SSHD(8)                                             BSD System Manager's Manual                                             SSHD(8)

NAME
     sshd — OpenSSH SSH daemon

SYNOPSIS
     sshd [-46DdeiqTt] [-C connection_spec] [-c host_certificate_file] [-E log_file] [-f config_file] [-g login_grace_time]
          [-h host_key_file] [-o option] [-p port] [-u len]

DESCRIPTION
     sshd (OpenSSH Daemon) is the daemon program for ssh(1).  Together these programs replace rlogin and rsh, and provide secure
     encrypted communications between two untrusted hosts over an insecure network.

     sshd listens for connections from clients.  It is normally started at boot from /etc/init.d/ssh.  It forks a new daemon for
     each incoming connection.  The forked daemons handle key exchange, encryption, authentication, command execution, and data ex‐
     change.

     sshd can be configured using command-line options or a configuration file (by default sshd_config(5)); command-line options
     override values specified in the configuration file.  sshd rereads its configuration file when it receives a hangup signal,
     SIGHUP, by executing itself with the name and options it was started with, e.g. /usr/sbin/sshd.

     The options are as follows:

     -4      Forces sshd to use IPv4 addresses only.

     -6      Forces sshd to use IPv6 addresses only.

     -C connection_spec
             Specify the connection parameters to use for the -T extended test mode.  If provided, any Match directives in the con‐
             figuration file that would apply are applied before the configuration is written to standard output.  The connection
             parameters are supplied as keyword=value pairs and may be supplied in any order, either with multiple -C options or as
             a comma-separated list.  The keywords are “addr,” “user”, “host”, “laddr”, “lport”, and “rdomain” and correspond to
             source address, user, resolved source host name, local address, local port number and routing domain respectively.

     -c host_certificate_file
             Specifies a path to a certificate file to identify sshd during key exchange.  The certificate file must match a host
             key file specified using the -h option or the HostKey configuration directive.

     -D      When this option is specified, sshd will not detach and does not become a daemon.  This allows easy monitoring of
             sshd.

     -d      Debug mode.  The server sends verbose debug output to standard error, 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 -d options increase the debugging level.  Maximum is 3.

     -E log_file
             Append debug logs to log_file instead of the system log.

     -e      Write debug logs to standard error instead of the system log.

     -f config_file
             Specifies the name of the configuration file.  The default is /etc/ssh/sshd_config.  sshd refuses to start if there is
             no configuration file.

     -g login_grace_time
             Gives the grace time for clients to authenticate themselves (default 120 seconds).  If the client fails to authenti‐
             cate the user within this many seconds, the server disconnects and exits.  A value of zero indicates no limit.

     -h host_key_file
             Specifies a file from which a host key is read.  This option must be given if sshd is not run as root (as the normal
             host key files are normally not readable by anyone but root).  The default is /etc/ssh/ssh_host_ecdsa_key,
             /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key.  It is possible to have multiple host key files for the
             different host key algorithms.

     -i      Specifies that sshd is being run from inetd(8).

     -o option
             Can be used to give options in the format used in the configuration file.  This is useful for specifying options for
             which there is no separate command-line flag.  For full details of the options, and their values, see sshd_config(5).

     -p port
             Specifies the port on which the server listens for connections (default 22).  Multiple port options are permitted.
             Ports specified in the configuration file with the Port option are ignored when a command-line port is specified.
             Ports specified using the ListenAddress option override command-line ports.

     -q      Quiet mode.  Nothing is sent to the system log.  Normally the beginning, authentication, and termination of each con‐
             nection is logged.

     -T      Extended test mode.  Check the validity of the configuration file, output the effective configuration to stdout and
             then exit.  Optionally, Match rules may be applied by specifying the connection parameters using one or more -C op‐
             tions.

     -t      Test mode.  Only check the validity of the configuration file and sanity of the keys.  This is useful for updating
             sshd reliably as configuration options may change.

