Ubuntu Manpage: login.defs - shadow password suite configuration

Provided by: login_4.13+dfsg1-4ubuntu3.2_amd64

NAME

       login.defs - shadow password suite configuration

DESCRIPTION

The /etc/login.defs file defines the site-specific configuration for the shadow password
suite. This file is required. Absence of this file will not prevent system operation, but
will probably result in undesirable operation.

This file is a readable text file, each line of the file describing one configuration
parameter. The lines consist of a configuration name and value, separated by whitespace.
Blank lines and comment lines are ignored. Comments are introduced with a "#" pound sign
and the pound sign must be the first non-white character of the line.

Parameter values may be of four types: strings, booleans, numbers, and long numbers. A
string is comprised of any printable characters. A boolean should be either the value yes
or no. An undefined boolean parameter or one with a value other than these will be given a
no value. Numbers (both regular and long) may be either decimal values, octal values
(precede the value with 0) or hexadecimal values (precede the value with 0x). The maximum
value of the regular and long numeric parameters is machine-dependent.

The following configuration items are provided:

CHFN_RESTRICT (string)
This parameter specifies which values in the gecos field of the /etc/passwd file may
be changed by regular users using the chfn program. It can be any combination of
letters f, r, w, h, for Full name, Room number, Work phone, and Home phone,
respectively. For backward compatibility, yes is equivalent to rwh and no is
equivalent to frwh. If not specified, only the superuser can make any changes. The
most restrictive setting is better achieved by not installing chfn SUID.

CONSOLE_GROUPS (string)
List of groups to add to the user's supplementary groups set when logging in on the
console (as determined by the CONSOLE setting). Default is none.

Use with caution - it is possible for users to gain permanent access to these groups,
even when not logged in on the console.

CREATE_HOME (boolean)
Indicate if a home directory should be created by default for new users.

This setting does not apply to system users, and can be overridden on the command
line.

DEFAULT_HOME (boolean)
Indicate if login is allowed if we can't cd to the home directory. Default is no.

If set to yes, the user will login in the root (/) directory if it is not possible to
cd to her home directory.

ENCRYPT_METHOD (string)
This defines the system default encryption algorithm for encrypting passwords (if no
algorithm are specified on the command line).

It can take one of these values: DES (default), MD5, SHA256, SHA512. MD5 and DES
should not be used for new hashes, see crypt(5) for recommendations.

Note: this parameter overrides the MD5_CRYPT_ENAB variable.

Note: This only affect the generation of group passwords. The generation of user
passwords is done by PAM and subject to the PAM configuration. It is recommended to
set this variable consistently with the PAM configuration.

ENV_HZ (string)
If set, it will be used to define the HZ environment variable when a user login. The
value must be preceded by HZ=. A common value on Linux is HZ=100.

The HZ environment variable is only set when the user (the superuser) logs in with
sulogin.

ENV_PATH (string)
If set, it will be used to define the PATH environment variable when a regular user
login. The value is a colon separated list of paths (for example /bin:/usr/bin) and
can be preceded by PATH=. The default value is PATH=/bin:/usr/bin.

ENV_SUPATH (string)
If set, it will be used to define the PATH environment variable when the superuser
login. The value is a colon separated list of paths (for example
/sbin:/bin:/usr/sbin:/usr/bin) and can be preceded by PATH=. The default value is
PATH=/sbin:/bin:/usr/sbin:/usr/bin.

ERASECHAR (number)
Terminal ERASE character (010 = backspace, 0177 = DEL).

The value can be prefixed "0" for an octal value, or "0x" for an hexadecimal value.

FAIL_DELAY (number)
Delay in seconds before being allowed another attempt after a login failure.

FAKE_SHELL (string)
If set, login will execute this shell instead of the users' shell specified in
/etc/passwd.

GID_MAX (number), GID_MIN (number)
Range of group IDs used for the creation of regular groups by useradd, groupadd, or
newusers.

