path: root/sshd.0

SSHD(8)                   BSD System ManagerM-bM-^@M-^Ys Manual                  SSHD(8)

^[[1mNAME^[[0m
     ^[[1msshd ^[[22mM-bMM-^R OpenSSH SSH daemon

^[[1mSYNOPSIS^[[0m
     ^[[1msshd ^[[22m[^[[1mM-bMM-^RdeiqtD46^[[22m] [^[[1mM-bMM-^Rb ^[[4m^[[22mbits^[[24m] [^[[1mM-bMM-^Rf ^[[4m^[[22mconfig_file^[[24m] [^[[1mM-bMM-^Rg ^[[4m^[[22mlogin_grace_time^[[24m]
          [^[[1mM-bMM-^Rh ^[[4m^[[22mhost_key_file^[[24m] [^[[1mM-bMM-^Rk ^[[4m^[[22mkey_gen_time^[[24m] [^[[1mM-bMM-^Ro ^[[4m^[[22moption^[[24m] [^[[1mM-bMM-^Rp ^[[4m^[[22mport^[[24m] [^[[1mM-bMM-^Ru ^[[4m^[[22mlen^[[24m]

^[[1mDESCRIPTION^[[0m
     ^[[1msshd ^[[22m(SSH Daemon) is the daemon program for ssh(1).  Together these proM-bM-^@M-^P
     grams replace rlogin and rsh, and provide secure encrypted communications
     between two untrusted hosts over an insecure network.  The programs are
     intended to be as easy to install and use as possible.

     ^[[1msshd ^[[22mis the daemon that listens for connections from clients.  It is norM-bM-^@M-^P
     mally started at boot from ^[[4m/etc/rc^[[24m.  It forks a new daemon for each
     incoming connection.  The forked daemons handle key exchange, encryption,
     authentication, command execution, and data exchange.  This implementaM-bM-^@M-^P
     tion of ^[[1msshd ^[[22msupports both SSH protocol version 1 and 2 simultaneously.
     ^[[1msshd ^[[22mworks as follows:

   ^[[1mSSH protocol version 1^[[0m

     Each host has a hostM-bM-^@M-^Pspecific RSA key (normally 1024 bits) used to idenM-bM-^@M-^P
     tify the host.  Additionally, when the daemon starts, it generates a
     server RSA key (normally 768 bits).  This key is normally regenerated
     every hour if it has been used, and is never stored on disk.

     Whenever a client connects, the daemon responds with its public host and
     server keys.  The client compares the RSA host key against its own
     database to verify that it has not changed.  The client then generates a
     256 bit random number.  It encrypts this random number using both the
     host key and the server key, and sends the encrypted number to the
     server.  Both sides then use this random number as a session key which is
     used to encrypt all further communications in the session.  The rest of
     the session is encrypted using a conventional cipher, currently Blowfish
     or 3DES, with 3DES being used by default.  The client selects the encrypM-bM-^@M-^P
     tion algorithm to use from those offered by the server.

     Next, the server and the client enter an authentication dialog.  The
     client tries to authenticate itself using ^[[4m.rhosts^[[24m authentication, ^[[4m.rhosts^[[0m
     authentication combined with RSA host authentication, RSA challengeM-bM-^@M-^P
     response authentication, or password based authentication.

     Rhosts authentication is normally disabled because it is fundamentally
     insecure, but can be enabled in the server configuration file if desired.
     System security is not improved unless ^[[1mrshd^[[22m, ^[[1mrlogind^[[22m, and ^[[1mrexecd ^[[22mare disM-bM-^@M-^P
     abled (thus completely disabling rlogin and rsh into the machine).

   ^[[1mSSH protocol version 2^[[0m

     Version 2 works similarly: Each host has a hostM-bM-^@M-^Pspecific key (RSA or DSA)
     used to identify the host.  However, when the daemon starts, it does not
     generate a server key.  Forward security is provided through a DiffieM-bM-^@M-^P
     Hellman key agreement.  This key agreement results in a shared session
     key.

