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PWCK(8) System Management Commands PWCK(8)


pwck - verify the integrity of password files


pwck [options] [PASSWORDFILE [ SHADOWFILE ]]


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 errors.

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

Checks for shadowed password information are enabled when the second file parameter SHADOWFILE 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 file

•shadow entries have the correct number of fields

•shadow entries are unique in shadow

•the last password changes are not in the future

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 warnings 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.

-h, --help

Display help message and exit.

-q, --quiet

Report errors only. The warnings which do not require any action from the user won't be displayed.

-r, --read-only

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. Only absolute paths are supported.

-s, --sort

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 shadow parameters.


The following configuration variables in /etc/login.defs change the behavior of this tool:


If a system account intentionally does not have a home directory that exists, this string can be provided in the /etc/passwd entry for the account to indicate this. The result is that pwck will not emit a spurious warning for this account.

PASS_MAX_DAYS (number)

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).

PASS_MIN_DAYS (number)

The minimum number of days allowed between password changes. Any password changes attempted sooner than this will be rejected. If not specified, 0 will be assumed (which disables the restriction).

PASS_WARN_AGE (number)

The number of days warning given before a password expires. A zero means warning is given only upon the day of expiration, a value of -1 means no warning is given. If not specified, no warning will be provided.



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


group(5), grpck(8), passwd(5), shadow(5), usermod(8).

06/18/2024 shadow-utils 4.16.0