Annotation of src/usr.bin/ssh/sshd.8, Revision 1.118
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,
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1.1 deraadt 36: .\"
1.118 ! deraadt 37: .\" $OpenBSD: sshd.8,v 1.117 2001/04/15 21:05:49 stevesk Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSHD 8
40: .Os
41: .Sh NAME
42: .Nm sshd
1.106 deraadt 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.
1.103 deraadt 137: The rest of the session is encrypted using a symmetric cipher, currently
138: Blowfish, 3DES, CAST128, Arcfour, 128 bit AES, or 256 bit AES.
1.49 markus 139: The client selects the encryption algorithm
140: to use from those offered by the server.
141: Additionally, session integrity is provided
1.51 hugh 142: through a cryptographic message authentication code
1.49 markus 143: (hmac-sha1 or hmac-md5).
144: .Pp
145: Protocol version 2 provides a public key based
1.72 markus 146: user authentication method (PubkeyAuthentication)
1.49 markus 147: and conventional password authentication.
148: .Pp
149: .Ss Command execution and data forwarding
150: .Pp
1.1 deraadt 151: If the client successfully authenticates itself, a dialog for
1.36 aaron 152: preparing the session is entered.
153: At this time the client may request
1.1 deraadt 154: things like allocating a pseudo-tty, forwarding X11 connections,
155: forwarding TCP/IP connections, or forwarding the authentication agent
156: connection over the secure channel.
1.2 deraadt 157: .Pp
1.1 deraadt 158: Finally, the client either requests a shell or execution of a command.
1.36 aaron 159: The sides then enter session mode.
160: In this mode, either side may send
1.1 deraadt 161: data at any time, and such data is forwarded to/from the shell or
162: command on the server side, and the user terminal in the client side.
1.2 deraadt 163: .Pp
1.1 deraadt 164: When the user program terminates and all forwarded X11 and other
165: connections have been closed, the server sends command exit status to
166: the client, and both sides exit.
1.2 deraadt 167: .Pp
168: .Nm
1.1 deraadt 169: can be configured using command-line options or a configuration
1.36 aaron 170: file.
171: Command-line options override values specified in the
1.1 deraadt 172: configuration file.
1.25 markus 173: .Pp
174: .Nm
175: rereads its configuration file when it receives a hangup signal,
1.97 deraadt 176: .Dv SIGHUP ,
177: by executing itself with the name it was started as, ie.
178: .Pa /usr/sbin/sshd .
1.18 aaron 179: .Pp
180: The options are as follows:
1.2 deraadt 181: .Bl -tag -width Ds
182: .It Fl b Ar bits
1.1 deraadt 183: Specifies the number of bits in the server key (default 768).
1.2 deraadt 184: .Pp
185: .It Fl d
1.36 aaron 186: Debug mode.
187: The server sends verbose debug output to the system
188: log, and does not put itself in the background.
189: The server also will not fork and will only process one connection.
190: This option is only intended for debugging for the server.
1.67 aaron 191: Multiple -d options increases the debugging level.
192: Maximum is 3.
1.2 deraadt 193: .It Fl f Ar configuration_file
1.36 aaron 194: Specifies the name of the configuration file.
195: The default is
1.2 deraadt 196: .Pa /etc/sshd_config .
1.16 markus 197: .Nm
198: refuses to start if there is no configuration file.
1.2 deraadt 199: .It Fl g Ar login_grace_time
1.1 deraadt 200: Gives the grace time for clients to authenticate themselves (default
1.77 markus 201: 600 seconds).
1.36 aaron 202: If the client fails to authenticate the user within
203: this many seconds, the server disconnects and exits.
204: A value of zero indicates no limit.
1.2 deraadt 205: .It Fl h Ar host_key_file
1.75 markus 206: Specifies the file from which the host key is read (default
1.2 deraadt 207: .Pa /etc/ssh_host_key ) .
1.7 markus 208: This option must be given if
209: .Nm
210: is not run as root (as the normal
1.1 deraadt 211: host file is normally not readable by anyone but root).
1.75 markus 212: It is possible to have multiple host key files for
213: the different protocol versions.
1.2 deraadt 214: .It Fl i
1.7 markus 215: Specifies that
216: .Nm
1.40 aaron 217: is being run from inetd.
1.7 markus 218: .Nm
219: is normally not run
1.1 deraadt 220: from inetd because it needs to generate the server key before it can
1.36 aaron 221: respond to the client, and this may take tens of seconds.
222: Clients would have to wait too long if the key was regenerated every time.
1.35 aaron 223: However, with small key sizes (e.g., 512) using
1.7 markus 224: .Nm
225: from inetd may
1.1 deraadt 226: be feasible.
1.2 deraadt 227: .It Fl k Ar key_gen_time
1.1 deraadt 228: Specifies how often the server key is regenerated (default 3600
1.36 aaron 229: seconds, or one hour).
230: The motivation for regenerating the key fairly
1.1 deraadt 231: often is that the key is not stored anywhere, and after about an hour,
232: it becomes impossible to recover the key for decrypting intercepted
233: communications even if the machine is cracked into or physically
1.36 aaron 234: seized.
235: A value of zero indicates that the key will never be regenerated.
1.2 deraadt 236: .It Fl p Ar port
1.1 deraadt 237: Specifies the port on which the server listens for connections
238: (default 22).
