RHCSA Linux Essentials Flashcards

Which command shows all active listening TCP and UDP ports with associated process names?

Answer: ss -tulnp

`ss -tulnp` shows TCP/UDP listening sockets with numeric addresses and the owning process.

You need to create a 2 GiB swap file at /swapfile. What is the correct sequence?

Answer: dd if=/dev/zero of=/swapfile bs=1M count=2048; chmod 600 /swapfile; mkswap /swapfile; swapon /swapfile

The full correct sequence creates the file, sets strict permissions (600), formats it as swap, then activates it.

Which firewalld command permanently opens port 8080/tcp in the public zone?

Answer: firewall-cmd --permanent --zone=public --add-port=8080/tcp

The `--permanent` flag writes the rule to the zone's XML config so it persists after a reload or reboot.

What does the `lsblk` command display?

Answer: Block device tree with mount points and sizes

`lsblk` lists block devices in a tree format showing name, size, type, and mount point.

A cron job entry reads: `*/15 * * * * /script.sh`. How often does it run?

Answer: Every 15 minutes

`*/15` in the minute field means 'every 15 minutes' (0, 15, 30, 45).

Which command would you use to restore the default SELinux context on a file?

Answer: restorecon /path/file

`restorecon` resets a file's SELinux context to the policy default stored in the file context database.

What command lists all enabled systemd services that start at boot?

Answer: systemctl list-unit-files --type=service --state=enabled

`systemctl list-unit-files --type=service --state=enabled` shows only unit files with enabled state.