Annotation of src/usr.bin/ssh/sshd.8, Revision 1.130
1.1 deraadt 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
1.64 deraadt 7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
1.99 deraadt 13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
1.64 deraadt 16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 25: .\"
1.64 deraadt 26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 36: .\"
1.130 ! markus 37: .\" $OpenBSD: sshd.8,v 1.129 2001/06/22 21:28:53 provos Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSHD 8
40: .Os
41: .Sh NAME
42: .Nm sshd
1.120 markus 43: .Nd OpenSSH SSH daemon
1.2 deraadt 44: .Sh SYNOPSIS
45: .Nm sshd
1.114 lebel 46: .Op Fl deiqD46
1.2 deraadt 47: .Op Fl b Ar bits
48: .Op Fl f Ar config_file
49: .Op Fl g Ar login_grace_time
50: .Op Fl h Ar host_key_file
51: .Op Fl k Ar key_gen_time
52: .Op Fl p Ar port
1.61 markus 53: .Op Fl u Ar len
1.26 markus 54: .Op Fl V Ar client_protocol_id
1.40 aaron 55: .Sh DESCRIPTION
1.2 deraadt 56: .Nm
1.106 deraadt 57: (SSH Daemon) is the daemon program for
1.2 deraadt 58: .Xr ssh 1 .
1.42 hugh 59: Together these programs replace rlogin and rsh, and
1.1 deraadt 60: provide secure encrypted communications between two untrusted hosts
1.36 aaron 61: over an insecure network.
62: The programs are intended to be as easy to
1.1 deraadt 63: install and use as possible.
1.2 deraadt 64: .Pp
65: .Nm
1.36 aaron 66: is the daemon that listens for connections from clients.
1.40 aaron 67: It is normally started at boot from
1.2 deraadt 68: .Pa /etc/rc .
69: It forks a new
1.36 aaron 70: daemon for each incoming connection.
71: The forked daemons handle
1.1 deraadt 72: key exchange, encryption, authentication, command execution,
73: and data exchange.
1.49 markus 74: This implementation of
75: .Nm
76: supports both SSH protocol version 1 and 2 simultaneously.
1.2 deraadt 77: .Nm
1.36 aaron 78: works as follows.
1.49 markus 79: .Pp
80: .Ss SSH protocol version 1
81: .Pp
1.36 aaron 82: Each host has a host-specific RSA key
83: (normally 1024 bits) used to identify the host.
84: Additionally, when
1.1 deraadt 85: the daemon starts, it generates a server RSA key (normally 768 bits).
86: This key is normally regenerated every hour if it has been used, and
87: is never stored on disk.
1.2 deraadt 88: .Pp
1.42 hugh 89: Whenever a client connects the daemon responds with its public
90: host and server keys.
1.36 aaron 91: The client compares the
1.49 markus 92: RSA host key against its own database to verify that it has not changed.
1.36 aaron 93: The client then generates a 256 bit random number.
94: It encrypts this
1.1 deraadt 95: random number using both the host key and the server key, and sends
1.36 aaron 96: the encrypted number to the server.
1.42 hugh 97: Both sides then use this
1.1 deraadt 98: random number as a session key which is used to encrypt all further
1.36 aaron 99: communications in the session.
100: The rest of the session is encrypted
1.42 hugh 101: using a conventional cipher, currently Blowfish or 3DES, with 3DES
1.39 deraadt 102: being used by default.
1.36 aaron 103: The client selects the encryption algorithm
1.5 deraadt 104: to use from those offered by the server.
1.2 deraadt 105: .Pp
1.36 aaron 106: Next, the server and the client enter an authentication dialog.
107: The client tries to authenticate itself using
1.2 deraadt 108: .Pa .rhosts
109: authentication,
110: .Pa .rhosts
111: authentication combined with RSA host
1.1 deraadt 112: authentication, RSA challenge-response authentication, or password
113: based authentication.
1.2 deraadt 114: .Pp
1.1 deraadt 115: Rhosts authentication is normally disabled
116: because it is fundamentally insecure, but can be enabled in the server
1.36 aaron 117: configuration file if desired.
118: System security is not improved unless
1.2 deraadt 119: .Xr rshd 8 ,
120: .Xr rlogind 8 ,
121: .Xr rexecd 8 ,
122: and
123: .Xr rexd 8
1.1 deraadt 124: are disabled (thus completely disabling
1.2 deraadt 125: .Xr rlogin 1
1.1 deraadt 126: and
1.2 deraadt 127: .Xr rsh 1
1.42 hugh 128: into the machine).
1.2 deraadt 129: .Pp
1.49 markus 130: .Ss SSH protocol version 2
131: .Pp
1.58 deraadt 132: Version 2 works similarly:
1.49 markus 133: Each host has a host-specific DSA key used to identify the host.
134: However, when the daemon starts, it does not generate a server key.
135: Forward security is provided through a Diffie-Hellman key agreement.
136: This key agreement results in a shared session key.
1.120 markus 137: .Pp
1.103 deraadt 138: The rest of the session is encrypted using a symmetric cipher, currently
1.120 markus 139: 128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES.
1.49 markus 140: The client selects the encryption algorithm
141: to use from those offered by the server.
142: Additionally, session integrity is provided
1.51 hugh 143: through a cryptographic message authentication code
1.49 markus 144: (hmac-sha1 or hmac-md5).
145: .Pp
146: Protocol version 2 provides a public key based
1.120 markus 147: user (PubkeyAuthentication) or
148: client host (HostbasedAuthentication) authentication method,
149: conventional password authentication and challenge response based methods.
1.49 markus 150: .Pp
151: .Ss Command execution and data forwarding
152: .Pp
1.1 deraadt 153: If the client successfully authenticates itself, a dialog for
1.36 aaron 154: preparing the session is entered.
155: At this time the client may request
1.1 deraadt 156: things like allocating a pseudo-tty, forwarding X11 connections,
157: forwarding TCP/IP connections, or forwarding the authentication agent
158: connection over the secure channel.
1.2 deraadt 159: .Pp
1.1 deraadt 160: Finally, the client either requests a shell or execution of a command.
1.36 aaron 161: The sides then enter session mode.
162: In this mode, either side may send
1.1 deraadt 163: data at any time, and such data is forwarded to/from the shell or
164: command on the server side, and the user terminal in the client side.
1.2 deraadt 165: .Pp
1.1 deraadt 166: When the user program terminates and all forwarded X11 and other
167: connections have been closed, the server sends command exit status to
168: the client, and both sides exit.
1.2 deraadt 169: .Pp
170: .Nm
1.1 deraadt 171: can be configured using command-line options or a configuration
1.36 aaron 172: file.
173: Command-line options override values specified in the
1.1 deraadt 174: configuration file.
