System Management practice questions

find . -name '*.log' -size +100MB

Why wrong: Size unit should be M, not MB.

find . -name '*.log' -size -100M

Why wrong: Finds files smaller than 100 MB.

find . -type f -size +100M

Why wrong: Missing -name filter for .log files.

chmod g+rw /dir

Why wrong: chmod changes standard file permissions (user/group/other), not ACL entries. It does not modify the full ACL structure, so it is incorrect.

getfacl /dir

Why wrong: getfacl displays ACLs but does not modify them. It is a read-only command.

setfacl -x g:developers /dir

Why wrong: setfacl -x removes an ACL entry. It does not add or modify permissions, so it is incorrect.

sed 'y/oldhost/newhost/' /etc/hostname

Why wrong: Incorrect. The y command translates characters one-by-one, not strings. It also lacks -i, so changes are not in-place.

sed 's/oldhost/newhost/g' /etc/hostname

Why wrong: Incorrect. This command performs substitution but without -i, so it outputs to stdout and does not modify the file in-place.

tail -f /var/log/syslog

Why wrong: Incorrect. tail -f displays the last 10 lines by default and follows new lines, not exactly the last 15 lines.

head -n 15 /var/log/syslog

Why wrong: Incorrect. head -n 15 shows the first 15 lines, not the last.

less +15 /var/log/syslog

Why wrong: Incorrect. less +15 goes to line 15 and shows from there, not the last 15 lines.

find /var -mmin 30 -size +10M

Why wrong: -mmin 30 matches files modified exactly 30 minutes ago, not within the last 30 minutes.

locate /var -mmin -30 -size +10M

Why wrong: locate does not support -mmin or -size options.

find /var -mtime -30 -size +10M

Why wrong: -mtime -30 matches files modified within the last 30 days, not minutes.

chmod 644 script.sh

Why wrong: 644 sets permissions to rw-r--r--, which does not include execute.

chmod u+x script.sh

Why wrong: This adds execute only for the owner, not all users.

chmod 755 script.sh

Why wrong: 755 sets rwxr-xr-x, which adds execute for all, but it also changes other permissions unnecessarily. a+x is more precise.

0222

Why wrong: 0222 would remove write for all, resulting in 444 for files (r--r--r--), not desired.

000

Why wrong: 000 would result in 666 for files and 777 for directories, which is too permissive.

077

Why wrong: 077 would remove all permissions for group and others, resulting in 600 for files and 700 for directories.

Change file owner to jdoe

Why wrong: Changing owner is not desired as per scenario.

Use chmod o+rw file

Why wrong: This grants read-write to all others, which is too permissive and not targeted.

Add jdoe to the root group

Why wrong: Adding to root group would give group permissions, but root group is typically sensitive and not appropriate.

cat filename | head -n 15

Why wrong: The pipeline `cat filename | head -n 15` works correctly but is unnecessarily inefficient: `head` can open the file directly, so the extra `cat` process adds a redundant read and pipe overhead without any benefit. It is tempting because many users habitually pipe `cat` into other commands as a generic pattern for feeding file content into a filter, and in scenarios where the file must be processed by multiple commands in sequence (e.g., `cat file | grep pattern | sort`), the `cat` is justified as the initial input source.

less -N 15 filename

Why wrong: less does not limit lines by default; -N shows line numbers.

tail -n 15 filename

Why wrong: tail shows the last lines, not the first.

grep -vi 'ERROR' /var/log

Why wrong: -v inverts match, showing lines without ERROR.

grep -rn 'ERROR' /var/log

Why wrong: Missing -i, so case-sensitive.

find /var/log -name '*ERROR*'

Why wrong: find searches file names, not file contents.

sed 's/oldhost/newhost/g' /etc/hosts

Why wrong: This prints the result to stdout but does not modify the file.

awk '{gsub(/oldhost/,"newhost")}1' /etc/hosts

Why wrong: This prints to stdout but does not modify the file.

grep -r 'oldhost' /etc/hosts | sed 's/oldhost/newhost/g'

Why wrong: This does not modify the file and is incorrect syntax.

kill -1 2345

Why wrong: SIGHUP (1) typically reloads configuration; does not stop.

pkill -15 -f processname

Why wrong: -15 sends SIGTERM, not SIGKILL.

kill -15 2345

Why wrong: SIGTERM (15) requests graceful termination; process may ignore it.

systemctl daemon-reload

Why wrong: Reloads systemd configuration but does not enable services.

systemctl start myapp

Why wrong: Starts the service now but does not enable it for boot.

systemctl reenable myapp

Why wrong: Not a standard systemctl command; use enable.

/usr/bin

Why wrong: /usr/bin contains non-essential user binaries, typically mounted later.

/sbin

Why wrong: /sbin contains system binaries for administration, but /bin is for essential user commands.

/opt

Why wrong: /opt is for optional third-party software.

systemctl status sshd | tail -20

Why wrong: systemctl status shows a limited log, but not the full journal.

journalctl -u sshd --since '1 hour ago'

Why wrong: Shows entries since 1 hour ago, not last 20 lines.

journalctl -u sshd -f

Why wrong: -f follows new entries, does not limit to last 20.

rpm -U package.rpm

Why wrong: -U upgrades or installs, but still does not resolve dependencies, but -i is more appropriate for fresh install.

yum localinstall package.rpm

Why wrong: yum localinstall resolves dependencies automatically.

dnf install ./package.rpm

Why wrong: dnf resolves dependencies automatically.

mount | column -t

Why wrong: mount | column -t lists mounts but does not show disk space usage.

lsblk

Why wrong: lsblk lists block devices but does not show filesystem space usage.

fdisk -l

Why wrong: fdisk -l displays partition tables, not filesystem usage.

graphical.target

Why wrong: graphical.target starts full GUI with network.

poweroff.target

Why wrong: poweroff.target shuts down the system.

multi-user.target

Why wrong: multi-user.target includes network services.

The source file must have the SUID bit set.

Why wrong: SUID bit is irrelevant for creating hard links.

The link must have the same name as the source.

Why wrong: The link can have a different name.

cat syslog

Why wrong: Cat shows the entire file, not just the last 10 lines.

head -10 syslog

Why wrong: Head shows the first lines, not the last.

less syslog

Why wrong: Less opens the file for interactive viewing, but does not directly show only the last 10 lines.