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Name

shadow - shadow password file

Description

/etc/shadow is an access-restricted ASCII system file that stores users’ encrypted passwords and related information. The shadow file can be used in conjunction with other shadow sources, including the NIS maps passwd.byname and passwd.byuid and the NIS+ table passwd. Programs use the getspnam(3C) routines to access this information.

The fields for each user entry are separated by colons. Each user is separated from the next by a newline. Unlike the /etc/passwd file, /etc/shadow does not have general read permission.

Each entry in the shadow file has the form:

username:password:lastchg:min:max:warn:inactive:expire:flagThe fields are defined as follows:
username
The user’s login name (UID ).
password
A 13-character encrypted password for the user, a lock string to indicate that the login is not accessible, or no string, which shows that there is no password for the login.
lastchg
The number of days between January 1, 1970, and the date that the password was last modified.
min
The minimum number of days required between password changes.
max
The maximum number of days the password is valid.
warn
The number of days before password expires that the user is warned.
inactive
The number of days of inactivity allowed for that user.
expire
An absolute date specifying when the login may no longer be used.
flag
Reserved for future use, set to zero. Currently not used.

The encrypted password consists of 13 characters chosen from a 64-character alphabet (., /, 0-9, A-Z, a-z). To update this file, use the passwd(1) , useradd(1M) , usermod(1M) , or userdel(1M) commands.

In order to make system administration manageable, /etc/shadow entries should appear in exactly the same order as /etc/passwd entries; this includes ‘‘+’’ and ‘‘-’’ entries if the compat source is being used (see nsswitch.conf(4) ).

Files

/etc/shadow
shadow password file
/etc/passwd
password file
/etc/nsswitch.conf
name-service switch configuration file

See Also

login(1) , passwd(1) , useradd(1M) , userdel(1M) , usermod(1M) , getspnam(3C) , putspent(3C) , nsswitch.conf(4) , passwd(4)

Notes

If password aging is turned on in any name service the passwd: line in the /etc/nsswitch.conf file must have a format specified in the nsswitch.conf(4) man page.

If the /etc/nsswitch.conf passwd policy is not in one of the supported formats, logins will not be allowed upon password expiration because the software does not know how to handle password updates under these conditions. See nsswitch.conf(4) for additional information.

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