1.25 markus 175: .Pp
176: .Nm
177: rereads its configuration file when it receives a hangup signal,
1.97 deraadt 178: .Dv SIGHUP ,
1.128 mpech 179: by executing itself with the name it was started as, i.e.,
1.97 deraadt 180: .Pa /usr/sbin/sshd .
1.18 aaron 181: .Pp
182: The options are as follows:
1.2 deraadt 183: .Bl -tag -width Ds
184: .It Fl b Ar bits
1.120 markus 185: Specifies the number of bits in the ephemeral protocol version 1
186: server key (default 768).
1.2 deraadt 187: .Pp
188: .It Fl d
1.36 aaron 189: Debug mode.
190: The server sends verbose debug output to the system
191: log, and does not put itself in the background.
192: The server also will not fork and will only process one connection.
193: This option is only intended for debugging for the server.
1.120 markus 194: Multiple -d options increase the debugging level.
1.67 aaron 195: Maximum is 3.
1.120 markus 196: .It Fl e
197: When this option is specified,
198: .Nm
199: will send the output to the standard error instead of the system log.
1.2 deraadt 200: .It Fl f Ar configuration_file
1.36 aaron 201: Specifies the name of the configuration file.
202: The default is
1.2 deraadt 203: .Pa /etc/sshd_config .
1.16 markus 204: .Nm
205: refuses to start if there is no configuration file.
1.2 deraadt 206: .It Fl g Ar login_grace_time
1.1 deraadt 207: Gives the grace time for clients to authenticate themselves (default
1.77 markus 208: 600 seconds).
1.36 aaron 209: If the client fails to authenticate the user within
210: this many seconds, the server disconnects and exits.
211: A value of zero indicates no limit.
1.2 deraadt 212: .It Fl h Ar host_key_file
1.75 markus 213: Specifies the file from which the host key is read (default
1.2 deraadt 214: .Pa /etc/ssh_host_key ) .
1.7 markus 215: This option must be given if
216: .Nm
217: is not run as root (as the normal
1.1 deraadt 218: host file is normally not readable by anyone but root).
1.75 markus 219: It is possible to have multiple host key files for
1.120 markus 220: the different protocol versions and host key algorithms.
1.2 deraadt 221: .It Fl i
1.7 markus 222: Specifies that
223: .Nm
1.40 aaron 224: is being run from inetd.
1.7 markus 225: .Nm
226: is normally not run
1.1 deraadt 227: from inetd because it needs to generate the server key before it can
1.36 aaron 228: respond to the client, and this may take tens of seconds.
229: Clients would have to wait too long if the key was regenerated every time.
1.35 aaron 230: However, with small key sizes (e.g., 512) using
1.7 markus 231: .Nm
232: from inetd may
1.1 deraadt 233: be feasible.
1.2 deraadt 234: .It Fl k Ar key_gen_time
1.120 markus 235: Specifies how often the ephemeral protocol version 1 server key is
236: regenerated (default 3600 seconds, or one hour).
1.36 aaron 237: The motivation for regenerating the key fairly
1.1 deraadt 238: often is that the key is not stored anywhere, and after about an hour,
239: it becomes impossible to recover the key for decrypting intercepted
240: communications even if the machine is cracked into or physically
1.36 aaron 241: seized.
242: A value of zero indicates that the key will never be regenerated.
1.2 deraadt 243: .It Fl p Ar port
1.1 deraadt 244: Specifies the port on which the server listens for connections
245: (default 22).
1.2 deraadt 246: .It Fl q
1.36 aaron 247: Quiet mode.
248: Nothing is sent to the system log.
249: Normally the beginning,
1.1 deraadt 250: authentication, and termination of each connection is logged.
1.61 markus 251: .It Fl u Ar len
252: This option is used to specify the size of the field
253: in the
254: .Li utmp
255: structure that holds the remote host name.
256: If the resolved host name is longer than
257: .Ar len ,
258: the dotted decimal value will be used instead.
259: This allows hosts with very long host names that
260: overflow this field to still be uniquely identified.
261: Specifying
262: .Fl u0
263: indicates that only dotted decimal addresses
264: should be put into the
265: .Pa utmp
266: file.
1.74 markus 267: .It Fl D
268: When this option is specified
269: .Nm
270: will not detach and does not become a daemon.
271: This allows easy monitoring of
1.76 markus 272: .Nm sshd .
1.29 markus 273: .It Fl 4
274: Forces
275: .Nm
276: to use IPv4 addresses only.
277: .It Fl 6
278: Forces
279: .Nm
280: to use IPv6 addresses only.
1.2 deraadt 281: .El
282: .Sh CONFIGURATION FILE
283: .Nm
1.40 aaron 284: reads configuration data from
1.2 deraadt 285: .Pa /etc/sshd_config
286: (or the file specified with
287: .Fl f
1.36 aaron 288: on the command line).
289: The file contains keyword-value pairs, one per line.
290: Lines starting with
1.2 deraadt 291: .Ql #
1.1 deraadt 292: and empty lines are interpreted as comments.
1.2 deraadt 293: .Pp
1.1 deraadt 294: The following keywords are possible.
1.2 deraadt 295: .Bl -tag -width Ds
296: .It Cm AFSTokenPassing
1.36 aaron 297: Specifies whether an AFS token may be forwarded to the server.
298: Default is
1.2 deraadt 299: .Dq yes .
1.11 markus 300: .It Cm AllowGroups
1.92 deraadt 301: This keyword can be followed by a list of group names, separated
1.36 aaron 302: by spaces.
303: If specified, login is allowed only for users whose primary
1.81 markus 304: group or supplementary group list matches one of the patterns.
1.11 markus 305: .Ql \&*
306: and
307: .Ql ?
308: can be used as
1.36 aaron 309: wildcards in the patterns.
1.58 deraadt 310: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 311: By default login is allowed regardless of the group list.
1.3 dugsong 312: .Pp
1.69 markus 313: .It Cm AllowTcpForwarding
314: Specifies whether TCP forwarding is permitted.
315: The default is
316: .Dq yes .
317: Note that disabling TCP forwarding does not improve security unless
318: users are also denied shell access, as they can always install their
319: own forwarders.
320: .Pp
1.11 markus 321: .It Cm AllowUsers
1.92 deraadt 322: This keyword can be followed by a list of user names, separated
1.36 aaron 323: by spaces.
324: If specified, login is allowed only for users names that
1.11 markus 325: match one of the patterns.
326: .Ql \&*
327: and
328: .Ql ?
329: can be used as
1.36 aaron 330: wildcards in the patterns.
1.58 deraadt 331: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 332: By default login is allowed regardless of the user name.
1.80 markus 333: .Pp
1.125 markus 334: .It Cm AuthorizedKeysFile
335: Specifies the file that contains the public RSA keys that can be used
336: for RSA authentication in protocol version 1.
