.\" incompatible with the protocol description in the RFC file, it must be
.\" called by a name other than "ssh" or "Secure Shell".
.\"
-.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
-.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
-.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
+.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
+.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
+.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" (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 1.83 2001/01/19 16:48:14 markus Exp $
+.\" $OpenBSD: sshd.8,v 1.115 2001/04/13 22:46:54 beck Exp $
.Dd September 25, 1999
.Dt SSHD 8
.Os
.Sh NAME
.Nm sshd
-.Nd secure shell daemon
+.Nd OpenSSH ssh daemon
.Sh SYNOPSIS
.Nm sshd
-.Op Fl diqDQ46
+.Op Fl deiqD46
.Op Fl b Ar bits
.Op Fl f Ar config_file
.Op Fl g Ar login_grace_time
.Op Fl V Ar client_protocol_id
.Sh DESCRIPTION
.Nm
-(Secure Shell Daemon) is the daemon program for
+(SSH Daemon) is the daemon program for
.Xr ssh 1 .
Together these programs replace rlogin and rsh, and
provide secure encrypted communications between two untrusted hosts
However, when the daemon starts, it does not generate a server key.
Forward security is provided through a Diffie-Hellman key agreement.
This key agreement results in a shared session key.
-The rest of the session is encrypted
-using a symmetric cipher, currently
-Blowfish, 3DES or CAST128 in CBC mode or Arcfour.
+The rest of the session is encrypted using a symmetric cipher, currently
+Blowfish, 3DES, CAST128, Arcfour, 128 bit AES, or 256 bit AES.
The client selects the encryption algorithm
to use from those offered by the server.
Additionally, session integrity is provided
.Pp
.Nm
rereads its configuration file when it receives a hangup signal,
-.Dv SIGHUP .
+.Dv SIGHUP ,
+by executing itself with the name it was started as, ie.
+.Pa /usr/sbin/sshd .
.Pp
The options are as follows:
.Bl -tag -width Ds
will not detach and does not become a daemon.
This allows easy monitoring of
.Nm sshd .
-.It Fl Q
-Do not print an error message if RSA support is missing.
+.It Fl e
+When this option is specified,
+.Nm
+will send the output to the standard error instead of the system log.
.It Fl V Ar client_protocol_id
SSH-2 compatibility mode.
When this option is specified
Default is
.Dq yes .
.It Cm AllowGroups
-This keyword can be followed by a number of group names, separated
+This keyword can be followed by a list of group names, separated
by spaces.
If specified, login is allowed only for users whose primary
group or supplementary group list matches one of the patterns.
own forwarders.
.Pp
.It Cm AllowUsers
-This keyword can be followed by a number of user names, separated
+This keyword can be followed by a list of user names, separated
by spaces.
If specified, login is allowed only for users names that
match one of the patterns.
authentication is allowed.
This option is only available for protocol version 2.
.Pp
+.It Cm ChallengeResponseAuthentication
+Specifies whether
+challenge response
+authentication is allowed.
+Currently there is only support for
+.Xr skey 1
+authentication.
+The default is
+.Dq yes .
.It Cm Ciphers
Specifies the ciphers allowed for protocol version 2.
Multiple ciphers must be comma-separated.
The default is
-.Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc .
+.Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
.It Cm CheckMail
Specifies whether
.Nm
should check for new mail for interactive logins.
The default is
.Dq no .
+.It Cm ClientAliveInterval
+Sets a timeout interval in seconds after which if no data has been received
+from the client,
+.Nm
+will send a message through the encrypted
+channel to request a response from the client. This may only be
+used on a server supporting only protocol version 2. The default
+is 0, indicating that these messages will not be sent to the client.
+.It Cm ClientAliveCountMax
+Sets the number of client alive messages (see above) which may be
+sent without
+.Nm
+receiving any messages back from the client. If this threshold is
+reached while client alive messages are being sent,
+.Nm
+will disconnect the client, terminating the session. It is important
+to note that the use of client alive messages is very different from
+Keepalive (below). The client alive messages are sent through the
+encrypted channel and therefore will not be spoofable. The TCP keepalive
+option enable by Keepalive is spoofable. You want to use the client
+alive mechanism when you are basing something important on
+clients having an active connection to the server.
+ The default is value is 3. If you set ClientAliveInterval
+(above) to 15, and leave this value 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
by spaces.
can be used as wildcards in the patterns.