     The rest of the session is encrypted using a symmetric cipher, currently
     128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 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
     through a cryptographic message authentication code (hmacM-bM-^@M-^Psha1 or hmacM-bM-^@M-^P
     md5).

     Protocol version 2 provides a public key based user (PubkeyAuthenticaM-bM-^@M-^P
     tion) or client host (HostbasedAuthentication) authentication method,
     conventional password authentication and challenge response based methM-bM-^@M-^P
     ods.

   ^[[1mCommand execution and data forwarding^[[0m

     If the client successfully authenticates itself, a dialog for preparing
     the session is entered.  At this time the client may request things like
     allocating a pseudoM-bM-^@M-^Ptty, forwarding X11 connections, forwarding TCP/IP
     connections, or forwarding the authentication agent connection over the
     secure channel.

     Finally, the client either requests a shell or execution of a command.
     The sides then enter session mode.  In this mode, either side may send
     data at any time, and such data is forwarded to/from the shell or command
     on the server side, and the user terminal in the client side.

     When the user program terminates and all forwarded X11 and other connecM-bM-^@M-^P
     tions have been closed, the server sends command exit status to the
     client, and both sides exit.

     ^[[1msshd ^[[22mcan be configured using commandM-bM-^@M-^Pline options or a configuration
     file.  CommandM-bM-^@M-^Pline options override values specified in the configuraM-bM-^@M-^P
     tion file.

     ^[[1msshd ^[[22mrereads its configuration file when it receives a hangup signal,
     SIGHUP, by executing itself with the name it was started as, i.e.,
     ^[[4m/usr/sbin/sshd^[[24m.

     The options are as follows:

     ^[[1mM-bMM-^Rb ^[[4m^[[22mbits^[[0m
             Specifies the number of bits in the ephemeral protocol version 1
             server key (default 768).

     ^[[1mM-bMM-^Rd      ^[[22mDebug mode.  The server sends verbose debug output to the system
             log, and does not put itself in the background.  The server also
             will not fork and will only process one connection.  This option
             is only intended for debugging for the server.  Multiple ^[[1mM-bMM-^Rd^[[0m
             options increase the debugging level.  Maximum is 3.

     ^[[1mM-bMM-^Re      ^[[22mWhen this option is specified, ^[[1msshd ^[[22mwill send the output to the
             standard error instead of the system log.

     ^[[1mM-bMM-^Rf ^[[4m^[[22mconfiguration_file^[[0m
             Specifies the name of the configuration file.  The default is
             ^[[4m/etc/ssh/sshd_config^[[24m.  ^[[1msshd ^[[22mrefuses to start if there is no conM-bM-^@M-^P
             figuration file.

     ^[[1mM-bMM-^Rg ^[[4m^[[22mlogin_grace_time^[[0m
             Gives the grace time for clients to authenticate themselves
             (default 120 seconds).  If the client fails to authenticate the
             user within this many seconds, the server disconnects and exits.
             A value of zero indicates no limit.

     ^[[1mM-bMM-^Rh ^[[4m^[[22mhost_key_file^[[0m
             Specifies a file from which a host key is read.  This option must
             be given if ^[[1msshd ^[[22mis not run as root (as the normal host key files
             are normally not readable by anyone but root).  The default is
             ^[[4m/etc/ssh/ssh_host_key^[[24m for protocol version 1, and
             ^[[4m/etc/ssh/ssh_host_rsa_key^[[24m and ^[[4m/etc/ssh/ssh_host_dsa_key^[[24m for proM-bM-^@M-^P
             tocol version 2.  It is possible to have multiple host key files
             for the different protocol versions and host key algorithms.

     ^[[1mM-bMM-^Ri      ^[[22mSpecifies that ^[[1msshd ^[[22mis being run from inetd(8).  ^[[1msshd ^[[22mis normally
             not run from inetd because it needs to generate the server key
             before it can respond to the client, and this may take tens of
             seconds.  Clients would have to wait too long if the key was
             regenerated every time.  However, with small key sizes (e.g.,
             512) using ^[[1msshd ^[[22mfrom inetd may be feasible.

