Here i will post all my favorite commands if you want to share others let me know:
Check for DOS attacks
netstat -anp|grep tcp|awk ‘{print $5}’| cut -d : -f1|sort|uniq -c|sort -n
Find large files on UNIX
find / -size +100000 -type f -ls | sort -n
Create a 30×30 matrix
hexdump -v -e ‘”%u”‘ </dev/urandom|fold -60|head -n 30|sed ‘s/(.{2})/1 /g’
Sort contents of a directory with human readable output
du -hs * | sort -h
Check if a computer is 32 or 64 bits
cat /proc/cpuinfo | grep ” lm ” > /dev/null && echo 64 bits || echo 32 bits
Resume scp of a big file
rsync -a -v –stats -e ssh /home root@<newserver>:/root/
Find out current working directory of a process
pwdx $(pgrep command)
Kill several processes of a user
ps -ef | grep user | awk ‘{print $2}’ | xargs -i -t kill -9 {}