Annotation of src/usr.bin/ssh/sshd.8, Revision 1.134
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: .\"
1.134 ! mpech 37: .\" $OpenBSD: sshd.8,v 1.133 2001/06/23 17:48:19 itojun 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: .It Fl d
1.36 aaron 188: Debug mode.
189: The server sends verbose debug output to the system
190: log, and does not put itself in the background.
191: The server also will not fork and will only process one connection.
192: This option is only intended for debugging for the server.
1.120 markus 193: Multiple -d options increase the debugging level.
1.67 aaron 194: Maximum is 3.
1.120 markus 195: .It Fl e
196: When this option is specified,
197: .Nm
198: will send the output to the standard error instead of the system log.
1.2 deraadt 199: .It Fl f Ar configuration_file
1.36 aaron 200: Specifies the name of the configuration file.
201: The default is
1.2 deraadt 202: .Pa /etc/sshd_config .
1.16 markus 203: .Nm
204: refuses to start if there is no configuration file.
1.2 deraadt 205: .It Fl g Ar login_grace_time
1.1 deraadt 206: Gives the grace time for clients to authenticate themselves (default
1.77 markus 207: 600 seconds).
1.36 aaron 208: If the client fails to authenticate the user within
209: this many seconds, the server disconnects and exits.
210: A value of zero indicates no limit.
1.2 deraadt 211: .It Fl h Ar host_key_file
1.75 markus 212: Specifies the file from which the host key is read (default
1.2 deraadt 213: .Pa /etc/ssh_host_key ) .
1.7 markus 214: This option must be given if
215: .Nm
216: is not run as root (as the normal
1.1 deraadt 217: host file is normally not readable by anyone but root).
1.75 markus 218: It is possible to have multiple host key files for
1.120 markus 219: the different protocol versions and host key algorithms.
1.2 deraadt 220: .It Fl i
1.7 markus 221: Specifies that
222: .Nm
1.40 aaron 223: is being run from inetd.
1.7 markus 224: .Nm
225: is normally not run
1.1 deraadt 226: from inetd because it needs to generate the server key before it can
1.36 aaron 227: respond to the client, and this may take tens of seconds.
228: Clients would have to wait too long if the key was regenerated every time.
1.35 aaron 229: However, with small key sizes (e.g., 512) using
1.7 markus 230: .Nm
231: from inetd may
1.1 deraadt 232: be feasible.
1.2 deraadt 233: .It Fl k Ar key_gen_time
1.120 markus 234: Specifies how often the ephemeral protocol version 1 server key is
235: regenerated (default 3600 seconds, or one hour).
1.36 aaron 236: The motivation for regenerating the key fairly
1.1 deraadt 237: often is that the key is not stored anywhere, and after about an hour,
238: it becomes impossible to recover the key for decrypting intercepted
239: communications even if the machine is cracked into or physically
1.36 aaron 240: seized.
241: A value of zero indicates that the key will never be regenerated.
1.2 deraadt 242: .It Fl p Ar port
1.1 deraadt 243: Specifies the port on which the server listens for connections
244: (default 22).
1.2 deraadt 245: .It Fl q
1.36 aaron 246: Quiet mode.
247: Nothing is sent to the system log.
248: Normally the beginning,
1.1 deraadt 249: authentication, and termination of each connection is logged.
1.61 markus 250: .It Fl u Ar len
251: This option is used to specify the size of the field
252: in the
253: .Li utmp
254: structure that holds the remote host name.
255: If the resolved host name is longer than
256: .Ar len ,
257: the dotted decimal value will be used instead.
258: This allows hosts with very long host names that
259: overflow this field to still be uniquely identified.
260: Specifying
261: .Fl u0
262: indicates that only dotted decimal addresses
263: should be put into the
264: .Pa utmp
265: file.
1.74 markus 266: .It Fl D
267: When this option is specified
268: .Nm
269: will not detach and does not become a daemon.
270: This allows easy monitoring of
1.76 markus 271: .Nm sshd .
1.29 markus 272: .It Fl 4
273: Forces
274: .Nm
275: to use IPv4 addresses only.
276: .It Fl 6
277: Forces
278: .Nm
279: to use IPv6 addresses only.
1.2 deraadt 280: .El
281: .Sh CONFIGURATION FILE
282: .Nm
1.40 aaron 283: reads configuration data from
1.2 deraadt 284: .Pa /etc/sshd_config
285: (or the file specified with
286: .Fl f
1.36 aaron 287: on the command line).
288: The file contains keyword-value pairs, one per line.
289: Lines starting with
1.2 deraadt 290: .Ql #
1.1 deraadt 291: and empty lines are interpreted as comments.
1.2 deraadt 292: .Pp
1.1 deraadt 293: The following keywords are possible.
1.2 deraadt 294: .Bl -tag -width Ds
295: .It Cm AFSTokenPassing
1.36 aaron 296: Specifies whether an AFS token may be forwarded to the server.
297: Default is
1.2 deraadt 298: .Dq yes .
1.11 markus 299: .It Cm AllowGroups
1.92 deraadt 300: This keyword can be followed by a list of group names, separated
1.36 aaron 301: by spaces.
302: If specified, login is allowed only for users whose primary
1.81 markus 303: group or supplementary group list matches one of the patterns.
1.11 markus 304: .Ql \&*
305: and
306: .Ql ?
307: can be used as
1.36 aaron 308: wildcards in the patterns.
1.58 deraadt 309: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 310: By default login is allowed regardless of the group list.
1.3 dugsong 311: .Pp
1.69 markus 312: .It Cm AllowTcpForwarding
313: Specifies whether TCP forwarding is permitted.
314: The default is
315: .Dq yes .
316: Note that disabling TCP forwarding does not improve security unless
317: users are also denied shell access, as they can always install their
318: own forwarders.
