LFCS Essential Commands Practice Test 6 — 15 Questions

Question 1

A system administrator has a cron job that runs a backup script. The script requires the variable BACKUP_DIR to be set, but the administrator cannot modify the script. Which is the most appropriate place to define the variable for cron?

Accepted Answer

In the crontab file with the line 'BACKUP_DIR=/var/backups' before the command. Cron jobs run in a minimal environment and do not source shell profiles or login scripts. Defining BACKUP_DIR directly in the crontab file before the command ensures the variable is set in the cron execution context, which is the only reliable way to pass environment variables to cron without modifying the script.

Answer

In /etc/profile.d/backup.sh

Answer

In /etc/environment

Answer

In ~/.bash_profile

Question 2

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' {} +. Option C is correct because 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 3

A user wants to view the contents of a compressed log file /var/log/syslog.2.gz without decompressing it first. Which command should they use?

Accepted Answer

zcat /var/log/syslog.2.gz. Option C is correct because `zcat` is a utility that reads compressed files (typically gzip-compressed) and outputs their decompressed content to standard output without permanently decompressing the file. This allows the user to view the contents of `/var/log/syslog.2.gz` directly in the terminal.

Answer

gunzip /var/log/syslog.2.gz

Answer

cat /var/log/syslog.2.gz

Answer

less /var/log/syslog.2.gz

Question 4

A security policy requires that all users in the 'webadmin' group should have read and write access to files in /var/www/html. New files created in that directory should automatically be assigned to the 'webadmin' group and have group read/write permissions. Which combination of permissions and group ownership should be set on /var/www/html?

Accepted Answer

chmod g+s /var/www/html; chmod 2775 /var/www/html; chown root:webadmin /var/www/html. Option D is correct because setting the setgid bit (g+s) on /var/www/html ensures that new files inherit the directory's group ('webadmin'), and the 2775 permissions grant group read/write/execute (rwx) while the setgid bit is represented by the leading 2. This combination satisfies the security policy: group ownership inheritance and group read/write access for all new files.

Answer

chmod o+t /var/www/html; chmod 1775 /var/www/html; chown root:webadmin /var/www/html

Answer

chmod g+s /var/www/html; chmod 2755 /var/www/html; chown root:webadmin /var/www/html

Answer

chmod u+s /var/www/html; chown root:webadmin /var/www/html

Question 5

Which command displays the amount of free and used memory in the system?

Accepted Answer

free -h. The `free -h` command displays the total, used, and free physical memory (RAM) and swap space in a human-readable format (e.g., GiB, MiB). The `-h` flag converts raw byte counts into appropriate units, making it the correct tool for checking memory usage.

Answer

df -h

Answer

ps aux

Answer

netstat -i

Question 6

An administrator wants to terminate a process with PID 1234 and all its child processes. Which command should be used?

Accepted Answer

kill -9 -1234. Option B is correct because the `kill` command with a negative PID (e.g., `kill -9 -1234`) sends the signal to the process group identified by the absolute value of the PID. Since process group IDs typically equal the PID of the group leader, using `-1234` targets the entire process group, terminating PID 1234 and all its child processes. The `-9` (SIGKILL) ensures immediate termination without cleanup.

Answer

pkill -P 1234

Answer

kill -15 1234

Answer

kill -9 1234

Question 7

Which TWO commands can be used to view the last 10 lines of a file and also follow new lines as they are written?

Accepted Answer

tail -f -n 10. Option A is correct because `tail -f -n 10` displays the last 10 lines of a file and then follows new lines as they are appended, using the `-f` (follow) flag. This is the standard way to monitor a log file in real time while initially showing the most recent 10 lines.

Answer

cat -n

Answer

tail -n 10

Answer

head -n 10

Question 8

Which THREE of the following commands can be used to search for a string in multiple files and display the matching lines?

Accepted Answer

ack 'pattern' /path. Option B is correct because `ack` is a Perl-based grep replacement that recursively searches for a pattern in files under a given path, displaying matching lines by default. It is designed for source code and text files, making it a valid tool for this task.

Answer

find /path -name '*.txt' -type f

Answer

sort /path/file

Question 9

Which TWO commands can be used to display the current working directory?

Accepted Answer

pwd. The `pwd` command (B) is the standard POSIX command that prints the full pathname of the current working directory. The shell variable `$PWD` (D) is automatically set by the shell to the current working directory, so `echo $PWD` outputs the same path. Both are valid ways to display the current working directory.

Answer

which pwd

Answer

date

Answer

whoami

Question 10

Refer to the exhibit. The nginx service failed to start. What is the most likely immediate next step to diagnose the issue?

