/etc/shadow

The fields, delimited by : are:

  1. Username
  2. Password (hashed)
  3. Last password change (in days since 1970-01-01)

Fields

Notes on specific fields.

Username

Fairly straightforward. The lenght used to be restricted to 8 characters maximum in very old distributions, now it's 32 characters on most distributions.

Password

An empty field, will allow the user to login without providing a password, whereas a field that starts with, or only contains an asterisk * indicates a disabled account.

The first characters of this field define the hashing algorithm, one of:

  1. MD5 - password starts with $1$
  2. Blowfish - password starts with $2a$
  3. SHA-256 - password starts with $5$
  4. SHA-512 - password starts with $6$