     ^[[1mM-bMM-^Rk ^[[4m^[[22mkey_gen_time^[[0m
             Specifies how often the ephemeral protocol version 1 server key
             is regenerated (default 3600 seconds, or one hour).  The motivaM-bM-^@M-^P
             tion for regenerating the key fairly often is that the key is not
             stored anywhere, and after about an hour, it becomes impossible
             to recover the key for decrypting intercepted communications even
             if the machine is cracked into or physically seized.  A value of
             zero indicates that the key will never be regenerated.

     ^[[1mM-bMM-^Ro ^[[4m^[[22moption^[[0m
             Can be used to give options in the format used in the configuraM-bM-^@M-^P
             tion file.  This is useful for specifying options for which there
             is no separate commandM-bM-^@M-^Pline flag.

     ^[[1mM-bMM-^Rp ^[[4m^[[22mport^[[0m
             Specifies the port on which the server listens for connections
             (default 22).  Multiple port options are permitted.  Ports speciM-bM-^@M-^P
             fied in the configuration file are ignored when a commandM-bM-^@M-^Pline
             port is specified.

     ^[[1mM-bMM-^Rq      ^[[22mQuiet mode.  Nothing is sent to the system log.  Normally the
             beginning, authentication, and termination of each connection is
             logged.

     ^[[1mM-bMM-^Rt      ^[[22mTest mode.  Only check the validity of the configuration file and
             sanity of the keys.  This is useful for updating ^[[1msshd ^[[22mreliably as
             configuration options may change.

     ^[[1mM-bMM-^Ru ^[[4m^[[22mlen^[[24m  This option is used to specify the size of the field in the utmp
             structure that holds the remote host name.  If the resolved host
             name is longer than ^[[4mlen^[[24m, the dotted decimal value will be used
             instead.  This allows hosts with very long host names that overM-bM-^@M-^P
             flow this field to still be uniquely identified.  Specifying ^[[1mM-bMM-^Ru0^[[0m
             indicates that only dotted decimal addresses should be put into
             the ^[[4mutmp^[[24m file.  ^[[1mM-bMM-^Ru0 ^[[22mmay also be used to prevent ^[[1msshd ^[[22mfrom making
             DNS requests unless the authentication mechanism or configuration
             requires it.  Authentication mechanisms that may require DNS
             include ^[[1mRhostsAuthentication^[[22m, ^[[1mRhostsRSAAuthentication^[[22m,
             ^[[1mHostbasedAuthentication ^[[22mand using a ^[[1mfrom="patternM-bM-^@M-^Plist" ^[[22moption in
             a key file.  Configuration options that require DNS include using
             a USER@HOST pattern in ^[[1mAllowUsers ^[[22mor ^[[1mDenyUsers^[[22m.

     ^[[1mM-bMM-^RD      ^[[22mWhen this option is specified ^[[1msshd ^[[22mwill not detach and does not
             become a daemon.  This allows easy monitoring of ^[[1msshd^[[22m.

     ^[[1mM-bMM-^R4      ^[[22mForces ^[[1msshd ^[[22mto use IPv4 addresses only.

     ^[[1mM-bMM-^R6      ^[[22mForces ^[[1msshd ^[[22mto use IPv6 addresses only.

^[[1mCONFIGURATION FILE^[[0m
     ^[[1msshd ^[[22mreads configuration data from ^[[4m/etc/ssh/sshd_config^[[24m (or the file
     specified with ^[[1mM-bMM-^Rf ^[[22mon the command line).  The file format and configuraM-bM-^@M-^P
     tion options are described in sshd_config(5).