Accepted Answer

Run nginx -t to test configuration. Option D is correct because `nginx -t` tests the configuration file syntax and validity before attempting to start the service. Since nginx failed to start, a configuration error is a common cause, and this command immediately identifies syntax errors or missing directives without restarting the service.

Answer

Run journalctl -u nginx.service -x -n 50

Answer

Run apt-get install nginx

Answer

Run systemctl restart nginx

Question 11

Refer to the exhibit. The administrator receives alerts that the root filesystem is almost full. Which command could free up space by removing old log files?

Accepted Answer

find /var/log -name '*.log' -mtime +30 -delete. Option A is correct because the `find` command with `-name '*.log'` targets log files, `-mtime +30` selects files modified more than 30 days ago, and `-delete` removes them. This safely frees space by purging only old logs, preserving recent logs needed for troubleshooting.

Answer

truncate -s 0 /var/log/syslog

Answer

rm -rf /var/log/*

Answer

du -sh /var/log

Question 12

A system administrator is managing a production web server running CentOS 7. The server hosts a critical application that depends on the 'httpd' package. Recently, the administrator attempted to install an updated version of httpd using 'yum update httpd', but the update failed with a dependency error: 'Error: Package: httpd-2.4.6-97.el7.centos.x86_64 requires libapr-1.so.0()(64bit)'. The administrator verifies that the apr package is installed (apr-1.5.2-6.el7.x86_64) and that the required library file exists at /usr/lib64/libapr-1.so.0. Despite this, yum continues to fail with the same error. After checking the yum repository configuration, the administrator notices that the base repository lists 'mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os' and the 'baseurl' is commented out. The system's /etc/yum.conf has 'keepcache=1'. What is the most likely cause of the dependency error, and which command should the administrator run to resolve it?

Accepted Answer

The repository metadata is stale; run 'yum clean all' then 'yum update'.. Option A is correct. The dependency error despite the library being present suggests stale repository metadata. yum clean all clears the cache and forces fresh metadata download, which often resolves such false positives. Option B is incorrect because the apr version provides the required library. Option C is similar to A but manual deletion is unnecessary. Option D bypasses dependency checks and risks breaking the system.

Answer

The yum cache is corrupted; delete /var/cache/yum manually and run 'yum makecache'.

Answer

The dependency is satisfied but yum's dependency resolver has a bug; use 'rpm -Uvh httpd.rpm --nodeps' to bypass dependency check.

Answer

The installed apr package is from a different version than what httpd expects; install a newer apr from a different repository.

Question 13

A system administrator notices that '/var/log/syslog' has grown very large and is consuming significant disk space. The administrator wants to identify the largest log files in the '/var/log' directory hierarchy. Which command should the administrator use?

Accepted Answer

du -ah /var/log | sort -hr | head -10. Option B is correct because `du -ah /var/log` calculates the disk usage of all files and directories in `/var/log` in human-readable format, then `sort -hr` sorts them by size in descending order, and `head -10` shows the top 10 largest entries. This directly identifies the largest log files in the hierarchy, which is exactly what the administrator needs.

Answer

find /var/log -size +100M -exec ls -lh {} \;

Answer

df -h /var/log

Answer

ls -lhS /var/log

Question 14

A developer reports that a compiled binary 'app' fails to execute with 'Permission denied' error when run from a mounted directory '/mnt/software'. The binary has execute permissions for all users. What is the most likely cause?

Accepted Answer

The filesystem is mounted with the 'noexec' option.. Option C is correct because if the filesystem is mounted with the 'noexec' option, no binaries can be executed from it, even if they have execute permissions. Option A (setuid) would not cause 'Permission denied' but rather may require root ownership. Option B (SELinux) could cause denial but is more specific; noexec is a common misconfiguration. Option D (missing libraries) results in 'cannot execute binary file' or 'error while loading shared libraries'.

Answer

SELinux is blocking execution.

Answer

The binary is linked against missing libraries.

Answer

The binary is setuid but owned by a user other than root.

Question 15

A system administrator needs to stop a misbehaving process gracefully, allowing it to clean up resources. The process is unresponsive to the standard SIGTERM signal. What should the administrator do next?

Accepted Answer

Use 'kill -15' again, wait a few seconds, then use 'kill -9' if still unresponsive.. Option A is correct because the standard escalation path for terminating an unresponsive process is to first send SIGTERM (signal 15) to request a graceful shutdown, then after a brief wait, send SIGKILL (signal 9) if the process has not terminated. This allows the process a chance to clean up resources before being forcibly killed, which is the recommended practice in Linux process management.

Answer

Wait for the process to finish on its own.

Answer

Use 'kill -9' immediately.

Answer

Send SIGTERM again with a higher priority.