1.2 deraadt 239: .It Fl q
1.36 aaron 240: Quiet mode.
241: Nothing is sent to the system log.
242: Normally the beginning,
1.1 deraadt 243: authentication, and termination of each connection is logged.
1.61 markus 244: .It Fl u Ar len
245: This option is used to specify the size of the field
246: in the
247: .Li utmp
248: structure that holds the remote host name.
249: If the resolved host name is longer than
250: .Ar len ,
251: the dotted decimal value will be used instead.
252: This allows hosts with very long host names that
253: overflow this field to still be uniquely identified.
254: Specifying
255: .Fl u0
256: indicates that only dotted decimal addresses
257: should be put into the
258: .Pa utmp
259: file.
1.74 markus 260: .It Fl D
261: When this option is specified
262: .Nm
263: will not detach and does not become a daemon.
264: This allows easy monitoring of
1.76 markus 265: .Nm sshd .
1.114 lebel 266: .It Fl e
267: When this option is specified,
268: .Nm
269: will send the output to the standard error instead of the system log.
1.26 markus 270: .It Fl V Ar client_protocol_id
1.68 markus 271: SSH-2 compatibility mode.
1.42 hugh 272: When this option is specified
1.26 markus 273: .Nm
1.42 hugh 274: assumes the client has sent the supplied version string
1.26 markus 275: and skips the
276: Protocol Version Identification Exchange.
1.68 markus 277: This option is not intended to be called directly.
1.29 markus 278: .It Fl 4
279: Forces
280: .Nm
281: to use IPv4 addresses only.
282: .It Fl 6
283: Forces
284: .Nm
285: to use IPv6 addresses only.
1.2 deraadt 286: .El
287: .Sh CONFIGURATION FILE
288: .Nm
1.40 aaron 289: reads configuration data from
1.2 deraadt 290: .Pa /etc/sshd_config
291: (or the file specified with
292: .Fl f
1.36 aaron 293: on the command line).
294: The file contains keyword-value pairs, one per line.
295: Lines starting with
1.2 deraadt 296: .Ql #
1.1 deraadt 297: and empty lines are interpreted as comments.
1.2 deraadt 298: .Pp
1.1 deraadt 299: The following keywords are possible.
1.2 deraadt 300: .Bl -tag -width Ds
301: .It Cm AFSTokenPassing
1.36 aaron 302: Specifies whether an AFS token may be forwarded to the server.
303: Default is
1.2 deraadt 304: .Dq yes .
1.11 markus 305: .It Cm AllowGroups
1.92 deraadt 306: This keyword can be followed by a list of group names, separated
1.36 aaron 307: by spaces.
308: If specified, login is allowed only for users whose primary
1.81 markus 309: group or supplementary group list matches one of the patterns.
1.11 markus 310: .Ql \&*
311: and
312: .Ql ?
313: can be used as
1.36 aaron 314: wildcards in the patterns.
1.58 deraadt 315: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 316: By default login is allowed regardless of the group list.
1.3 dugsong 317: .Pp
1.69 markus 318: .It Cm AllowTcpForwarding
319: Specifies whether TCP forwarding is permitted.
320: The default is
321: .Dq yes .
322: Note that disabling TCP forwarding does not improve security unless
323: users are also denied shell access, as they can always install their
324: own forwarders.
325: .Pp
1.11 markus 326: .It Cm AllowUsers
1.92 deraadt 327: This keyword can be followed by a list of user names, separated
1.36 aaron 328: by spaces.
329: If specified, login is allowed only for users names that
1.11 markus 330: match one of the patterns.
331: .Ql \&*
332: and
333: .Ql ?
334: can be used as
1.36 aaron 335: wildcards in the patterns.
1.58 deraadt 336: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 337: By default login is allowed regardless of the user name.
1.80 markus 338: .Pp
339: .It Cm Banner
340: In some jurisdictions, sending a warning message before authentication
341: may be relevant for getting legal protection.
342: The contents of the specified file are sent to the remote user before
343: authentication is allowed.
344: This option is only available for protocol version 2.
1.11 markus 345: .Pp
1.104 deraadt 346: .It Cm ChallengeResponseAuthentication
347: Specifies whether
348: challenge response
349: authentication is allowed.
350: Currently there is only support for
351: .Xr skey 1
352: authentication.
353: The default is
354: .Dq yes .
1.41 markus 355: .It Cm Ciphers
356: Specifies the ciphers allowed for protocol version 2.
357: Multiple ciphers must be comma-separated.
358: The default is
1.105 deraadt 359: .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
1.8 markus 360: .It Cm CheckMail
361: Specifies whether
362: .Nm
363: should check for new mail for interactive logins.
364: The default is
365: .Dq no .
1.115 beck 366: .It Cm ClientAliveInterval
367: Sets a timeout interval in seconds after which if no data has been received
368: from the client,
369: .Nm
370: will send a message through the encrypted
1.116 stevesk 371: channel to request a response from the client.
372: The default
1.115 beck 373: is 0, indicating that these messages will not be sent to the client.
1.116 stevesk 374: This option applies to protocol version 2 only.