^[[1mLOGIN PROCESS^[[0m
     When a user successfully logs in, ^[[1msshd ^[[22mdoes the following:

           1.   If the login is on a tty, and no command has been specified,
                prints last login time and ^[[4m/etc/motd^[[24m (unless prevented in the
                configuration file or by ^[[4m$HOME/.hushlogin^[[24m; see the ^[[4mFILES^[[24m secM-bM-^@M-^P
                tion).

           2.   If the login is on a tty, records login time.

           3.   Checks ^[[4m/etc/nologin^[[24m; if it exists, prints contents and quits
                (unless root).

           4.   Changes to run with normal user privileges.

           5.   Sets up basic environment.

           6.   Reads ^[[4m$HOME/.ssh/environment^[[24m if it exists and users are
                allowed to change their environment.  See the
                ^[[1mPermitUserEnvironment ^[[22moption in sshd_config(5).

           7.   Changes to userM-bM-^@M-^Ys home directory.

           8.   If ^[[4m$HOME/.ssh/rc^[[24m exists, runs it; else if ^[[4m/etc/ssh/sshrc^[[0m
                exists, runs it; otherwise runs xauth.  The M-bM-^@M-^\rcM-bM-^@M-^] files are
                given the X11 authentication protocol and cookie in standard
                input.

           9.   Runs userM-bM-^@M-^Ys shell or command.

^[[1mAUTHORIZED_KEYS FILE FORMAT^[[0m
     ^[[4m$HOME/.ssh/authorized_keys^[[24m is the default file that lists the public keys
     that are permitted for RSA authentication in protocol version 1 and for
     public key authentication (PubkeyAuthentication) in protocol version 2.
     ^[[1mAuthorizedKeysFile ^[[22mmay be used to specify an alternative file.

     Each line of the file contains one key (empty lines and lines starting
     with a M-bM-^@M-^X#M-bM-^@M-^Y are ignored as comments).  Each RSA public key consists of the
     following fields, separated by spaces: options, bits, exponent, modulus,
     comment.  Each protocol version 2 public key consists of: options, keyM-bM-^@M-^P
     type, base64 encoded key, comment.  The options field is optional; its
     presence is determined by whether the line starts with a number or not
     (the options field never starts with a number).  The bits, exponent, modM-bM-^@M-^P
     ulus and comment fields give the RSA key for protocol version 1; the comM-bM-^@M-^P
     ment field is not used for anything (but may be convenient for the user
     to identify the key).  For protocol version 2 the keytype is M-bM-^@M-^\sshM-bM-^@M-^PdssM-bM-^@M-^] or
     M-bM-^@M-^\sshM-bM-^@M-^PrsaM-bM-^@M-^].

     Note that lines in this file are usually several hundred bytes long
     (because of the size of the public key encoding).  You donM-bM-^@M-^Yt want to type
     them in; instead, copy the ^[[4midentity.pub^[[24m, ^[[4mid_dsa.pub^[[24m or the ^[[4mid_rsa.pub^[[0m
     file and edit it.

     ^[[1msshd ^[[22menforces a minimum RSA key modulus size for protocol 1 and protocol
     2 keys of 768 bits.

     The options (if present) consist of commaM-bM-^@M-^Pseparated option specificaM-bM-^@M-^P
     tions.  No spaces are permitted, except within double quotes.  The folM-bM-^@M-^P
     lowing option specifications are supported (note that option keywords are
     caseM-bM-^@M-^Pinsensitive):

     ^[[1mfrom="patternM-bM-^@M-^Plist"^[[0m
             Specifies that in addition to public key authentication, the
             canonical name of the remote host must be present in the commaM-bM-^@M-^P
             separated list of patterns (M-bM-^@M-^X*M-bM-^@M-^Y and M-bM-^@M-^XM-bM-^@M-^Y?  serve as wildcards).
             The list may also contain patterns negated by prefixing them with
             M-bM-^@M-^XM-bM-^@M-^Y!; if the canonical host name matches a negated pattern, the
             key is not accepted.  The purpose of this option is to optionally
             increase security: public key authentication by itself does not
             trust the network or name servers or anything (but the key); howM-bM-^@M-^P
             ever, if somebody somehow steals the key, the key permits an
             intruder to log in from anywhere in the world.  This additional
             option makes using a stolen key more difficult (name servers
             and/or routers would have to be compromised in addition to just
             the key).