319: .Pp
1.11 markus 320: .It Cm AllowUsers
1.92 deraadt 321: This keyword can be followed by a list of user names, separated
1.36 aaron 322: by spaces.
323: If specified, login is allowed only for users names that
1.11 markus 324: match one of the patterns.
325: .Ql \&*
326: and
327: .Ql ?
328: can be used as
1.36 aaron 329: wildcards in the patterns.
1.58 deraadt 330: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 331: By default login is allowed regardless of the user name.
1.80 markus 332: .Pp
1.125 markus 333: .It Cm AuthorizedKeysFile
334: Specifies the file that contains the public RSA keys that can be used
335: for RSA authentication in protocol version 1.
336: .Cm AuthorizedKeysFile
337: may contain tokens of the form %T which are substituted during connection
338: set-up. The following tokens are defined; %% is replaces by a literal '%',
339: %h is replaced by the home directory of the user being authenticated and
340: %u is replaced by the username of that user.
341: After expansion,
342: .Cm AuthorizedKeysFile
1.126 markus 343: is taken to be an absolute path or one relative to the user's home
1.125 markus 344: directory.
345: The default is
346: .Dq .ssh/authorized_keys
1.80 markus 347: .It Cm Banner
348: In some jurisdictions, sending a warning message before authentication
349: may be relevant for getting legal protection.
350: The contents of the specified file are sent to the remote user before
351: authentication is allowed.
352: This option is only available for protocol version 2.
1.11 markus 353: .Pp
1.104 deraadt 354: .It Cm ChallengeResponseAuthentication
355: Specifies whether
356: challenge response
357: authentication is allowed.
358: Currently there is only support for
359: .Xr skey 1
360: authentication.
361: The default is
362: .Dq yes .
1.8 markus 363: .It Cm CheckMail
364: Specifies whether
365: .Nm
366: should check for new mail for interactive logins.
367: The default is
368: .Dq no .
1.122 markus 369: .It Cm Ciphers
370: Specifies the ciphers allowed for protocol version 2.
371: Multiple ciphers must be comma-separated.
372: The default is
373: .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
1.115 beck 374: .It Cm ClientAliveInterval
375: Sets a timeout interval in seconds after which if no data has been received
1.133 itojun 376: from the client,
1.115 beck 377: .Nm
378: will send a message through the encrypted
1.116 stevesk 379: channel to request a response from the client.
380: The default
1.115 beck 381: is 0, indicating that these messages will not be sent to the client.
1.116 stevesk 382: This option applies to protocol version 2 only.
1.115 beck 383: .It Cm ClientAliveCountMax
384: Sets the number of client alive messages (see above) which may be
385: sent without
386: .Nm
387: receiving any messages back from the client. If this threshold is
1.133 itojun 388: reached while client alive messages are being sent,
1.115 beck 389: .Nm
390: will disconnect the client, terminating the session. It is important
1.133 itojun 391: to note that the use of client alive messages is very different from
1.116 stevesk 392: .Cm Keepalive
393: (below). The client alive messages are sent through the
1.115 beck 394: encrypted channel and therefore will not be spoofable. The TCP keepalive
1.116 stevesk 395: option enabled by
396: .Cm Keepalive
397: is spoofable. You want to use the client
1.115 beck 398: alive mechanism when you are basing something important on
399: clients having an active connection to the server.
1.116 stevesk 400: .Pp
401: The default value is 3. If you set
402: .Cm ClientAliveInterval
1.115 beck 403: (above) to 15, and leave this value at the default, unresponsive ssh clients
1.133 itojun 404: will be disconnected after approximately 45 seconds.
1.11 markus 405: .It Cm DenyGroups
406: This keyword can be followed by a number of group names, separated
1.36 aaron 407: by spaces.
1.81 markus 408: Users whose primary group or supplementary group list matches
409: one of the patterns aren't allowed to log in.
1.11 markus 410: .Ql \&*
411: and
412: .Ql ?
413: can be used as
1.36 aaron 414: wildcards in the patterns.
1.58 deraadt 415: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 416: By default login is allowed regardless of the group list.
1.11 markus 417: .Pp
418: .It Cm DenyUsers
419: This keyword can be followed by a number of user names, separated
1.36 aaron 420: by spaces.
421: Login is disallowed for user names that match one of the patterns.
1.11 markus 422: .Ql \&*
423: and
424: .Ql ?
1.36 aaron 425: can be used as wildcards in the patterns.
1.58 deraadt 426: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 427: By default login is allowed regardless of the user name.
1.47 markus 428: .It Cm GatewayPorts
429: Specifies whether remote hosts are allowed to connect to ports
430: forwarded for the client.
431: The argument must be
432: .Dq yes
433: or
434: .Dq no .
435: The default is
436: .Dq no .
1.120 markus 437: .It Cm HostbasedAuthentication
438: Specifies whether rhosts or /etc/hosts.equiv authentication together
439: with successful public key client host authentication is allowed
440: (hostbased authentication).
441: This option is similar to
442: .Cm RhostsRSAAuthentication
443: and applies to protocol version 2 only.
444: The default is
445: .Dq no .
1.2 deraadt 446: .It Cm HostKey
1.72 markus 447: Specifies the file containing the private host keys (default
1.46 markus 448: .Pa /etc/ssh_host_key )
1.72 markus 449: used by SSH protocol versions 1 and 2.
1.9 markus 450: Note that
451: .Nm
1.83 markus 452: will refuse to use a file if it is group/world-accessible.
1.72 markus 453: It is possible to have multiple host key files.
454: .Dq rsa1
455: keys are used for version 1 and
456: .Dq dsa
457: or
458: .Dq rsa
459: are used for version 2 of the SSH protocol.