1.115 beck 375: .It Cm ClientAliveCountMax
376: Sets the number of client alive messages (see above) which may be
377: sent without
378: .Nm
379: receiving any messages back from the client. If this threshold is
380: reached while client alive messages are being sent,
381: .Nm
382: will disconnect the client, terminating the session. It is important
383: to note that the use of client alive messages is very different from
1.116 stevesk 384: .Cm Keepalive
385: (below). The client alive messages are sent through the
1.115 beck 386: encrypted channel and therefore will not be spoofable. The TCP keepalive
1.116 stevesk 387: option enabled by
388: .Cm Keepalive
389: is spoofable. You want to use the client
1.115 beck 390: alive mechanism when you are basing something important on
391: clients having an active connection to the server.
1.116 stevesk 392: .Pp
393: The default value is 3. If you set
394: .Cm ClientAliveInterval
1.115 beck 395: (above) to 15, and leave this value at the default, unresponsive ssh clients
396: will be disconnected after approximately 45 seconds.
1.11 markus 397: .It Cm DenyGroups
398: This keyword can be followed by a number of group names, separated
1.36 aaron 399: by spaces.
1.81 markus 400: Users whose primary group or supplementary group list matches
401: one of the patterns aren't allowed to log in.
1.11 markus 402: .Ql \&*
403: and
404: .Ql ?
405: can be used as
1.36 aaron 406: wildcards in the patterns.
1.58 deraadt 407: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 408: By default login is allowed regardless of the group list.
1.11 markus 409: .Pp
410: .It Cm DenyUsers
411: This keyword can be followed by a number of user names, separated
1.36 aaron 412: by spaces.
413: Login is disallowed for user names that match one of the patterns.
1.11 markus 414: .Ql \&*
415: and
416: .Ql ?
1.36 aaron 417: can be used as wildcards in the patterns.
1.58 deraadt 418: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 419: By default login is allowed regardless of the user name.
1.47 markus 420: .It Cm GatewayPorts
421: Specifies whether remote hosts are allowed to connect to ports
422: forwarded for the client.
423: The argument must be
424: .Dq yes
425: or
426: .Dq no .
427: The default is
428: .Dq no .
1.2 deraadt 429: .It Cm HostKey
1.72 markus 430: Specifies the file containing the private host keys (default
1.46 markus 431: .Pa /etc/ssh_host_key )
1.72 markus 432: used by SSH protocol versions 1 and 2.
1.9 markus 433: Note that
434: .Nm
1.83 markus 435: will refuse to use a file if it is group/world-accessible.
1.72 markus 436: It is possible to have multiple host key files.
437: .Dq rsa1
438: keys are used for version 1 and
439: .Dq dsa
440: or
441: .Dq rsa
442: are used for version 2 of the SSH protocol.
1.2 deraadt 443: .It Cm IgnoreRhosts
1.34 markus 444: Specifies that
445: .Pa .rhosts
1.40 aaron 446: and
1.34 markus 447: .Pa .shosts
448: files will not be used in authentication.
1.2 deraadt 449: .Pa /etc/hosts.equiv
1.1 deraadt 450: and
1.40 aaron 451: .Pa /etc/shosts.equiv
1.36 aaron 452: are still used.
1.40 aaron 453: The default is
1.34 markus 454: .Dq yes .
1.24 markus 455: .It Cm IgnoreUserKnownHosts
456: Specifies whether
457: .Nm
458: should ignore the user's
459: .Pa $HOME/.ssh/known_hosts
1.45 markus 460: during
1.24 markus 461: .Cm RhostsRSAAuthentication .
462: The default is
1.2 deraadt 463: .Dq no .
464: .It Cm KeepAlive
1.1 deraadt 465: Specifies whether the system should send keepalive messages to the
1.36 aaron 466: other side.
467: If they are sent, death of the connection or crash of one
468: of the machines will be properly noticed.
469: However, this means that
1.1 deraadt 470: connections will die if the route is down temporarily, and some people
1.36 aaron 471: find it annoying.
1.51 hugh 472: On the other hand, if keepalives are not sent,
1.2 deraadt 473: sessions may hang indefinitely on the server, leaving
474: .Dq ghost
475: users and consuming server resources.
476: .Pp
477: The default is
478: .Dq yes
479: (to send keepalives), and the server will notice
1.36 aaron 480: if the network goes down or the client host reboots.
481: This avoids infinitely hanging sessions.
1.2 deraadt 482: .Pp
483: To disable keepalives, the value should be set to
484: .Dq no
485: in both the server and the client configuration files.
486: .It Cm KerberosAuthentication
1.36 aaron 487: Specifies whether Kerberos authentication is allowed.
488: This can be in the form of a Kerberos ticket, or if
1.7 markus 489: .Cm PasswordAuthentication
1.1 deraadt 490: is yes, the password provided by the user will be validated through
1.67 aaron 491: the Kerberos KDC.
492: To use this option, the server needs a
1.59 provos 493: Kerberos servtab which allows the verification of the KDC's identity.
1.36 aaron 494: Default is
1.60 provos 495: .Dq yes .
1.2 deraadt 496: .It Cm KerberosOrLocalPasswd
1.1 deraadt 497: If set then if password authentication through Kerberos fails then
498: the password will be validated via any additional local mechanism
1.2 deraadt 499: such as
1.66 markus 500: .Pa /etc/passwd .
