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author | des <des@FreeBSD.org> | 2008-07-22 19:01:18 +0000 |
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committer | des <des@FreeBSD.org> | 2008-07-22 19:01:18 +0000 |
commit | f1596419c2717cb81dd4b676d5e0cf1a3e30e98c (patch) | |
tree | 9827eb822991aa369cf5d220fce40c3d2011c19f /sshd.8 | |
parent | 666aa9cc1660793c97ef29a6cb66dfbb894dde8f (diff) | |
download | FreeBSD-src-f1596419c2717cb81dd4b676d5e0cf1a3e30e98c.zip FreeBSD-src-f1596419c2717cb81dd4b676d5e0cf1a3e30e98c.tar.gz |
Properly flatten openssh/dist.
Diffstat (limited to 'sshd.8')
-rw-r--r-- | sshd.8 | 857 |
1 files changed, 857 insertions, 0 deletions
@@ -0,0 +1,857 @@ +.\" -*- nroff -*- +.\" +.\" Author: Tatu Ylonen <ylo@cs.hut.fi> +.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland +.\" All rights reserved +.\" +.\" As far as I am concerned, the code I have written for this software +.\" can be used freely for any purpose. Any derived versions of this +.\" software must be clearly marked as such, and if the derived work is +.\" incompatible with the protocol description in the RFC file, it must be +.\" called by a name other than "ssh" or "Secure Shell". +.\" +.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. +.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. +.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR +.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES +.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. +.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, +.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT +.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF +.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +.\" +.\" $OpenBSD: sshd.8,v 1.234 2006/08/21 08:15:57 dtucker Exp $ +.Dd September 25, 1999 +.Dt SSHD 8 +.Os +.Sh NAME +.Nm sshd +.Nd OpenSSH SSH daemon +.Sh SYNOPSIS +.Nm sshd +.Bk -words +.Op Fl 46Ddeiqt +.Op Fl b Ar bits +.Op Fl f Ar config_file +.Op Fl g Ar login_grace_time +.Op Fl h Ar host_key_file +.Op Fl k Ar key_gen_time +.Op Fl o Ar option +.Op Fl p Ar port +.Op Fl u Ar len +.Ek +.Sh DESCRIPTION +.Nm +(OpenSSH Daemon) is the daemon program for +.Xr ssh 1 . +Together these programs replace rlogin and rsh, and +provide secure encrypted communications between two untrusted hosts +over an insecure network. +.Pp +.Nm +listens for connections from clients. +It is normally started at boot from +.Pa /etc/rc . +It forks a new +daemon for each incoming connection. +The forked daemons handle +key exchange, encryption, authentication, command execution, +and data exchange. +.Pp +.Nm +can be configured using command-line options or a configuration file +(by default +.Xr sshd_config 5 ) ; +command-line options override values specified in the +configuration file. +.Nm +rereads its configuration file when it receives a hangup signal, +.Dv SIGHUP , +by executing itself with the name and options it was started with, e.g.\& +.Pa /usr/sbin/sshd . +.Pp +The options are as follows: +.Bl -tag -width Ds +.It Fl 4 +Forces +.Nm +to use IPv4 addresses only. +.It Fl 6 +Forces +.Nm +to use IPv6 addresses only. +.It Fl b Ar bits +Specifies the number of bits in the ephemeral protocol version 1 +server key (default 768). +.It Fl D +When this option is specified, +.Nm +will not detach and does not become a daemon. +This allows easy monitoring of +.Nm sshd . +.It Fl d +Debug mode. +The server sends verbose debug output to the system +log, and does not put itself in the background. +The server also will not fork and will only process one connection. +This option is only intended for debugging for the server. +Multiple +.Fl d +options increase the debugging level. +Maximum is 3. +.It Fl e +When this option is specified, +.Nm +will send the output to the standard error instead of the system log. +.It Fl f Ar configuration_file +Specifies the name of the configuration file. +The default is +.Pa /etc/ssh/sshd_config . +.Nm +refuses to start if there is no configuration file. +.It Fl g Ar 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. +.It Fl h Ar host_key_file +Specifies a file from which a host key is read. +This option must be given if +.Nm +is not run as root (as the normal +host key files are normally not readable by anyone but root). +The default is +.Pa /etc/ssh/ssh_host_key +for protocol version 1, and +.Pa /etc/ssh/ssh_host_rsa_key +and +.Pa /etc/ssh/ssh_host_dsa_key +for protocol version 2. +It is possible to have multiple host key files for +the different protocol versions and host key algorithms. +.It Fl i +Specifies that +.Nm +is being run from +.Xr inetd 8 . +.Nm +is normally not run +from inetd because it needs to generate the server key before