337: .Cm AuthorizedKeysFile
338: may contain tokens of the form %T which are substituted during connection
339: set-up. The following tokens are defined; %% is replaces by a literal '%',
340: %h is replaced by the home directory of the user being authenticated and
341: %u is replaced by the username of that user.
342: After expansion,
343: .Cm AuthorizedKeysFile
1.126 markus 344: is taken to be an absolute path or one relative to the user's home
1.125 markus 345: directory.
346: The default is
347: .Dq .ssh/authorized_keys
1.80 markus 348: .It Cm Banner
349: In some jurisdictions, sending a warning message before authentication
350: may be relevant for getting legal protection.
351: The contents of the specified file are sent to the remote user before
352: authentication is allowed.
353: This option is only available for protocol version 2.
1.11 markus 354: .Pp
1.104 deraadt 355: .It Cm ChallengeResponseAuthentication
356: Specifies whether
357: challenge response
358: authentication is allowed.
359: Currently there is only support for
360: .Xr skey 1
361: authentication.
362: The default is
363: .Dq yes .
1.8 markus 364: .It Cm CheckMail
365: Specifies whether
366: .Nm
367: should check for new mail for interactive logins.
368: The default is
369: .Dq no .
1.122 markus 370: .It Cm Ciphers
371: Specifies the ciphers allowed for protocol version 2.
372: Multiple ciphers must be comma-separated.
373: The default is
374: .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
1.115 beck 375: .It Cm ClientAliveInterval
376: Sets a timeout interval in seconds after which if no data has been received
377: from the client,
378: .Nm
379: will send a message through the encrypted
1.116 stevesk 380: channel to request a response from the client.
381: The default
1.115 beck 382: is 0, indicating that these messages will not be sent to the client.
1.116 stevesk 383: This option applies to protocol version 2 only.
1.115 beck 384: .It Cm ClientAliveCountMax
385: Sets the number of client alive messages (see above) which may be
386: sent without
387: .Nm
388: receiving any messages back from the client. If this threshold is
389: reached while client alive messages are being sent,
390: .Nm
391: will disconnect the client, terminating the session. It is important
392: to note that the use of client alive messages is very different from
1.116 stevesk 393: .Cm Keepalive
394: (below). The client alive messages are sent through the
1.115 beck 395: encrypted channel and therefore will not be spoofable. The TCP keepalive
1.116 stevesk 396: option enabled by
397: .Cm Keepalive
398: is spoofable. You want to use the client
1.115 beck 399: alive mechanism when you are basing something important on
400: clients having an active connection to the server.
1.116 stevesk 401: .Pp
402: The default value is 3. If you set
403: .Cm ClientAliveInterval
1.115 beck 404: (above) to 15, and leave this value at the default, unresponsive ssh clients
405: will be disconnected after approximately 45 seconds.
1.11 markus 406: .It Cm DenyGroups
407: This keyword can be followed by a number of group names, separated
1.36 aaron 408: by spaces.
1.81 markus 409: Users whose primary group or supplementary group list matches
410: one of the patterns aren't allowed to log in.
1.11 markus 411: .Ql \&*
412: and
413: .Ql ?
414: can be used as
1.36 aaron 415: wildcards in the patterns.
1.58 deraadt 416: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 417: By default login is allowed regardless of the group list.
1.11 markus 418: .Pp
419: .It Cm DenyUsers
420: This keyword can be followed by a number of user names, separated
1.36 aaron 421: by spaces.
422: Login is disallowed for user names that match one of the patterns.
1.11 markus 423: .Ql \&*
424: and
425: .Ql ?
1.36 aaron 426: can be used as wildcards in the patterns.
1.58 deraadt 427: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 428: By default login is allowed regardless of the user name.
1.47 markus 429: .It Cm GatewayPorts
430: Specifies whether remote hosts are allowed to connect to ports
431: forwarded for the client.
432: The argument must be
433: .Dq yes
434: or
435: .Dq no .
436: The default is
437: .Dq no .
1.120 markus 438: .It Cm HostbasedAuthentication
439: Specifies whether rhosts or /etc/hosts.equiv authentication together
440: with successful public key client host authentication is allowed
441: (hostbased authentication).
442: This option is similar to
443: .Cm RhostsRSAAuthentication
444: and applies to protocol version 2 only.
445: The default is
446: .Dq no .
1.2 deraadt 447: .It Cm HostKey
1.72 markus 448: Specifies the file containing the private host keys (default
1.46 markus 449: .Pa /etc/ssh_host_key )
1.72 markus 450: used by SSH protocol versions 1 and 2.
1.9 markus 451: Note that
452: .Nm
1.83 markus 453: will refuse to use a file if it is group/world-accessible.
1.72 markus 454: It is possible to have multiple host key files.
455: .Dq rsa1
456: keys are used for version 1 and
457: .Dq dsa
458: or
459: .Dq rsa
460: are used for version 2 of the SSH protocol.
1.2 deraadt 461: .It Cm IgnoreRhosts
1.34 markus 462: Specifies that
463: .Pa .rhosts
1.40 aaron 464: and
1.34 markus 465: .Pa .shosts
1.120 markus 466: files will not be used in
467: .Cm RhostsAuthentication ,
468: .Cm RhostsRSAAuthentication
469: or
470: .Cm HostbasedAuthentication .
471: .Pp
1.2 deraadt 472: .Pa /etc/hosts.equiv
1.1 deraadt 473: and
1.40 aaron 474: .Pa /etc/shosts.equiv
1.36 aaron 475: are still used.
1.40 aaron 476: The default is
1.34 markus 477: .Dq yes .
1.24 markus 478: .It Cm IgnoreUserKnownHosts
479: Specifies whether
480: .Nm
481: should ignore the user's
482: .Pa $HOME/.ssh/known_hosts
1.45 markus 483: during
1.120 markus 484: .Cm RhostsRSAAuthentication
485: or
486: .Cm HostbasedAuthentication .
1.24 markus 487: The default is
1.2 deraadt 488: .Dq no .
489: .It Cm KeepAlive
1.1 deraadt 490: Specifies whether the system should send keepalive messages to the
1.36 aaron 491: other side.
492: If they are sent, death of the connection or crash of one
493: of the machines will be properly noticed.
494: However, this means that
1.1 deraadt 495: connections will die if the route is down temporarily, and some people
1.36 aaron 496: find it annoying.
1.51 hugh 497: On the other hand, if keepalives are not sent,
1.2 deraadt 498: sessions may hang indefinitely on the server, leaving
499: .Dq ghost
500: users and consuming server resources.
501: .Pp
502: The default is
503: .Dq yes
504: (to send keepalives), and the server will notice
1.36 aaron 505: if the network goes down or the client host reboots.
