Linux basics quiz

pwd prints the working directory. ls lists files, cd changes directory and whoami shows your username.

6 = read+write, 4 = read, 0 = nothing. So the owner can read and write, the group can read and others have no access.

sudo runs one command as root (if you are allowed), and records it in the logs. su switches to another user entirely.

ip a (ip address) is the modern command. ifconfig is older; ipconfig and netsh are Windows commands.

ss -tulpn shows TCP and UDP listening sockets with process names. It replaces the older netstat -tulpn.

systemctl controls services on systemd distributions such as Ubuntu, Debian and RHEL.

tail -f keeps the file open and prints new lines as they arrive, which is ideal for watching logs live.

/var/log holds logs such as auth.log or secure. On systemd systems, journalctl also reads the journal.

grep -r searches recursively and -i ignores case. find searches file names, not their contents.

SSH keys are much harder to steal or guess than passwords. Disable direct root login and password authentication where you can.

ls -l gives the long format and -a includes hidden files that start with a dot.

chown changes ownership. chmod changes permissions and chgrp changes the group.

/etc/hosts is checked locally. /etc/resolv.conf lists DNS servers.

top (or htop) shows a live view. ps gives a snapshot, df disk space and free memory.

df -h shows filesystem usage in human-readable units. du shows the size of files and folders.

A pipe passes standard output of the first command to the input of the next, for example dmesg | grep usb.

enable sets it to start at boot; start runs it now. Use enable --now to do both.

sshd_config configures the server. ssh_config configures the client.

PermitRootLogin no forces admins to log in as themselves and use sudo, which is safer and auditable.

ufw (Uncomplicated Firewall) provides simple commands such as ufw allow 22/tcp and ufw enable.