NAME | SYNOPSIS | DESCRIPTION | AUTHENTICATION | LOGIN PROCESS | SSHRC | AUTHORIZED_KEYS FILE FORMAT | SSH_KNOWN_HOSTS FILE FORMAT | FILES | SEE ALSO | AUTHORS | COLOPHON

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

NAME         top

     sshd — OpenSSH SSH daemon

SYNOPSIS         top

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

DESCRIPTION         top

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

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

     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.

     -b bits
             Specifies the number of bits in the ephemeral protocol version
             1 server key (default 1024).

     -C connection_spec
             Specify the connection parameters to use for the -T extended
             test mode.  If provided, any Match directives in the configura‐
             tion file that would apply to the specified user, host, and
             address will be set before the configuration is written to
             standard output.  The connection parameters are supplied as
             keyword=value pairs.  The keywords are “user”, “host”, “laddr”,
             “lport”, and “addr”.  All are required and may be supplied in
             any order, either with multiple -C options or as a comma-sepa‐
             rated list.

     -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 authenticate 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_key for protocol version 1, and
             /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_ecdsa_key.
             /etc/ssh/ssh_host_ed25519_key and /etc/ssh/ssh_host_rsa_key for
             protocol version 2.  It is possible to have multiple host key
             files for the different protocol versions and host key algo‐
             rithms.

     -i      Specifies that sshd is being run from inetd(8).  If SSH proto‐
             col 1 is enabled, sshd should not  normally be run from inetd
             because it needs to generate the server key before it can
             respond to the client, and this may take some time.  Clients
             may have to wait too long if the key was regenerated every
             time.

     -k key_gen_time
             Specifies how often the ephemeral protocol version 1 server key
             is regenerated (default 3600 seconds, or one hour).  The moti‐
             vation for regenerating the key fairly often is that the key is
             not stored anywhere, and after about an hour it becomes impos‐
             sible to recover the key for decrypting intercepted communica‐
             tions even if the machine is cracked into or physically seized.
             A value of zero indicates that the key will never be regener‐
             ated.

     -o option
             Can be used to give options in the format used in the configu‐
             ration 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 connection
             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 options.

     -t      Test mode.  Only check the validity of the configuration file
             and sanity of the keys.  This is useful for updating sshd reli‐
             ably 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 pre‐
             vent sshd from making DNS requests unless the authentication
             mechanism or configuration requires it.  Authentication mecha‐
             nisms that may require DNS include RhostsRSAAuthentication,
             HostbasedAuthentication, and using a from="pattern-list" option
             in a key file.  Configuration options that require DNS include
             using a USER@HOST pattern in AllowUsers or DenyUsers.

AUTHENTICATION         top

     The OpenSSH SSH daemon supports SSH protocols 1 and 2.  The default is
     to use protocol 2 only, though this can be changed via the Protocol
     option in sshd_config(5).  Protocol 1 should not be used and is only
     offered to support legacy devices.

     Each host has a host-specific key, used to identify the host.  Partial
     forward security for protocol 1 is provided through an additional
     server key, normally 1024 bits, generated when the server starts.  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 encryption algorithm to use from those offered
     by the server.

     For protocol 2, 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, cur‐
     rently 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 pro‐
     vided through a cryptographic message authentication code (hmac-md5,
     hmac-sha1, umac-64, umac-128, hmac-ripemd160, 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 pass‐
     word 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 defini‐
     tion of a locked account is system dependant. 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 authentication agent connection over
     the secure channel.

     After this, the client either requests a shell or execution of a com‐
     mand.  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 con‐
     nections have been closed, the server sends command exit status to the
     client, and both sides exit.

LOGIN PROCESS         top

     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 password
                database.

SSHRC         top

     If the file ~/.ssh/rc exists, sh(1) runs it after reading the environ‐
     ment files but before starting the user's shell or command.  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 cook‐
     ies.

