strace -e open firefox

ltrace -c ls

ngrep -d lo 5000

tcpdump

mitmproxy

find ftrace for kernel functions

cat /proc/10000/stack -> check if program is waiting  on what...

dstat -d

to check disk usage while programs run (leap opensuse)

netstat -ntlp 147.95.34.76



transfer a file to your friend on your local network with netcat.
Also it is pretty fun to watch the transfer with Wireshark.
netcat -l 12345 > file.pdf or netcat -l -p 12345 > file.pdf
depending on my version of netcat. (BSD vs not-BSD or something)
You run netcat $MY_IP_ADDRESS 12345 < file.pdf

