The ‘systemctl enable nginx’ command creates the necessary symlinks to start the nginx service at boot on a systemd-based system. ‘systemctl start’ only starts it for the current session, ‘chkconfig’ is for SysV init systems, and ‘service nginx enable’ is not a standard command.

The standard ‘rm’ command does not remove directories. To remove a directory and its contents recursively, the ‘-r’ flag is required. The error message is misleading but classic for using ‘rm’ on a directory without the recursive option. ‘rmdir’ only works on empty directories.

Best practice is to first send the TERM signal (signal 15, the default for ‘kill’) to allow the process to shut down gracefully, cleaning up temporary files and closing connections. If it does not respond, then the KILL signal (9) can be used as a last resort, as it forces immediate termination without cleanup.

The octal mode 774 translates to: owner (7=rwx), group (7=rwx), others (4=r–). This gives read, write, and execute to the owner and group, but only read to others. 775 would give execute to others, 664 gives no execute to anyone, and 755 is a common but less restrictive pattern giving execute to all.

‘netstat -tulpn | grep 5432’ (or the equivalent ‘ss -tulpn’) will show if a process is actively listening on port 5432 (the default PostgreSQL port). ‘ps aux’ shows running processes but not open ports. ‘systemctl status’ confirms the service is active but not necessarily listening. ‘telnet’ tests connectivity but won’t show the listening state from the server side.

This command correctly combines two criteria: 1) ‘find’ locates files ending in ‘.log’. 2) ‘-mtime -1’ filters for files modified in the last 24 hours. 3) ‘-exec grep’ searches within those recent files for the string. Option A searches all log files regardless of age. Option B may fail due to shell globbing limits. Option D (‘tail -f’) follows new output in real-time, not historical data.

The ‘/etc/sudoers’ file is the main configuration file for sudo. It should always be viewed using ‘sudo’ (or as root) and preferably with ‘visudo’ for safe editing, but ‘sudo cat’ is acceptable for reading. The other files list user accounts and group memberships but do not define the sudo rules themselves.

‘du -sh /home/*’ estimates disk usage for each item directly under /home in a human-readable format. ‘sort -rh’ sorts numerically in reverse order (largest first). ‘head -5’ shows the top five results. Option A sorts file sizes from ‘ls’, which is less accurate for directories. Option C shows filesystem usage, not directory details. Option D is more complex and searches all files, which is slower.

The most logical first step is to verify the service state. ‘sudo systemctl status cron’ (or ‘crond’ on some systems) will show if the service is active, running, enabled, and display recent log entries. Restarting it (Option B) should not be done before diagnosis. Checking the user’s crontab (A) or a specific log file (D) comes after confirming the service is operational.

The ‘systemctl enable nginx’ command creates the necessary symlinks to start the nginx service at boot on a systemd-based system. ‘systemctl start’ only starts it for the current session, ‘chkconfig’ is for SysV init systems, and ‘service nginx enable’ is not a standard command.0