it can +respond to the client, and this may take tens of seconds. +Clients would have to wait too long if the key was regenerated every time. +However, with small key sizes (e.g. 512) using +.Nm +from inetd may +be feasible. +.It Fl k Ar key_gen_time +Specifies how often the ephemeral protocol version 1 server key is +regenerated (default 3600 seconds, or one hour). +The motivation for regenerating the key fairly +often is that the key is not stored anywhere, and after about an hour +it becomes impossible to recover the key for decrypting intercepted +communications even if the machine is cracked into or physically +seized. +A value of zero indicates that the key will never be regenerated. +.It Fl o Ar 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 +.Xr sshd_config 5 . +.It Fl p Ar 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 +.Cm Port +option are ignored when a command-line port is specified. +Ports specified using the +.Cm ListenAddress +option override command-line ports. +.It Fl q +Quiet mode. +Nothing is sent to the system log. +Normally the beginning, +authentication, and termination of each connection is logged. +.It Fl t +Test mode. +Only check the validity of the configuration file and sanity of the keys. +This is useful for updating +.Nm +reliably as configuration options may change. +.It Fl u Ar len +This option is used to specify the size of the field +in the +.Li utmp +structure that holds the remote host name. +If the resolved host name is longer than +.Ar 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 +.Fl u0 +indicates that only dotted decimal addresses +should be put into the +.Pa utmp +file. +.Fl u0 +may also be used to prevent +.Nm +from making DNS requests unless the authentication +mechanism or configuration requires it. +Authentication mechanisms that may require DNS include +.Cm RhostsRSAAuthentication , +.Cm HostbasedAuthentication , +and using a +.Cm from="pattern-list" +option in a key file. +Configuration options that require DNS include using a +USER@HOST pattern in +.Cm AllowUsers +or +.Cm DenyUsers . +.El +.Sh AUTHENTICATION +The OpenSSH SSH daemon supports SSH protocols 1 and 2. +Both protocols are supported by default, +though this can be changed via the +.Cm Protocol +option in +.Xr sshd_config 5 . +Protocol 2 supports both RSA and DSA keys; +protocol 1 only supports RSA keys. +For both protocols, +each host has a host-specific key, +normally 2048 bits, +used to identify the host. +.Pp +Forward security for protocol 1 is provided through +an additional server key, +normally 768 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. +.Pp +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, currently +128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. +The client selects the encryption algorithm +to use from those offered by the server. +Additionally, session integrity is provided +through a cryptographic message authentication code +(hmac-sha1 or hmac-md5). +.Pp +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. +.Pp +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 +.Cm DenyUsers +or its group is listed in +.Cm DenyGroups +\&. The definition of a locked account is system dependant. Some platforms +have their own account database (eg AIX) and some modify the passwd field ( +.Ql \&*LK\&* +on Solaris and UnixWare, +.Ql \&* +on HP-UX, containing +.Ql Nologin +on Tru64, +a leading +.Ql \&*LOCKED\&* +on FreeBSD and a leading +.Ql \&!! +on Linux). 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 +.Ql NP +or +.Ql \&*NP\&* +). +.Pp +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. +.Pp +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. +.Pp +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. +.Sh LOGIN PROCESS +When a user successfully logs in, +.Nm +does the following: +.Bl -enum -offset indent +.It +If the login is on a tty, and no command has been specified, +prints last login time and +.Pa /etc/motd +(unless prevented in the configuration file or by +.Pa ~/.hushlogin ; +see the +.Sx FILES +section). +.It +If the login is on a tty, records login time. +.It +Checks +.Pa /etc/nologin ; +if it exists, prints contents and quits +(unless root). +.It +Changes to run with normal user privileges. +.It +Sets up basic environment. +.It +Reads the file +.Pa ~/.ssh/environment , +if it exists, and users are allowed to change their environment. +See the +.Cm PermitUserEnvironment +option in +.Xr sshd_config 5 . +.It +Changes to user's home directory. +.It +If +.Pa ~/.ssh/rc +exists, runs it; else if +.Pa /etc/ssh/sshrc +exists, runs +it; otherwise runs xauth. +The +.Dq rc +files are given the X11 +authentication protocol and cookie in standard