1.36 aaron 501: Default is
1.20 dugsong 502: .Dq yes .
1.2 deraadt 503: .It Cm KerberosTgtPassing
1.1 deraadt 504: Specifies whether a Kerberos TGT may be forwarded to the server.
1.40 aaron 505: Default is
1.3 dugsong 506: .Dq no ,
507: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 508: .It Cm KerberosTicketCleanup
1.7 markus 509: Specifies whether to automatically destroy the user's ticket cache
1.36 aaron 510: file on logout.
511: Default is
1.3 dugsong 512: .Dq yes .
1.2 deraadt 513: .It Cm KeyRegenerationInterval
1.1 deraadt 514: The server key is automatically regenerated after this many seconds
1.36 aaron 515: (if it has been used).
516: The purpose of regeneration is to prevent
1.1 deraadt 517: decrypting captured sessions by later breaking into the machine and
1.36 aaron 518: stealing the keys.
519: The key is never stored anywhere.
520: If the value is 0, the key is never regenerated.
521: The default is 3600 (seconds).
1.7 markus 522: .It Cm ListenAddress
1.110 stevesk 523: Specifies the local addresses
1.112 stevesk 524: .Xr sshd 8
1.7 markus 525: should listen on.
1.110 stevesk 526: The following forms may be used:
527: .Pp
528: .Bl -item -offset indent -compact
529: .It
530: .Cm ListenAddress
1.112 stevesk 531: .Sm off
532: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
533: .Sm on
1.110 stevesk 534: .It
535: .Cm ListenAddress
1.112 stevesk 536: .Sm off
537: .Ar host No | Ar IPv4_addr No : Ar port
538: .Sm on
1.110 stevesk 539: .It
540: .Cm ListenAddress
1.112 stevesk 541: .Sm off
542: .Oo
543: .Ar host No | Ar IPv6_addr Oc : Ar port
544: .Sm on
1.110 stevesk 545: .El
546: .Pp
547: If
1.112 stevesk 548: .Ar port
1.110 stevesk 549: is not specified,
1.112 stevesk 550: .Xr sshd 8
1.110 stevesk 551: will listen on the address and all prior
552: .Cm Port
553: options specified. The default is to listen on all local
554: addresses. Multiple
555: .Cm ListenAddress
556: options are permitted. Additionally, any
557: .Cm Port
558: options must precede this option for non port qualified addresses.
1.2 deraadt 559: .It Cm LoginGraceTime
1.1 deraadt 560: The server disconnects after this time if the user has not
1.36 aaron 561: successfully logged in.
562: If the value is 0, there is no time limit.
1.1 deraadt 563: The default is 600 (seconds).
1.23 markus 564: .It Cm LogLevel
565: Gives the verbosity level that is used when logging messages from
566: .Nm sshd .
567: The possible values are:
1.82 markus 568: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
569: The default is INFO.
1.23 markus 570: Logging with level DEBUG violates the privacy of users
571: and is not recommended.
1.93 markus 572: .It Cm MACs
573: Specifies the available MAC (message authentication code) algorithms.
574: The MAC algorithm is used in protocol version 2
575: for data integrity protection.
576: Multiple algorithms must be comma-separated.
577: The default is
578: .Pp
579: .Bd -literal
1.105 deraadt 580: ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
1.93 markus 581: hmac-sha1-96,hmac-md5-96''
582: .Ed
1.55 markus 583: .It Cm MaxStartups
584: Specifies the maximum number of concurrent unauthenticated connections to the
585: .Nm
586: daemon.
587: Additional connections will be dropped until authentication succeeds or the
588: .Cm LoginGraceTime
589: expires for a connection.
590: The default is 10.
1.57 markus 591: .Pp
592: Alternatively, random early drop can be enabled by specifying
593: the three colon separated values
594: .Dq start:rate:full
1.67 aaron 595: (e.g., "10:30:60").
1.57 markus 596: .Nm
1.86 stevesk 597: will refuse connection attempts with a probability of
1.57 markus 598: .Dq rate/100
599: (30%)
600: if there are currently
601: .Dq start
602: (10)
603: unauthenticated connections.
1.86 stevesk 604: The probability increases linearly and all connection attempts
1.57 markus 605: are refused if the number of unauthenticated connections reaches
606: .Dq full
607: (60).
1.2 deraadt 608: .It Cm PasswordAuthentication
1.1 deraadt 609: Specifies whether password authentication is allowed.
1.2 deraadt 610: The default is
611: .Dq yes .
1.58 deraadt 612: Note that this option applies to both protocol versions 1 and 2.
1.2 deraadt 613: .It Cm PermitEmptyPasswords
1.1 deraadt 614: When password authentication is allowed, it specifies whether the
1.36 aaron 615: server allows login to accounts with empty password strings.
616: The default is
1.34 markus 617: .Dq no .
1.2 deraadt 618: .It Cm PermitRootLogin
1.100 stevesk 619: Specifies whether root can login using
1.2 deraadt 620: .Xr ssh 1 .
1.15 markus 621: The argument must be
622: .Dq yes ,
1.94 markus 623: .Dq without-password ,
624: .Dq forced-commands-only
1.15 markus 625: or
626: .Dq no .
1.2 deraadt 627: The default is
628: .Dq yes .