     The primary purpose of this file is to run any initialization routines
     which may be needed before the user's home directory becomes accessi‐
     ble; 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         top

     AuthorizedKeysFile specifies the files containing public keys for pub‐
     lic 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).  Protocol 1 public keys consist of the following
     space-separated fields: options, bits, exponent, modulus, comment.
     Protocol 2 public key consist of: options, keytype, 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, modulus, and comment fields
     give the RSA key for protocol version 1; the comment field is not used
     for anything (but may be convenient for the user to identify the key).
     For protocol version 2 the keytype is “ecdsa-sha2-nistp256”,
     “ecdsa-sha2-nistp384”, “ecdsa-sha2-nistp521”, “ssh-ed25519”, “ssh-dss”
     or “ssh-rsa”.

     Note that lines in this file are usually 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; instead, copy the
     identity.pub, 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 for protocol 1 and proto‐
     col 2 keys of 768 bits.

     The options (if present) consist of comma-separated option specifica‐
     tions.  No spaces are permitted, except within double quotes.  The fol‐
     lowing 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 opera‐
             tion.  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.  The com‐
             mand 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 either a
             sshd_config(5) ForceCommand directive or a command embedded in
             a certificate.

     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 processing is
             disabled by default and is controlled via the
             PermitUserEnvironment option.  This option is automatically
             disabled if UseLogin is enabled.

     from="pattern-list"
             Specifies that in addition to public key authentication, either
             the canonical name of the remote host or its IP address 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 addresses
             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 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).

     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 authentica‐
             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-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 authentica‐
             tion.  Any X11 forward requests by the client will return an
             error.

     permitopen="host:port"
             Limit local port forwarding with ssh(1) -L 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 applied separated by commas.
             No pattern matching is performed on the specified hostnames,
             they must be literal domains or addresses.  A port specifica‐
             tion of * matches any port.

     port-forwarding
             Enable port forwarding previously disabled by the restrict

     principals="principals"
             On a cert-authority line, specifies allowed principals for cer‐
             tificate 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 for‐
             warding, as well as disabling PTY allocation and execution 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 requests 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-dss
        AAAAC3...51R== example.net
        permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
        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         top

     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 auto‐
     matically: 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: markers
     (optional), hostnames, bits, exponent, modulus, 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 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.  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 disclosed.  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.

     Bits, exponent, and modulus are taken directly from the RSA host key;
     they can be obtained, for example, 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; 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 described above.

     The known hosts file also provides a facility to mark keys as revoked,
     for example when it is known that the associated private 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 authenti‐
     cation 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 dif‐
     ferent 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 conflicting information; authen‐
     tication 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
     /etc/ssh/ssh_host_key.pub and adding the host names at the front.
     ssh-keygen(1) also offers some basic automated editing for
     ~/.ssh/known_hosts including 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         top

     ~/.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 parti‐
             tion, because sshd reads it as root.  Additionally, 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 gen‐
             eral 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 sensi‐
             tive, 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 direc‐
             tory are writable by other users, then the file could be modi‐
             fied 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.equiv
             This file is for host-based authentication (see ssh(1)).  It
             should only be writable by root.

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

     /etc/ssh/ssh_host_key
     /etc/ssh/ssh_host_dsa_key
     /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_key.pub
     /etc/ssh/ssh_host_dsa_key.pub
     /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 pre‐
             pared 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 con‐
             figuration options are described in sshd_config(5).

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

     /var/empty
             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.

     /var/run/sshd.pid
             Contains the process ID of the sshd listening for connections
             (if there are several daemons running concurrently for differ‐
             ent 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         top

     scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1),
     ssh-keyscan(1), chroot(2), login.conf(5), moduli(5), sshd_config(5),
     inetd(8), sftp-server(8)

AUTHORS         top

     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.  Niels Provos and Markus Friedl
     contributed support for privilege separation.

COLOPHON         top

     This page is part of the openssh (Portable OpenSSH) project.  Informa‐
     tion about the project can be found at
     http://www.openssh.com/portable.html.  If you have a bug report for
     this manual page, see http://www.openssh.com/report.html.  This page
     was obtained from the tarball openssh-7.2p2.tar.gz fetched from
     http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/ on 2016-07-16.
     If you discover any rendering problems in this HTML version of the
     page, or you believe there is a better or more up-to-date source for
     the page, or you have corrections or improvements to the information in
     this COLOPHON (which is not part of the original manual page), send a
     mail to man-pages@man7.org

BSD                           February 17, 2016                          BSD