input. +See +.Sx SSHRC , +below. +.It +Runs user's shell or command. +.El +.Sh SSHRC +If the file +.Pa ~/.ssh/rc +exists, +.Xr 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 +.Ev DISPLAY +in its environment). +The script must call +.Xr xauth 1 +because +.Nm +will not run xauth automatically to add X11 cookies. +.Pp +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. +.Pp +This file will probably contain some initialization code followed by +something similar to: +.Bd -literal -offset 3n +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 +.Ed +.Pp +If this file does not exist, +.Pa /etc/ssh/sshrc +is run, and if that +does not exist either, xauth is used to add the cookie. +.Sh AUTHORIZED_KEYS FILE FORMAT +.Cm AuthorizedKeysFile +specifies the file containing public keys for +public key authentication; +if none is specified, the default is +.Pa ~/.ssh/authorized_keys . +Each line of the file contains one +key (empty lines and lines starting with a +.Ql # +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 +.Dq ssh-dss +or +.Dq ssh-rsa . +.Pp +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 +.Pa identity.pub , +.Pa id_dsa.pub , +or the +.Pa id_rsa.pub +file and edit it. +.Pp +.Nm +enforces a minimum RSA key modulus size for protocol 1 +and protocol 2 keys of 768 bits. +.Pp +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): +.Bl -tag -width Ds +.It Cm 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 +.Cm 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. +The command originally supplied by the client is available in the +.Ev SSH_ORIGINAL_COMMAND +environment variable. +Note that this option applies to shell, command or subsystem execution. +.It Cm 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 +.Cm PermitUserEnvironment +option. +This option is automatically disabled if +.Cm UseLogin +is enabled. +.It Cm from="pattern-list" +Specifies that in addition to public key authentication, the canonical name +of the remote host must be present in the comma-separated list of +patterns. +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). +.Pp +See +.Sx PATTERNS +in +.Xr ssh_config 5 +for more information on patterns. +.It Cm no-agent-forwarding +Forbids authentication agent forwarding when this key is used for +authentication. +.It Cm 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 +.Cm command +option. +.It Cm no-pty +Prevents tty allocation (a request to allocate a pty will fail). +.It Cm no-X11-forwarding +Forbids X11 forwarding when this key is used for authentication. +Any X11 forward requests by the client will return an error. +.It Cm permitopen="host:port" +Limit local +.Li ``ssh -L'' +port forwarding such that it may only connect to the specified host and +port. +IPv6 addresses can be specified with an alternative syntax: +.Ar host Ns / Ns Ar port . +Multiple +.Cm permitopen +options may be applied separated by commas. +No pattern matching is performed on the specified hostnames, +they must be literal domains or addresses. +.It Cm tunnel="n" +Force a +.Xr tun 4 +device on the server. +Without this option, the next available device will be used if +the client requests a tunnel. +.El +.Pp +An example authorized_keys file: +.Bd -literal -offset 3n +# 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 +.Ed +.Sh SSH_KNOWN_HOSTS FILE FORMAT +The +.Pa /etc/ssh/ssh_known_hosts +and +.Pa ~/.ssh/known_hosts +files contain host public keys for all known hosts. +The global file should +be prepared by the administrator (optional), and the per-user file is +maintained automatically: whenever the user connects from an unknown host, +its key is added to the per-user file. +.Pp +Each line in these files contains the following fields: hostnames, +bits, exponent, modulus, comment. +The fields are separated by spaces. +.Pp +Hostnames is a comma-separated list of patterns +.Pf ( Ql * +and +.Ql \&? +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 +.Ql \&! +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 +.Ql \&[ +and +.Ql \&] +brackets then followed by +.Ql \&: +and a non-standard port number. +.Pp +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 +.Ql | +character. +Only one hashed hostname may appear on a single line and none of the above +negation or wildcard operators may be applied. +.Pp +Bits, exponent, and modulus are taken directly from the RSA host key; they +can be obtained, for example, from +.Pa /etc/ssh/ssh_host_key.pub . +The optional comment field continues to the end of the line, and is not used. +.Pp +Lines starting with +.Ql # +and empty lines are ignored as comments. +.Pp +When performing host authentication, authentication is accepted if any +matching line has the proper key. +It is thus 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 conflicting information; authentication is +accepted if valid information can be found from either file. +.Pp +Note that the lines in these files are typically hundreds of characters +long, and you definitely don't want to type in the host keys by hand. +Rather, generate them by a script +or by taking +.Pa /etc/ssh/ssh_host_key.pub +and adding the host names at the front. +.Pp +An example ssh_known_hosts file: +.Bd -literal -offset 3n +# 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.....