Understanding /etc/shadow file

Understanding /etc/shadow file

In this tutorial we will discuss about the topic Understanding /etc/shadow file in Linux.

The /etc/shadow file is also very important in Linux. It stores all the users passwords (in crypted format) and other security user account information.

The /etc/shadow file can be edited only by root and read by root and the group shadow:

# ls -l /etc/shadow
-rw-r----- 1 root shadow 1162 2012-06-02 08:15 /etc/shadow

The /etc/shadow contains a line for every user in the system. Each line has 8 fields, separated by colon (:).

# < /etc/shadow grep razvan
razvan:$6$vAnN6uO5$yol51:15481:0:99999:7:::

The 8 fields are:

  • Username – the user’s login name
  • Password – the password in crypted form. if instead of a password hash there is ! , that user cannot log in.
  • Last password change – the date is displayed as the number of days since the 1st of January 1970
  • Minimum – the minimum number of days between to password changes
  • Maximum – the maximum number of days the password is valid
  • Warn – how many days before the password expires is the user warned to change it’s password
  • Inactive – the number of days that can pass after the password expiration before the account gets deactivated
  • Expire – the day when the account will expire displayed as the number of days since the 1st of January 1970

Be carefull not to damage the /etc/password and the /etc/shadow file, or your system my crush.

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Understanding /etc/shadow file
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