     ^[[1mcommand="command"^[[0m
             Specifies that the command is executed whenever this key is used
             for authentication.  The command supplied by the user (if any) is
             ignored.  The command is run on a pty if the client requests a
             pty; otherwise it is run without a tty.  If an 8M-bM-^@M-^Pbit clean chanM-bM-^@M-^P
             nel is required, one must not request a pty or should specify
             ^[[1mnoM-bM-^@M-^Ppty^[[22m.  A quote may be included in the command by quoting it
             with a backslash.  This option might be useful to restrict cerM-bM-^@M-^P
             tain public keys to perform just a specific operation.  An examM-bM-^@M-^P
             ple 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.

     ^[[1menvironment="NAME=value"^[[0m
             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.  Environment processing is disabled by
             default and is controlled via the ^[[1mPermitUserEnvironment ^[[22moption.
             This option is automatically disabled if ^[[1mUseLogin ^[[22mis enabled.

     ^[[1mnoM-bM-^@M-^PportM-bM-^@M-^Pforwarding^[[0m
             Forbids TCP/IP forwarding when this key is used for authenticaM-bM-^@M-^P
             tion.  Any port forward requests by the client will return an
             error.  This might be used, e.g., in connection with the ^[[1mcommand^[[0m
             option.

     ^[[1mnoM-bM-^@M-^PX11M-bM-^@M-^Pforwarding^[[0m
             Forbids X11 forwarding when this key is used for authentication.
             Any X11 forward requests by the client will return an error.

     ^[[1mnoM-bM-^@M-^PagentM-bM-^@M-^Pforwarding^[[0m
             Forbids authentication agent forwarding when this key is used for
             authentication.

     ^[[1mnoM-bM-^@M-^Ppty  ^[[22mPrevents tty allocation (a request to allocate a pty will fail).

     ^[[1mpermitopen="host:port"^[[0m
             Limit local M-bM-^@M-^XM-bM-^@M-^Xssh M-bM-^@M-^PLM-bM-^@M-^YM-bM-^@M-^Y port forwarding such that it may only conM-bM-^@M-^P
             nect to the specified host and port.  IPv6 addresses can be specM-bM-^@M-^P
             ified with an alternative syntax: ^[[4mhost/port^[[24m.  Multiple ^[[1mpermitopen^[[0m
             options may be applied separated by commas. No pattern matching
             is performed on the specified hostnames, they must be literal
             domains or addresses.

   ^[[1mExamples^[[0m
     1024 33 12121...312314325 ylo@foo.bar

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

     command="dump /home",noM-bM-^@M-^Ppty,noM-bM-^@M-^PportM-bM-^@M-^Pforwarding 1024 33 23...2323
     backup.hut.fi

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

^[[1mSSH_KNOWN_HOSTS FILE FORMAT^[[0m
     The ^[[4m/etc/ssh/ssh_known_hosts^[[24m and ^[[4m$HOME/.ssh/known_hosts^[[24m files contain
     host public keys for all known hosts.  The global file should be prepared
     by the administrator (optional), and the perM-bM-^@M-^Puser file is maintained
     automatically: whenever the user connects from an unknown host its key is
     added to the perM-bM-^@M-^Puser file.

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

     Hostnames is a commaM-bM-^@M-^Pseparated list of patterns (M-bM-^@M-^Y*M-bM-^@M-^Y and M-bM-^@M-^Y?M-bM-^@M-^Y act as wildM-bM-^@M-^P
     cards); each pattern in turn is matched against the canonical host name
     (when authenticating a client) or against the userM-bM-^@M-^Psupplied name (when
     authenticating a server).  A pattern may also be preceded by M-bM-^@M-^XM-bM-^@M-^Y!  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 ^[[4m/etc/ssh/ssh_host_key.pub^[[24m.  The optional
     comment field continues to the end of the line, and is not used.