1.94 markus 629: .Pp
630: If this option is set to
1.15 markus 631: .Dq without-password
1.94 markus 632: password authentication is disabled for root.
1.2 deraadt 633: .Pp
1.94 markus 634: If this option is set to
635: .Dq forced-commands-only
636: root login with public key authentication will be allowed,
637: but only if the
1.2 deraadt 638: .Ar command
1.94 markus 639: option has been specified
1.1 deraadt 640: (which may be useful for taking remote backups even if root login is
1.94 markus 641: normally not allowed). All other authentication methods are disabled
642: for root.
1.100 stevesk 643: .Pp
644: If this option is set to
645: .Dq no
646: root is not allowed to login.
1.43 markus 647: .It Cm PidFile
648: Specifies the file that contains the process identifier of the
649: .Nm
650: daemon.
651: The default is
652: .Pa /var/run/sshd.pid .
1.2 deraadt 653: .It Cm Port
1.1 deraadt 654: Specifies the port number that
1.2 deraadt 655: .Nm
1.36 aaron 656: listens on.
657: The default is 22.
1.28 markus 658: Multiple options of this type are permitted.
1.108 stevesk 659: .It Cm PrintLastLog
660: Specifies whether
661: .Nm
662: should print the date and time when the user last logged in.
663: The default is
664: .Dq yes .
1.2 deraadt 665: .It Cm PrintMotd
1.1 deraadt 666: Specifies whether
1.2 deraadt 667: .Nm
1.40 aaron 668: should print
1.2 deraadt 669: .Pa /etc/motd
1.36 aaron 670: when a user logs in interactively.
671: (On some systems it is also printed by the shell,
1.2 deraadt 672: .Pa /etc/profile ,
1.36 aaron 673: or equivalent.)
674: The default is
1.2 deraadt 675: .Dq yes .
1.41 markus 676: .It Cm Protocol
677: Specifies the protocol versions
678: .Nm
679: should support.
680: The possible values are
681: .Dq 1
682: and
683: .Dq 2 .
684: Multiple versions must be comma-separated.
685: The default is
1.118 ! deraadt 686: .Dq 2,1 .
1.104 deraadt 687: .It Cm PubkeyAuthentication
688: Specifies whether public key authentication is allowed.
689: The default is
690: .Dq yes .
691: Note that this option applies to protocol version 2 only.
1.87 markus 692: .It Cm ReverseMappingCheck
693: Specifies whether
694: .Nm
695: should try to verify the remote host name and check that
696: the resolved host name for the remote IP address maps back to the
697: very same IP address.
698: The default is
699: .Dq no .
1.2 deraadt 700: .It Cm RhostsAuthentication
1.1 deraadt 701: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 702: files is sufficient.
703: Normally, this method should not be permitted because it is insecure.
1.7 markus 704: .Cm RhostsRSAAuthentication
705: should be used
1.1 deraadt 706: instead, because it performs RSA-based host authentication in addition
707: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 708: The default is
709: .Dq no .
710: .It Cm RhostsRSAAuthentication
1.1 deraadt 711: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 712: with successful RSA host authentication is allowed.
713: The default is
1.34 markus 714: .Dq no .
1.2 deraadt 715: .It Cm RSAAuthentication
1.36 aaron 716: Specifies whether pure RSA authentication is allowed.
717: The default is
1.2 deraadt 718: .Dq yes .
1.49 markus 719: Note that this option applies to protocol version 1 only.
1.2 deraadt 720: .It Cm ServerKeyBits
1.36 aaron 721: Defines the number of bits in the server key.
722: The minimum value is 512, and the default is 768.
1.2 deraadt 723: .It Cm StrictModes
1.12 markus 724: Specifies whether
725: .Nm
726: should check file modes and ownership of the
1.36 aaron 727: user's files and home directory before accepting login.
728: This is normally desirable because novices sometimes accidentally leave their
729: directory or files world-writable.
730: The default is
1.7 markus 731: .Dq yes .
1.54 jakob 732: .It Cm Subsystem
1.67 aaron 733: Configures an external subsystem (e.g., file transfer daemon).
734: Arguments should be a subsystem name and a command to execute upon subsystem
735: request.
1.63 markus 736: The command
737: .Xr sftp-server 8
738: implements the
739: .Dq sftp
740: file transfer subsystem.
1.54 jakob 741: By default no subsystems are defined.
742: Note that this option applies to protocol version 2 only.
1.2 deraadt 743: .It Cm SyslogFacility
1.1 deraadt 744: Gives the facility code that is used when logging messages from
1.2 deraadt 745: .Nm sshd .
1.1 deraadt 746: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 747: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
748: The default is AUTH.
1.10 markus 749: .It Cm UseLogin
750: Specifies whether
751: .Xr login 1
1.53 markus 752: is used for interactive login sessions.
753: Note that
754: .Xr login 1
1.58 deraadt 755: is never used for remote command execution.
1.36 aaron 756: The default is
1.10 markus 757: .Dq no .
1.6 aaron 758: .It Cm X11DisplayOffset
759: Specifies the first display number available for
760: .Nm sshd Ns 's
1.36 aaron 761: X11 forwarding.
762: This prevents
1.6 aaron 763: .Nm
764: from interfering with real X11 servers.
1.34 markus 765: The default is 10.
