** head -n 5 input.txt prints the prefix and returns success if it can read the file. **2. Chain status messages:** && writes Done to status.log after success; || writes Error in input to error.log after failure of the preceding AND-list. This is option A. **Answer: A — head -n 5 input.txt && echo "Done" > status.log || echo "Error in input" > error.log.** **Convention note:** In A && B || C, C also runs if B fails, for example if status.log cannot be written. A is the intended answer assuming the log writes succeed. A: **Correct:** It places success after && and the fallback after ||. B: **Incorrect:** It swaps the success/failure branches and then chains an extra command. C: **Incorrect:** A pipeline to echo does not test head’s success under normal pipeline status rules. D: **Incorrect:** It writes the failure text on success and the success text on failure.

**1. Identify interface-address commands:** ifconfig displays interface configuration when installed; ip addr displays interfaces and their assigned addresses. **2. Exclude other tools:** ping probes reachability, netstat focuses on sockets/routes/statistics, and ipconf is not the standard Ubuntu command in the list. **Answer: B, E — ifconfig and ip addr.** A: **Incorrect:** It probes a target rather than listing local interface configuration. B: **Correct:** It displays interface addresses when the net-tools command is available. C: **Incorrect:** It is not the direct interface-address listing command asked for. D: **Incorrect:** ipconf is not the listed standard interface utility. E: **Correct:** ip addr directly displays interfaces and assigned IP addresses.

**1. Expand the first command:** test-{0..3} becomes test-0 through test-3, creating four directories. Its success enables the && command. **2. Expand the second command:** test-{4..6} creates three more directories and succeeds. Therefore the || fallback for test-7 through test-10 is skipped. **3. Add:** \(4+3=7\) directories are created. **Answer: 7.**

**1. Decode the range:** The alternatives match first octets 1–9,10–99,100–119,120–126, followed by a literal dot. They exclude loopback 127 and all larger octets. **2. Check the supplied list:** 10.0.0.1, 8.8.8.8, 15.12.34.56, 1.2.3.4 and 100.50.25.75 match. wc -l therefore prints 5. **Answer: 5.**

**1. Use the existing parent:** Resources already exists, so mkdir Resources/Reference creates the required subdirectory. **2. Create the file:** A addresses the file using its full relative path; B enters the new directory and touches index.md there. Both place it correctly. **Answer: A, B — Command sets A and B.** A: **Correct:** It creates the specified directory and file by relative paths. B: **Correct:** It creates the directory, enters it and touches the required file. C: **Incorrect:** It swaps the file and directory names and types. D: **Incorrect:** It creates Reference under home instead of under Resources.

**1. Move the file:** mv Projects/ProjectA/main.py Projects/ProjectB/ leaves ProjectA empty and puts main.py alongside app.js in ProjectB. **2. Remove the empty directory and list destination:** A uses rmdir, D uses rm -rf; both then list Projects/ProjectB. **Answer: A, D — Command sets A and D.** A: **Correct:** It completes the move, removes the empty source directory and lists the destination. B: **Incorrect:** Plain rm refuses the directory. C: **Incorrect:** cp leaves main.py in the source, so rmdir fails; it also lists the source rather than the destination. D: **Correct:** It removes the now-empty source recursively and lists the correct destination.