What is "if a password hash starts with $6$?

If a password hash starts with $6$, it means that the hash algorithm used is SHA-512. The $6$ signifies the hashing algorithm being used, in this case SHA-512. SHA-512 is a widely used cryptographic hash function that produces a 512-bit hash value. It is considered to be secure and suitable for storing passwords.

When a password is hashed using SHA-512, it is combined with a random salt value before being hashed. This salt value is stored alongside the hash, making it more difficult for attackers to crack the password using methods like rainbow tables or brute-force attacks.

Overall, if a password hash starts with $6$, it indicates the use of the SHA-512 hashing algorithm, which is a strong and secure method for storing passwords.