Linux man pages : shadow (5)
shadow - encrypted password file
shadow contains the encrypted password information for user's accounts
and optional the password aging information. Included is
Days since Jan 1, 1970 that password was last changed
Days before password may be changed
Days after which password must be changed
Days before password is to expire that user is warned
Days after password expires that account is disabled
Days since Jan 1, 1970 that account is disabled
A reserved field
The password field must be filled. The encryped password consists of
13 to 24 characters from the 64 character alphabet a thru z, A thru Z,
0 thru 9, . and /. Refer to crypt(3) for details on how this string is
The date of the last password change is given as the number of days
since Jan 1, 1970. The password may not be changed again until the
proper number of days have passed, and must be changed after the maxi-
mum number of days. If the minimum number of days required is greater
than the maximum number of day allowed, this password may not be
changed by the user.
An account is considered to be inactive and is disabled if the password
is not changed within the specified number of days after the password
expires. An account will also be disabled on the specified day regard-
less of other password expiration information.
This information supercedes any password or password age information
present in /etc/passwd.
This file must not be readable by regular users if password security is
to be maintained.
/etc/passwd - user account information
/etc/shadow - encrypted user passwords
chage(1), login(1), passwd(1), su(1), passwd(5), pwconv(8), pwunconv(8)
Julianne Frances Haugh (firstname.lastname@example.org)