1.30 markus 766: .It Cm X11Forwarding
1.36 aaron 767: Specifies whether X11 forwarding is permitted.
768: The default is
1.34 markus 769: .Dq no .
1.30 markus 770: Note that disabling X11 forwarding does not improve security in any
771: way, as users can always install their own forwarders.
1.52 markus 772: .It Cm XAuthLocation
773: Specifies the location of the
774: .Xr xauth 1
775: program.
776: The default is
777: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 778: .El
779: .Sh LOGIN PROCESS
1.1 deraadt 780: When a user successfully logs in,
1.2 deraadt 781: .Nm
1.1 deraadt 782: does the following:
1.2 deraadt 783: .Bl -enum -offset indent
784: .It
1.1 deraadt 785: If the login is on a tty, and no command has been specified,
1.40 aaron 786: prints last login time and
1.2 deraadt 787: .Pa /etc/motd
1.1 deraadt 788: (unless prevented in the configuration file or by
1.2 deraadt 789: .Pa $HOME/.hushlogin ;
790: see the
1.40 aaron 791: .Sx FILES
1.2 deraadt 792: section).
793: .It
1.1 deraadt 794: If the login is on a tty, records login time.
1.2 deraadt 795: .It
796: Checks
797: .Pa /etc/nologin ;
798: if it exists, prints contents and quits
1.1 deraadt 799: (unless root).
1.2 deraadt 800: .It
1.1 deraadt 801: Changes to run with normal user privileges.
1.2 deraadt 802: .It
1.1 deraadt 803: Sets up basic environment.
1.2 deraadt 804: .It
805: Reads
806: .Pa $HOME/.ssh/environment
807: if it exists.
808: .It
1.1 deraadt 809: Changes to user's home directory.
1.2 deraadt 810: .It
811: If
812: .Pa $HOME/.ssh/rc
813: exists, runs it; else if
814: .Pa /etc/sshrc
815: exists, runs
1.36 aaron 816: it; otherwise runs xauth.
817: The
1.2 deraadt 818: .Dq rc
819: files are given the X11
1.1 deraadt 820: authentication protocol and cookie in standard input.
1.2 deraadt 821: .It
1.1 deraadt 822: Runs user's shell or command.
1.2 deraadt 823: .El
824: .Sh AUTHORIZED_KEYS FILE FORMAT
1.40 aaron 825: The
1.2 deraadt 826: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 827: file lists the RSA keys that are
1.44 deraadt 828: permitted for RSA authentication in SSH protocols 1.3 and 1.5
1.51 hugh 829: Similarly, the
1.44 deraadt 830: .Pa $HOME/.ssh/authorized_keys2
1.75 markus 831: file lists the DSA and RSA keys that are
832: permitted for public key authentication (PubkeyAuthentication)
833: in SSH protocol 2.0.
834: .Pp
1.36 aaron 835: Each line of the file contains one
1.2 deraadt 836: key (empty lines and lines starting with a
837: .Ql #
838: are ignored as
1.36 aaron 839: comments).
1.75 markus 840: Each RSA public key consists of the following fields, separated by
1.36 aaron 841: spaces: options, bits, exponent, modulus, comment.
1.75 markus 842: Each protocol version 2 public key consists of:
843: options, keytype, base64 encoded key, comment.
844: The options fields
845: are optional; its presence is determined by whether the line starts
1.1 deraadt 846: with a number or not (the option field never starts with a number).
1.75 markus 847: The bits, exponent, modulus and comment fields give the RSA key for
848: protocol version 1; the
1.1 deraadt 849: comment field is not used for anything (but may be convenient for the
850: user to identify the key).
1.75 markus 851: For protocol version 2 the keytype is
852: .Dq ssh-dss
853: or
854: .Dq ssh-rsa .
1.2 deraadt 855: .Pp
1.1 deraadt 856: Note that lines in this file are usually several hundred bytes long
1.36 aaron 857: (because of the size of the RSA key modulus).
858: You don't want to type them in; instead, copy the
1.113 itojun 859: .Pa identity.pub ,
860: .Pa id_dsa.pub
1.75 markus 861: or the
1.113 itojun 862: .Pa id_rsa.pub
1.1 deraadt 863: file and edit it.
1.2 deraadt 864: .Pp
1.58 deraadt 865: The options (if present) consist of comma-separated option
1.36 aaron 866: specifications.
867: No spaces are permitted, except within double quotes.
1.1 deraadt 868: The following option specifications are supported:
1.2 deraadt 869: .Bl -tag -width Ds
870: .It Cm from="pattern-list"
1.1 deraadt 871: Specifies that in addition to RSA authentication, the canonical name
872: of the remote host must be present in the comma-separated list of
1.36 aaron 873: patterns
874: .Pf ( Ql *
875: and
876: .Ql ?
877: serve as wildcards).
878: The list may also contain
879: patterns negated by prefixing them with
880: .Ql ! ;
881: if the canonical host name matches a negated pattern, the key is not accepted.
882: The purpose
1.1 deraadt 883: of this option is to optionally increase security: RSA authentication
884: by itself does not trust the network or name servers or anything (but
885: the key); however, if somebody somehow steals the key, the key
1.36 aaron 886: permits an intruder to log in from anywhere in the world.
