login class capability
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.
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 to keep the database version in sync with the plain file.
getcap(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.|
||Allowed authentication styles. The first value is the default styles.|
|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.|
||If the user's account will expire within this length of time then warn the user of this.|
|filesize||size||Maximum file size limit.|
||Same as having a $HOME/.hushlogin file. See login(1).|
||Not affected by nologin files. See login(1).|
|localcipher||string||blowfish,8||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
|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.|
||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.|
||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
|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.|
Default search path. See /usr/include/paths.h.
|priority||number||Initial priority (nice) level.|
||Require home directory to login.|
|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
|tc||string||Interpolate/expands records from corresponding login.conf. See getcap(3).|
||Default terminal type if not able to determine from other means.|
||Initial umask. Should always have a leading
|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
these are reserved for external use (unless included through contributed
The argument types are defined as:
- 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.
- Path name to a text file.
- A comma-separated list of values.
- A number. A leading
0ximplies the number is expressed in hexadecimal. A leading
0implies the number is expressed in octal. Any other number is treated as decimal.
- A space-separated list of path names. Login name and directory are
substituted as for
~is only expanded at the beginning of a path name.
- A path name to program.
- A number which expresses a size. By default, the
size is specified in bytes. It may have a trailing
tto indicate that the value is in 512-byte blocks, kilobytes, megabytes, gigabytes, or terabytes, respectively.
- 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
- Indicates a number of 365 day years.
- Indicates a number of 7 day weeks.
- Indicates a number of 24 hour days.
- Indicates a number of 60 minute hours.
- Indicates a number of 60 second minutes.
- Indicates a number of seconds.
For example, to indicate 1 and 1/2 hours, the following string could be used:
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).
- 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 the 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
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
:-slick would be used.
Authentication requires several pieces of information:
- The login class being used.
- 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
The service type
loginis appropriate for most situations. Two other service types,
response, are provided for use by programs like ftpd(8) and radiusd(8). If no service type is specified,
- The authentication style being used.
- The authentication type, used to determine the available authentication styles.
- 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
authentication, and su(1) will always request 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
The class to be used is normally determined by the
class field in the password file (see
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:
-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
- The type of authentication to use.
- The hostname provided to login by the
- The name login(1) will place in the utmp file for the remote hostname.
- The local IP address given to
login(1) by the
- 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
- The style of authentication used for this user (see approval scripts below).
The su(1) program provides the following through the
- 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
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.
- 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).
- Authorization was rejected and a challenge has been made available via the
- Authorization is rejected, but no error messages should be generated.
- If the login session fails for any reason, remove file before termination.
- If the login session succeeds, the environment variable name should be set to the specified value.
- If the login session succeeds, the environment variable name should be removed.
- 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.
- The character represented by the octal value xxx. The value may be one, two, or three octal digits.
- 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
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
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
(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:
-vname=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 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:
See login(1) for a description of 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
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.
cap_mkdb(1), login(1), authenticate(3), bsd_auth(3), getcap(3), login_cap(3), passwd(5), ttys(5), ftpd(8)