pwck - verify integrity of password files
[passwd [ shadow ]]
The pwck command verifies the integrity of the users and authentication
information. It checks that all entries in /etc/passwd and /etc/shadow have
the proper format and contain valid data. The user is prompted to delete
entries that are improperly formatted or which have other uncorrectable
Checks are made to verify that each entry has:
•the correct number of fields
•a unique and valid user name
•a valid user and group identifier
•a valid primary group
•a valid home directory
•a valid login shell
shadow checks are enabled when a second file parameter is
specified or when /etc/shadow exists on the system.
These checks are the following:
•every passwd entry has a matching shadow entry,
and every shadow entry has a matching passwd entry
•passwords are specified in the shadowed
•shadow entries have the correct number of
•shadow entries are unique in shadow
•the last password changes are not in the
The checks for correct number of fields and unique user name are
fatal. If the entry has the wrong number of fields, the user will be
prompted to delete the entire line. If the user does not answer
affirmatively, all further checks are bypassed. An entry with a duplicated
user name is prompted for deletion, but the remaining checks will still be
made. All other errors are warning and the user is encouraged to run the
usermod command to correct the error.
The commands which operate on the /etc/passwd file are not able to
alter corrupted or duplicated entries. pwck should be used in those
circumstances to remove the offending entry.
The -r and -s options cannot be combined.
The options which apply to the pwck command are:
Allow names that do not conform to standards.
Display help message and exit.
Report errors only. The warnings which do not require any
action from the user won't be displayed.
Execute the pwck command in read-only mode.
-R, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use
the configuration files from the CHROOT_DIR directory.
Sort entries in /etc/passwd and /etc/shadow by UID.
By default, pwck operates on the files /etc/passwd and
/etc/shadow. The user may select alternate files with the passwd and
The following configuration variables in /etc/login.defs change the behavior of
The maximum number of days a password may be used. If the
password is older than this, a password change will be forced. If not
specified, -1 will be assumed (which disables the restriction).
The minimum number of days allowed between password
changes. Any password changes attempted sooner than this will be rejected. If
not specified, -1 will be assumed (which disables the restriction).
The number of days warning given before a password
expires. A zero means warning is given only upon the day of expiration, a
negative value means no warning is given. If not specified, no warning will be
Group account information.
User account information.
Secure user account information.
The pwck command exits with the following values:
invalid command syntax
one or more bad password entries
can't open password files
can't lock password files
can't update password files
can't sort password files