Linux administration

  • create Linux user without password

bash useradd -m -d /home/username -s /bin/bash username - delete Linux user's password

bash passwd -d username - display pub key from a private key (useful when there are multiple pub keys in authorized_key file)

bash ssh-keygen -y -f /path/to/privatekey > /path/to/pubkey - OpenSSL Operations - generate self-signed certificate

```bash
openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365 -subj '/CN=localhost'
```

  • convert certificate and key to PFX format

    bash openssl pkcs12 -inkey key.pem -in cert.cert -export -out pfx.pfx - convert PFX to certificate and key format

    bash # extract key openssl pkcs12 -in [yourfile.pfx] -nocerts -out [keyfile-encrypted.key] # extract certificate openssl pkcs12 -in [yourfile.pfx] -clcerts -nokeys -out [certificate.crt] # if you need to have an unencrypted key (no passphrase) openssl rsa -in [keyfile-encrypted.key] -out [keyfile-decrypted.key] # if you need to convert from key to pem format openssl rsa -in [keyfile-encrypted.key] -outform PEM -out [keyfile-encrypted-pem.pem] # to convert from crt to pem format openssl x509 -in [certificate.crt] -out [certificate.pem] -outform PEM

  • add root and intermediate chain to PFX

    bash # copy both root and intermediate public certs in Base-64 encoded (.cer/.pem) # then create new (.cer/.pem) file pasting the content of intermediate then root certs back to back openssl pkcs12 -export -out your_cert.pfx -inkey your_private.key -in your_cert.cer -certfile verisign-chain.cer

  • find installed package version on Debian systems

bash dpkg -s PACKAGE-NAME | grep '^Version:'