.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.\" $OpenBSD: sshd.8,v 1.161 2002/01/05 21:51:56 stevesk Exp $
+.\" $OpenBSD: sshd.8,v 1.174 2002/03/26 11:34:49 markus Exp $
.Dd September 25, 1999
.Dt SSHD 8
.Os
.It Fl f Ar configuration_file
Specifies the name of the configuration file.
The default is
-.Pa /etc/sshd_config .
+.Pa /etc/ssh/sshd_config .
.Nm
refuses to start if there is no configuration file.
.It Fl g Ar login_grace_time
is not run as root (as the normal
host key files are normally not readable by anyone but root).
The default is
-.Pa /etc/ssh_host_key
+.Pa /etc/ssh/ssh_host_key
for protocol version 1, and
-.Pa /etc/ssh_host_rsa_key
+.Pa /etc/ssh/ssh_host_rsa_key
and
-.Pa /etc/ssh_host_dsa_key
+.Pa /etc/ssh/ssh_host_dsa_key
for protocol version 2.
It is possible to have multiple host key files for
the different protocol versions and host key algorithms.
and using a
.Cm from="pattern-list"
option in a key file.
+Configuration options that require DNS include using a
+USER@HOST pattern in
+.Cm AllowUsers
+or
+.Cm DenyUsers .
.It Fl D
When this option is specified
.Nm
.Sh CONFIGURATION FILE
.Nm
reads configuration data from
-.Pa /etc/sshd_config
+.Pa /etc/ssh/sshd_config
(or the file specified with
.Fl f
on the command line).
Default is
.Dq yes .
.It Cm AllowGroups
-This keyword can be followed by a list of group names, separated
+This keyword can be followed by a list of group name patterns, separated
by spaces.
If specified, login is allowed only for users whose primary
group or supplementary group list matches one of the patterns.
can be used as
wildcards in the patterns.
Only group names are valid; a numerical group ID is not recognized.
-By default login is allowed regardless of the group list.
+By default, login is allowed for all groups.
.Pp
.It Cm AllowTcpForwarding
Specifies whether TCP forwarding is permitted.
own forwarders.
.Pp
.It Cm AllowUsers
-This keyword can be followed by a list of user names, separated
+This keyword can be followed by a list of user name patterns, separated
by spaces.
If specified, login is allowed only for users names that
match one of the patterns.
can be used as
wildcards in the patterns.
Only user names are valid; a numerical user ID is not recognized.
-By default login is allowed regardless of the user name.
+By default, login is allowed for all users.
If the pattern takes the form USER@HOST then USER and HOST
are separately checked, restricting logins to particular
users from particular hosts.
The contents of the specified file are sent to the remote user before
authentication is allowed.
This option is only available for protocol version 2.
+By default, no banner is displayed.
.Pp
.It Cm ChallengeResponseAuthentication
Specifies whether challenge response authentication is allowed.
Specifies the ciphers allowed for protocol version 2.
Multiple ciphers must be comma-separated.
The default is
-.Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour .
+.Pp
+.Bd -literal
+ ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
+ aes192-cbc,aes256-cbc''
+.Ed
.It Cm ClientAliveInterval
Sets a timeout interval in seconds after which if no data has been received
from the client,
is left at the default, unresponsive ssh clients
will be disconnected after approximately 45 seconds.
.It Cm DenyGroups
-This keyword can be followed by a number of group names, separated
+This keyword can be followed by a list of group name patterns, separated
by spaces.
-Users whose primary group or supplementary group list matches
-one of the patterns aren't allowed to log in.
+Login is disallowed for users whose primary group or supplementary
+group list matches one of the patterns.
.Ql \&*
and
.Ql ?
can be used as
wildcards in the patterns.
Only group names are valid; a numerical group ID is not recognized.
-By default login is allowed regardless of the group list.
+By default, login is allowed for all groups.
.Pp
.It Cm DenyUsers
-This keyword can be followed by a number of user names, separated
+This keyword can be followed by a list of user name patterns, separated
by spaces.
Login is disallowed for user names that match one of the patterns.
.Ql \&*
.Ql ?
can be used as wildcards in the patterns.
Only user names are valid; a numerical user ID is not recognized.
-By default login is allowed regardless of the user name.
+By default, login is allowed for all users.
+If the pattern takes the form USER@HOST then USER and HOST
+are separately checked, restricting logins to particular
+users from particular hosts.
.It Cm GatewayPorts
Specifies whether remote hosts are allowed to connect to ports
forwarded for the client.
Specifies a file containing a private host key
used by SSH.
The default is
-.Pa /etc/ssh_host_key
+.Pa /etc/ssh/ssh_host_key
for protocol version 1, and
-.Pa /etc/ssh_host_rsa_key
+.Pa /etc/ssh/ssh_host_rsa_key
and
-.Pa /etc/ssh_host_dsa_key
+.Pa /etc/ssh/ssh_host_dsa_key
for protocol version 2.
Note that
.Nm
The default is
.Dq no .
.It Cm KeepAlive
-Specifies whether the system should send keepalive messages to the
+Specifies whether the system should send TCP keepalive messages to the
other side.
If they are sent, death of the connection or crash of one
of the machines will be properly noticed.
The default is
.Dq yes
(to send keepalives), and the server will notice
-if the network goes down or the client host reboots.
+if the network goes down or the client host crashes.
This avoids infinitely hanging sessions.
.Pp
To disable keepalives, the value should be set to
-.Dq no
-in both the server and the client configuration files.
+.Dq no .
.It Cm KerberosAuthentication
Specifies whether Kerberos authentication is allowed.
This can be in the form of a Kerberos ticket, or if
The default is
.Dq yes .
Note that this option applies to protocol version 2 only.