     -u len  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 len, the dotted decimal value will be used instead.  This allows hosts with very
             long host names that overflow this field to still be uniquely identified.  Specifying -u0 indicates that only dotted
             decimal addresses should be put into the utmp file.  -u0 may also be used to prevent sshd from making DNS requests un‐
             less the authentication mechanism or configuration requires it.  Authentication mechanisms that may require DNS in‐
             clude HostbasedAuthentication and using a from="pattern-list" option in a key file.  Configuration options that re‐
             quire DNS include using a USER@HOST pattern in AllowUsers or DenyUsers.

AUTHENTICATION
     The OpenSSH SSH daemon supports SSH protocol 2 only.  Each host has a host-specific key, used to identify the host.  Whenever
     a client connects, the daemon responds with its public host key.  The client compares the host key against its own database to
     verify that it has not changed.  Forward security is provided through a Diffie-Hellman key agreement.  This key agreement re‐
     sults in a shared session key.  The rest of the session is encrypted using a symmetric cipher, currently 128-bit AES, Blow‐
     fish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.  The client selects the encryption algorithm to use from those of‐
     fered by the server.  Additionally, session integrity is provided through a cryptographic message authentication code (hmac-
     md5, hmac-sha1, umac-64, umac-128, hmac-sha2-256 or hmac-sha2-512).

     Finally, the server and the client enter an authentication dialog.  The client tries to authenticate itself using host-based
     authentication, public key authentication, challenge-response authentication, or password authentication.

     Regardless of the authentication type, the account is checked to ensure that it is accessible.  An account is not accessible
     if it is locked, listed in DenyUsers or its group is listed in DenyGroups .  The definition of a locked account is system de‐
     pendent. Some platforms have their own account database (eg AIX) and some modify the passwd field ( ‘*LK*’ on Solaris and
     UnixWare, ‘*’ on HP-UX, containing ‘Nologin’ on Tru64, a leading ‘*LOCKED*’ on FreeBSD and a leading ‘!’ on most Linuxes).  If
     there is a requirement to disable password authentication for the account while allowing still public-key, then the passwd
     field should be set to something other than these values (eg ‘NP’ or ‘*NP*’ ).

     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 pseudo-tty, forwarding X11 connections, forwarding TCP connections, or forwarding the authen‐
     tication agent connection over the secure channel.

     After this, 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 connections have been closed, the server sends command exit
     status to the client, and both sides exit.

LOGIN PROCESS
     When a user successfully logs in, sshd does the following:

           1.   If the login is on a tty, and no command has been specified, prints last login time and /etc/motd (unless prevented
                in the configuration file or by ~/.hushlogin; see the FILES section).

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

           3.   Checks /etc/nologin; if it exists, prints contents and quits (unless root).

           4.   Changes to run with normal user privileges.

           5.   Sets up basic environment.

           6.   Reads the file ~/.ssh/environment, if it exists, and users are allowed to change their environment.  See the
                PermitUserEnvironment option in sshd_config(5).

           7.   Changes to user's home directory.

           8.   If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option is set, runs it; else if /etc/ssh/sshrc exists, runs
                it; otherwise runs xauth.  The “rc” files are given the X11 authentication protocol and cookie in standard input.
                See SSHRC, below.

           9.   Runs user's shell or command.  All commands are run under the user's login shell as specified in the system pass‐
                word database.

SSHRC
     If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment files but before starting the user's shell or com‐
     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 environment.

     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
                        echo add unix:`echo $DISPLAY |
                            cut -c11-` $proto $cookie
                else
                        # X11UseLocalhost=no
                        echo add $DISPLAY $proto $cookie
                fi | xauth -q -
        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.

AUTHORIZED_KEYS FILE FORMAT
     AuthorizedKeysFile specifies the files containing public keys for public key authentication; if this option is not specified,
     the default is ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2.  Each line of the file contains one key (empty lines and
     lines starting with a ‘#’ are ignored as comments).  Public keys consist of the following space-separated fields: options,
     keytype, base64-encoded key, comment.  The options field is optional.  The keytype is “ecdsa-sha2-nistp256”,
     “ecdsa-sha2-nistp384”, “ecdsa-sha2-nistp521”, “ssh-ed25519”, “ssh-dss” or “ssh-rsa”; the comment field is not used for any‐
     thing (but may be convenient for the user to identify the key).