506: This avoids infinitely hanging sessions.
1.2 deraadt 507: .Pp
508: To disable keepalives, the value should be set to
509: .Dq no
510: in both the server and the client configuration files.
511: .It Cm KerberosAuthentication
1.36 aaron 512: Specifies whether Kerberos authentication is allowed.
513: This can be in the form of a Kerberos ticket, or if
1.7 markus 514: .Cm PasswordAuthentication
1.1 deraadt 515: is yes, the password provided by the user will be validated through
1.67 aaron 516: the Kerberos KDC.
517: To use this option, the server needs a
1.59 provos 518: Kerberos servtab which allows the verification of the KDC's identity.
1.36 aaron 519: Default is
1.60 provos 520: .Dq yes .
1.2 deraadt 521: .It Cm KerberosOrLocalPasswd
1.1 deraadt 522: If set then if password authentication through Kerberos fails then
523: the password will be validated via any additional local mechanism
1.2 deraadt 524: such as
1.66 markus 525: .Pa /etc/passwd .
1.36 aaron 526: Default is
1.20 dugsong 527: .Dq yes .
1.2 deraadt 528: .It Cm KerberosTgtPassing
1.1 deraadt 529: Specifies whether a Kerberos TGT may be forwarded to the server.
1.40 aaron 530: Default is
1.3 dugsong 531: .Dq no ,
532: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 533: .It Cm KerberosTicketCleanup
1.7 markus 534: Specifies whether to automatically destroy the user's ticket cache
1.36 aaron 535: file on logout.
536: Default is
1.3 dugsong 537: .Dq yes .
1.2 deraadt 538: .It Cm KeyRegenerationInterval
1.120 markus 539: In protocol version 1, the ephemeral server key is automatically regenerated
540: after this many seconds (if it has been used).
1.36 aaron 541: The purpose of regeneration is to prevent
1.1 deraadt 542: decrypting captured sessions by later breaking into the machine and
1.36 aaron 543: stealing the keys.
544: The key is never stored anywhere.
545: If the value is 0, the key is never regenerated.
546: The default is 3600 (seconds).
1.7 markus 547: .It Cm ListenAddress
1.110 stevesk 548: Specifies the local addresses
1.120 markus 549: .Nm
1.7 markus 550: should listen on.
1.110 stevesk 551: The following forms may be used:
552: .Pp
553: .Bl -item -offset indent -compact
554: .It
555: .Cm ListenAddress
1.112 stevesk 556: .Sm off
557: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
558: .Sm on
1.110 stevesk 559: .It
560: .Cm ListenAddress
1.112 stevesk 561: .Sm off
562: .Ar host No | Ar IPv4_addr No : Ar port
563: .Sm on
1.110 stevesk 564: .It
565: .Cm ListenAddress
1.112 stevesk 566: .Sm off
567: .Oo
568: .Ar host No | Ar IPv6_addr Oc : Ar port
569: .Sm on
1.110 stevesk 570: .El
571: .Pp
572: If
1.112 stevesk 573: .Ar port
1.110 stevesk 574: is not specified,
1.120 markus 575: .Nm
1.110 stevesk 576: will listen on the address and all prior
577: .Cm Port
578: options specified. The default is to listen on all local
579: addresses. Multiple
580: .Cm ListenAddress
581: options are permitted. Additionally, any
582: .Cm Port
583: options must precede this option for non port qualified addresses.
1.2 deraadt 584: .It Cm LoginGraceTime
1.1 deraadt 585: The server disconnects after this time if the user has not
1.36 aaron 586: successfully logged in.
587: If the value is 0, there is no time limit.
1.1 deraadt 588: The default is 600 (seconds).
1.23 markus 589: .It Cm LogLevel
590: Gives the verbosity level that is used when logging messages from
591: .Nm sshd .
592: The possible values are:
1.82 markus 593: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
594: The default is INFO.
1.23 markus 595: Logging with level DEBUG violates the privacy of users
596: and is not recommended.
1.93 markus 597: .It Cm MACs
598: Specifies the available MAC (message authentication code) algorithms.
599: The MAC algorithm is used in protocol version 2
600: for data integrity protection.
601: Multiple algorithms must be comma-separated.
602: The default is
1.123 markus 603: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
1.55 markus 604: .It Cm MaxStartups
605: Specifies the maximum number of concurrent unauthenticated connections to the
606: .Nm
607: daemon.
608: Additional connections will be dropped until authentication succeeds or the
609: .Cm LoginGraceTime
610: expires for a connection.
611: The default is 10.
1.57 markus 612: .Pp
613: Alternatively, random early drop can be enabled by specifying
614: the three colon separated values
615: .Dq start:rate:full
1.67 aaron 616: (e.g., "10:30:60").
1.57 markus 617: .Nm
1.86 stevesk 618: will refuse connection attempts with a probability of
1.57 markus 619: .Dq rate/100
620: (30%)
621: if there are currently
622: .Dq start
623: (10)
624: unauthenticated connections.
1.86 stevesk 625: The probability increases linearly and all connection attempts
1.57 markus 626: are refused if the number of unauthenticated connections reaches
627: .Dq full
628: (60).
1.2 deraadt 629: .It Cm PasswordAuthentication
1.1 deraadt 630: Specifies whether password authentication is allowed.
1.2 deraadt 631: The default is
632: .Dq yes .
633: .It Cm PermitEmptyPasswords
1.1 deraadt 634: When password authentication is allowed, it specifies whether the
1.36 aaron 635: server allows login to accounts with empty password strings.
636: The default is
1.34 markus 637: .Dq no .
1.2 deraadt 638: .It Cm PermitRootLogin
1.100 stevesk 639: Specifies whether root can login using
1.2 deraadt 640: .Xr ssh 1 .
1.15 markus 641: The argument must be
642: .Dq yes ,
1.94 markus 643: .Dq without-password ,
644: .Dq forced-commands-only
1.15 markus 645: or
646: .Dq no .
1.2 deraadt 647: The default is
648: .Dq yes .
1.94 markus 649: .Pp
650: If this option is set to
1.15 markus 651: .Dq without-password
1.94 markus 652: password authentication is disabled for root.
1.2 deraadt 653: .Pp
1.94 markus 654: If this option is set to
655: .Dq forced-commands-only
656: root login with public key authentication will be allowed,
657: but only if the
1.2 deraadt 658: .Ar command
1.94 markus 659: option has been specified
1.1 deraadt 660: (which may be useful for taking remote backups even if root login is
1.94 markus 661: normally not allowed). All other authentication methods are disabled
662: for root.
1.100 stevesk 663: .Pp
664: If this option is set to
665: .Dq no
666: root is not allowed to login.
