LFCS Essential Commands — Timed 20 Questions

Question 1

A user reports that a script fails with 'Permission denied' when executed. The script has permissions -rw-r--r-- and is owned by the user. Which command should the user run to make the script executable for the owner only?

Accepted Answer

chmod u+x script.sh. Option B is correct because the script currently has permissions `-rw-r--r--`, meaning the owner has read and write but not execute permission. The `chmod u+x` command adds the execute permission for the owner only, which is exactly what the user needs to run the script without affecting group or others.

Answer

chmod u+s script.sh

Answer

chown :users script.sh

Answer

chmod +x script.sh

Question 2

A system administrator needs to find all files in /var/log that have been modified in the last 7 days. Which command accomplishes this?

Accepted Answer

find /var/log -type f -mtime -7. Option D is correct because the `find` command with `-mtime -7` searches for files whose modification time (content change) is less than 7 days ago, which matches the requirement of 'modified in the last 7 days'. The `-type f` restricts the search to regular files, and `/var/log` is the target directory.

Answer

find /var/log -type f -atime -7

Answer

find /var/log -type f -ctime -7

Answer

find /var/log -type f -mtime +7

Question 3

An administrator wants to ensure that a background process continues running after logout. Which command should be used to start the process?

Accepted Answer

nohup sleep 100 &. The correct answer is A because `nohup` allows a process to ignore the SIGHUP signal that is sent to background processes when the parent shell exits, ensuring it continues running after logout. The `&` places the command in the background, and `nohup` redirects output to `nohup.out` by default, making it the standard way to run a process immune to hangups.

Answer

runproc sleep 100 &

Answer

sleep 100 &

Answer

sleep 100 & disown

Question 4

A technician needs to display the contents of a compressed file named archive.tar.gz without extracting it. Which command should be used?

Accepted Answer

zcat archive.tar.gz | tar -t. Option C is correct because it uses `zcat` to decompress the `.gz` layer on the fly and pipes the resulting uncompressed tar archive into `tar -t`, which lists the contents without extracting. This allows viewing the file listing without first decompressing to disk, satisfying the requirement to display contents without extraction.

Answer

tar -tf archive.tar

Answer

tar -xzf archive.tar.gz

Answer

zcat archive.tar.gz

Question 5

A user wants to find the location of the 'grep' binary. Which command should they use?

Accepted Answer

which grep. The 'which' command is specifically designed to locate the binary (executable) of a command by searching the directories listed in the user's PATH environment variable. Option B, 'which grep', will output the full path to the grep binary, such as '/usr/bin/grep', directly answering the user's request.

Answer

man grep

Answer

uname -a

Answer

grep -r 'grep' /usr/bin

Question 6

Which TWO commands can be used to create a new empty file?

Accepted Answer

touch file. Option A is correct because the `touch` command is specifically designed to create an empty file if it does not already exist, or update its timestamps if it does. Option D is correct because using the shell redirection operator `>` with no command before it (or with a null command) creates an empty file by truncating any existing content or creating a new zero-byte file.

Answer

mkdir file

Answer

cat file

Answer

echo 'text' > file

Question 7

Which THREE commands can be used to view the contents of a file?

Accepted Answer

cat. The `cat` command (option C) is a standard Unix utility that reads files sequentially and outputs their contents to the standard output. It is one of the most basic and direct ways to view the entire content of a file in the terminal.

Answer

grep

Answer

find

Question 8

What is the purpose of the chmod 755 command in this exhibit?

Accepted Answer

Set permissions to rwxr-xr-x. The chmod 755 command sets the file permissions to rwxr-xr-x, meaning the owner has read, write, and execute permissions (7), while the group and others have read and execute permissions (5). This is a common permission set for executable scripts and directories to allow execution without granting write access to non-owners.

Answer

Add execute permission for the owner only

Answer

Remove write permission for others

Answer

Set the setuid bit

Question 9

Based on the exhibit, which process will be affected if the root user runs 'kill 5678'?

Accepted Answer

The www-data process with PID 5678. The 'kill 5678' command sends the default SIGTERM (signal 15) to the process with PID 5678. Since the root user has the CAP_KILL capability and is not subject to the ordinary permission checks that restrict non-root users, root can send signals to any process, including those owned by www-data. Therefore, the www-data process with PID 5678 will be terminated.