     Lines starting with M-bM-^@M-^X#M-bM-^@M-^Y 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-bM-^@M-^P
     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-bM-^@M-^P
     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 donM-bM-^@M-^Yt want to type in the host keys by hand.
     Rather, generate them by a script or by taking ^[[4m/etc/ssh/ssh_host_key.pub^[[0m
     and adding the host names at the front.

   ^[[1mExamples^[[0m

     closenet,...,130.233.208.41 1024 37 159...93 closenet.hut.fi
     cvs.openbsd.org,199.185.137.3 sshM-bM-^@M-^Prsa AAAA1234.....=

^[[1mFILES^[[0m
     /etc/ssh/sshd_config
             Contains configuration data for ^[[1msshd^[[22m.  The file format and conM-bM-^@M-^P
             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 ^[[1msshd ^[[22mdoes not start if
             this file is group/worldM-bM-^@M-^Paccessible.

     /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 worldM-bM-^@M-^Preadable 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 sshM-bM-^@M-^Pkeygen(1).

     /etc/moduli
             Contains DiffieM-bM-^@M-^PHellman groups used for the "DiffieM-bM-^@M-^PHellman Group
             Exchange".  The file format is described in moduli(5).

     /var/empty
             chroot(2) directory used by ^[[1msshd ^[[22mduring privilege separation in
             the preM-bM-^@M-^Pauthentication phase.  The directory should not contain
             any files and must be owned by root and not group or worldM-bM-^@M-^P
             writable.

     /var/run/sshd.pid
             Contains the process ID of the ^[[1msshd ^[[22mlistening for connections (if
             there are several daemons running concurrently for different
             ports, this contains the process ID of the one started last).
             The content of this file is not sensitive; it can be worldM-bM-^@M-^PreadM-bM-^@M-^P
             able.

     $HOME/.ssh/authorized_keys
             Lists the public keys (RSA or DSA) that can be used to log into
             the userM-bM-^@M-^Ys account.  This file must be readable by root (which
             may on some machines imply it being worldM-bM-^@M-^Preadable if the userM-bM-^@M-^Ys
             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
             ^[[4midentity.pub^[[24m, ^[[4mid_dsa.pub^[[24m and/or ^[[4mid_rsa.pub^[[24m files into this file,
             as described in sshM-bM-^@M-^Pkeygen(1).

     /etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts
             These files are consulted when using rhosts with RSA host authenM-bM-^@M-^P
             tication or protocol version 2 hostbased authentication to check
             the public key of the host.  The key must be listed in one of
             these files to be accepted.  The client uses the same files to
             verify that it is connecting to the correct remote host.  These
             files should be writable only by root/the owner.
             ^[[4m/etc/ssh/ssh_known_hosts^[[24m should be worldM-bM-^@M-^Preadable, and
             ^[[4m$HOME/.ssh/known_hosts^[[24m can, but need not be, worldM-bM-^@M-^Preadable.

     /etc/nologin
             If this file exists, ^[[1msshd ^[[22mrefuses to let anyone except root log
             in.  The contents of the file are displayed to anyone trying to
             log in, and nonM-bM-^@M-^Proot connections are refused.  The file should be
             worldM-bM-^@M-^Preadable.

     /etc/hosts.allow, /etc/hosts.deny
             Access controls that should be enforced by tcpM-bM-^@M-^Pwrappers are
             defined here.  Further details are described in hosts_access(5).

     $HOME/.rhosts
             This file contains hostM-bM-^@M-^Pusername pairs, separated by a space, one
             per line.  The given user on the corresponding host is permitted
             to log in without a password.  The same file is used by rlogind
             and rshd.  The file must be writable only by the user; it is recM-bM-^@M-^P
             ommended 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 ^[[4m.rhosts^[[24m.  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 ^[[4m.rhosts^[[24m 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 ^[[4many^[[24m user on this machine (except root).  Additionally, the
             syntax M-bM-^@M-^\+@groupM-bM-^@M-^] can be used to specify netgroups.  Negated
             entries start with M-bM-^@M-^XM-bM-^@M-^PM-bM-^@M-^Y.

