If salt is a character string starting with the characters "$id$"
followed by a string optionally terminated by "$", then the result
has the form:
$id$salt$encrypted
id identifies the encryption method used instead of DES and this then
determines how the rest of the password string is interpreted. The
following values of id are supported:
ID | Method
1 | MD5
2a | Blowfish (not in mainline glibc; added in some Linux distributions)
5 | SHA-256 (since glibc 2.7)
6 | SHA-512 (since glibc 2.7)