1.43 markus 667: .It Cm PidFile
668: Specifies the file that contains the process identifier of the
669: .Nm
670: daemon.
671: The default is
672: .Pa /var/run/sshd.pid .
1.2 deraadt 673: .It Cm Port
1.1 deraadt 674: Specifies the port number that
1.2 deraadt 675: .Nm
1.36 aaron 676: listens on.
677: The default is 22.
1.28 markus 678: Multiple options of this type are permitted.
1.120 markus 679: See also
680: .Cm ListenAddress .
1.108 stevesk 681: .It Cm PrintLastLog
682: Specifies whether
683: .Nm
684: should print the date and time when the user last logged in.
685: The default is
686: .Dq yes .
1.2 deraadt 687: .It Cm PrintMotd
1.1 deraadt 688: Specifies whether
1.2 deraadt 689: .Nm
1.40 aaron 690: should print
1.2 deraadt 691: .Pa /etc/motd
1.36 aaron 692: when a user logs in interactively.
693: (On some systems it is also printed by the shell,
1.2 deraadt 694: .Pa /etc/profile ,
1.36 aaron 695: or equivalent.)
696: The default is
1.2 deraadt 697: .Dq yes .
1.41 markus 698: .It Cm Protocol
699: Specifies the protocol versions
700: .Nm
701: should support.
702: The possible values are
703: .Dq 1
704: and
705: .Dq 2 .
706: Multiple versions must be comma-separated.
707: The default is
1.118 deraadt 708: .Dq 2,1 .
1.104 deraadt 709: .It Cm PubkeyAuthentication
710: Specifies whether public key authentication is allowed.
711: The default is
712: .Dq yes .
713: Note that this option applies to protocol version 2 only.
1.87 markus 714: .It Cm ReverseMappingCheck
715: Specifies whether
716: .Nm
717: should try to verify the remote host name and check that
718: the resolved host name for the remote IP address maps back to the
719: very same IP address.
720: The default is
721: .Dq no .
1.2 deraadt 722: .It Cm RhostsAuthentication
1.1 deraadt 723: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 724: files is sufficient.
725: Normally, this method should not be permitted because it is insecure.
1.7 markus 726: .Cm RhostsRSAAuthentication
727: should be used
1.1 deraadt 728: instead, because it performs RSA-based host authentication in addition
729: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 730: The default is
731: .Dq no .
1.120 markus 732: This option applies to protocol version 1 only.
1.2 deraadt 733: .It Cm RhostsRSAAuthentication
1.1 deraadt 734: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 735: with successful RSA host authentication is allowed.
736: The default is
1.34 markus 737: .Dq no .
1.120 markus 738: This option applies to protocol version 1 only.
1.2 deraadt 739: .It Cm RSAAuthentication
1.36 aaron 740: Specifies whether pure RSA authentication is allowed.
741: The default is
1.2 deraadt 742: .Dq yes .
1.120 markus 743: This option applies to protocol version 1 only.
1.2 deraadt 744: .It Cm ServerKeyBits
1.120 markus 745: Defines the number of bits in the ephemeral protocol version 1 server key.
1.36 aaron 746: The minimum value is 512, and the default is 768.
1.2 deraadt 747: .It Cm StrictModes
1.12 markus 748: Specifies whether
749: .Nm
750: should check file modes and ownership of the
1.36 aaron 751: user's files and home directory before accepting login.
752: This is normally desirable because novices sometimes accidentally leave their
753: directory or files world-writable.
754: The default is
1.7 markus 755: .Dq yes .
1.54 jakob 756: .It Cm Subsystem
1.67 aaron 757: Configures an external subsystem (e.g., file transfer daemon).
758: Arguments should be a subsystem name and a command to execute upon subsystem
759: request.
1.63 markus 760: The command
761: .Xr sftp-server 8
762: implements the
763: .Dq sftp
764: file transfer subsystem.
1.54 jakob 765: By default no subsystems are defined.
766: Note that this option applies to protocol version 2 only.
1.2 deraadt 767: .It Cm SyslogFacility
1.1 deraadt 768: Gives the facility code that is used when logging messages from
1.2 deraadt 769: .Nm sshd .
1.1 deraadt 770: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 771: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
772: The default is AUTH.
1.10 markus 773: .It Cm UseLogin
774: Specifies whether
775: .Xr login 1
1.53 markus 776: is used for interactive login sessions.
1.127 markus 777: The default is
778: .Dq no .
1.53 markus 779: Note that
780: .Xr login 1
1.58 deraadt 781: is never used for remote command execution.
1.127 markus 782: Note also, that if this is enabled,
783: .Cm X11Forwarding
784: will be disabled because
785: .Xr login 1
786: does not know how to handle
787: .Xr xauth 1
788: cookies.
1.6 aaron 789: .It Cm X11DisplayOffset
790: Specifies the first display number available for
791: .Nm sshd Ns 's
1.36 aaron 792: X11 forwarding.
793: This prevents
1.6 aaron 794: .Nm
795: from interfering with real X11 servers.
1.34 markus 796: The default is 10.
1.30 markus 797: .It Cm X11Forwarding
1.36 aaron 798: Specifies whether X11 forwarding is permitted.
799: The default is
1.34 markus 800: .Dq no .
1.30 markus 801: Note that disabling X11 forwarding does not improve security in any
802: way, as users can always install their own forwarders.
1.127 markus 803: X11 forwarding is automatically disabled if
804: .Cm UseLogin
805: is enabled.
1.52 markus 806: .It Cm XAuthLocation
807: Specifies the location of the
808: .Xr xauth 1
809: program.
810: The default is
811: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 812: .El
1.124 stevesk 813: .Ss Time Formats
814: .Pp
815: .Nm
816: command-line arguments and configuration file options that specify time
817: may be expressed using a sequence of the form:
818: .Sm off
819: .Ar time Oo Ar qualifier Oc ,
820: .Sm on
821: where
822: .Ar time
823: is a positive integer value and
824: .Ar qualifier
825: is one of the following:
826: .Pp
827: .Bl -tag -width Ds -compact -offset indent
828: .It Cm <none>
829: seconds
830: .It Cm s | Cm S
831: seconds
832: .It Cm m | Cm M
833: minutes
834: .It Cm h | Cm H
835: hours
836: .It Cm d | Cm D
837: days
838: .It Cm w | Cm W
839: weeks
840: .El
841: .Pp
842: Each member of the sequence is added together to calculate
843: the total time value.
