Shell

find exposed ports:

netstat -lntu
ss -lntu

find process on port

lsof -nP -iTCP -sTCP:LISTEN | grep <port-number>

try to find error logs of some running process

#find PID
ps aux | grep httpd
#PID -> 1234
#then find open log files with lsof
lsof -p 1234 | grep log

apply command to several items

echo {1..4} | xargs -n1 -I{} ssh root@www{}.example.com hostname

recursive search in files

grep -r "searchterm"
# recursive search with maxdepth
find . -maxdepth 5 -type d | grep "searchterm"

OpenSSL

#generate private key
openssl genrsa -out key.pem 4096
#generate key and self-signed cert
openssl req -x509 -newkey rsa:4096 -keyout demo_ca_key.pem -out demo_ca_cert.pem -nodes -days 365
#generate key and certificate signing request
openssl req -x509 -newkey rsa:4096 -keyout demo_ca_key.pem -out demo_ca_cert.pem -nodes -days 365
#sign certificate
openssl x509 -req -in demo_csr.pem -CA demo_ca_cert.pem -CAkey demo_ca_key.pem -out demo_cert.pem -set_serial 01 -days 365