     Note that lines in this file can be several hundred bytes long (because of the size of the public key encoding) up to a limit
     of 8 kilobytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16 kilobits.  You don't want to type them in; in‐
     stead, copy the id_dsa.pub, id_ecdsa.pub, id_ed25519.pub, or the id_rsa.pub file and edit it.

     sshd enforces a minimum RSA key modulus size of 1024 bits.

     The options (if present) consist of comma-separated option specifications.  No spaces are permitted, except within double
     quotes.  The following option specifications are supported (note that option keywords are case-insensitive):

     agent-forwarding
             Enable authentication agent forwarding previously disabled by the restrict option.

     cert-authority
             Specifies that the listed key is a certification authority (CA) that is trusted to validate signed certificates for
             user authentication.

             Certificates may encode access restrictions similar to these key options.  If both certificate restrictions and key
             options are present, the most restrictive union of the two is applied.

     command="command"
             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 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 backslash.

             This option might be useful to restrict certain public 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 and/or X11 forwarding unless
             they are explicitly prohibited, e.g. using the restrict key option.

             The command originally supplied by the client is available in the SSH_ORIGINAL_COMMAND environment variable.  Note
             that this option applies to shell, command or subsystem execution.  Also note that this command may be superseded by a
             sshd_config(5) ForceCommand directive.

             If a command is specified and a forced-command is embedded in a certificate used for authentication, then the certifi‐
             cate will be accepted only if the two commands are identical.

     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.  Environment pro‐
             cessing is disabled by default and is controlled via the PermitUserEnvironment option.

     expiry-time="timespec"
             Specifies a time after which the key will not be accepted.  The time may be specified as a YYYYMMDD date or a YYYYMMD‐
             DHHMM[SS] time in the system time-zone.

     from="pattern-list"
             Specifies that in addition to public key authentication, either the canonical name of the remote host or its IP ad‐
             dress must be present in the comma-separated list of patterns.  See PATTERNS in ssh_config(5) for more information on
             patterns.

             In addition to the wildcard matching that may be applied to hostnames or addresses, a from stanza may match IP ad‐
             dresses using CIDR address/masklen notation.

             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); however, if somebody somehow steals the key, the key permits an in‐
             truder 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).

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

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

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

     no-user-rc
             Disables execution of ~/.ssh/rc.

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

     permitlisten="[host:]port"
             Limit remote port forwarding with the ssh(1) -R option such that it may only listen on the specified host (optional)
             and port.  IPv6 addresses can be specified by enclosing the address in square brackets.  Multiple permitlisten options
             may be applied separated by commas.  Hostnames may include wildcards as described in the PATTERNS section in
             ssh_config(5).  A port specification of * matches any port.  Note that the setting of GatewayPorts may further re‐
             strict listen addresses.  Note that ssh(1) will send a hostname of “localhost” if a listen host was not specified when
             the forwarding was requested, and that this name is treated differently to the explicit localhost addresses
             “127.0.0.1” and “::1”.

     permitopen="host:port"
             Limit local port forwarding with the ssh(1) -L option such that it may only connect to the specified host and port.
             IPv6 addresses can be specified by enclosing the address in square brackets.  Multiple permitopen options may be ap‐
             plied separated by commas.  No pattern matching is performed on the specified hostnames, they must be literal domains
             or addresses.  A port specification of * matches any port.

     port-forwarding
             Enable port forwarding previously disabled by the restrict option.

     principals="principals"
             On a cert-authority line, specifies allowed principals for certificate authentication as a comma-separated list.  At
             least one name from the list must appear in the certificate's list of principals for the certificate to be accepted.
             This option is ignored for keys that are not marked as trusted certificate signers using the cert-authority option.

     pty     Permits tty allocation previously disabled by the restrict option.

     restrict
             Enable all restrictions, i.e. disable port, agent and X11 forwarding, as well as disabling PTY allocation and execu‐
             tion of ~/.ssh/rc.  If any future restriction capabilities are added to authorized_keys files they will be included in
             this set.

     tunnel="n"
             Force a tun(4) device on the server.  Without this option, the next available device will be used if the client re‐
             quests a tunnel.

     user-rc
             Enables execution of ~/.ssh/rc previously disabled by the restrict option.

