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LOGIN.CONF(5) File Formats Manual LOGIN.CONF(5)

login.conf — login class capability database

The login.conf file describes the various attributes of login classes. A login class determines what styles of authentication are available as well as session resource limits and environment setup. While designed primarily for the login(1) program, it is also used by other programs, such as ftpd(8), to determine what means of authentication are available. It is also used by programs which need to set up a user environment.

A special record, “default”, in /etc/login.conf is used for any user without a valid login class in /etc/master.passwd.

In case the /etc/login.conf.d/${class} file exists, it will take precedence over the same login class defined in /etc/login.conf.

Sites with very large /etc/login.conf files may wish to create a database version of the file, /etc/login.conf.db, for improved performance. Using a database version for small files does not result in a performance improvement. To build /etc/login.conf.db from /etc/login.conf the following command may be used:

# cap_mkdb /etc/login.conf

Note that cap_mkdb(1) must be run after each edit of /etc/login.conf or the /etc/login.conf.d/${class} file to keep the database version in sync with the plain file.

Refer to cgetent(3) for a description of the file layout. All entries in the login.conf file are either boolean or use a ‘=’ to separate the capability from the value. The types are described after the capability table.

approve program Default program to approve login.

approve-service program Program to approve login for service.

auth list Allowed authentication styles. The first value is the default style.

auth-type list Allowed authentication styles for the authentication type type.

classify program Classify type of login.

copyright file File containing additional copyright information.

coredumpsize size Maximum coredump size limit.

cputime time CPU usage limit.

datasize size Maximum data size limit.

expire-warn time If the user's account will expire within this length of time then warn the user of this.

filesize size Maximum file size limit.

hushlogin bool Same as having a $HOME/.hushlogin file. See login(1).

ignorenologin bool Not affected by nologin files. See login(1).

localcipher string bcrypt,a The cipher to use for encrypting passwords. Refer to crypt_newhash(3) for possible values.

login-backoff number 3 After login-backoff unsuccessful login attempts during a single session, login(1) will start sleeping a bit in between attempts.

login-timeout time 300 Number of seconds before login(1) times out at the password prompt. Note that this setting is only valid for the default record.

login-tries number 10 Number of tries a user gets to successfully login before login(1) closes the connection.

stacksize size Maximum stack size limit.

maxproc number Maximum number of processes.

memorylocked size Maximum locked in core memory size limit.

memoryuse size Maximum in core memoryuse size limit.

minpasswordlen number 6 The minimum length a local password may be. If a negative value or zero, no length restrictions are enforced. Used by the passwd(1) utility.

nologin file If the file exists, it will be displayed and the login session will be terminated.

openfiles number Maximum number of open file descriptors per process.

password-dead time Length of time a password may be expired but not quite dead yet. When set (for both the client and remote server machine when doing remote authentication), a user is allowed to log in just one more time after their password (but not account) has expired. This allows a grace period for updating their password.

password-warn time If the user's password will expire within this length of time then warn the user of this.

passwordcheck program An external program that checks the quality of the password. The password is passed to the program on stdin. An exit code of 0 indicates that the quality of the password is sufficient, an exit code of 1 signals that the password failed the check.

passwordtime time The lifetime of a password in seconds, reset every time a user changes their password. When this value is exceeded, the user will no longer be able to login unless the password-dead option has been specified. Used by the passwd(1) utility.

passwordtries number 3 The number of times the passwd(1) utility enforces a check on the password. If 0, the new password will only be accepted if it passes the password quality check.

path path value of _PATH_DEFPATH
Default search path. See /usr/include/paths.h.

priority number Initial priority (nice) level.

requirehome bool Require home directory to login.

rtable number Rtable to be set for the class.

setenv envlist A list of environment variables and associated values to be set for the class.

shell program Session shell to execute rather than the shell specified in the password file. The SHELL environment variable will contain the shell specified in the password file.

tc string Interpolate/expands records from corresponding login.conf. See cgetent(3).

term string Default terminal type if not able to determine from other means.

umask number Initial umask. Should always have a leading 0 to ensure octal interpretation. See umask(2).

vmemoryuse size Maximum virtual memoryuse size limit.

welcome file /etc/motd File containing welcome message.

The resource limit entries (cputime, filesize, datasize, stacksize, coredumpsize, memoryuse, memorylocked, maxproc, and openfiles) actually specify both the maximum and current limits (see getrlimit(2)). The current limit is the one normally used, although the user is permitted to increase the current limit to the maximum limit. The maximum and current limits may be specified individually by appending a -max or -cur to the capability name (e.g., openfiles-max and openfiles-cur).

