LFCS Practice Exam 4 — 20 Questions

Question 1

A user reports that they cannot delete a file named 'important.txt' located in their home directory. The file is owned by the user and the user has write permission on the directory. Running 'rm important.txt' produces the error: 'rm: cannot remove 'important.txt': Operation not permitted'. The user has also tried using 'sudo rm' but gets the same error. Which of the following is the most likely cause and correct solution?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The file has the immutable attribute set. Use 'lsattr important.txt' and if the 'i' attribute is present, remove it with 'chattr -i important.txt'.. The error 'Operation not permitted' despite the user owning the file and having write permission on the directory indicates a filesystem-level restriction rather than a permission or ACL issue. The immutable attribute (i) on the file prevents any modification, including deletion, even by the root user. Running 'lsattr' reveals the attribute, and 'chattr -i' removes it, allowing deletion.

Answer

The file has an ACL that denies deletion. Use 'setfacl -b important.txt' to remove ACLs.

Answer

The file is currently in use by another process. Use 'lsof' to find the process and kill it.

Answer

The directory has the sticky bit set, preventing deletion. Use 'chmod o-t .' to remove the sticky bit.

Question 2

A security policy requires that all users in the 'admin' group must have a umask of 027 set automatically upon login. An administrator adds 'umask 027' to /etc/profile. However, users report that the umask is still 022. What is a likely cause?

Accepted Answer

The umask in /etc/profile is overridden by user-specific .bash_profile or .bashrc files.. User-specific shell configuration files (like ~/.bash_profile, ~/.bash_login, or ~/.profile for login shells, and ~/.bashrc for interactive non-login shells) are sourced after /etc/profile. These files can override the system-wide umask setting with a user-defined value, such as the default 022. Since the administrator only modified /etc/profile, any existing user-specific umask command in their personal dotfiles will take precedence.

Answer

The umask command in /etc/profile has a syntax error that is silently ignored.

Answer

The admin placed the umask command after the call to /etc/bash.bashrc which resets it.

Answer

The admin forgot to run 'source /etc/profile' on each user's session.

Question 3

After deleting user 'alice', the system administrator wants to also remove the home directory and mail spool. Which command should be used?

Accepted Answer

userdel -r alice. The correct option is B, userdel -r alice. The -r flag removes the user's home directory and mail spool, along with the user account. This is the standard flag for removing user data along with the account.

Answer

userdel -Z alice

Answer

userdel -f alice

Answer

userdel --remove alice

Question 4

An administrator receives a report that a specific directory /var/log is consuming too much disk space. Which command should be used to determine the total disk space used by that directory?

Accepted Answer

du -sh /var/log. The `du -sh /var/log` command calculates the total disk space used by the specified directory. The `-s` flag summarizes the total size, `-h` provides human-readable output (e.g., in KB, MB, GB), and the path `/var/log` targets the directory in question. This is the standard Linux command for determining directory disk usage.

Answer

df -h /var/log

Answer

ls -la /var/log

Answer

fdisk /var/log

Question 5

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. 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 6

After attempting to log in as user 'alice', the system rejects the password. The admin checks /etc/passwd and sees 'alice:x:1001:1001::/home/alice:/bin/bash'. The /etc/shadow shows 'alice:!!:18200:0:99999:7:::', indicating the account is locked. Which command will unlock the account?

Accepted Answer

usermod -U alice. The `usermod -U alice` command unlocks the user account by removing the `!` from the password hash field in `/etc/shadow`. The `!!` in the shadow file indicates the account is locked (password disabled), and `-U` explicitly unlocks it, restoring the password hash to an active state.

Answer

passwd -S alice

Answer

passwd -u alice

Answer

chage -d 0 alice

Question 7

Based on the exhibit, which process is using the most physical memory (RES)?

Accepted Answer

mysqld (PID 9101). The exhibit shows the output of the `top` command, where the RES column indicates the resident memory (physical RAM) used by each process. mysqld (PID 9101) has a RES value of 2.5g, which is significantly higher than nginx (PID 5678) with 128m and systemd (PID 1234) with 48m, making it the process using the most physical memory.

Answer

Not determinable from exhibit

Answer

nginx (PID 5678)

Answer

systemd (PID 1234)

Question 8

A user reports that a shell script 'backup.sh' in /home/user/scripts fails to execute. What is the most likely cause?