     X11-forwarding
             Permits X11 forwarding previously disabled by the restrict option.

     An example authorized_keys file:

        # Comments allowed at start of line
        ssh-rsa AAAAB3Nza...LiPk== user@example.net
        from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
        AAAAB2...19Q== john@example.net
        command="dump /home",no-pty,no-port-forwarding ssh-rsa
        AAAAC3...51R== example.net
        permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-rsa
        AAAAB5...21S==
        permitlisten="localhost:8080",permitopen="localhost:22000" ssh-rsa
        AAAAB5...21S==
        tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
        jane@example.net
        restrict,command="uptime" ssh-rsa AAAA1C8...32Tv==
        user@example.net
        restrict,pty,command="nethack" ssh-rsa AAAA1f8...IrrC5==
        user@example.net

SSH_KNOWN_HOSTS FILE FORMAT
     The /etc/ssh/ssh_known_hosts and ~/.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 con‐
     nects to an unknown host, its key is added to the per-user file.

     Each line in these files contains the following fields: markers (optional), hostnames, keytype, base64-encoded key, comment.
     The fields are separated by spaces.

     The marker is optional, but if it is present then it must be one of “@cert-authority”, to indicate that the line contains a
     certification authority (CA) key, or “@revoked”, to indicate that the key contained on the line is revoked and must not ever
     be accepted.  Only one marker should be used on a key line.

     Hostnames is a comma-separated list of patterns (‘*’ and ‘?’ act as wildcards); each pattern in turn is matched against the
     host name.  When sshd is authenticating a client, such as when using HostbasedAuthentication, this will be the canonical
     client host name.  When ssh(1) is authenticating a server, this will be the host name given by the user, the value of the
     ssh(1) HostkeyAlias if it was specified, or the canonical server hostname if the ssh(1) CanonicalizeHostname option was used.

     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.  A hostname or address may optionally be enclosed within ‘[’ and
     ‘]’ brackets then followed by ‘:’ and a non-standard port number.

     Alternately, hostnames may be stored in a hashed form which hides host names and addresses should the file's contents be dis‐
     closed.  Hashed hostnames start with a ‘|’ character.  Only one hashed hostname may appear on a single line and none of the
     above negation or wildcard operators may be applied.

     The keytype and base64-encoded key are taken directly from the host key; they can be obtained, for example, from
     /etc/ssh/ssh_host_rsa_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; either one that
     matches exactly or, if the server has presented a certificate for authentication, the key of the certification authority that
     signed the certificate.  For a key to be trusted as a certification authority, it must use the “@cert-authority” marker de‐
     scribed above.

     The known hosts file also provides a facility to mark keys as revoked, for example when it is known that the associated pri‐
     vate key has been stolen.  Revoked keys are specified by including the “@revoked” marker at the beginning of the key line, and
     are never accepted for authentication or as certification authorities, but instead will produce a warning from ssh(1) when
     they are encountered.

     It is permissible (but not recommended) 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 con‐
     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, ssh-keyscan(1) or by taking, for example, /etc/ssh/ssh_host_rsa_key.pub
     and adding the host names at the front.  ssh-keygen(1) also offers some basic automated editing for ~/.ssh/known_hosts includ‐
     ing removing hosts matching a host name and converting all host names to their hashed representations.

     An example ssh_known_hosts file:

        # Comments allowed at start of line
        closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
        cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
        # A hashed hostname
        |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
        AAAA1234.....=
        # A revoked key
        @revoked * ssh-rsa AAAAB5W...
        # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
        @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...