887: This additional option makes using a stolen key more difficult (name
1.1 deraadt 888: servers and/or routers would have to be compromised in addition to
889: just the key).
1.2 deraadt 890: .It Cm command="command"
1.1 deraadt 891: Specifies that the command is executed whenever this key is used for
1.36 aaron 892: authentication.
893: The command supplied by the user (if any) is ignored.
1.1 deraadt 894: The command is run on a pty if the connection requests a pty;
1.36 aaron 895: otherwise it is run without a tty.
1.89 markus 896: Note that if you want a 8-bit clean channel,
897: you must not request a pty or should specify
898: .Cm no-pty .
1.36 aaron 899: A quote may be included in the command by quoting it with a backslash.
900: This option might be useful
901: to restrict certain RSA keys to perform just a specific operation.
902: An example might be a key that permits remote backups but nothing else.
1.51 hugh 903: Note that the client may specify TCP/IP and/or X11
904: forwarding unless they are explicitly prohibited.
1.2 deraadt 905: .It Cm environment="NAME=value"
1.1 deraadt 906: Specifies that the string is to be added to the environment when
1.36 aaron 907: logging in using this key.
908: Environment variables set this way
909: override other default environment values.
910: Multiple options of this type are permitted.
1.2 deraadt 911: .It Cm no-port-forwarding
1.1 deraadt 912: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 913: Any port forward requests by the client will return an error.
914: This might be used, e.g., in connection with the
1.2 deraadt 915: .Cm command
1.1 deraadt 916: option.
1.2 deraadt 917: .It Cm no-X11-forwarding
1.1 deraadt 918: Forbids X11 forwarding when this key is used for authentication.
919: Any X11 forward requests by the client will return an error.
1.2 deraadt 920: .It Cm no-agent-forwarding
1.1 deraadt 921: Forbids authentication agent forwarding when this key is used for
922: authentication.
1.2 deraadt 923: .It Cm no-pty
1.1 deraadt 924: Prevents tty allocation (a request to allocate a pty will fail).
1.107 djm 925: .It Cm permitopen="host:port"
926: Limit local
927: .Li ``ssh -L''
1.111 stevesk 928: port forwarding such that it may only connect to the specified host and
1.107 djm 929: port. Multiple
930: .Cm permitopen
1.111 stevesk 931: options may be applied separated by commas. No pattern matching is
1.107 djm 932: performed on the specified hostnames, they must be literal domains or
933: addresses.
1.2 deraadt 934: .El
935: .Ss Examples
1.1 deraadt 936: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 937: .Pp
1.1 deraadt 938: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 939: .Pp
1.1 deraadt 940: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.107 djm 941: .Pp
942: permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
1.2 deraadt 943: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 944: The
1.44 deraadt 945: .Pa /etc/ssh_known_hosts ,
946: .Pa /etc/ssh_known_hosts2 ,
947: .Pa $HOME/.ssh/known_hosts ,
1.40 aaron 948: and
1.44 deraadt 949: .Pa $HOME/.ssh/known_hosts2
1.36 aaron 950: files contain host public keys for all known hosts.
951: The global file should
1.37 brad 952: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 953: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 954: its key is added to the per-user file.
1.2 deraadt 955: .Pp
1.1 deraadt 956: Each line in these files contains the following fields: hostnames,
1.36 aaron 957: bits, exponent, modulus, comment.
958: The fields are separated by spaces.
1.2 deraadt 959: .Pp
1.1 deraadt 960: Hostnames is a comma-separated list of patterns ('*' and '?' act as
961: wildcards); each pattern in turn is matched against the canonical host
962: name (when authenticating a client) or against the user-supplied
1.36 aaron 963: name (when authenticating a server).
964: A pattern may also be preceded by
1.2 deraadt 965: .Ql !
966: to indicate negation: if the host name matches a negated
1.1 deraadt 967: pattern, it is not accepted (by that line) even if it matched another
968: pattern on the line.
1.2 deraadt 969: .Pp
1.49 markus 970: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 971: can be obtained, e.g., from
972: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 973: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 974: .Pp
975: Lines starting with
976: .Ql #
977: and empty lines are ignored as comments.
978: .Pp
1.1 deraadt 979: When performing host authentication, authentication is accepted if any
1.36 aaron 980: matching line has the proper key.
981: It is thus permissible (but not
1.1 deraadt 982: recommended) to have several lines or different host keys for the same
1.36 aaron 983: names.
984: This will inevitably happen when short forms of host names
985: from different domains are put in the file.
986: It is possible
1.1 deraadt 987: that the files contain conflicting information; authentication is
988: accepted if valid information can be found from either file.
1.2 deraadt 989: .Pp
1.1 deraadt 990: Note that the lines in these files are typically hundreds of characters
991: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 992: Rather, generate them by a script
1.40 aaron 993: or by taking
1.2 deraadt 994: .Pa /etc/ssh_host_key.pub
1.1 deraadt 995: and adding the host names at the front.
1.2 deraadt 996: .Ss Examples
1.1 deraadt 997: closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1.2 deraadt 998: .Sh FILES
999: .Bl -tag -width Ds
1000: .It Pa /etc/sshd_config
1.1 deraadt 1001: Contains configuration data for
1.2 deraadt 1002: .Nm sshd .
1.1 deraadt 1003: This file should be writable by root only, but it is recommended
1004: (though not necessary) that it be world-readable.
