sshd.0

OpenSSL Source code for SFTP, SSH, and many others

             pty; otherwise it is run without a tty.  If a 8-bit clean channel
             is required, one must not request a pty or should specify no-pty.
             A quote may be included in the command by quoting it with a backM--
             slash.  This option might be useful to restrict certain RSA keys
             to perform just a specific operation.  An example might be a key
             that permits remote backups but nothing else.  Note that the
             client may specify TCP/IP and/or X11 forwarding unless they are
             explicitly prohibited.  Note that this option applies to shell,
             command or subsystem execution.

     environment="NAME=value"
             Specifies that the string is to be added to the environment when
             logging in using this key.  Environment variables set this way
             override other default environment values.  Multiple options of
             this type are permitted.  This option is automatically disabled
             if UseLogin is enabled.

     no-port-forwarding
             Forbids TCP/IP forwarding when this key is used for authenticaM--
             tion.  Any port forward requests by the client will return an
             error.  This might be used, e.g., in connection with the command
             option.

     no-X11-forwarding
             Forbids X11 forwarding when this key is used for authentication.
             Any X11 forward requests by the client will return an error.

     no-agent-forwarding
             Forbids authentication agent forwarding when this key is used for
             authentication.

     no-pty  Prevents tty allocation (a request to allocate a pty will fail).

     permitopen="host:port"
             Limit local ``ssh -L'' port forwarding such that it may only conM--
             nect to the specified host and port.  IPv6 addresses can be specM--
             ified with an alternative syntax: host/port.  Multiple permitopen
             options may be applied separated by commas. No pattern matching
             is performed on the specified hostnames, they must be literal
             domains or addresses.

   Examples
     1024 33 12121...312314325 [e-mail]

     from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23...2334 ylo@niksula

     command="dump /home",no-pty,no-port-forwarding 1024 33 23...2323
     backup.hut.fi

     permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23...2323

SSH_KNOWN_HOSTS FILE FORMAT
     The /etc/ssh/ssh_known_hosts, and $HOME/.ssh/known_hosts files contain
     host public keys for all known hosts.  The global file should be prepared
     by the administrator (optional), and the per-user file is maintained
     automatically: whenever the user connects from an unknown host its key is
     added to the per-user file.

     Each line in these files contains the following fields: hostnames, bits,
     exponent, modulus, comment.  The fields are separated by spaces.

     Hostnames is a comma-separated list of patterns ('*' and '?' act as wildM--
     cards); each pattern in turn is matched against the canonical host name
     (when authenticating a client) or against the user-supplied name (when
     authenticating a server).  A pattern may also be preceded by `'!  to
     indicate negation: if the host name matches a negated pattern, it is not
     accepted (by that line) even if it matched another pattern on the line.

     Bits, exponent, and modulus are taken directly from the RSA host key;
     they can be obtained, e.g., from /etc/ssh/ssh_host_key.pub.  The optional
     comment field continues to the end of the line, and is not used.

     Lines starting with `#' and empty lines are ignored as comments.

     When performing host authentication, authentication is accepted if any
     matching line has the proper key.  It is thus permissible (but not recomM--
     mended) to have several lines or different host keys for the same names.
     This will inevitably happen when short forms of host names from different
     domains are put in the file.  It is possible that the files contain conM--
     flicting information; authentication is accepted if valid information can
     be found from either file.

     Note that the lines in these files are typically hundreds of characters
     long, and you definitely don't want to type in the host keys by hand.
     Rather, generate them by a script or by taking /etc/ssh/ssh_host_key.pub
     and adding the host names at the front.

   Examples

     closenet,...,130.233.208.41 1024 37 159...93 closenet.hut.fi
     cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....=

FILES
     /etc/ssh/sshd_config
             Contains configuration data for sshd.  The file format and conM--
             figuration options are described in sshd_config(5).

     /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 sshd does not start if
             this file is group/world-accessible.

     /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.
             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 ssh-keygen(1).

     /etc/moduli
             Contains Diffie-Hellman groups used for the "Diffie-Hellman Group
             Exchange".

     /var/run/sshd.pid
             Contains the process ID of the sshd listening for connections (if
             there are several daemons running concurrently for different
             ports, this contains the pid of the one started last).  The conM--
             tent of this file is not sensitive; it can be world-readable.

     $HOME/.ssh/authorized_keys
             Lists the public keys (RSA or DSA) that can be used to log into
             the user's account.  This file must be readable by root (which
             may on some machines imply it being world-readable if the user's
             home directory resides on an NFS volume).  It is recommended that
             it not be accessible by others.  The format of this file is
             described above.  Users will place the contents of their
             identity.pub, id_dsa.pub and/or id_rsa.pub files into this file,
             as described in ssh-keygen(1).