Accepted Answer

The script does not have execute permission for the user.. The most likely cause is that the script lacks execute permission for the user. In Linux, a file must have the execute bit set (e.g., `chmod +x backup.sh`) to be run as a script. Without it, the shell will refuse to execute the file, even if the user has read access and the script is syntactically correct.

Answer

The script is not in the user's PATH.

Answer

The script must be owned by root.

Answer

The script does not have a shebang line (#!/bin/bash) at the top.

Question 9

The backup script fails to run as user 'backup' with sudo. What is the issue?

Accepted Answer

The script does not have execute permission for the 'backup' user.. For a script to be executed via sudo, the user (backup) must have execute permission on the script file. Even if sudo is configured to allow the user to run the script, the operating system enforces file permission checks at execution time. Without the execute bit set for the backup user (or for others, depending on the sudo runas context), the kernel will refuse to execve() the script, resulting in a 'Permission denied' error.

Answer

The script has a restrictive umask.

Answer

The script is not owned by 'backup'.

Answer

The 'backup' user is not in the sudoers file.

Question 10

An administrator needs to create a system user that runs a service (no login, no home directory). Which command is appropriate?

Accepted Answer

useradd -r -M myservice. The `-r` flag creates a system user (UID below SYSTEM_UID_MIN, typically 1000) without a home directory by default, and `-M` explicitly overrides any default that might create a home directory, ensuring no home directory is created. This matches the requirement for a service account that does not need login or a home directory.

Answer

useradd -r myservice

Answer

useradd -r -m myservice

Answer

useradd -M myservice

Question 11

Which THREE of the following statements about Linux file permissions are correct?

Accepted Answer

The command 'chmod 400 secret.txt' sets read-only permission for the owner only.. The numeric permission mode 400 corresponds to read (4) for the owner, with no permissions for the group or others (0 and 0). This sets the file's permissions to r--------, meaning only the owner can read the file, and no one can write or execute it.

Answer

The command 'chmod a+w file' removes write permission for all.

Answer

The command 'chmod 644 file' sets permissions to rw-rw-rw-.

Question 12

A developer needs to extract the third column from a CSV file where columns are separated by commas, but some fields contain commas within double quotes. Which command correctly handles this?

Accepted Answer

awk 'BEGIN { FPAT = "[^,]*|\"[^\"]+\"" } { print $3 }' file.csv. It uses `awk` with the `FPAT` variable to define a field pattern that correctly handles commas inside double-quoted fields. The pattern `[^,]*|"[^"]+"` matches either a sequence of non-comma characters or a double-quoted string (including any commas within it), ensuring that the third column is extracted accurately even when fields contain embedded commas.

Answer

cut -d',' -f3 file.csv

Answer

awk -F',' '{ print $3 }' file.csv

Answer

sed 's/[^,]*,[^,]*,$[^,]*$.*/\1/' file.csv

Question 13

A cron job runs a script every hour but sometimes fails because the script cannot find commands like 'tar' and 'gzip'. The script works when run manually from a terminal. What is the best fix?

Accepted Answer

Use absolute paths for all commands in the script.. Cron jobs run in a minimal environment with a restricted PATH (often just /usr/bin:/bin). When the script uses commands like 'tar' and 'gzip' without absolute paths, the shell cannot locate them. Using absolute paths (e.g., /bin/tar, /bin/gzip) ensures the script always finds the commands regardless of the environment.

Answer

Run the cron job as root.

Answer

Modify the script to source the user's .bashrc.

Answer

Add a PATH statement to the cron job definition.

Question 14

A system administrator needs to find all files in /var/log that have been modified in the last 24 hours. Which command accomplishes this?

Accepted Answer

find /var/log -mtime -1. `find /var/log -mtime -1` finds files modified less than 1 day ago (i.e., within the last 24 hours). The `-mtime` option with a negative number (`-1`) matches files whose content was modified less than n*24 hours ago, which is exactly what the question requires.

Answer

find /var/log -mtime 0

Answer

find /var/log -newer /var/log/syslog

Answer

find /var/log -mtime 1

Question 15

A junior admin runs 'ls -l' and sees permissions '-rwxrwxr-x' on a file. What is the octal representation?