The default value for GID_MIN (resp. GID_MAX) is 1000 (resp. 60000).

HOME_MODE (number)
The mode for new home directories. If not specified, the UMASK is used to create the
mode.

useradd and newusers use this to set the mode of the home directory they create.

HUSHLOGIN_FILE (string)
If defined, this file can inhibit all the usual chatter during the login sequence. If
a full pathname is specified, then hushed mode will be enabled if the user's name or
shell are found in the file. If not a full pathname, then hushed mode will be enabled
if the file exists in the user's home directory.

KILLCHAR (number)
Terminal KILL character (025 = CTRL/U).

The value can be prefixed "0" for an octal value, or "0x" for an hexadecimal value.

LASTLOG_UID_MAX (number)
Highest user ID number for which the lastlog entries should be updated. As higher user
IDs are usually tracked by remote user identity and authentication services there is
no need to create a huge sparse lastlog file for them.

No LASTLOG_UID_MAX option present in the configuration means that there is no user ID
limit for writing lastlog entries.

LOG_OK_LOGINS (boolean)
Enable logging of successful logins.

LOG_UNKFAIL_ENAB (boolean)
Enable display of unknown usernames when login failures are recorded.

Note: logging unknown usernames may be a security issue if an user enter her password
instead of her login name.

LOGIN_RETRIES (number)
Maximum number of login retries in case of bad password.

This will most likely be overridden by PAM, since the default pam_unix module has its
own built in of 3 retries. However, this is a safe fallback in case you are using an
authentication module that does not enforce PAM_MAXTRIES.

LOGIN_TIMEOUT (number)
Max time in seconds for login.

MAIL_DIR (string)
The mail spool directory. This is needed to manipulate the mailbox when its
corresponding user account is modified or deleted. If not specified, a compile-time
default is used. The parameter CREATE_MAIL_SPOOL in /etc/default/useradd determines
whether the mail spool should be created.

MAIL_FILE (string)
Defines the location of the users mail spool files relatively to their home directory.

The MAIL_DIR and MAIL_FILE variables are used by useradd, usermod, and userdel to create,
move, or delete the user's mail spool.

MAX_MEMBERS_PER_GROUP (number)
Maximum members per group entry. When the maximum is reached, a new group entry (line)
is started in /etc/group (with the same name, same password, and same GID).

The default value is 0, meaning that there are no limits in the number of members in a
group.

This feature (split group) permits to limit the length of lines in the group file.
This is useful to make sure that lines for NIS groups are not larger than 1024
characters.

If you need to enforce such limit, you can use 25.

Note: split groups may not be supported by all tools (even in the Shadow toolsuite).
You should not use this variable unless you really need it.

MD5_CRYPT_ENAB (boolean)
Indicate if passwords must be encrypted using the MD5-based algorithm. If set to yes,
new passwords will be encrypted using the MD5-based algorithm compatible with the one
used by recent releases of FreeBSD. It supports passwords of unlimited length and
longer salt strings. Set to no if you need to copy encrypted passwords to other
systems which don't understand the new algorithm. Default is no.

This variable is superseded by the ENCRYPT_METHOD variable or by any command line
option used to configure the encryption algorithm.

This variable is deprecated. You should use ENCRYPT_METHOD.

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 negative value means no warning is given. If
not specified, no warning will be provided.

PASS_MAX_DAYS, PASS_MIN_DAYS and PASS_WARN_AGE are only used at the time of account
creation. Any changes to these settings won't affect existing accounts.

SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the number of SHA rounds
used by the encryption algorithm by default (when the number of rounds is not
specified on the command line).

With a lot of rounds, it is more difficult to brute forcing the password. But note
also that more CPU resources will be needed to authenticate users.

If not specified, the libc will choose the default number of rounds (5000), which is
orders of magnitude too low for modern hardware.

The values must be inside the 1000-999,999,999 range.

If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS values is set, then
this value will be used.

If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value will be used.

SULOG_FILE (string)
If defined, all su activity is logged to this file.