OpenBSD will never define capabilities which start with x- or X-, these are reserved for external use (unless included through contributed software).

The argument types are defined as:

envlist
A comma-separated list of environment variables of the form variable=value. If no value is specified, the ‘=’ is optional. A ~ in the path name is expanded to the user's home directory if it is at the end of a string or is followed by a slash (‘/’) or the user's login name. A $ in the path name is expanded to the user's login name.
file
Path name to a text file.
list
A comma-separated list of values.
number
A number. A leading 0x implies the number is expressed in hexadecimal. A leading 0 implies the number is expressed in octal. Any other number is treated as decimal.
path
A space-separated list of path names. Login name and directory are substituted as for . Additionally, a ~ is only expanded at the beginning of a path name.
program
A path name to program.
size
A number which expresses a size. By default, the size is specified in bytes. It may have a trailing b, k, m, g or t to indicate that the value is in 512-byte blocks, kilobytes, megabytes, gigabytes, or terabytes, respectively.
time
A time in seconds. A time may be expressed as a series of numbers which are added together. Each number may have a trailing character to represent time units:
y
Indicates a number of 365 day years.
w
Indicates a number of 7 day weeks.
d
Indicates a number of 24 hour days.
h
Indicates a number of 60 minute hours.
m
Indicates a number of 60 second minutes.
s
Indicates a number of seconds.

For example, to indicate 1 and 1/2 hours, the following string could be used: 1h30m.

OpenBSD uses BSD Authentication, which is made up of a variety of authentication styles. The authentication styles currently provided are:

Authenticate using an ActivCard token. See login_activ(8).
Change user's password. See login_chpass(8).
Authenticate using a CRYPTOCard token. See login_crypto(8).
Change user's local password. See login_lchpass(8).
Authenticate using an LDAP server. See login_ldap(8).
Request a password and check it against the password in the master.passwd file. See login_passwd(8).
Normally linked to another authentication type, contact a RADIUS server to do authentication. See login_radius(8).
Request a password and reject any request. See login_reject(8).
Send a challenge and request a response, checking it with S/Key (tm) authentication. See login_skey(8).
Authenticate using a SecureNet Key token. See login_snk(8).
Authenticate using a generic X9.9 token. See login_token(8).
Authenticate using a Yubico YubiKey token. See login_yubikey(8).

Local authentication styles may be added by creating a login script for the style (see below). To prevent collisions with future official BSD Authentication style names, all local style names should start with a dash (-). Current plans are for all official BSD Authentication style names to begin with a lower case alphabetic character. For example, if you have a new style you refer to as slick then you should create an authentication script named /usr/libexec/auth/login_-slick using the style name -slick. When logging in via the login(1) program, the syntax user:-slick would be used.

Authentication requires several pieces of information:

class
The login class being used.
service
The type of service requesting authentication. The service type is used to determine what information the authentication program can provide to the user and what information the user can provide to the authentication program.

The service type login is appropriate for most situations. Two other service types, challenge and response, are provided for use by programs like ftpd(8) and radiusd(8). If no service type is specified, login is used.

style
The authentication style being used.
type
The authentication type, used to determine the available authentication styles.
username
The name of the user to authenticate. The name may contain an instance. If the authentication style being used does not support such instances, the request will fail.

The program requesting authentication must specify a username and an authentication style. (For example, login(1) requests a username from the user. Users may enter usernames of the form “user:style” to optionally specify the authentication style.) The requesting program may also specify the type of authentication that will be done. Most programs will only have a single type, if any at all, i.e., ftpd(8) will always request the ftp type authentication, and su(1) will always request the su type authentication. The login(1) utility is special in that it may select an authentication type based on information found in the /etc/ttys file for the appropriate tty (see ttys(5)).

The class to be used is normally determined by the class field in the password file (see passwd(5)).

The class is used to look up a corresponding entry in the login.conf file. If an authentication type is defined and a value for auth-type exists in that entry, it will be used as a list of potential authentication styles. If an authentication type is not defined, or auth-type is not specified for the class, the value of auth is used as the list of available authentication styles.

If the user did not specify an authentication style, the first style in the list of available styles is used. If the user did specify an authentication style and the style is in the list of available styles it will be used, otherwise the request is rejected.

For any given style, the program /usr/libexec/auth/login_style is used to perform the authentication. The synopsis of this program is:

/usr/libexec/auth/login_style [-v name=value] [-s service] username class

The -v option is used to specify arbitrary information to the authentication programs. Any number of -v options may be used. The login(1) program provides the following through the -v option:

The type of authentication to use.
The hostname provided to login by the -h option.
The name login(1) will place in the utmp file for the remote hostname.
The local IP address given to login(1) by the -L option.
Set to “yes” when a user's password has expired but the user is being given one last chance to login and update the password.
This is a new login session (as opposed to a simple identity check).
The remote IP address given to login(1) by the -R option.
The style of authentication used for this user (see approval scripts below).

