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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CONFIGURATION | FILES | EXIT VALUES | SEE ALSO | COLOPHON |
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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:
--badname
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:
NONEXISTENT (string)
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.
/etc/group
Group account information.
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
The pwck command exits with the following values:
0
success
1
invalid command syntax
2
one or more bad password entries
3
can't open password files
4
can't lock password files
5
can't update password files
6
can't sort password files
group(5), grpck(8), passwd(5), shadow(5), usermod(8).
This page is part of the shadow-utils (utilities for managing
accounts and shadow password files) project. Information about
the project can be found at
⟨https://github.com/shadow-maint/shadow⟩. If you have a bug report
for this manual page, send it to
[email protected]. This page was obtained
from the project's upstream Git repository
⟨https://github.com/shadow-maint/shadow⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-10.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
shadow-utils 4.18.0 08/11/2025 PWCK(8)
Pages that refer to this page: passwd(5@@shadow-utils), shadow(5), grpck(8), pwconv(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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