SU_NAME (string)
If defined, the command name to display when running "su -". For example, if this is
defined as "su" then a "ps" will display the command is "-su". If not defined, then
"ps" would display the name of the shell actually being run, e.g. something like
"-sh".

SUB_GID_MIN (number), SUB_GID_MAX (number), SUB_GID_COUNT (number)
If /etc/subuid exists, the commands useradd and newusers (unless the user already have
subordinate group IDs) allocate SUB_GID_COUNT unused group IDs from the range
SUB_GID_MIN to SUB_GID_MAX for each new user.

The default values for SUB_GID_MIN, SUB_GID_MAX, SUB_GID_COUNT are respectively
100000, 600100000 and 65536.

SUB_UID_MIN (number), SUB_UID_MAX (number), SUB_UID_COUNT (number)
If /etc/subuid exists, the commands useradd and newusers (unless the user already have
subordinate user IDs) allocate SUB_UID_COUNT unused user IDs from the range
SUB_UID_MIN to SUB_UID_MAX for each new user.

The default values for SUB_UID_MIN, SUB_UID_MAX, SUB_UID_COUNT are respectively
100000, 600100000 and 65536.

SYS_GID_MAX (number), SYS_GID_MIN (number)
Range of group IDs used for the creation of system groups by useradd, groupadd, or
newusers.

The default value for SYS_GID_MIN (resp. SYS_GID_MAX) is 101 (resp. GID_MIN-1).

SYS_UID_MAX (number), SYS_UID_MIN (number)
Range of user IDs used for the creation of system users by useradd or newusers.

The default value for SYS_UID_MIN (resp. SYS_UID_MAX) is 101 (resp. UID_MIN-1).

SYSLOG_SG_ENAB (boolean)
Enable "syslog" logging of sg activity.

SYSLOG_SU_ENAB (boolean)
Enable "syslog" logging of su activity - in addition to sulog file logging.

TTYGROUP (string), TTYPERM (string)
The terminal permissions: the login tty will be owned by the TTYGROUP group, and the
permissions will be set to TTYPERM.

By default, the ownership of the terminal is set to the user's primary group and the
permissions are set to 0600.

TTYGROUP can be either the name of a group or a numeric group identifier.

If you have a write program which is "setgid" to a special group which owns the
terminals, define TTYGROUP to the group number and TTYPERM to 0620. Otherwise leave
TTYGROUP commented out and assign TTYPERM to either 622 or 600.

TTYTYPE_FILE (string)
If defined, file which maps tty line to TERM environment parameter. Each line of the
file is in a format something like "vt100 tty01".

UID_MAX (number), UID_MIN (number)
Range of user IDs used for the creation of regular users by useradd or newusers.

The default value for UID_MIN (resp. UID_MAX) is 1000 (resp. 60000).

UMASK (number)
The file mode creation mask is initialized to this value. If not specified, the mask
will be initialized to 022.

useradd and newusers use this mask to set the mode of the home directory they create
if HOME_MODE is not set.

It is also used by pam_umask as the default umask value.

USERDEL_CMD (string)
If defined, this command is run when removing a user. It should remove any
at/cron/print jobs etc. owned by the user to be removed (passed as the first
argument).

The return code of the script is not taken into account.

Here is an example script, which removes the user's cron, at and print jobs:

#! /bin/sh

# Check for the required argument.
if [ $# != 1 ]; then
echo "Usage: $0 username"
exit 1
fi

# Remove cron jobs.
crontab -r -u $1

# Remove at jobs.
# Note that it will remove any jobs owned by the same UID,
# even if it was shared by a different username.
AT_SPOOL_DIR=/var/spool/cron/atjobs
find $AT_SPOOL_DIR -name "[^.]*" -type f -user $1 -delete \;

# Remove print jobs.
lprm $1

# All done.
exit 0

USERGROUPS_ENAB (boolean)
If set to yes, userdel will remove the user's group if it contains no more members,
and useradd will create by default a group with the name of the user.