Accepted Answer

775. The permissions '-rwxrwxr-x' break down as: owner (rwx = 4+2+1 = 7), group (rwx = 4+2+1 = 7), others (r-x = 4+0+1 = 5). This gives the octal value 775. Option C is correct because it matches this calculation exactly.

Answer

755

Answer

770

Answer

777

Question 16

An administrator needs to replace all occurrences of the string 'foo' with 'bar' in all files under /etc/config, but only in files ending with .conf. The replacement must be done in-place, and backup copies should be created with a .bak extension. Which command accomplishes this?

Accepted Answer

find /etc/config -name '*.conf' -exec sed -i.bak 's/foo/bar/g' {} +. It uses `sed -i.bak` which creates a backup file with the .bak extension before performing the in-place substitution, and the `find -exec ... +` variant efficiently processes multiple files at once. The `-i` option with an argument (no space) specifies the backup suffix directly, satisfying the requirement for backup copies.

Answer

find /etc/config -name '*.conf' -exec sed -i .bak 's/foo/bar/g' {} +

Answer

find /etc/config -name '*.conf' -exec sed 's/foo/bar/g' {} \;

Answer

find /etc/config -name '*.conf' -exec sed -i 's/foo/bar/g' {} +

Question 17

Which nmcli command creates a VLAN interface with tag 10 on device eth0?

Accepted Answer

nmcli connection add type vlan con-name vlan10 dev eth0 id 10. The `nmcli connection add` command with `type vlan` requires the `dev` option to specify the parent interface (eth0) and the `id` option to set the VLAN tag (10). The `con-name` assigns a name to the connection profile, and the resulting interface will be named automatically (e.g., eth0.10) unless overridden by `ifname`. This creates a VLAN interface that tags frames with ID 10 on the parent device eth0.

Answer

nmcli connection add type vlan con-name vlan10 ifname eth0 id 10

Answer

nmcli device add vlan con-name vlan10 dev eth0 id 10

Answer

nmcli connection add type vlan con-name vlan10 ifname eth0.10

Question 18

Refer to the exhibit.

A user attempts to create a file in /backup/snapshots/ but receives an error. What is the most likely cause?

Accepted Answer

The /backup filesystem is mounted read-only.. The error occurs because the /backup filesystem is mounted read-only, which prevents any write operations, including file creation, regardless of directory permissions or available space. This is a common scenario when a filesystem is intentionally mounted with the 'ro' option in /etc/fstab or via the mount command to protect data integrity.

Answer

The /backup directory does not exist.

Answer

The user does not have write permission on /backup.

Answer

The /backup filesystem is full.

Question 19

A system administrator needs to ensure that a Linux server can communicate with other hosts on the same subnet. Which command should be used to verify the IP address and netmask configuration?

Accepted Answer

ip addr show. The `ip addr show` command is the modern, recommended tool in Linux for viewing IP addresses and netmasks (prefix lengths) assigned to network interfaces. It directly displays the configuration needed to verify subnet communication, unlike legacy tools that may not show the netmask clearly or mix routing information.

Answer

netstat -rn

Answer

route -n

Answer

ifconfig

Question 20

A Linux server is unable to resolve the hostname 'app.internal.example.com' but can resolve other names. The /etc/nsswitch.conf file contains: hosts: files mdns4_minimal [NOTFOUND=return] dns. The /etc/hosts file does not list the hostname. Which configuration change would most likely resolve the issue?

Accepted Answer

Remove the mdns4_minimal entry or change it to 'mdns4' without the NOTFOUND=return. The issue is that mdns4_minimal with [NOTFOUND=return] causes the resolver to stop after a failed mDNS query, preventing it from falling back to DNS. Since the hostname is not in /etc/hosts and not reachable via mDNS, the resolver returns 'not found' immediately without querying DNS. Removing the mdns4_minimal entry or changing it to 'mdns4' (without the NOTFOUND=return) allows the resolver to proceed to DNS if mDNS fails.

Answer

Change the hosts line to: hosts: dns files mdns4_minimal

Answer

Configure /etc/resolv.conf to use a different DNS server

Answer

Add the hostname to the local multicast DNS configuration