The su(1) program provides the following through the -v option:

Set to either “yes” or “no” to indicate if the user is in group wheel when they are trying to become root. Some authentication types require the user to be in group wheel when using the su(1) program to become super user.

When the authentication program is executed, the environment will only contain the values PATH=/bin:/usr/bin and SHELL=/bin/sh. File descriptor 3 will be open for reading and writing. The authentication program should write one or more of the following strings to this file descriptor:

The user has been authorized.
authorize secure
The user has been authorized and root should be allowed to login even if this is not a secure terminal. This should only be sent by authentication styles that are secure over insecure lines.
Authorization is rejected. This overrides any indication that the user was authorized (though one would question the wisdom in sending both a reject and an authorize command).
reject challenge
Authorization was rejected and a challenge has been made available via the value challenge.
reject silent
Authorization is rejected, but no error messages should be generated.
file
If the login session fails for any reason, remove file before termination.
name value
If the login session succeeds, the environment variable name should be set to the specified value.
name
If the login session succeeds, the environment variable name should be removed.
name value
Set the internal variable name to the specified value. The value should only contain printable characters. Several \ sequences may be used to introduce non printing characters. These are:
A newline.
A carriage return.
A tab.
\xxx
The character represented by the octal value xxx. The value may be one, two, or three octal digits.
\c
The string is replaced by the value of c. This allows quoting an initial space or the \ character itself.

The following values are currently defined:

See section on challenges below.
If set, the value is the reason authentication failed. The calling program may choose to display this when rejecting the user, but display is not required.

In order for authentication to be successful, the authentication program must exit with a value of 0 as well as provide an authorize or authorize root statement on file descriptor 3.

An authentication program must not assume it will be called as root, nor must it assume it will not be called as root. If it needs special permissions to access files, it should be setuid or setgid to the appropriate user/group. See chmod(1).

When an authentication program is called with a service of challenge it should do one of three things:

If this style of authentication supports challenge response, it should set the internal variable challenge to be the appropriate challenge for the user. This is done by the value command listed above. The program should also issue a reject challenge and then exit with a 0 status. See the section on responses below.

If this style of authentication does not support challenge response, but does support the response service (described below) it should issue reject silent and then exit with a 0 status.

If this style of authentication does not support the response service it should simply fail, complaining about an unknown service type. It should exit with a non-zero status.

When an authentication program is called with a service of response, and this style supports this mode of authentication, it should read two null terminated strings from file descriptor 3. The first string is a challenge that was issued to the user (obtained from the challenge service above). The second string is the response the user gave (i.e., the password). If the response is correct for the specified challenge, the authentication should be accepted, else it should be rejected. It is possible for the challenge to be an empty string, which implies the calling program did first obtain a challenge prior to getting a response from the user. Not all authentication styles support empty challenges.

An approval program has the synopsis of:

approve [-v name=value] username class service

Just as with an authentication program, file descriptor 3 will be open for writing when the approval program is executed. The -v option is the same as in the authentication program. Unlike an authentication program, the approval program need not explicitly send an authorize or authorize root statement, it only need exit with a value of 0 or non-zero. An exit value of 0 is equivalent to an authorize statement, and non-zero to a reject statement. This allows for simple programs which have no information to provide other than approval or denial.

A classify program has the synopsis of:

classify [-v name=value] [-f] [user]

See login(1) for a description of the -f, option. The -v option is the same as for the authentication programs. The user is the username passed to login(1) login, if any.

The typical job of the classify program is to determine what authentication type should actually be used, presumably based on the remote IP address. It might also re-specify the hostname to be included in the utmp(5) file, reject the login attempt outright, or even print an additional login banner (e.g., /etc/issue).

The classify entry is only valid for the default class as it is used prior to knowing who the user is. The classify script may pass environment variables or other commands back to login(1) on file descriptor 3, just as an authentication program does. The two variables AUTH_TYPE and REMOTE_NAME are used to specify a new authentication type (the type must have the form auth-type) and override the -h option to login, respectively.

/etc/login.conf
Login class capability database.
/etc/login.conf.d/${class}
Login class capability database for the specified login class.

cap_mkdb(1), login(1), auth_subr(3), authenticate(3), cgetent(3), login_cap(3), passwd(5), ttys(5), ftpd(8)

January 22, 2024 OpenBSD-7.6