1.2 deraadt 460: .It Cm IgnoreRhosts
1.34 markus 461: Specifies that
462: .Pa .rhosts
1.40 aaron 463: and
1.34 markus 464: .Pa .shosts
1.120 markus 465: files will not be used in
466: .Cm RhostsAuthentication ,
467: .Cm RhostsRSAAuthentication
468: or
469: .Cm HostbasedAuthentication .
470: .Pp
1.2 deraadt 471: .Pa /etc/hosts.equiv
1.1 deraadt 472: and
1.40 aaron 473: .Pa /etc/shosts.equiv
1.36 aaron 474: are still used.
1.40 aaron 475: The default is
1.34 markus 476: .Dq yes .
1.24 markus 477: .It Cm IgnoreUserKnownHosts
478: Specifies whether
479: .Nm
480: should ignore the user's
481: .Pa $HOME/.ssh/known_hosts
1.45 markus 482: during
1.120 markus 483: .Cm RhostsRSAAuthentication
484: or
485: .Cm HostbasedAuthentication .
1.24 markus 486: The default is
1.2 deraadt 487: .Dq no .
488: .It Cm KeepAlive
1.1 deraadt 489: Specifies whether the system should send keepalive messages to the
1.36 aaron 490: other side.
491: If they are sent, death of the connection or crash of one
492: of the machines will be properly noticed.
493: However, this means that
1.1 deraadt 494: connections will die if the route is down temporarily, and some people
1.36 aaron 495: find it annoying.
1.51 hugh 496: On the other hand, if keepalives are not sent,
1.2 deraadt 497: sessions may hang indefinitely on the server, leaving
498: .Dq ghost
499: users and consuming server resources.
500: .Pp
501: The default is
502: .Dq yes
503: (to send keepalives), and the server will notice
1.36 aaron 504: if the network goes down or the client host reboots.
505: This avoids infinitely hanging sessions.
1.2 deraadt 506: .Pp
507: To disable keepalives, the value should be set to
508: .Dq no
509: in both the server and the client configuration files.
510: .It Cm KerberosAuthentication
1.36 aaron 511: Specifies whether Kerberos authentication is allowed.
512: This can be in the form of a Kerberos ticket, or if
1.7 markus 513: .Cm PasswordAuthentication
1.1 deraadt 514: is yes, the password provided by the user will be validated through
1.67 aaron 515: the Kerberos KDC.
516: To use this option, the server needs a
1.59 provos 517: Kerberos servtab which allows the verification of the KDC's identity.
1.36 aaron 518: Default is
1.60 provos 519: .Dq yes .
1.2 deraadt 520: .It Cm KerberosOrLocalPasswd
1.1 deraadt 521: If set then if password authentication through Kerberos fails then
522: the password will be validated via any additional local mechanism
1.2 deraadt 523: such as
1.66 markus 524: .Pa /etc/passwd .
1.36 aaron 525: Default is
1.20 dugsong 526: .Dq yes .
1.2 deraadt 527: .It Cm KerberosTgtPassing
1.1 deraadt 528: Specifies whether a Kerberos TGT may be forwarded to the server.
1.40 aaron 529: Default is
1.3 dugsong 530: .Dq no ,
531: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 532: .It Cm KerberosTicketCleanup
1.7 markus 533: Specifies whether to automatically destroy the user's ticket cache
1.36 aaron 534: file on logout.
535: Default is
1.3 dugsong 536: .Dq yes .
1.2 deraadt 537: .It Cm KeyRegenerationInterval
1.120 markus 538: In protocol version 1, the ephemeral server key is automatically regenerated
539: after this many seconds (if it has been used).
1.36 aaron 540: The purpose of regeneration is to prevent
1.1 deraadt 541: decrypting captured sessions by later breaking into the machine and
1.36 aaron 542: stealing the keys.
543: The key is never stored anywhere.
544: If the value is 0, the key is never regenerated.
545: The default is 3600 (seconds).
1.7 markus 546: .It Cm ListenAddress
1.110 stevesk 547: Specifies the local addresses
1.120 markus 548: .Nm
1.7 markus 549: should listen on.
1.110 stevesk 550: The following forms may be used:
551: .Pp
552: .Bl -item -offset indent -compact
553: .It
554: .Cm ListenAddress
1.112 stevesk 555: .Sm off
556: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
557: .Sm on
1.110 stevesk 558: .It
559: .Cm ListenAddress
1.112 stevesk 560: .Sm off
561: .Ar host No | Ar IPv4_addr No : Ar port
562: .Sm on
1.110 stevesk 563: .It
564: .Cm ListenAddress
1.112 stevesk 565: .Sm off
566: .Oo
567: .Ar host No | Ar IPv6_addr Oc : Ar port
568: .Sm on
1.110 stevesk 569: .El
570: .Pp
571: If
1.112 stevesk 572: .Ar port
1.110 stevesk 573: is not specified,
1.120 markus 574: .Nm
1.110 stevesk 575: will listen on the address and all prior
576: .Cm Port
577: options specified. The default is to listen on all local
578: addresses. Multiple
579: .Cm ListenAddress
580: options are permitted. Additionally, any
581: .Cm Port
582: options must precede this option for non port qualified addresses.
1.2 deraadt 583: .It Cm LoginGraceTime
1.1 deraadt 584: The server disconnects after this time if the user has not
1.36 aaron 585: successfully logged in.
586: If the value is 0, there is no time limit.
1.1 deraadt 587: The default is 600 (seconds).
1.23 markus 588: .It Cm LogLevel
589: Gives the verbosity level that is used when logging messages from
590: .Nm sshd .
591: The possible values are:
1.82 markus 592: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
593: The default is INFO.
1.23 markus 594: Logging with level DEBUG violates the privacy of users
595: and is not recommended.
1.93 markus 596: .It Cm MACs
597: Specifies the available MAC (message authentication code) algorithms.
598: The MAC algorithm is used in protocol version 2
599: for data integrity protection.
600: Multiple algorithms must be comma-separated.