     /etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts
             These files are consulted when using rhosts with RSA host authenM--
             tication or protocol version 2 hostbased 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 it is connecting to the correct remote host.  These
             files should be writable only by root/the owner.
             /etc/ssh/ssh_known_hosts should be world-readable, and
             $HOME/.ssh/known_hosts can but need not be world-readable.

     /etc/nologin
             If this file exists, sshd refuses to let anyone except root log
             in.  The contents of the file are displayed to anyone trying to
             log in, and non-root connections are refused.  The file should be
             world-readable.

     /etc/hosts.allow, /etc/hosts.deny
             Access controls that should be enforced by tcp-wrappers are
             defined here.  Further details are described in hosts_access(5).

     $HOME/.rhosts
             This file contains host-username pairs, separated by a space, one
             per line.  The given user on the corresponding host is permitted
             to log in without password.  The same file is used by rlogind and
             rshd.  The file must be writable only by the user; it is recomM--
             mended that it not be accessible by others.

             If is also possible to use netgroups in the file.  Either host or
             user name may be of the form +@groupname to specify all hosts or
             all users in the group.

     $HOME/.shosts
             For ssh, this file is exactly the same as for .rhosts.  However,
             this file is not used by rlogin and rshd, so using this permits
             access using SSH only.

     /etc/hosts.equiv
             This file is used during .rhosts authentication.  In the simplest
             form, this file contains host names, one per line.  Users on
             those hosts are permitted to log in without a password, provided
             they have the same user name on both machines.  The host name may
             also be followed by a user name; such users are permitted to log
             in as any user on this machine (except root).  Additionally, the
             syntax ``+@group'' can be used to specify netgroups.  Negated
             entries start with `-'.

             If the client host/user is successfully matched in this file,
             login is automatically permitted provided the client and server
             user names are the same.  Additionally, successful RSA host
             authentication is normally required.  This file must be writable
             only by root; it is recommended that it be world-readable.

             Warning: It is almost never a good idea to use user names in
             hosts.equiv.  Beware that it really means that the named user(s)
             can log in as anybody, which includes bin, daemon, adm, and other
             accounts that own critical binaries and directories.  Using a
             user name practically grants the user root access.  The only
             valid use for user names that I can think of is in negative
             entries.

             Note that this warning also applies to rsh/rlogin.

     /etc/shosts.equiv
             This is processed exactly as /etc/hosts.equiv.  However, this
             file may be useful in environments that want to run both
             rsh/rlogin and ssh.

     $HOME/.ssh/environment
             This file is read into the environment at login (if it exists).
             It can only contain empty lines, comment lines (that start with
             `#'), and assignment lines of the form name=value.  The file
             should be writable only by the user; it need not be readable by
             anyone else.

     $HOME/.ssh/rc
             If this file exists, it is run with /bin/sh after reading the
             environment files but before starting the user's shell or comM--
             mand.  It must not produce any output on stdout; stderr must be
             used instead.  If X11 forwarding is in use, it will receive the
             "proto cookie" pair in its standard input (and DISPLAY in its
             environment).  The script must call xauth(1) because sshd will
             not run xauth automatically to add X11 cookies.

             The primary purpose of this file is to run any initialization
             routines which may be needed before the user's home directory
             becomes accessible; AFS is a particular example of such an enviM--
             ronment.

             This file will probably contain some initialization code followed
             by something similar to:

             if read proto cookie && [ -n "$DISPLAY" ]; then
                     if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
                             # X11UseLocalhost=yes
                             xauth add unix:`echo $DISPLAY |
                                 cut -c11-` $proto $cookie
                     else
                             # X11UseLocalhost=no
                             xauth add $DISPLAY $proto $cookie
                     fi
             fi

             If this file does not exist, /etc/ssh/sshrc is run, and if that
             does not exist either, xauth is used to add the cookie.

             This file should be writable only by the user, and need not be
             readable by anyone else.

     /etc/ssh/sshrc
             Like $HOME/.ssh/rc.  This can be used to specify machine-specific
             login-time initializations globally.  This file should be
             writable only by root, and should be world-readable.

AUTHORS
     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 creM--
     ated 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.

SEE ALSO
     scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
     login.conf(5), moduli(5), sshd_config(5), sftp-server(8)

     T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, SSH
     Protocol Architecture, draft-ietf-secsh-architecture-12.txt, January
     2002, work in progress material.

     M. Friedl, N. Provos, and W. A. Simpson, Diffie-Hellman Group Exchange
     for the SSH Transport Layer Protocol, draft-ietf-secsh-dh-group-
     exchange-02.txt, January 2002, work in progress material.

BSD                           September 25, 1999                           BSD