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Some useful TCP ports and their default services

21, FTP, not HIPAA compliant!
22, SSH and SFTP
23, telnet used for checking ports
25, SMTP
53, domain name services (such as BIND); TCP and UDP are the same
80, HTTP
110, Post Office Protocol 3
443, HTTPS

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Some useful OpenSSL commands

Generate self-signed SSL and key,
sudo openssl req -x509 -days 365 -newkey rsa:2048 -keyout /etc/apache2/ssl/apache.key -out /etc/apache2/ssl/apache.cert

/etc/apache2 (deb)
/etc/httpd/conf.d (rpm)

Generate CSR:
openssl req -nodes -newkey rsa:4096 -keyout privkey.pem -out csr.pem

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Some useful database commands

PostgreSQL/PSQL

To access postgres from database server as postgres user,
su - postgres
psql

To access as specific user to specific database,
psql -d DATABASE -U USER -W

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Some useful CSF firewall commands

csf -a IP; Allow IP, use /etc/csf/csf.allow instead
csf -d IP; Block an IP
csf -dr IP; Remove an IP block
csf -e; Enable csf
csf -g IP; Check for blocks on IP
csf -ra; Restart csf
csf -cd; cluster deny ip
csf -cr; cluster unblock ip

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Some useful PowerShell commands

Check disk use (Windows), run in PowerShell as admin:
Get-ChildItem c:\ -r -ErrorAction SilentlyContinue –Force |sort -descending -property length | select -first 10 name, DirectoryName, @{Name="MB";Expression={[Math]::round($_.length / 1MB, 2)}}
gci C:\inetpub -r| sort -descending -property length | select -first 10 name, @{Name="GB";Expression={[Math]::round($_.length / 1GB, 2)}}

Get subdirectory size in PowerShell:
$colItems = Get-ChildItem C:\ -ErrorAction SilentlyContinue -Force | Where-Object {$_.PSIsContainer -eq $true} | Sort-Object
foreach ($i in $colItems)
{

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Some useful commands for Linux Disk and Inode space checking

Check disk space availability
df -h

Get size of folder
du -sh FOLDER

Get size of files in folder
ls -l --block-size=M

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Some Useful Google Cloud CLI Commands

If not done already, configure Google Cloud CLI.
Instructions below assume DEB based distro like Debian or Ubuntu.
Instructions from Google Cloud SDK Docs

Pre-requisities to install Google CLI (skip if already done)
Add GPG key,
curl https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/cloud.google.gpg

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Some useful kubectl commands

Authenticate with cluster if using gcloud CLI,
gcloud container clusters get-credentials CLUSTER_NAME --region=COMPUTE_REGION

Run again with different value to set a new default cluster

List pods in cluster,
kubectl get pods