authorized_keys

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

NAME

   sshd — OpenSSH daemon

SYNOPSIS

   sshd [-46DdeGiqTtV] [-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).  It provides 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 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.

   -C connection_spec
           Specify  the  connection  parameters to use for the -T extended test mode.  If provided, any Match directives in the configuration 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, lo‐
           cal address, local port number and routing domain respectively.  Additionally the “invalid-user” flag (which does not take a value argument) may be  specified  to  simulate  a
           connection from an unrecognised username.

   -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 con‐
           figuration 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(2) 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      Parse and print configuration file.  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.

   -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 discon‐
           nects 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 dif‐
           ferent 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 op‐
           tion 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 spec‐
           ifying the connection parameters using one or more -C options.  This is similar to the -G flag, but it includes the additional testing performed by the -t flag.

   -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 unless the authentication mechanism or configuration re‐
           quires it.  Authentication mechanisms that may require DNS include 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.

   -V      Display the version number and exit.

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 secrecy 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.  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 (MAC).

   Finally, the server and the client enter an authentication dialog.  The client tries to authenticate itself using host-based authentication, public key  authentication,  challenge-re‐
   sponse 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 dependent. 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 an interactive shell or execution of a non-interactive command, which sshd will execute via the user's shell using its -c option.  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.

   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(1).  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

   If the file ~/.ssh/rc exists, sh(1) runs it after reading the environment 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 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-sepa‐
   rated fields: options, keytype, base64-encoded key, comment.  The options field is optional.  The supported key types are:

         sk-ecdsa-sha2-nistp256@openssh.com
         ecdsa-sha2-nistp256
         ecdsa-sha2-nistp384
         ecdsa-sha2-nistp521
         sk-ssh-ed25519@openssh.com
         ssh-ed25519
         ssh-rsa

   The comment field is not used for anything (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 RSA keys up to 16 kilobits.
   You don't want to type them in; instead, copy the id_ecdsa.pub, id_ecdsa_sk.pub, id_ed25519.pub, id_ed25519_sk.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 exe‐
           cution.  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 certificate will be accepted only if the two commands are identi‐
           cal.

   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.

   expiry-time="timespec"
           Specifies a time after which the key will not be accepted.  The time may be specified as a YYYYMMDD[Z] date or a YYYYMMDDHHMM[SS][Z] time.  Dates and times will be interpreted
           in the system time zone unless suffixed by a Z character, in which case they will be interpreted in the UTC time zone.

   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 pat‐
           terns.  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);  how‐
           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).

   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 restrict listen addresses.  Note that ssh(1) will send a host‐
           name 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 applied separated by commas.  No pattern matching or name lookup is performed on the specified hostnames, they must  be
           literal host names and/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 certifi‐
           cate'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  op‐
           tion.

   pty     Permits tty allocation previously disabled by the restrict option.

   no-touch-required
           Do not require demonstration of user presence for signatures made using this key.  This option only makes sense for the FIDO authenticator algorithms ecdsa-sk and ed25519-sk.

   verify-required
           Require  that  signatures  made using this key attest that they verified the user, e.g. via a PIN.  This option only makes sense for the FIDO authenticator algorithms ecdsa-sk
           and ed25519-sk.

   restrict
           Enable all restrictions, i.e. disable port, agent and X11 forwarding, 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 are allowed at start of line. Blank lines are allowed.
      # Plain key, no restrictions
      ssh-rsa ...
      # Forced command, disable PTY and all forwarding
      restrict,command="dump /home" ssh-rsa ...
      # Restriction of ssh -L forwarding destinations
      permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-rsa ...
      # Restriction of ssh -R forwarding listeners
      permitlisten="localhost:8080",permitlisten="[::1]:22000" ssh-rsa ...
      # Configuration for tunnel forwarding
      tunnel="0",command="sh /etc/netstart tun0" ssh-rsa ...
      # Override of restriction to allow PTY allocation
      restrict,pty,command="nethack" ssh-rsa ...
      # Allow FIDO key without requiring touch
      no-touch-required sk-ecdsa-sha2-nistp256@openssh.com ...
      # Require user-verification (e.g. PIN or biometric) for FIDO key
      verify-required sk-ecdsa-sha2-nistp256@openssh.com ...
      # Trust CA key, allow touch-less FIDO if requested in certificate
      cert-authority,no-touch-required,principals="user_a" ssh-rsa ...

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 connects to an unknown host, its key is added to the per-user file.

   Each line in these files contains the following fields: marker (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  indi‐
   cate 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 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.

   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
   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 in‐
   cluding 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 do‐
   mains are put in the file.  It is possible that the files contain conflicting 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 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
      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 ban‐
           ner 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.  Additionally, this file must be owned by the user, and must not have write permissions for anyone else.  The recommended per‐
           mission 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 (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 login 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.