Publicly available dns google => 8.8.8.8 8.8.4.4 cloudfare => 1.1.1.1 9.9.9.9
DNS(Records => A,NS,MX,TXT,CNAME) => resolve domain into ip A => NS => MX => mail TXT => textual values for spf , dns challenges CNAME => aliasing name
`xyz.com A 1.2.3.4`
`www.xyz.com CNAME xyz.com`check dns propagation: https://www.whatsmydns.net/
check public ip https://whatsmyip.net/ https://whatsmyip.com/
check mail server black lists https://mxtoolbox.com/blacklists.aspx
[user]@[hostname]:[PWD][local_user_account/root_user_account]
example:
bad-logic@mac:~$
bad-logic@mac:~#
$ ping google.com
$ dig google.com
$ dig google.com @8.8.8.8 # check using another dns server
$ dig google.com mx # check for mx record
$ traceroute google.com # shows the path to reach the destination
$ telnet xyz.com 80 # check if the port is listening or not
$ curl -vvv <https_site> # check tls handshake
$ wget <file_path> # download files
$ tcpdump # check traffic
$ netstat # lists ports, server is listening inwireshark (gui tool for tcpdump)
$ du # disk utilization
$ du -sh
$ du -h
$ top # cpu utilization
$ ps # running processes
$ ps aux
$ kill <process_id> # sends (15) SIGTERM, graceful termination
$ kill -9 <process_id> # sends SIGKILL (9), forceful termination$ tail -f /var/log/syslog
$ tail -n100 /var/log/syslog
$ journalctl -u <service_name> -f
$ systemctl status <service_name>
$ systemctl ls-active
$ find <find_in_folder> -type d => d -> directory
$ find ./ -type d -mtime +7 => older than seven days
$ find ./ -type d -name [0-9]\*
$ uptime # time from which the server has been up
$ w # logged in users list
$ cat /etc/shells # list of available shells