= +.Ed +.Sh FILES +.Bl -tag -width Ds -compact +.It ~/.hushlogin +This file is used to suppress printing the last login time and +.Pa /etc/motd , +if +.Cm PrintLastLog +and +.Cm PrintMotd , +respectively, +are enabled. +It does not suppress printing of the banner specified by +.Cm Banner . +.Pp +.It ~/.rhosts +This file is used for host-based authentication (see +.Xr 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 +.Nm +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. +.Pp +.It ~/.shosts +This file is used in exactly the same way as +.Pa .rhosts , +but allows host-based authentication without permitting login with +rlogin/rsh. +.Pp +.It ~/.ssh/authorized_keys +Lists the public keys (RSA/DSA) 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. +.Pp +If this file, the +.Pa ~/.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, +.Nm +will not allow it to be used unless the +.Cm StrictModes +option has been set to +.Dq no . +The recommended permissions can be set by executing +.Dq chmod go-w ~/ ~/.ssh ~/.ssh/authorized_keys . +.Pp +.It ~/.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 +.Ql # ) , +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 +.Cm PermitUserEnvironment +option. +.Pp +.It ~/.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. +.Pp +.It ~/.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. +.Pp +.It /etc/hosts.allow +.It /etc/hosts.deny +Access controls that should be enforced by tcp-wrappers are defined here. +Further details are described in +.Xr hosts_access 5 . +.Pp +.It /etc/hosts.equiv +This file is for host-based authentication (see +.Xr ssh 1 ) . +It should only be writable by root. +.Pp +.It /etc/moduli +Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". +The file format is described in +.Xr moduli 5 . +.Pp +.It /etc/motd +See +.Xr motd 5 . +.Pp +.It /etc/nologin +If this file exists, +.Nm +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. +.Pp +.It /etc/shosts.equiv +This file is used in exactly the same way as +.Pa hosts.equiv , +but allows host-based authentication without permitting login with +rlogin/rsh. +.Pp +.It /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. +.Pp +.It /etc/ssh/ssh_host_key +.It /etc/ssh/ssh_host_dsa_key +.It /etc/ssh/ssh_host_rsa_key +These three files contain the private parts of the host keys. +These files should only be owned by root, readable only by root, and not +accessible to others. +Note that +.Nm +does not start if these files are group/world-accessible. +.Pp +.It /etc/ssh/ssh_host_key.pub +.It /etc/ssh/ssh_host_dsa_key.pub +.It /etc/ssh/ssh_host_rsa_key.pub +These three files contain the public parts of the host keys. +These files should be world-readable but writable only by +root. +Their contents should match the respective private parts. +These files are not +really used for anything; they are provided for the convenience of +the user so their contents can be copied to known hosts files. +These files are created using +.Xr ssh-keygen 1 . +.Pp +.It /etc/ssh/sshd_config +Contains configuration data for +.Nm sshd . +The file format and configuration options are described in +.Xr sshd_config 5 . +.Pp +.It /etc/ssh/sshrc +Similar to +.Pa ~/.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. +.Pp +.It /var/empty +.Xr chroot 2 +directory used by +.Nm +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. +.Pp +.It /var/run/sshd.pid +Contains the process ID of the +.Nm +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. +.El +.Sh SEE ALSO +.Xr scp 1 , +.Xr sftp 1 , +.Xr ssh 1 , +.Xr ssh-add 1 , +.Xr ssh-agent 1 , +.Xr ssh-keygen 1 , +.Xr chroot 2 , +.Xr hosts_access 5 , +.Xr login.conf 5 , +.Xr moduli 5 , +.Xr sshd_config 5 , +.Xr inetd 8 , +.Xr sftp-server 8 +.Sh 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 contributed the support for SSH +protocol versions 1.5 and 2.0. +Niels Provos and Markus Friedl contributed support +for privilege separation. +.Sh CAVEATS +System security is not improved unless +.Nm rshd , +.Nm rlogind , +and +.Nm rexecd +are disabled (thus completely disabling +.Xr rlogin +and +.Xr rsh +into the machine). |