Answer

The root process (PID 1234)

Answer

All www-data processes

Answer

No process, because root cannot kill www-data processes

Question 10

A developer accidentally deleted a critical file /var/log/app.log. The system administrator knows that the file was recently backed up using a cron job that runs 'tar -czf /backup/logs.tar.gz /var/log/'. Which command should the administrator use to restore the file from the backup without extracting the entire archive?

Accepted Answer

tar -xzf /backup/logs.tar.gz --to-stdout var/log/app.log > /var/log/app.log. Option C is correct because `tar -xzf` extracts the specified file (`var/log/app.log`) from the compressed archive and `--to-stdout` sends its content to standard output, which is then redirected to recreate the file at `/var/log/app.log`. This restores the single file without extracting the entire archive, matching the requirement precisely.

Answer

tar -xf /backup/logs.tar.gz var/log/app.log

Answer

tar -tf /backup/logs.tar.gz | grep app.log

Answer

cp /backup/logs.tar.gz:/var/log/app.log /var/log/app.log

Question 11

A system administrator needs to find all files in /home that are owned by user 'alice' and have been modified in the last 7 days. The administrator then wants to compress those files into a single archive named alice_recent.tar.gz. Which of the following commands accomplishes this?

Accepted Answer

find /home -user alice -mtime -7 -exec tar -rf alice_recent.tar.gz {} +. Option A is correct because it uses `find` with `-user alice` and `-mtime -7` to locate files owned by alice modified within the last 7 days, then executes `tar -rf` with `{} +` to append those files to an archive. The `-r` flag appends files to an existing archive (or creates one if it doesn't exist), and `{} +` efficiently passes multiple filenames to a single `tar` invocation, avoiding command-line length limits.

Answer

find /home -user alice -mtime -7 -print | cpio -o > alice_recent.tar.gz

Answer

tar -czf alice_recent.tar.gz -T <(find /home -user alice -mtime -7)

Answer

find /home -user alice -mtime -7 | tar -cvf alice_recent.tar.gz

Question 12

A junior administrator needs to display the first 10 lines of a file named 'data.csv'. Which command should they use?

Accepted Answer

head data.csv. The `head` command is specifically designed to display the first 10 lines of a file by default. Running `head data.csv` will output the first 10 lines of the CSV file, making it the correct choice for this task.

Answer

less data.csv

Answer

tail data.csv

Answer

cat data.csv

Question 13

A system administrator is troubleshooting a user's report that a command 'myapp' is not found. The administrator checks the PATH variable and sees it includes /usr/local/bin. The administrator verifies that the binary 'myapp' exists in /usr/local/bin with permissions 755. However, running 'myapp' still fails with 'command not found'. What is the most likely cause?

Accepted Answer

The shell's hash table is stale; run 'hash -r'. Option C is correct because the shell caches the locations of executables in a hash table to avoid searching PATH repeatedly. When a new binary is added to a directory already in PATH, the shell may still have a stale entry (or no entry) for that command, causing it to report 'command not found' even though the binary exists. Running 'hash -r' clears the entire hash table, forcing the shell to re-scan PATH on the next invocation.

Answer

The user's PATH does not include /usr/local/bin

Answer

The binary is a shell script missing a shebang

Answer

The binary does not have execute permission for the user

Question 14

Which TWO commands can be used to display the current working directory? (Choose exactly two.)

Accepted Answer

echo $PWD. Option B is correct because the shell stores the current working directory path in the environment variable `$PWD`, and `echo $PWD` prints its value. This is a reliable way to display the current directory, as the shell updates `PWD` automatically on every `cd` command.

Answer

ls

Answer

dirname

Answer

cd

Question 15

Which THREE of the following commands can be used to view the contents of a compressed file named 'file.gz' without permanently decompressing it? (Choose exactly three.)

Accepted Answer

zmore file.gz. Option B is correct because `zmore` is a utility that allows you to view the contents of a compressed file (such as `file.gz`) page by page without permanently decompressing it. It internally decompresses the file on the fly and pipes the output through `more`, making it ideal for inspecting large compressed files without modifying the original archive.

Answer

gzip file.gz

Answer

gunzip file.gz

Question 16

A user with uid 1000 tries to read /etc/shadow and gets 'Permission denied'. The user is not in the shadow group. Which of the following actions would allow the user to read the file without changing the file's group or permissions?