CROSS REFERENCES

       The following cross references show which programs in the shadow password suite use which
       parameters.

       chfn
           CHFN_RESTRICT

       chgpasswd
           ENCRYPT_METHOD MAX_MEMBERS_PER_GROUP MD5_CRYPT_ENAB SHA_CRYPT_MAX_ROUNDS
           SHA_CRYPT_MIN_ROUNDS

       chpasswd
           SHA_CRYPT_MAX_ROUNDS SHA_CRYPT_MIN_ROUNDS

       gpasswd
           ENCRYPT_METHOD MAX_MEMBERS_PER_GROUP MD5_CRYPT_ENAB SHA_CRYPT_MAX_ROUNDS
           SHA_CRYPT_MIN_ROUNDS

       groupadd
           GID_MAX GID_MIN MAX_MEMBERS_PER_GROUP SYS_GID_MAX SYS_GID_MIN

       groupdel
           MAX_MEMBERS_PER_GROUP

       groupmems
           MAX_MEMBERS_PER_GROUP

       groupmod
           MAX_MEMBERS_PER_GROUP

       grpck
           MAX_MEMBERS_PER_GROUP

       grpconv
           MAX_MEMBERS_PER_GROUP

       grpunconv
           MAX_MEMBERS_PER_GROUP

       lastlog
           LASTLOG_UID_MAX

       login
           CONSOLE_GROUPS DEFAULT_HOME ERASECHAR FAIL_DELAY FAKE_SHELL HUSHLOGIN_FILE KILLCHAR
           LOGIN_RETRIES LOGIN_TIMEOUT LOG_OK_LOGINS LOG_UNKFAIL_ENAB TTYGROUP TTYPERM
           TTYTYPE_FILE USERGROUPS_ENAB

       newgrp / sg
           SYSLOG_SG_ENAB

       newusers
           ENCRYPT_METHOD GID_MAX GID_MIN MAX_MEMBERS_PER_GROUP MD5_CRYPT_ENAB HOME_MODE
           PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE SHA_CRYPT_MAX_ROUNDS SHA_CRYPT_MIN_ROUNDS
           SUB_GID_COUNT SUB_GID_MAX SUB_GID_MIN SUB_UID_COUNT SUB_UID_MAX SUB_UID_MIN
           SYS_GID_MAX SYS_GID_MIN SYS_UID_MAX SYS_UID_MIN UID_MAX UID_MIN UMASK

       pwck
           PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE

       pwconv
           PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE

       su
           CONSOLE_GROUPS DEFAULT_HOME ENV_PATH ENV_SUPATH SULOG_FILE SU_NAME SYSLOG_SU_ENAB

       sulogin
           ENV_HZ

       useradd
           CREATE_HOME GID_MAX GID_MIN HOME_MODE LASTLOG_UID_MAX MAIL_DIR MAX_MEMBERS_PER_GROUP
           PASS_MAX_DAYS PASS_MIN_DAYS PASS_WARN_AGE SUB_GID_COUNT SUB_GID_MAX SUB_GID_MIN
           SUB_UID_COUNT SUB_UID_MAX SUB_UID_MIN SYS_GID_MAX SYS_GID_MIN SYS_UID_MAX SYS_UID_MIN
           UID_MAX UID_MIN UMASK

       userdel
           MAIL_DIR MAIL_FILE MAX_MEMBERS_PER_GROUP USERDEL_CMD USERGROUPS_ENAB

       usermod
           LASTLOG_UID_MAX MAIL_DIR MAIL_FILE MAX_MEMBERS_PER_GROUP

BUGS

       Much of the functionality that used to be provided by the shadow password suite is now
       handled by PAM. Thus, /etc/login.defs is no longer used by passwd(1), or less used by
       login(1), and su(1). Please refer to the corresponding PAM configuration files instead.

NAME

DESCRIPTION

CROSS REFERENCES

BUGS

SEE ALSO