844: .Pp
845: Time format examples:
846: .Pp
847: .Bl -tag -width Ds -compact -offset indent
848: .It 600
849: 600 seconds (10 minutes)
850: .It 10m
851: 10 minutes
852: .It 1h30m
853: 1 hour 30 minutes (90 minutes)
854: .El
1.2 deraadt 855: .Sh LOGIN PROCESS
1.1 deraadt 856: When a user successfully logs in,
1.2 deraadt 857: .Nm
1.1 deraadt 858: does the following:
1.2 deraadt 859: .Bl -enum -offset indent
860: .It
1.1 deraadt 861: If the login is on a tty, and no command has been specified,
1.40 aaron 862: prints last login time and
1.2 deraadt 863: .Pa /etc/motd
1.1 deraadt 864: (unless prevented in the configuration file or by
1.2 deraadt 865: .Pa $HOME/.hushlogin ;
866: see the
1.40 aaron 867: .Sx FILES
1.2 deraadt 868: section).
869: .It
1.1 deraadt 870: If the login is on a tty, records login time.
1.2 deraadt 871: .It
872: Checks
873: .Pa /etc/nologin ;
874: if it exists, prints contents and quits
1.1 deraadt 875: (unless root).
1.2 deraadt 876: .It
1.1 deraadt 877: Changes to run with normal user privileges.
1.2 deraadt 878: .It
1.1 deraadt 879: Sets up basic environment.
1.2 deraadt 880: .It
881: Reads
882: .Pa $HOME/.ssh/environment
883: if it exists.
884: .It
1.1 deraadt 885: Changes to user's home directory.
1.2 deraadt 886: .It
887: If
888: .Pa $HOME/.ssh/rc
889: exists, runs it; else if
890: .Pa /etc/sshrc
891: exists, runs
1.36 aaron 892: it; otherwise runs xauth.
893: The
1.2 deraadt 894: .Dq rc
895: files are given the X11
1.1 deraadt 896: authentication protocol and cookie in standard input.
1.2 deraadt 897: .It
1.1 deraadt 898: Runs user's shell or command.
1.2 deraadt 899: .El
900: .Sh AUTHORIZED_KEYS FILE FORMAT
901: .Pa $HOME/.ssh/authorized_keys
1.130 ! markus 902: is the default file that lists the public keys that are
! 903: permitted for RSA authentication in protocol version 1
! 904: and for public key authentication (PubkeyAuthentication)
! 905: in protocol version 2.
1.125 markus 906: .Cm AuthorizedKeysFile
907: may be used to specify an alternative file.
1.75 markus 908: .Pp
1.36 aaron 909: Each line of the file contains one
1.2 deraadt 910: key (empty lines and lines starting with a
911: .Ql #
912: are ignored as
1.36 aaron 913: comments).
1.75 markus 914: Each RSA public key consists of the following fields, separated by
1.36 aaron 915: spaces: options, bits, exponent, modulus, comment.
1.75 markus 916: Each protocol version 2 public key consists of:
917: options, keytype, base64 encoded key, comment.
918: The options fields
919: are optional; its presence is determined by whether the line starts
1.1 deraadt 920: with a number or not (the option field never starts with a number).
1.75 markus 921: The bits, exponent, modulus and comment fields give the RSA key for
922: protocol version 1; the
1.1 deraadt 923: comment field is not used for anything (but may be convenient for the
924: user to identify the key).
1.75 markus 925: For protocol version 2 the keytype is
926: .Dq ssh-dss
927: or
928: .Dq ssh-rsa .
1.2 deraadt 929: .Pp
1.1 deraadt 930: Note that lines in this file are usually several hundred bytes long
1.36 aaron 931: (because of the size of the RSA key modulus).
932: You don't want to type them in; instead, copy the
1.113 itojun 933: .Pa identity.pub ,
934: .Pa id_dsa.pub
1.75 markus 935: or the
1.113 itojun 936: .Pa id_rsa.pub
1.1 deraadt 937: file and edit it.
1.2 deraadt 938: .Pp
1.58 deraadt 939: The options (if present) consist of comma-separated option
1.36 aaron 940: specifications.
941: No spaces are permitted, except within double quotes.
1.1 deraadt 942: The following option specifications are supported:
1.2 deraadt 943: .Bl -tag -width Ds
944: .It Cm from="pattern-list"
1.1 deraadt 945: Specifies that in addition to RSA authentication, the canonical name
946: of the remote host must be present in the comma-separated list of
1.36 aaron 947: patterns
948: .Pf ( Ql *
949: and
950: .Ql ?
951: serve as wildcards).
952: The list may also contain
953: patterns negated by prefixing them with
954: .Ql ! ;
955: if the canonical host name matches a negated pattern, the key is not accepted.
956: The purpose
1.1 deraadt 957: of this option is to optionally increase security: RSA authentication
958: by itself does not trust the network or name servers or anything (but
959: the key); however, if somebody somehow steals the key, the key
1.36 aaron 960: permits an intruder to log in from anywhere in the world.
961: This additional option makes using a stolen key more difficult (name
1.1 deraadt 962: servers and/or routers would have to be compromised in addition to
963: just the key).
1.2 deraadt 964: .It Cm command="command"
1.1 deraadt 965: Specifies that the command is executed whenever this key is used for
1.36 aaron 966: authentication.
967: The command supplied by the user (if any) is ignored.
1.1 deraadt 968: The command is run on a pty if the connection requests a pty;
1.36 aaron 969: otherwise it is run without a tty.
1.89 markus 970: Note that if you want a 8-bit clean channel,
971: you must not request a pty or should specify
972: .Cm no-pty .
1.36 aaron 973: A quote may be included in the command by quoting it with a backslash.
974: This option might be useful
975: to restrict certain RSA keys to perform just a specific operation.
976: An example might be a key that permits remote backups but nothing else.
1.51 hugh 977: Note that the client may specify TCP/IP and/or X11
978: forwarding unless they are explicitly prohibited.
1.2 deraadt 979: .It Cm environment="NAME=value"
1.1 deraadt 980: Specifies that the string is to be added to the environment when
1.36 aaron 981: logging in using this key.
982: Environment variables set this way
983: override other default environment values.
984: Multiple options of this type are permitted.
1.2 deraadt 985: .It Cm no-port-forwarding
1.1 deraadt 986: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 987: Any port forward requests by the client will return an error.
988: This might be used, e.g., in connection with the
1.2 deraadt 989: .Cm command
1.1 deraadt 990: option.
1.2 deraadt 991: .It Cm no-X11-forwarding
1.1 deraadt 992: Forbids X11 forwarding when this key is used for authentication.
993: Any X11 forward requests by the client will return an error.
1.2 deraadt 994: .It Cm no-agent-forwarding
1.1 deraadt 995: Forbids authentication agent forwarding when this key is used for
996: authentication.
1.2 deraadt 997: .It Cm no-pty
1.1 deraadt 998: Prevents tty allocation (a request to allocate a pty will fail).