Only user names are valid; a numerical user ID isn't recognized.
By default login is allowed regardless of the user name.
-.It Cm PubkeyAuthentication
-Specifies whether public key authentication is allowed.
-The default is
-.Dq yes .
-Note that this option applies to protocol version 2 only.
.It Cm GatewayPorts
Specifies whether remote hosts are allowed to connect to ports
forwarded for the client.
If the value is 0, the key is never regenerated.
The default is 3600 (seconds).
.It Cm ListenAddress
-Specifies what local address
-.Nm
+Specifies the local addresses
+.Xr sshd 8
should listen on.
-The default is to listen to all local addresses.
-Multiple options of this type are permitted.
-Additionally, the
-.Cm Ports
-options must precede this option.
+The following forms may be used:
+.Pp
+.Bl -item -offset indent -compact
+.It
+.Cm ListenAddress
+.Sm off
+.Ar host No | Ar IPv4_addr No | Ar IPv6_addr
+.Sm on
+.It
+.Cm ListenAddress
+.Sm off
+.Ar host No | Ar IPv4_addr No : Ar port
+.Sm on
+.It
+.Cm ListenAddress
+.Sm off
+.Oo
+.Ar host No | Ar IPv6_addr Oc : Ar port
+.Sm on
+.El
+.Pp
+If
+.Ar port
+is not specified,
+.Xr sshd 8
+will listen on the address and all prior
+.Cm Port
+options specified. The default is to listen on all local
+addresses. Multiple
+.Cm ListenAddress
+options are permitted. Additionally, any
+.Cm Port
+options must precede this option for non port qualified addresses.
.It Cm LoginGraceTime
The server disconnects after this time if the user has not
successfully logged in.
The default is INFO.
Logging with level DEBUG violates the privacy of users
and is not recommended.
+.It Cm MACs
+Specifies the available MAC (message authentication code) algorithms.
+The MAC algorithm is used in protocol version 2
+for data integrity protection.
+Multiple algorithms must be comma-separated.
+The default is
+.Pp
+.Bd -literal
+ ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
+ hmac-sha1-96,hmac-md5-96''
+.Ed
.It Cm MaxStartups
Specifies the maximum number of concurrent unauthenticated connections to the
.Nm
.Dq start:rate:full
(e.g., "10:30:60").
.Nm
-will refuse connection attempts with a probabillity of
+will refuse connection attempts with a probability of
.Dq rate/100
(30%)
if there are currently
.Dq start
(10)
unauthenticated connections.
-The probabillity increases linearly and all connection attempts
+The probability increases linearly and all connection attempts
are refused if the number of unauthenticated connections reaches
.Dq full
(60).
The default is
.Dq no .
.It Cm PermitRootLogin
-Specifies whether the root can log in using
+Specifies whether root can login using
.Xr ssh 1 .
The argument must be
.Dq yes ,
-.Dq without-password
+.Dq without-password ,
+.Dq forced-commands-only
or
.Dq no .
The default is
.Dq yes .
-If this options is set to
+.Pp
+If this option is set to
.Dq without-password
-only password authentication is disabled for root.
+password authentication is disabled for root.
.Pp
-Root login with RSA authentication when the
+If this option is set to
+.Dq forced-commands-only
+root login with public key authentication will be allowed,
+but only if the
.Ar command
-option has been
-specified will be allowed regardless of the value of this setting
+option has been specified
(which may be useful for taking remote backups even if root login is
-normally not allowed).
+normally not allowed). All other authentication methods are disabled
+for root.
+.Pp
+If this option is set to
+.Dq no
+root is not allowed to login.
.It Cm PidFile
Specifies the file that contains the process identifier of the
.Nm
listens on.
The default is 22.
Multiple options of this type are permitted.
+.It Cm PrintLastLog
+Specifies whether
+.Nm
+should print the date and time when the user last logged in.
+The default is
+.Dq yes .
.It Cm PrintMotd
Specifies whether
.Nm
Multiple versions must be comma-separated.
The default is
.Dq 1 .
-.It Cm RandomSeed
-Obsolete.
-Random number generation uses other techniques.
+.It Cm PubkeyAuthentication
+Specifies whether public key authentication is allowed.
+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.
.It Cm ServerKeyBits
Defines the number of bits in the server key.