601: The default is
1.123 markus 602: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
1.55 markus 603: .It Cm MaxStartups
604: Specifies the maximum number of concurrent unauthenticated connections to the
605: .Nm
606: daemon.
607: Additional connections will be dropped until authentication succeeds or the
608: .Cm LoginGraceTime
609: expires for a connection.
610: The default is 10.
1.57 markus 611: .Pp
612: Alternatively, random early drop can be enabled by specifying
613: the three colon separated values
614: .Dq start:rate:full
1.67 aaron 615: (e.g., "10:30:60").
1.57 markus 616: .Nm
1.86 stevesk 617: will refuse connection attempts with a probability of
1.57 markus 618: .Dq rate/100
619: (30%)
620: if there are currently
621: .Dq start
622: (10)
623: unauthenticated connections.
1.86 stevesk 624: The probability increases linearly and all connection attempts
1.57 markus 625: are refused if the number of unauthenticated connections reaches
626: .Dq full
627: (60).
1.2 deraadt 628: .It Cm PasswordAuthentication
1.1 deraadt 629: Specifies whether password authentication is allowed.
1.2 deraadt 630: The default is
631: .Dq yes .
632: .It Cm PermitEmptyPasswords
1.1 deraadt 633: When password authentication is allowed, it specifies whether the
1.36 aaron 634: server allows login to accounts with empty password strings.
635: The default is
1.34 markus 636: .Dq no .
1.2 deraadt 637: .It Cm PermitRootLogin
1.100 stevesk 638: Specifies whether root can login using
1.2 deraadt 639: .Xr ssh 1 .
1.15 markus 640: The argument must be
641: .Dq yes ,
1.94 markus 642: .Dq without-password ,
643: .Dq forced-commands-only
1.15 markus 644: or
645: .Dq no .
1.2 deraadt 646: The default is
647: .Dq yes .
1.94 markus 648: .Pp
649: If this option is set to
1.15 markus 650: .Dq without-password
1.94 markus 651: password authentication is disabled for root.
1.2 deraadt 652: .Pp
1.94 markus 653: If this option is set to
654: .Dq forced-commands-only
655: root login with public key authentication will be allowed,
656: but only if the
1.2 deraadt 657: .Ar command
1.94 markus 658: option has been specified
1.1 deraadt 659: (which may be useful for taking remote backups even if root login is
1.94 markus 660: normally not allowed). All other authentication methods are disabled
661: for root.
1.100 stevesk 662: .Pp
663: If this option is set to
664: .Dq no
665: root is not allowed to login.
1.43 markus 666: .It Cm PidFile
667: Specifies the file that contains the process identifier of the
668: .Nm
669: daemon.
670: The default is
671: .Pa /var/run/sshd.pid .
1.2 deraadt 672: .It Cm Port
1.1 deraadt 673: Specifies the port number that
1.2 deraadt 674: .Nm
1.36 aaron 675: listens on.
676: The default is 22.
1.28 markus 677: Multiple options of this type are permitted.
1.120 markus 678: See also
679: .Cm ListenAddress .
1.108 stevesk 680: .It Cm PrintLastLog
681: Specifies whether
682: .Nm
683: should print the date and time when the user last logged in.
684: The default is
685: .Dq yes .
1.2 deraadt 686: .It Cm PrintMotd
1.1 deraadt 687: Specifies whether
1.2 deraadt 688: .Nm
1.40 aaron 689: should print
1.2 deraadt 690: .Pa /etc/motd
1.36 aaron 691: when a user logs in interactively.
692: (On some systems it is also printed by the shell,
1.2 deraadt 693: .Pa /etc/profile ,
1.36 aaron 694: or equivalent.)
695: The default is
1.2 deraadt 696: .Dq yes .
1.41 markus 697: .It Cm Protocol
698: Specifies the protocol versions
699: .Nm
700: should support.
701: The possible values are
702: .Dq 1
703: and
704: .Dq 2 .
705: Multiple versions must be comma-separated.
706: The default is
1.118 deraadt 707: .Dq 2,1 .
1.104 deraadt 708: .It Cm PubkeyAuthentication
709: Specifies whether public key authentication is allowed.
710: The default is
711: .Dq yes .
712: Note that this option applies to protocol version 2 only.
1.87 markus 713: .It Cm ReverseMappingCheck
714: Specifies whether
715: .Nm
716: should try to verify the remote host name and check that
717: the resolved host name for the remote IP address maps back to the
718: very same IP address.
719: The default is
720: .Dq no .
1.2 deraadt 721: .It Cm RhostsAuthentication
1.1 deraadt 722: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 723: files is sufficient.
724: Normally, this method should not be permitted because it is insecure.
1.7 markus 725: .Cm RhostsRSAAuthentication
726: should be used
1.1 deraadt 727: instead, because it performs RSA-based host authentication in addition
728: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 729: The default is
730: .Dq no .
1.120 markus 731: This option applies to protocol version 1 only.
1.2 deraadt 732: .It Cm RhostsRSAAuthentication
1.1 deraadt 733: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 734: with successful RSA host authentication is allowed.
735: The default is
1.34 markus 736: .Dq no .
1.120 markus 737: This option applies to protocol version 1 only.
1.2 deraadt 738: .It Cm RSAAuthentication
1.36 aaron 739: Specifies whether pure RSA authentication is allowed.
740: The default is
1.2 deraadt 741: .Dq yes .
1.120 markus 742: This option applies to protocol version 1 only.
1.2 deraadt 743: .It Cm ServerKeyBits
1.120 markus 744: Defines the number of bits in the ephemeral protocol version 1 server key.
1.36 aaron 745: The minimum value is 512, and the default is 768.
1.2 deraadt 746: .It Cm StrictModes
1.12 markus 747: Specifies whether
748: .Nm
749: should check file modes and ownership of the
1.36 aaron 750: user's files and home directory before accepting login.