1.107 djm 999: .It Cm permitopen="host:port"
1000: Limit local
1001: .Li ``ssh -L''
1.111 stevesk 1002: port forwarding such that it may only connect to the specified host and
1.107 djm 1003: port. Multiple
1004: .Cm permitopen
1.111 stevesk 1005: options may be applied separated by commas. No pattern matching is
1.107 djm 1006: performed on the specified hostnames, they must be literal domains or
1007: addresses.
1.2 deraadt 1008: .El
1009: .Ss Examples
1.1 deraadt 1010: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 1011: .Pp
1.1 deraadt 1012: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 1013: .Pp
1.1 deraadt 1014: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.107 djm 1015: .Pp
1016: permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
1.2 deraadt 1017: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 1018: The
1.44 deraadt 1019: .Pa /etc/ssh_known_hosts ,
1020: .Pa /etc/ssh_known_hosts2 ,
1021: .Pa $HOME/.ssh/known_hosts ,
1.40 aaron 1022: and
1.44 deraadt 1023: .Pa $HOME/.ssh/known_hosts2
1.36 aaron 1024: files contain host public keys for all known hosts.
1025: The global file should
1.37 brad 1026: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 1027: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 1028: its key is added to the per-user file.
1.2 deraadt 1029: .Pp
1.1 deraadt 1030: Each line in these files contains the following fields: hostnames,
1.36 aaron 1031: bits, exponent, modulus, comment.
1032: The fields are separated by spaces.
1.2 deraadt 1033: .Pp
1.1 deraadt 1034: Hostnames is a comma-separated list of patterns ('*' and '?' act as
1035: wildcards); each pattern in turn is matched against the canonical host
1036: name (when authenticating a client) or against the user-supplied
1.36 aaron 1037: name (when authenticating a server).
1038: A pattern may also be preceded by
1.2 deraadt 1039: .Ql !
1040: to indicate negation: if the host name matches a negated
1.1 deraadt 1041: pattern, it is not accepted (by that line) even if it matched another
1042: pattern on the line.
1.2 deraadt 1043: .Pp
1.49 markus 1044: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 1045: can be obtained, e.g., from
1046: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 1047: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 1048: .Pp
1049: Lines starting with
1050: .Ql #
1051: and empty lines are ignored as comments.
1052: .Pp
1.1 deraadt 1053: When performing host authentication, authentication is accepted if any
1.36 aaron 1054: matching line has the proper key.
1055: It is thus permissible (but not
1.1 deraadt 1056: recommended) to have several lines or different host keys for the same
1.36 aaron 1057: names.
1058: This will inevitably happen when short forms of host names
1059: from different domains are put in the file.
1060: It is possible
1.1 deraadt 1061: that the files contain conflicting information; authentication is
1062: accepted if valid information can be found from either file.
1.2 deraadt 1063: .Pp
1.1 deraadt 1064: Note that the lines in these files are typically hundreds of characters
1065: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 1066: Rather, generate them by a script
1.40 aaron 1067: or by taking
1.2 deraadt 1068: .Pa /etc/ssh_host_key.pub
1.1 deraadt 1069: and adding the host names at the front.
1.2 deraadt 1070: .Ss Examples
1.120 markus 1071: .Bd -literal
1072: closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1073: cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....=
1074: .Ed
1.2 deraadt 1075: .Sh FILES
1076: .Bl -tag -width Ds
1077: .It Pa /etc/sshd_config
1.1 deraadt 1078: Contains configuration data for
1.2 deraadt 1079: .Nm sshd .
1.1 deraadt 1080: This file should be writable by root only, but it is recommended
1081: (though not necessary) that it be world-readable.
1.98 deraadt 1082: .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
1.120 markus 1083: These three files contain the private parts of the host keys.
1.98 deraadt 1084: These files should only be owned by root, readable only by root, and not
1.1 deraadt 1085: accessible to others.
1.14 markus 1086: Note that
1087: .Nm
1088: does not start if this file is group/world-accessible.
1.98 deraadt 1089: .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1.120 markus 1090: These three files contain the public parts of the host keys.
1.98 deraadt 1091: These files should be world-readable but writable only by
1.36 aaron 1092: root.
1.98 deraadt 1093: Their contents should match the respective private parts.
1094: These files are not
1095: really used for anything; they are provided for the convenience of
1096: the user so their contents can be copied to known hosts files.
1097: These files are created using
1.7 markus 1098: .Xr ssh-keygen 1 .
1.129 provos 1099: .It Pa /etc/moduli
1.73 provos 1100: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 1101: .It Pa /var/run/sshd.pid
1102: Contains the process ID of the
1103: .Nm
1.1 deraadt 1104: listening for connections (if there are several daemons running
1105: concurrently for different ports, this contains the pid of the one
1.36 aaron 1106: started last).
1.58 deraadt 1107: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 1108: .It Pa $HOME/.ssh/authorized_keys
1.120 markus 1109: Lists the public keys (RSA or DSA) that can be used to log into the user's account.
1.44 deraadt 1110: This file must be readable by root (which may on some machines imply
1111: it being world-readable if the user's home directory resides on an NFS
1112: volume).
1113: It is recommended that it not be accessible by others.
1114: The format of this file is described above.
1115: Users will place the contents of their
1.130 ! markus 1116: .Pa identity.pub ,
1.44 deraadt 1117: .Pa id_dsa.pub
1.113 itojun 1118: and/or
1119: .Pa id_rsa.pub
1.44 deraadt 1120: files into this file, as described in
1121: .Xr ssh-keygen 1 .
1.22 markus 1122: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1123: These files are consulted when using rhosts with RSA host
1.36 aaron 1124: authentication to check the public key of the host.
1125: The key must be listed in one of these files to be accepted.
1.22 markus 1126: The client uses the same files
1.96 markus 1127: to verify that it is connecting to the correct remote host.
1.36 aaron 1128: These files should be writable only by root/the owner.
1.2 deraadt 1129: .Pa /etc/ssh_known_hosts
1130: should be world-readable, and
1131: .Pa $HOME/.ssh/known_hosts
1132: can but need not be world-readable.
1.120 markus 1133: .It Pa "/etc/ssh_known_hosts2" and "$HOME/.ssh/known_hosts2"
1134: These files are consulted when using protocol version 2 hostbased
1135: authentication to check the public key of the host.
1136: The key must be listed in one of these files to be accepted.
1137: The client uses the same files
1138: to verify that it is connecting to the correct remote host.
1139: These files should be writable only by root/the owner.
1140: .Pa /etc/ssh_known_hosts2
1141: should be world-readable, and
1142: .Pa $HOME/.ssh/known_hosts2
1143: can but need not be world-readable.
1.6 aaron 1144: .It Pa /etc/nologin
1.40 aaron 1145: If this file exists,
1.2 deraadt 1146: .Nm
1.36 aaron 1147: refuses to let anyone except root log in.