             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 worldM-bM-^@M-^Preadable.

             ^[[1mWarning: It is almost never a good idea to use user names in^[[0m
             ^[[4mhosts.equiv^[[24m.  Beware that it really means that the named user(s)
             can log in as ^[[4manybody^[[24m, 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 ^[[4m/etc/hosts.equiv^[[24m.  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
             M-bM-^@M-^X#M-bM-^@M-^Y), 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.  Environment processing is disabled by default and
             is controlled via the ^[[1mPermitUserEnvironment ^[[22moption.

     $HOME/.ssh/rc
             If this file exists, it is run with ^[[4m/bin/sh^[[24m after reading the
             environment files but before starting the userM-bM-^@M-^Ys shell or comM-bM-^@M-^P
             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 ^[[1msshd ^[[22mwill
             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 userM-bM-^@M-^Ys home directory
             becomes accessible; AFS is a particular example of such an enviM-bM-^@M-^P
             ronment.

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

             if read proto cookie && [ M-bM-^@M-^Pn "$DISPLAY" ]; then
                     if [ M-bM-^@M-^Xecho $DISPLAY | cut M-bM-^@M-^Pc1M-bM-^@M-^P10M-bM-^@M-^X = M-bM-^@M-^Ylocalhost:M-bM-^@M-^Y ]; then
                             # X11UseLocalhost=yes
                             echo add unix:M-bM-^@M-^Xecho $DISPLAY |
                                 cut M-bM-^@M-^Pc11M-bM-^@M-^PM-bM-^@M-^X $proto $cookie
                     else
                             # X11UseLocalhost=no
                             echo add $DISPLAY $proto $cookie
                     fi | xauth M-bM-^@M-^Pq M-bM-^@M-^P
             fi

             If this file does not exist, ^[[4m/etc/ssh/sshrc^[[24m 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 ^[[4m$HOME/.ssh/rc^[[24m.  This can be used to specify machineM-bM-^@M-^Pspecific
             loginM-bM-^@M-^Ptime initializations globally.  This file should be
             writable only by root, and should be worldM-bM-^@M-^Preadable.

^[[1mAUTHORS^[[0m
     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, reM-bM-^@M-^Padded newer features and creM-bM-^@M-^P
     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.

^[[1mSEE ALSO^[[0m
     scp(1), sftp(1), ssh(1), sshM-bM-^@M-^Padd(1), sshM-bM-^@M-^Pagent(1), sshM-bM-^@M-^Pkeygen(1),
     login.conf(5), moduli(5), sshd_config(5), sftpM-bM-^@M-^Pserver(8)

     T. Ylonen, T. Kivinen, M. Saarinen, T. Rinne, and S. Lehtinen, ^[[4mSSH^[[0m
     ^[[4mProtocol^[[24m ^[[4mArchitecture^[[24m, draftM-bM-^@M-^PietfM-bM-^@M-^PsecshM-bM-^@M-^ParchitectureM-bM-^@M-^P12.txt, January
     2002, work in progress material.

     M. Friedl, N. Provos, and W. A. Simpson, ^[[4mDiffieM-bM-^@M-^PHellman^[[24m ^[[4mGroup^[[24m ^[[4mExchange^[[0m
     ^[[4mfor^[[24m ^[[4mthe^[[24m ^[[4mSSH^[[24m ^[[4mTransport^[[24m ^[[4mLayer^[[24m ^[[4mProtocol^[[24m, draftM-bM-^@M-^PietfM-bM-^@M-^PsecshM-bM-^@M-^PdhM-bM-^@M-^PgroupM-bM-^@M-^P
     exchangeM-bM-^@M-^P02.txt, January 2002, work in progress material.

BSD                           September 25, 1999                           BSD