751: This is normally desirable because novices sometimes accidentally leave their
752: directory or files world-writable.
753: The default is
1.7 markus 754: .Dq yes .
1.54 jakob 755: .It Cm Subsystem
1.67 aaron 756: Configures an external subsystem (e.g., file transfer daemon).
757: Arguments should be a subsystem name and a command to execute upon subsystem
758: request.
1.63 markus 759: The command
760: .Xr sftp-server 8
761: implements the
762: .Dq sftp
763: file transfer subsystem.
1.54 jakob 764: By default no subsystems are defined.
765: Note that this option applies to protocol version 2 only.
1.2 deraadt 766: .It Cm SyslogFacility
1.1 deraadt 767: Gives the facility code that is used when logging messages from
1.2 deraadt 768: .Nm sshd .
1.1 deraadt 769: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 770: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
771: The default is AUTH.
1.10 markus 772: .It Cm UseLogin
773: Specifies whether
774: .Xr login 1
1.53 markus 775: is used for interactive login sessions.
1.127 markus 776: The default is
777: .Dq no .
1.53 markus 778: Note that
779: .Xr login 1
1.58 deraadt 780: is never used for remote command execution.
1.133 itojun 781: Note also, that if this is enabled,
782: .Cm X11Forwarding
1.127 markus 783: will be disabled because
784: .Xr login 1
785: does not know how to handle
1.133 itojun 786: .Xr xauth 1
1.127 markus 787: cookies.
1.6 aaron 788: .It Cm X11DisplayOffset
789: Specifies the first display number available for
790: .Nm sshd Ns 's
1.36 aaron 791: X11 forwarding.
792: This prevents
1.6 aaron 793: .Nm
794: from interfering with real X11 servers.
1.34 markus 795: The default is 10.
1.30 markus 796: .It Cm X11Forwarding
1.36 aaron 797: Specifies whether X11 forwarding is permitted.
798: The default is
1.34 markus 799: .Dq no .
1.30 markus 800: Note that disabling X11 forwarding does not improve security in any
801: way, as users can always install their own forwarders.
1.133 itojun 802: X11 forwarding is automatically disabled if
803: .Cm UseLogin
804: is enabled.
1.52 markus 805: .It Cm XAuthLocation
806: Specifies the location of the
807: .Xr xauth 1
808: program.
809: The default is
810: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 811: .El
1.124 stevesk 812: .Ss Time Formats
813: .Pp
814: .Nm
815: command-line arguments and configuration file options that specify time
816: may be expressed using a sequence of the form:
817: .Sm off
818: .Ar time Oo Ar qualifier Oc ,
819: .Sm on
820: where
821: .Ar time
822: is a positive integer value and
823: .Ar qualifier
824: is one of the following:
825: .Pp
826: .Bl -tag -width Ds -compact -offset indent
827: .It Cm <none>
828: seconds
829: .It Cm s | Cm S
830: seconds
831: .It Cm m | Cm M
832: minutes
833: .It Cm h | Cm H
834: hours
835: .It Cm d | Cm D
836: days
837: .It Cm w | Cm W
838: weeks
839: .El
840: .Pp
841: Each member of the sequence is added together to calculate
842: the total time value.
843: .Pp
844: Time format examples:
845: .Pp
846: .Bl -tag -width Ds -compact -offset indent
847: .It 600
848: 600 seconds (10 minutes)
849: .It 10m
850: 10 minutes
851: .It 1h30m
852: 1 hour 30 minutes (90 minutes)
853: .El
1.2 deraadt 854: .Sh LOGIN PROCESS
1.1 deraadt 855: When a user successfully logs in,
1.2 deraadt 856: .Nm
1.1 deraadt 857: does the following:
1.2 deraadt 858: .Bl -enum -offset indent
859: .It
1.1 deraadt 860: If the login is on a tty, and no command has been specified,
1.40 aaron 861: prints last login time and
1.2 deraadt 862: .Pa /etc/motd
1.1 deraadt 863: (unless prevented in the configuration file or by
1.2 deraadt 864: .Pa $HOME/.hushlogin ;
865: see the
1.40 aaron 866: .Sx FILES
1.2 deraadt 867: section).
868: .It
1.1 deraadt 869: If the login is on a tty, records login time.
1.2 deraadt 870: .It
871: Checks
872: .Pa /etc/nologin ;
873: if it exists, prints contents and quits
1.1 deraadt 874: (unless root).
1.2 deraadt 875: .It
1.1 deraadt 876: Changes to run with normal user privileges.
1.2 deraadt 877: .It
1.1 deraadt 878: Sets up basic environment.
1.2 deraadt 879: .It
880: Reads
881: .Pa $HOME/.ssh/environment
882: if it exists.
883: .It
1.1 deraadt 884: Changes to user's home directory.
1.2 deraadt 885: .It
886: If
887: .Pa $HOME/.ssh/rc
888: exists, runs it; else if
889: .Pa /etc/sshrc
890: exists, runs
1.36 aaron 891: it; otherwise runs xauth.
892: The
1.2 deraadt 893: .Dq rc
894: files are given the X11
1.1 deraadt 895: authentication protocol and cookie in standard input.
1.2 deraadt 896: .It
1.1 deraadt 897: Runs user's shell or command.
1.2 deraadt 898: .El
899: .Sh AUTHORIZED_KEYS FILE FORMAT
900: .Pa $HOME/.ssh/authorized_keys
1.130 markus 901: is the default file that lists the public keys that are
902: permitted for RSA authentication in protocol version 1
903: and for public key authentication (PubkeyAuthentication)
904: in protocol version 2.
1.125 markus 905: .Cm AuthorizedKeysFile
906: may be used to specify an alternative file.