The minimum value is 512, and the default is 768.
-.It Cm SkeyAuthentication
-Specifies whether
-.Xr skey 1
-authentication is allowed.
-The default is
-.Dq yes .
-Note that s/key authentication is enabled only if
-.Cm PasswordAuthentication
-is allowed, too.
.It Cm StrictModes
Specifies whether
.Nm
Note that lines in this file are usually several hundred bytes long
(because of the size of the RSA key modulus).
You don't want to type them in; instead, copy the
-.Pa identity.pub
-or the
+.Pa identity.pub ,
.Pa id_dsa.pub
+or the
+.Pa id_rsa.pub
file and edit it.
.Pp
The options (if present) consist of comma-separated option
The command supplied by the user (if any) is ignored.
The command is run on a pty if the connection requests a pty;
otherwise it is run without a tty.
+Note that if you want a 8-bit clean channel,
+you must not request a pty or should specify
+.Cm no-pty .
A quote may be included in the command by quoting it with a backslash.
This option might be useful
to restrict certain RSA keys to perform just a specific operation.
authentication.
.It Cm no-pty
Prevents tty allocation (a request to allocate a pty will fail).
+.It Cm permitopen="host:port"
+Limit local
+.Li ``ssh -L''
+port forwarding such that it may only connect to the specified host and
+port. Multiple
+.Cm permitopen
+options may be applied separated by commas. No pattern matching is
+performed on the specified hostnames, they must be literal domains or
+addresses.
.El
.Ss Examples
1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
.Pp
command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
+.Pp
+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 ,
.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
-Contains the private part of the host key.
-This file should only be owned by root, readable only by root, and not
+.It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
+These three files contain the private parts of the
+(SSH1, SSH2 DSA, and SSH2 RSA) 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
-Contains the public part of the host key.
-This file should be world-readable but writable only by
+.It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
+These three files contain the public parts of the
+(SSH1, SSH2 DSA, and SSH2 RSA) host keys.
+These files should be world-readable but writable only by
root.
-Its contents should match the private part.
-This file is not
-really used for anything; it is only provided for the convenience of
-the user so its contents can be copied to known hosts files.
-These two files are created using
+Their contents should match the respective private parts.
+These files are not
+really used for anything; they are provided for the convenience of
+the user so their contents can be copied to known hosts files.
+These files are created using
.Xr ssh-keygen 1 .
.It Pa /etc/primes
Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
The format of this file is described above.
Users will place the contents of their
.Pa id_dsa.pub
+and/or
+.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"
authentication to check the public key of the host.
The key must be listed in one of these files to be accepted.
The client uses the same files
-to verify that the remote host is the one it intended to connect.
+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
should be world-readable, and
This file should be writable only by root, and should be world-readable.
.El
.Sh AUTHORS
-OpenSSH
-is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
-but with bugs removed and newer features re-added.
-Rapidly after the
-1.2.12 release, newer versions of the original ssh bore successively
-more restrictive licenses, and thus demand for a free version was born.
-.Pp
-This version of OpenSSH
-.Bl -bullet
-.It
-has all components of a restrictive nature (i.e., patents, see
-.Xr ssl 8 )
-directly removed from the source code; any licensed or patented components
-are chosen from
-external libraries.
-.It
-has been updated to support SSH protocol 1.5 and 2, making it compatible with
-all other SSH clients and servers.
-.It
-contains added support for
-.Xr kerberos 8
-authentication and ticket passing.
-.It
-supports one-time password authentication with
-.Xr skey 1 .
-.El
-.Pp
-OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
-Niels Provos, Theo de Raadt, and Dug Song.
-.Pp
-The support for SSH protocol 2 was written by Markus Friedl.
+OpenSSH is a derivative of the original and free
+ssh 1.2.12 release by Tatu Ylonen.
+Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
+Theo de Raadt and Dug Song
+removed many bugs, re-added newer features and
+created OpenSSH.
+Markus Friedl contributed the support for SSH
+protocol versions 1.5 and 2.0.
.Sh SEE ALSO
.Xr scp 1 ,
+.Xr sftp 1 ,
.Xr sftp-server 8 ,
.Xr ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
.Xr ssh-keygen 1 ,
-.Xr ssl 8 ,
.Xr rlogin 1 ,
.Xr rsh 1
andersk / openssh.git / blobdiff