Accepted Answer

Add user1 to the shadow group using usermod -aG shadow user1. Option C is correct because adding user1 to the shadow group grants group-level read access to /etc/shadow without altering the file's permissions or group ownership. The file is typically owned by root:shadow with permissions 640 (rw-r-----), so members of the shadow group can read it. The usermod -aG command appends the user to the supplementary group, preserving existing group memberships.

Answer

Set an ACL using setfacl to grant user1 read access

Answer

Use chmod o+r /etc/shadow as root

Answer

Change the file owner to user1 using chown

Question 17

You are a system administrator for a company that runs a web server on a Linux system. The web server logs are stored in /var/log/nginx/access.log. The log file grows rapidly and rotates weekly via logrotate. The system has been running for several months. Recently, the development team reported that the web server is responding slowly. You suspect that the disk I/O might be high due to log file activity. You check the disk usage and find that /var/log/nginx/access.log is 4 GB, and the rotated logs (access.log.1.gz, access.log.2.gz, etc.) total another 10 GB. The /var partition has 20 GB total, so it's 70% full. You decide to reduce the disk usage by compressing the current log file and truncating it without stopping the nginx service. Which command sequence should you use to safely achieve this?

Accepted Answer

cp /var/log/nginx/access.log /var/log/nginx/access.log.bak && :> /var/log/nginx/access.log && gzip /var/log/nginx/access.log.bak. Option B is correct because it first copies the current log file to a backup, then truncates the original file in place using the shell null command (`:>`) without stopping nginx, and finally compresses the backup. This ensures nginx continues writing to the same inode (file descriptor remains valid) and the disk space is reclaimed after compression.

Answer

:> /var/log/nginx/access.log && cp /var/log/nginx/access.log /var/log/nginx/access.log.bak && gzip /var/log/nginx/access.log.bak

Answer

rm /var/log/nginx/access.log && touch /var/log/nginx/access.log && chmod 644 /var/log/nginx/access.log

Answer

mv /var/log/nginx/access.log /var/log/nginx/access.log.bak && touch /var/log/nginx/access.log && gzip /var/log/nginx/access.log.bak

Question 18

You are managing a Linux server that hosts a critical web application. The server is running low on disk space in the root filesystem, and you need to free up space urgently. You run 'df -h' and see that /dev/sda1 is mounted on / and is 95% full. You also notice that /var/log/messages is over 2 GB in size. The application writes logs to /var/log/app.log, which is also large. The server has a separate /var partition that has plenty of free space. The application must continue running with minimal downtime. You need to compress and rotate logs without losing any data, and ensure that the root filesystem has at least 10% free space. Which of the following actions should you take first to achieve this goal?

Accepted Answer

Use logrotate with the 'copytruncate' option to rotate /var/log/app.log and move the rotated file to /var/old_logs/.. Option C is correct because logrotate with the 'copytruncate' option allows the application to continue writing to the same file descriptor while the current log is copied and then truncated to zero length. This avoids any application downtime and the rotated log can be moved to the separate /var partition (which has free space) for compression or archiving, freeing space on the root filesystem without data loss.

Answer

Delete /var/log/app.log and /var/log/messages to free space quickly.

Answer

Stop the application, truncate /var/log/app.log, then restart the application.

Answer

Compress /var/log/app.log using gzip and keep it in place.

Question 19

A system administrator needs to list all files in the current directory, including hidden files, in a long listing format sorted by modification time (oldest first). Which command achieves this?

Accepted Answer

ls -lart. Option B is correct because `ls -lart` combines the `-l` (long listing), `-a` (include hidden files starting with dot), `-r` (reverse order), and `-t` (sort by modification time, newest first). The reverse flag flips the sort to oldest first, meeting the requirement exactly.

Answer

ls -lihrt

Answer

ls -lat

Answer

ls -lrt

Question 20

A user wants to find all files in /var/log that have been modified within the last 2 days. Which command should they use?

Accepted Answer

find /var/log -mtime -2. Option A is correct because the `find` command with `-mtime -2` searches for files whose content was last modified less than 2 days ago (i.e., within the last 48 hours). The minus sign before the number indicates 'less than' or 'within the last N days', which matches the user's requirement to find files modified within the last 2 days.

Answer

find /var/log -mmin -2880

Answer

find /var/log -mtime +2

Answer

find /var/log -mtime 2