1.75 markus 907: .Pp
1.36 aaron 908: Each line of the file contains one
1.2 deraadt 909: key (empty lines and lines starting with a
910: .Ql #
911: are ignored as
1.36 aaron 912: comments).
1.75 markus 913: Each RSA public key consists of the following fields, separated by
1.36 aaron 914: spaces: options, bits, exponent, modulus, comment.
1.75 markus 915: Each protocol version 2 public key consists of:
916: options, keytype, base64 encoded key, comment.
917: The options fields
918: are optional; its presence is determined by whether the line starts
1.1 deraadt 919: with a number or not (the option field never starts with a number).
1.75 markus 920: The bits, exponent, modulus and comment fields give the RSA key for
921: protocol version 1; the
1.1 deraadt 922: comment field is not used for anything (but may be convenient for the
923: user to identify the key).
1.75 markus 924: For protocol version 2 the keytype is
925: .Dq ssh-dss
926: or
927: .Dq ssh-rsa .
1.2 deraadt 928: .Pp
1.1 deraadt 929: Note that lines in this file are usually several hundred bytes long
1.36 aaron 930: (because of the size of the RSA key modulus).
931: You don't want to type them in; instead, copy the
1.113 itojun 932: .Pa identity.pub ,
933: .Pa id_dsa.pub
1.75 markus 934: or the
1.113 itojun 935: .Pa id_rsa.pub
1.1 deraadt 936: file and edit it.
1.2 deraadt 937: .Pp
1.58 deraadt 938: The options (if present) consist of comma-separated option
1.36 aaron 939: specifications.
940: No spaces are permitted, except within double quotes.
1.1 deraadt 941: The following option specifications are supported:
1.2 deraadt 942: .Bl -tag -width Ds
943: .It Cm from="pattern-list"
1.1 deraadt 944: Specifies that in addition to RSA authentication, the canonical name
945: of the remote host must be present in the comma-separated list of
1.36 aaron 946: patterns
947: .Pf ( Ql *
948: and
949: .Ql ?
950: serve as wildcards).
951: The list may also contain
952: patterns negated by prefixing them with
953: .Ql ! ;
954: if the canonical host name matches a negated pattern, the key is not accepted.
955: The purpose
1.1 deraadt 956: of this option is to optionally increase security: RSA authentication
957: by itself does not trust the network or name servers or anything (but
958: the key); however, if somebody somehow steals the key, the key
1.36 aaron 959: permits an intruder to log in from anywhere in the world.
960: This additional option makes using a stolen key more difficult (name
1.1 deraadt 961: servers and/or routers would have to be compromised in addition to
962: just the key).
1.2 deraadt 963: .It Cm command="command"
1.1 deraadt 964: Specifies that the command is executed whenever this key is used for
1.36 aaron 965: authentication.
966: The command supplied by the user (if any) is ignored.
1.1 deraadt 967: The command is run on a pty if the connection requests a pty;
1.36 aaron 968: otherwise it is run without a tty.
1.89 markus 969: Note that if you want a 8-bit clean channel,
970: you must not request a pty or should specify
971: .Cm no-pty .
1.36 aaron 972: A quote may be included in the command by quoting it with a backslash.
973: This option might be useful
974: to restrict certain RSA keys to perform just a specific operation.
975: An example might be a key that permits remote backups but nothing else.
1.51 hugh 976: Note that the client may specify TCP/IP and/or X11
977: forwarding unless they are explicitly prohibited.
1.2 deraadt 978: .It Cm environment="NAME=value"
1.1 deraadt 979: Specifies that the string is to be added to the environment when
1.36 aaron 980: logging in using this key.
981: Environment variables set this way
982: override other default environment values.
983: Multiple options of this type are permitted.
1.2 deraadt 984: .It Cm no-port-forwarding
1.1 deraadt 985: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 986: Any port forward requests by the client will return an error.
987: This might be used, e.g., in connection with the
1.2 deraadt 988: .Cm command
1.1 deraadt 989: option.
1.2 deraadt 990: .It Cm no-X11-forwarding
1.1 deraadt 991: Forbids X11 forwarding when this key is used for authentication.
992: Any X11 forward requests by the client will return an error.
1.2 deraadt 993: .It Cm no-agent-forwarding
1.1 deraadt 994: Forbids authentication agent forwarding when this key is used for
995: authentication.
1.2 deraadt 996: .It Cm no-pty
1.1 deraadt 997: Prevents tty allocation (a request to allocate a pty will fail).
1.107 djm 998: .It Cm permitopen="host:port"
1.133 itojun 999: Limit local
1.107 djm 1000: .Li ``ssh -L''
1.111 stevesk 1001: port forwarding such that it may only connect to the specified host and
1.133 itojun 1002: port. Multiple
1.107 djm 1003: .Cm permitopen
1.133 itojun 1004: options may be applied separated by commas. No pattern matching is
1005: performed on the specified hostnames, they must be literal domains or
1.107 djm 1006: addresses.
1.2 deraadt 1007: .El
1008: .Ss Examples
1.1 deraadt 1009: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 1010: .Pp
1.1 deraadt 1011: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 1012: .Pp
1.1 deraadt 1013: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.107 djm 1014: .Pp
1015: permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
1.2 deraadt 1016: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 1017: The
1.44 deraadt 1018: .Pa /etc/ssh_known_hosts ,
1.40 aaron 1019: and
1.131 markus 1020: .Pa $HOME/.ssh/known_hosts
1.36 aaron 1021: files contain host public keys for all known hosts.
1022: The global file should
1.37 brad 1023: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 1024: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 1025: its key is added to the per-user file.
1.2 deraadt 1026: .Pp
1.1 deraadt 1027: Each line in these files contains the following fields: hostnames,
1.36 aaron 1028: bits, exponent, modulus, comment.
1029: The fields are separated by spaces.