1148: The contents of the file
1.1 deraadt 1149: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 1150: refused.
1151: The file should be world-readable.
1.19 dugsong 1152: .It Pa /etc/hosts.allow, /etc/hosts.deny
1153: If compiled with
1154: .Sy LIBWRAP
1155: support, tcp-wrappers access controls may be defined here as described in
1156: .Xr hosts_access 5 .
1.6 aaron 1157: .It Pa $HOME/.rhosts
1.1 deraadt 1158: This file contains host-username pairs, separated by a space, one per
1.36 aaron 1159: line.
1160: The given user on the corresponding host is permitted to log in
1161: without password.
1162: The same file is used by rlogind and rshd.
1.6 aaron 1163: The file must
1.1 deraadt 1164: be writable only by the user; it is recommended that it not be
1165: accessible by others.
1.2 deraadt 1166: .Pp
1.36 aaron 1167: If is also possible to use netgroups in the file.
1168: Either host or user
1.1 deraadt 1169: name may be of the form +@groupname to specify all hosts or all users
1170: in the group.
1.2 deraadt 1171: .It Pa $HOME/.shosts
1172: For ssh,
1173: this file is exactly the same as for
1174: .Pa .rhosts .
1175: However, this file is
1176: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 1177: .It Pa /etc/hosts.equiv
1.2 deraadt 1178: This file is used during
1179: .Pa .rhosts
1.36 aaron 1180: authentication.
1181: In the simplest form, this file contains host names, one per line.
1182: Users on
1.1 deraadt 1183: those hosts are permitted to log in without a password, provided they
1.36 aaron 1184: have the same user name on both machines.
1185: The host name may also be
1.1 deraadt 1186: followed by a user name; such users are permitted to log in as
1.2 deraadt 1187: .Em any
1.36 aaron 1188: user on this machine (except root).
1189: Additionally, the syntax
1.2 deraadt 1190: .Dq +@group
1.36 aaron 1191: can be used to specify netgroups.
1192: Negated entries start with
1.2 deraadt 1193: .Ql \&- .
1194: .Pp
1.1 deraadt 1195: If the client host/user is successfully matched in this file, login is
1196: automatically permitted provided the client and server user names are the
1.36 aaron 1197: same.
1198: Additionally, successful RSA host authentication is normally required.
1199: This file must be writable only by root; it is recommended
1.1 deraadt 1200: that it be world-readable.
1.2 deraadt 1201: .Pp
1.6 aaron 1202: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1203: .Pa hosts.equiv .
1.1 deraadt 1204: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1205: .Em anybody ,
1.1 deraadt 1206: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1207: binaries and directories.
1208: Using a user name practically grants the user root access.
1209: The only valid use for user names that I can think
1.1 deraadt 1210: of is in negative entries.
1.2 deraadt 1211: .Pp
1212: Note that this warning also applies to rsh/rlogin.
1213: .It Pa /etc/shosts.equiv
1.1 deraadt 1214: This is processed exactly as
1.2 deraadt 1215: .Pa /etc/hosts.equiv .
1.1 deraadt 1216: However, this file may be useful in environments that want to run both
1.2 deraadt 1217: rsh/rlogin and ssh.
1.6 aaron 1218: .It Pa $HOME/.ssh/environment
1.36 aaron 1219: This file is read into the environment at login (if it exists).
1220: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1221: .Ql # ) ,
1.36 aaron 1222: and assignment lines of the form name=value.
1223: The file should be writable
1.6 aaron 1224: only by the user; it need not be readable by anyone else.
1.2 deraadt 1225: .It Pa $HOME/.ssh/rc
1.1 deraadt 1226: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1227: environment files but before starting the user's shell or command.
1228: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1229: standard input (and
1230: .Ev DISPLAY
1.36 aaron 1231: in environment).
1232: This must call
1.2 deraadt 1233: .Xr xauth 1
1234: in that case.
1235: .Pp
1.1 deraadt 1236: The primary purpose of this file is to run any initialization routines
1237: which may be needed before the user's home directory becomes
1238: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1239: .Pp
1.1 deraadt 1240: This file will probably contain some initialization code followed by
1.120 markus 1241: something similar to:
1242: .Bd -literal
1243: if read proto cookie; then
1244: echo add $DISPLAY $proto $cookie | xauth -q -
1245: fi
1246: .Ed
1.2 deraadt 1247: .Pp
1248: If this file does not exist,
1249: .Pa /etc/sshrc
1250: is run, and if that
1.1 deraadt 1251: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1252: .Pp
1.1 deraadt 1253: This file should be writable only by the user, and need not be
1254: readable by anyone else.
1.2 deraadt 1255: .It Pa /etc/sshrc
1256: Like
1257: .Pa $HOME/.ssh/rc .
1258: This can be used to specify
1.36 aaron 1259: machine-specific login-time initializations globally.
1260: This file should be writable only by root, and should be world-readable.
1.56 aaron 1261: .El
1.71 aaron 1262: .Sh AUTHORS
1.84 markus 1263: OpenSSH is a derivative of the original and free
1264: ssh 1.2.12 release by Tatu Ylonen.
1265: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1266: Theo de Raadt and Dug Song
1267: removed many bugs, re-added newer features and
1268: created OpenSSH.
1269: Markus Friedl contributed the support for SSH
1270: protocol versions 1.5 and 2.0.
1.2 deraadt 1271: .Sh SEE ALSO
1.129 provos 1272: .Xr moduli 5 ,
1.128 mpech 1273: .Xr rlogin 1 ,
1274: .Xr rsh 1 ,
1.2 deraadt 1275: .Xr scp 1 ,
1.90 djm 1276: .Xr sftp 1 ,
1.2 deraadt 1277: .Xr ssh 1 ,
1.5 deraadt 1278: .Xr ssh-add 1 ,
1.2 deraadt 1279: .Xr ssh-agent 1 ,
1.5 deraadt 1280: .Xr ssh-keygen 1 ,
1.128 mpech 1281: .Xr sftp-server 8
1.119 markus 1282: .Rs
1283: .%A T. Ylonen
1284: .%A T. Kivinen
1285: .%A M. Saarinen
1286: .%A T. Rinne
1287: .%A S. Lehtinen
1288: .%T "SSH Protocol Architecture"
1289: .%N draft-ietf-secsh-architecture-07.txt
1.120 markus 1290: .%D January 2001
1291: .%O work in progress material
1292: .Re
1293: .Rs
1294: .%A M. Friedl
1295: .%A N. Provos
1296: .%A W. A. Simpson
1297: .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol"
1298: .%N draft-ietf-secsh-dh-group-exchange-00.txt
1.119 markus 1299: .%D January 2001
1300: .%O work in progress material
1301: .Re
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