FILES
     ~/.hushlogin
             This file is used to suppress printing the last login time and /etc/motd, if PrintLastLog and PrintMotd, respectively,
             are enabled.  It does not suppress printing of the banner specified by Banner.

     ~/.rhosts
             This file is used for host-based authentication (see ssh(1) for more information).  On some machines this file may
             need to be world-readable if the user's home directory is on an NFS partition, because sshd reads it as root.  Addi‐
             tionally, this file must be owned by the user, and must not have write permissions for anyone else.  The recommended
             permission for most machines is read/write for the user, and not accessible by others.

     ~/.shosts
             This file is used in exactly the same way as .rhosts, but allows host-based authentication without permitting login
             with rlogin/rsh.

     ~/.ssh/
             This directory is the default location for all user-specific configuration and authentication information.  There is
             no general requirement to keep the entire contents of this directory secret, but the recommended permissions are
             read/write/execute for the user, and not accessible by others.

     ~/.ssh/authorized_keys
             Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used for logging in as this user.  The format of this
             file is described above.  The content of the file is not highly sensitive, but the recommended permissions are
             read/write for the user, and not accessible by others.

             If this file, the ~/.ssh directory, or the user's home directory are writable by other users, then the file could be
             modified or replaced by unauthorized users.  In this case, sshd will not allow it to be used unless the StrictModes
             option has been set to “no”.

     ~/.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.  Environment processing is disabled by default and is controlled via the
             PermitUserEnvironment option.

     ~/.ssh/known_hosts
             Contains a list of host keys for all hosts the user has logged into that are not already in the systemwide list of
             known host keys.  The format of this file is described above.  This file should be writable only by root/the owner and
             can, but need not be, world-readable.

     ~/.ssh/rc
             Contains initialization routines to be run before the user's home directory becomes accessible.  This file should be
             writable only by the user, and need not be readable by anyone else.

     /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).

     /etc/hosts.equiv
             This file is for host-based authentication (see ssh(1)).  It should only be writable by root.

     /etc/ssh/moduli
             Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange" key exchange method.  The file format is
             described in moduli(5).  If no usable groups are found in this file then fixed internal groups will be used.

     /etc/motd
             See motd(5).

     /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/ssh/shosts.equiv
             This file is used in exactly the same way as hosts.equiv, but allows host-based authentication without permitting lo‐
             gin with rlogin/rsh.

     /etc/ssh/ssh_host_ecdsa_key
     /etc/ssh/ssh_host_ed25519_key
     /etc/ssh/ssh_host_rsa_key
             These 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 these files are group/world-accessible.

     /etc/ssh/ssh_host_ecdsa_key.pub
     /etc/ssh/ssh_host_ed25519_key.pub
     /etc/ssh/ssh_host_rsa_key.pub
             These 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/ssh/ssh_known_hosts
             Systemwide list of known host keys.  This file should be prepared by the system administrator to contain the public
             host keys of all machines in the organization.  The format of this file is described above.  This file should be
             writable only by root/the owner and should be world-readable.

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

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

     /run/sshd
             chroot(2) directory used by sshd during privilege separation in the pre-authentication phase.  The directory should
             not contain any files and must be owned by root and not group or world-writable.

     /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 process ID of the one started last).  The content of this file is not sensitive; it
             can be world-readable.

SEE ALSO
     scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), ssh-keyscan(1), chroot(2), hosts_access(5), moduli(5),
     sshd_config(5), inetd(8), sftp-server(8)

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 created OpenSSH.  Markus Friedl con‐
     tributed the support for SSH protocol versions 1.5 and 2.0.  Niels Provos and Markus Friedl contributed support for privilege
     separation.

BSD                                                        July 22, 2018                                                        BSD

OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1n  15 Mar 2022
usage: sshd [-46DdeiqTt] [-C connection_spec] [-c host_cert_file]
            [-E log_file] [-f config_file] [-g login_grace_time]
            [-h host_key_file] [-o option] [-p port] [-u len]