1.2 deraadt 1030: .Pp
1.1 deraadt 1031: Hostnames is a comma-separated list of patterns ('*' and '?' act as
1032: wildcards); each pattern in turn is matched against the canonical host
1033: name (when authenticating a client) or against the user-supplied
1.36 aaron 1034: name (when authenticating a server).
1035: A pattern may also be preceded by
1.2 deraadt 1036: .Ql !
1037: to indicate negation: if the host name matches a negated
1.1 deraadt 1038: pattern, it is not accepted (by that line) even if it matched another
1039: pattern on the line.
1.2 deraadt 1040: .Pp
1.49 markus 1041: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 1042: can be obtained, e.g., from
1043: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 1044: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 1045: .Pp
1046: Lines starting with
1047: .Ql #
1048: and empty lines are ignored as comments.
1049: .Pp
1.1 deraadt 1050: When performing host authentication, authentication is accepted if any
1.36 aaron 1051: matching line has the proper key.
1052: It is thus permissible (but not
1.1 deraadt 1053: recommended) to have several lines or different host keys for the same
1.36 aaron 1054: names.
1055: This will inevitably happen when short forms of host names
1056: from different domains are put in the file.
1057: It is possible
1.1 deraadt 1058: that the files contain conflicting information; authentication is
1059: accepted if valid information can be found from either file.
1.2 deraadt 1060: .Pp
1.1 deraadt 1061: Note that the lines in these files are typically hundreds of characters
1062: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 1063: Rather, generate them by a script
1.40 aaron 1064: or by taking
1.2 deraadt 1065: .Pa /etc/ssh_host_key.pub
1.1 deraadt 1066: and adding the host names at the front.
1.2 deraadt 1067: .Ss Examples
1.120 markus 1068: .Bd -literal
1069: closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1070: cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....=
1071: .Ed
1.2 deraadt 1072: .Sh FILES
1073: .Bl -tag -width Ds
1074: .It Pa /etc/sshd_config
1.1 deraadt 1075: Contains configuration data for
1.2 deraadt 1076: .Nm sshd .
1.1 deraadt 1077: This file should be writable by root only, but it is recommended
1078: (though not necessary) that it be world-readable.
1.98 deraadt 1079: .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
1.120 markus 1080: These three files contain the private parts of the host keys.
1.98 deraadt 1081: These files should only be owned by root, readable only by root, and not
1.1 deraadt 1082: accessible to others.
1.14 markus 1083: Note that
1084: .Nm
1085: does not start if this file is group/world-accessible.
1.98 deraadt 1086: .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1.120 markus 1087: These three files contain the public parts of the host keys.
1.98 deraadt 1088: These files should be world-readable but writable only by
1.36 aaron 1089: root.
1.98 deraadt 1090: Their contents should match the respective private parts.
1091: These files are not
1092: really used for anything; they are provided for the convenience of
1093: the user so their contents can be copied to known hosts files.
1094: These files are created using
1.7 markus 1095: .Xr ssh-keygen 1 .
1.129 provos 1096: .It Pa /etc/moduli
1.73 provos 1097: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 1098: .It Pa /var/run/sshd.pid
1099: Contains the process ID of the
1100: .Nm
1.1 deraadt 1101: listening for connections (if there are several daemons running
1102: concurrently for different ports, this contains the pid of the one
1.36 aaron 1103: started last).
1.58 deraadt 1104: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 1105: .It Pa $HOME/.ssh/authorized_keys
1.120 markus 1106: Lists the public keys (RSA or DSA) that can be used to log into the user's account.
1.44 deraadt 1107: This file must be readable by root (which may on some machines imply
1108: it being world-readable if the user's home directory resides on an NFS
1109: volume).
1110: It is recommended that it not be accessible by others.
1111: The format of this file is described above.
1112: Users will place the contents of their
1.130 markus 1113: .Pa identity.pub ,
1.44 deraadt 1114: .Pa id_dsa.pub
1.113 itojun 1115: and/or
1116: .Pa id_rsa.pub
1.44 deraadt 1117: files into this file, as described in
1118: .Xr ssh-keygen 1 .
1.22 markus 1119: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1120: These files are consulted when using rhosts with RSA host
1.131 markus 1121: authentication or protocol version 2 hostbased authentication
1122: to check the public key of the host.
1.36 aaron 1123: The key must be listed in one of these files to be accepted.
1.22 markus 1124: The client uses the same files
1.96 markus 1125: to verify that it is connecting to the correct remote host.
1.36 aaron 1126: These files should be writable only by root/the owner.
1.2 deraadt 1127: .Pa /etc/ssh_known_hosts
1128: should be world-readable, and
1129: .Pa $HOME/.ssh/known_hosts
1.120 markus 1130: can but need not be world-readable.
1.6 aaron 1131: .It Pa /etc/nologin
1.40 aaron 1132: If this file exists,
1.2 deraadt 1133: .Nm
1.36 aaron 1134: refuses to let anyone except root log in.
1135: The contents of the file
1.1 deraadt 1136: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 1137: refused.
1138: The file should be world-readable.
1.19 dugsong 1139: .It Pa /etc/hosts.allow, /etc/hosts.deny
1140: If compiled with
1141: .Sy LIBWRAP
1142: support, tcp-wrappers access controls may be defined here as described in
1143: .Xr hosts_access 5 .
1.6 aaron 1144: .It Pa $HOME/.rhosts
1.1 deraadt 1145: This file contains host-username pairs, separated by a space, one per
1.36 aaron 1146: line.
1147: The given user on the corresponding host is permitted to log in
1148: without password.
1149: The same file is used by rlogind and rshd.
1.6 aaron 1150: The file must
1.1 deraadt 1151: be writable only by the user; it is recommended that it not be
1152: accessible by others.
1.2 deraadt 1153: .Pp
1.36 aaron 1154: If is also possible to use netgroups in the file.
