nmap - checking open ports and footprinting
MSF - Metasploit framework
DIRB - enumerate files on webserver
Wireshark - network analytics
Wfuzz - bruteforcing web applications
sqlmap - detection and exploitation of SQL injection flaws

10 pillars of IT security:
1. Sanitize Inputs
2. Audit services
3. Backups onsite && ofsite , test backups
4. Principle of least privileges (no one logs as root, ever)
5. Zero trust networks, 2FA
6. Key-based authetification

In case you accidentally commit file you did not want, e.g. .swp from vim use:

git rm unwanted_file.swp

Check if file does not appear anymore
git commit --amend

Export and Import packages list

Export
dpkg --get-selections

Import
dpkt --set-selections

In order to issue direct command on server via ansible:

ansible [pattern] -m [module] -a "[module options]"
ansible webservers -e "ansible_user=root" -m shell -a "/etc/init.d/nginx restart"

Stash all changed files
git stash --include-untracked

Stash with comments
git stash save --include-untracked 'message'

Unstash changes back to branch
git stash pop
git stash pop stash@{STASH_NUMBER}

Reinstall package and recreate files
apt-get -o Dpkg::Options::="--force-confmiss" install --reinstall PACKAGE_NAME

ansible-playbook --limit '!hoost1:!host2' yourPlaybook.yml

Move shards from one node to another
curl -XPOST 'http://localhost:9200/_cluster/reroute' -d '{"commands" : [{"move" :{"index" : "indexname", "shard" : 1,"from_node" : "nodename", "to_node" : "nodename"}}]}'