Essential Commands practice questions

find /home -type f -size +100000000c

Why wrong: Incorrect: `+100000000c` matches files larger than 100,000,000 bytes, which is about 95.4 MB, not 100 MB.

find /home -type f -size +100MB

Why wrong: Incorrect: `MB` is not a valid size suffix; find expects `M` for mebibytes or `k` for kibibytes.

find /home -type f -size 100M

Why wrong: Incorrect: `-size 100M` matches files exactly 100 MB in size, not larger than 100 MB.

chmod 755 file.txt

Why wrong: Incorrect. `chmod` sets file permissions, not ownership.

usermod -G staff alice

Why wrong: Incorrect. `usermod -G staff alice` modifies the supplementary group membership of user `alice`; it does not change file ownership.

passwd alice

Why wrong: Incorrect. `passwd` changes a user's password, not file ownership.

chmod u+s script.sh

Why wrong: Sets the setuid bit, not execute.

chown :users script.sh

Why wrong: Changes group ownership, not permissions.

chmod +x script.sh

Why wrong: Adds execute for all users, not just owner.

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

Why wrong: Uses access time, not modification time.

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

Why wrong: Uses change time (inode change), not modification time.

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

Why wrong: Finds files modified more than 7 days ago.

runproc sleep 100 &

Why wrong: Not a valid command.

sleep 100 &

Why wrong: Runs in background but will be terminated on logout.

sleep 100 & disown

Why wrong: Does remove job from shell's job control, but SIGHUP may still be sent if not handled; nohup is preferred.

tar -tf archive.tar

Why wrong: Used for uncompressed tar files.

tar -xzf archive.tar.gz

Why wrong: Extracts files, does not just list.

zcat archive.tar.gz

Why wrong: Only decompresses, does not list tar contents.

man grep

Why wrong: Displays the manual page, not location.

uname -a

Why wrong: Shows system information, not command location.

grep -r 'grep' /usr/bin

Why wrong: Searches for string in files, not location.

mkdir file

Why wrong: Creates a directory, not a file.

cat file

Why wrong: Concatenates file content, does not create.

echo 'text' > file

Why wrong: Creates a file with content, not empty.

grep

Why wrong: Searches for patterns, not for viewing entire file.

find

Why wrong: Searches for files, does not display contents.

Add execute permission for the owner only

Why wrong: 755 adds execute for all, not just owner.

Remove write permission for others

Why wrong: Others already had read-only; 755 does not remove write because they had none.

Set the setuid bit

Why wrong: chmod 755 does not set setuid; that would be 4755.

The root process (PID 1234)

Why wrong: PID 5678 is different from 1234.

All www-data processes

Why wrong: Only the process with PID 5678 is killed.

No process, because root cannot kill www-data processes

Why wrong: Root can kill any process.

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

Why wrong: Extracts only the specified file, but fails to decompress the gzip archive because the -z flag is omitted, so it will likely produce an error or extract corrupted data.

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

Why wrong: Lists the contents of the archive and filters for app.log, but does not extract any file.

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

Why wrong: Uses an invalid syntax for cp; it cannot directly reference files inside a tar archive.

find /home -user alice -mtime -7 -exec tar -rf alice_recent.tar.gz {} +

Why wrong: Uses `tar -rf` which appends files to a tar archive but does not compress them. The resulting file is a plain tar archive, not a .tar.gz compressed file, so it does not meet the requirement for compression.

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

Why wrong: Pipes `find` output to `cpio -o`, which creates a cpio archive, not a tar archive. The output is then redirected to a file named .tar.gz, but the content is not gzip compressed, resulting in an incorrect format.

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

Why wrong: Pipes `find` output directly to `tar -cvf`, but `tar` expects a list of files on the command line, not via stdin. This command will fail to create the archive because `tar -cvf` does not read file names from stdin.

less data.csv

Why wrong: Opens file in interactive viewer showing entire content.

tail data.csv

Why wrong: Displays last 10 lines.

cat data.csv

Why wrong: Displays entire file.

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

Why wrong: The administrator checked the PATH and it includes the directory, but this is the administrator's PATH, not the user's. However, the question implies the administrator is testing as the user or the user's environment is similar.

The binary is a shell script missing a shebang

Why wrong: If it's a binary, no shebang needed. If it's a script, missing shebang would cause different error.

The binary does not have execute permission for the user

Why wrong: Permissions are 755, so execute is allowed.

ls

Why wrong: Lists files, not current directory.

dirname

Why wrong: Extracts directory part of a file path, not current directory.

cd

Why wrong: Changes directory, does not display it.

gzip file.gz

Why wrong: Compresses files.

gunzip file.gz

Why wrong: Decompresses permanently.

Set an ACL using setfacl to grant user1 read access

Why wrong: This would work but is not listed as an option; also it changes the file's ACL, which is not 'without changing file's group or permissions'.

Use chmod o+r /etc/shadow as root

Why wrong: This changes permissions, which is not allowed per the question.

Change the file owner to user1 using chown

Why wrong: Only root can change ownership.

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

Why wrong: Truncating first loses current log content before copy.

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

Why wrong: Deleting and recreating changes inode; nginx may stop writing.

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

Why wrong: Moving changes inode; nginx will not write to new file until restarted.

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

Why wrong: Deleting logs loses data and may violate compliance requirements.

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

Why wrong: Stopping the application causes downtime, which is not acceptable.

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

Why wrong: Compression alone may not free enough space on root, and the file remains on the root filesystem.