1155: Either host or user
1.1 deraadt 1156: name may be of the form +@groupname to specify all hosts or all users
1157: in the group.
1.2 deraadt 1158: .It Pa $HOME/.shosts
1159: For ssh,
1160: this file is exactly the same as for
1161: .Pa .rhosts .
1162: However, this file is
1163: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 1164: .It Pa /etc/hosts.equiv
1.2 deraadt 1165: This file is used during
1166: .Pa .rhosts
1.36 aaron 1167: authentication.
1168: In the simplest form, this file contains host names, one per line.
1169: Users on
1.1 deraadt 1170: those hosts are permitted to log in without a password, provided they
1.36 aaron 1171: have the same user name on both machines.
1172: The host name may also be
1.1 deraadt 1173: followed by a user name; such users are permitted to log in as
1.2 deraadt 1174: .Em any
1.36 aaron 1175: user on this machine (except root).
1176: Additionally, the syntax
1.2 deraadt 1177: .Dq +@group
1.36 aaron 1178: can be used to specify netgroups.
1179: Negated entries start with
1.2 deraadt 1180: .Ql \&- .
1181: .Pp
1.1 deraadt 1182: If the client host/user is successfully matched in this file, login is
1183: automatically permitted provided the client and server user names are the
1.36 aaron 1184: same.
1185: Additionally, successful RSA host authentication is normally required.
1186: This file must be writable only by root; it is recommended
1.1 deraadt 1187: that it be world-readable.
1.2 deraadt 1188: .Pp
1.6 aaron 1189: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1190: .Pa hosts.equiv .
1.1 deraadt 1191: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1192: .Em anybody ,
1.1 deraadt 1193: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1194: binaries and directories.
1195: Using a user name practically grants the user root access.
1196: The only valid use for user names that I can think
1.1 deraadt 1197: of is in negative entries.
1.2 deraadt 1198: .Pp
1199: Note that this warning also applies to rsh/rlogin.
1200: .It Pa /etc/shosts.equiv
1.1 deraadt 1201: This is processed exactly as
1.2 deraadt 1202: .Pa /etc/hosts.equiv .
1.1 deraadt 1203: However, this file may be useful in environments that want to run both
1.2 deraadt 1204: rsh/rlogin and ssh.
1.6 aaron 1205: .It Pa $HOME/.ssh/environment
1.36 aaron 1206: This file is read into the environment at login (if it exists).
1207: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1208: .Ql # ) ,
1.36 aaron 1209: and assignment lines of the form name=value.
1210: The file should be writable
1.6 aaron 1211: only by the user; it need not be readable by anyone else.
1.2 deraadt 1212: .It Pa $HOME/.ssh/rc
1.1 deraadt 1213: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1214: environment files but before starting the user's shell or command.
1215: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1216: standard input (and
1217: .Ev DISPLAY
1.36 aaron 1218: in environment).
1219: This must call
1.2 deraadt 1220: .Xr xauth 1
1221: in that case.
1222: .Pp
1.1 deraadt 1223: The primary purpose of this file is to run any initialization routines
1224: which may be needed before the user's home directory becomes
1225: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1226: .Pp
1.1 deraadt 1227: This file will probably contain some initialization code followed by
1.120 markus 1228: something similar to:
1229: .Bd -literal
1230: if read proto cookie; then
1231: echo add $DISPLAY $proto $cookie | xauth -q -
1232: fi
1233: .Ed
1.2 deraadt 1234: .Pp
1235: If this file does not exist,
1236: .Pa /etc/sshrc
1237: is run, and if that
1.1 deraadt 1238: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1239: .Pp
1.1 deraadt 1240: This file should be writable only by the user, and need not be
1241: readable by anyone else.
1.2 deraadt 1242: .It Pa /etc/sshrc
1243: Like
1244: .Pa $HOME/.ssh/rc .
1245: This can be used to specify
1.36 aaron 1246: machine-specific login-time initializations globally.
1247: This file should be writable only by root, and should be world-readable.
1.56 aaron 1248: .El
1.71 aaron 1249: .Sh AUTHORS
1.84 markus 1250: OpenSSH is a derivative of the original and free
1251: ssh 1.2.12 release by Tatu Ylonen.
1252: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1253: Theo de Raadt and Dug Song
1254: removed many bugs, re-added newer features and
1255: created OpenSSH.
1256: Markus Friedl contributed the support for SSH
1257: protocol versions 1.5 and 2.0.
1.2 deraadt 1258: .Sh SEE ALSO
1.129 provos 1259: .Xr moduli 5 ,
1.128 mpech 1260: .Xr rlogin 1 ,
1261: .Xr rsh 1 ,
1.2 deraadt 1262: .Xr scp 1 ,
1.90 djm 1263: .Xr sftp 1 ,
1.2 deraadt 1264: .Xr ssh 1 ,
1.5 deraadt 1265: .Xr ssh-add 1 ,
1.2 deraadt 1266: .Xr ssh-agent 1 ,
1.5 deraadt 1267: .Xr ssh-keygen 1 ,
1.128 mpech 1268: .Xr sftp-server 8
1.119 markus 1269: .Rs
1270: .%A T. Ylonen
1271: .%A T. Kivinen
1272: .%A M. Saarinen
1273: .%A T. Rinne
1274: .%A S. Lehtinen
1275: .%T "SSH Protocol Architecture"
1276: .%N draft-ietf-secsh-architecture-07.txt
1.120 markus 1277: .%D January 2001
1278: .%O work in progress material
1279: .Re
1280: .Rs
1281: .%A M. Friedl
1282: .%A N. Provos
1283: .%A W. A. Simpson
1284: .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol"
1.132 markus 1285: .%N draft-ietf-secsh-dh-group-exchange-01.txt
1286: .%D April 2001
1.119 markus 1287: .%O work in progress material
1288: .Re
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