-.It Cm ReverseMappingCheck
-Specifies whether
-.Nm
-should try to verify the remote host name and check that
-the resolved host name for the remote IP address maps back to the
-very same IP address.
-The default is
-.Dq no .
.It Cm RhostsAuthentication
Specifies whether authentication using rhosts or /etc/hosts.equiv
files is sufficient.
.Xr login 1
does not know how to handle
.Xr xauth 1
-cookies.
+cookies. If
+.Cm UsePrivilegeSeparation
+is specified, it will be disabled after authentication.
+.It Cm UsePrivilegeSeparation
+Specifies whether
+.Nm
+separated privileges by creating an unprivileged child process
+to deal with incoming network traffic. After successful authentication,
+another process will be created that has the privilege of the authenticated
+user. The goal of privilege separation is to prevent privilege
+escalation by containing any corruption within the unprivileged processes.
+The default is
+.Dq no .
+.It Cm VerifyReverseMapping
+Specifies whether
+.Nm
+should try to verify the remote host name and check that
+the resolved host name for the remote IP address maps back to the
+very same IP address.
+The default is
+.Dq no .
.It Cm X11DisplayOffset
Specifies the first display number available for
.Nm sshd Ns 's
X11 forwarding is automatically disabled if
.Cm UseLogin
is enabled.
+.It Cm X11UseLocalhost
+Specifies whether
+.Nm
+should bind the X11 forwarding server to the loopback address or to
+the wildcard address. By default,
+.Nm
+binds the forwarding server to the loopback address and sets the
+hostname part of the
+.Ev DISPLAY
+environment variable to
+.Dq localhost .
+This prevents remote hosts from connecting to the fake display.
+However, some older X11 clients may not function with this
+configuration.
+.Cm X11UseLocalhost
+may be set to
+.Dq no
+to specify that the forwarding server should be bound to the wildcard
+address.
+The argument must be
+.Dq yes
+or
+.Dq no .
+The default is
+.Dq yes .
.It Cm XAuthLocation
Specifies the location of the
.Xr xauth 1
If
.Pa $HOME/.ssh/rc
exists, runs it; else if
-.Pa /etc/sshrc
+.Pa /etc/ssh/sshrc
exists, runs
it; otherwise runs xauth.
The
permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
.Sh SSH_KNOWN_HOSTS FILE FORMAT
The
-.Pa /etc/ssh_known_hosts ,
+.Pa /etc/ssh/ssh_known_hosts ,
and
.Pa $HOME/.ssh/known_hosts
files contain host public keys for all known hosts.
.Pp
Bits, exponent, and modulus are taken directly from the RSA host key; they
can be obtained, e.g., from
-.Pa /etc/ssh_host_key.pub .
+.Pa /etc/ssh/ssh_host_key.pub .
The optional comment field continues to the end of the line, and is not used.
.Pp
Lines starting with
long, and you definitely don't want to type in the host keys by hand.
Rather, generate them by a script
or by taking
-.Pa /etc/ssh_host_key.pub
+.Pa /etc/ssh/ssh_host_key.pub
and adding the host names at the front.
.Ss Examples
.Bd -literal
.Ed
.Sh FILES
.Bl -tag -width Ds
-.It Pa /etc/sshd_config
+.It Pa /etc/ssh/sshd_config
Contains configuration data for
.Nm sshd .
This file should be writable by root only, but it is recommended
(though not necessary) that it be world-readable.
-.It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
+.It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
These three files contain the private parts of the host keys.
These files should only be owned by root, readable only by root, and not
accessible to others.
Note that
.Nm
does not start if this file is group/world-accessible.
-.It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
+.It Pa /etc/ssh/ssh_host_key.pub, /etc/ssh/ssh_host_dsa_key.pub, /etc/ssh/ssh_host_rsa_key.pub
These three files contain the public parts of the host keys.
These files should be world-readable but writable only by
root.
.Pa id_rsa.pub
files into this file, as described in
.Xr ssh-keygen 1 .
-.It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
+.It Pa "/etc/ssh/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
These files are consulted when using rhosts with RSA host
authentication or protocol version 2 hostbased authentication
to check the public key of the host.
The client uses the same files
to verify that it is connecting to the correct remote host.
These files should be writable only by root/the owner.
-.Pa /etc/ssh_known_hosts
+.Pa /etc/ssh/ssh_known_hosts
should be world-readable, and
.Pa $HOME/.ssh/known_hosts
can but need not be world-readable.
.Ed
.Pp
If this file does not exist,
-.Pa /etc/sshrc
+.Pa /etc/ssh/sshrc
is run, and if that
does not exist either, xauth is used to store the cookie.
.Pp
This file should be writable only by the user, and need not be
readable by anyone else.
-.It Pa /etc/sshrc
+.It Pa /etc/ssh/sshrc
Like
.Pa $HOME/.ssh/rc .
This can be used to specify
created OpenSSH.
Markus Friedl contributed the support for SSH
protocol versions 1.5 and 2.0.
+Niels Provos and Markus Friedl contributed support
+for privilege separation.
.Sh SEE ALSO
.Xr scp 1 ,
.Xr sftp 1 ,
.%A T. Rinne
.%A S. Lehtinen
.%T "SSH Protocol Architecture"
-.%N draft-ietf-secsh-architecture-09.txt
-.%D July 2001
+.%N draft-ietf-secsh-architecture-12.txt
+.%D January 2002
.%O work in progress material
.Re
.Rs
.%A N. Provos
.%A W. A. Simpson
.%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol"
-.%N draft-ietf-secsh-dh-group-exchange-01.txt
-.%D April 2001
+.%N draft-ietf-secsh-dh-group-exchange-02.txt
+.%D January 2002
.%O work in progress material
.Re
andersk / openssh.git / blobdiff