1.98 deraadt 1005: .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
1006: These three files contain the private parts of the
1007: (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
1008: These files should only be owned by root, readable only by root, and not
1.1 deraadt 1009: accessible to others.
1.14 markus 1010: Note that
1011: .Nm
1012: does not start if this file is group/world-accessible.
1.98 deraadt 1013: .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1.109 stevesk 1014: These three files contain the public parts of the
1.98 deraadt 1015: (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
1016: These files should be world-readable but writable only by
1.36 aaron 1017: root.
1.98 deraadt 1018: Their contents should match the respective private parts.
1019: These files are not
1020: really used for anything; they are provided for the convenience of
1021: the user so their contents can be copied to known hosts files.
1022: These files are created using
1.7 markus 1023: .Xr ssh-keygen 1 .
1.73 provos 1024: .It Pa /etc/primes
1025: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 1026: .It Pa /var/run/sshd.pid
1027: Contains the process ID of the
1028: .Nm
1.1 deraadt 1029: listening for connections (if there are several daemons running
1030: concurrently for different ports, this contains the pid of the one
1.36 aaron 1031: started last).
1.58 deraadt 1032: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 1033: .It Pa $HOME/.ssh/authorized_keys
1.1 deraadt 1034: Lists the RSA keys that can be used to log into the user's account.
1035: This file must be readable by root (which may on some machines imply
1036: it being world-readable if the user's home directory resides on an NFS
1.36 aaron 1037: volume).
1038: It is recommended that it not be accessible by others.
1039: The format of this file is described above.
1.44 deraadt 1040: Users will place the contents of their
1041: .Pa identity.pub
1042: files into this file, as described in
1043: .Xr ssh-keygen 1 .
1044: .It Pa $HOME/.ssh/authorized_keys2
1045: Lists the DSA keys that can be used to log into the user's account.
1046: This file must be readable by root (which may on some machines imply
1047: it being world-readable if the user's home directory resides on an NFS
1048: volume).
1049: It is recommended that it not be accessible by others.
1050: The format of this file is described above.
1051: Users will place the contents of their
1052: .Pa id_dsa.pub
1.113 itojun 1053: and/or
1054: .Pa id_rsa.pub
1.44 deraadt 1055: files into this file, as described in
1056: .Xr ssh-keygen 1 .
1.22 markus 1057: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1058: These files are consulted when using rhosts with RSA host
1.36 aaron 1059: authentication to check the public key of the host.
1060: The key must be listed in one of these files to be accepted.
1.22 markus 1061: The client uses the same files
1.96 markus 1062: to verify that it is connecting to the correct remote host.
1.36 aaron 1063: These files should be writable only by root/the owner.
1.2 deraadt 1064: .Pa /etc/ssh_known_hosts
1065: should be world-readable, and
1066: .Pa $HOME/.ssh/known_hosts
1067: can but need not be world-readable.
1.6 aaron 1068: .It Pa /etc/nologin
1.40 aaron 1069: If this file exists,
1.2 deraadt 1070: .Nm
1.36 aaron 1071: refuses to let anyone except root log in.
1072: The contents of the file
1.1 deraadt 1073: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 1074: refused.
1075: The file should be world-readable.
1.19 dugsong 1076: .It Pa /etc/hosts.allow, /etc/hosts.deny
1077: If compiled with
1078: .Sy LIBWRAP
1079: support, tcp-wrappers access controls may be defined here as described in
1080: .Xr hosts_access 5 .
1.6 aaron 1081: .It Pa $HOME/.rhosts
1.1 deraadt 1082: This file contains host-username pairs, separated by a space, one per
1.36 aaron 1083: line.
1084: The given user on the corresponding host is permitted to log in
1085: without password.
1086: The same file is used by rlogind and rshd.
1.6 aaron 1087: The file must
1.1 deraadt 1088: be writable only by the user; it is recommended that it not be
1089: accessible by others.
1.2 deraadt 1090: .Pp
1.36 aaron 1091: If is also possible to use netgroups in the file.
1092: Either host or user
1.1 deraadt 1093: name may be of the form +@groupname to specify all hosts or all users
1094: in the group.
1.2 deraadt 1095: .It Pa $HOME/.shosts
1096: For ssh,
1097: this file is exactly the same as for
1098: .Pa .rhosts .
1099: However, this file is
1100: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 1101: .It Pa /etc/hosts.equiv
1.2 deraadt 1102: This file is used during
1103: .Pa .rhosts
1.36 aaron 1104: authentication.
1105: In the simplest form, this file contains host names, one per line.
1106: Users on
1.1 deraadt 1107: those hosts are permitted to log in without a password, provided they
1.36 aaron 1108: have the same user name on both machines.
1109: The host name may also be
1.1 deraadt 1110: followed by a user name; such users are permitted to log in as
1.2 deraadt 1111: .Em any
1.36 aaron 1112: user on this machine (except root).
1113: Additionally, the syntax
1.2 deraadt 1114: .Dq +@group
1.36 aaron 1115: can be used to specify netgroups.
1116: Negated entries start with
1.2 deraadt 1117: .Ql \&- .
1118: .Pp
1.1 deraadt 1119: If the client host/user is successfully matched in this file, login is
1120: automatically permitted provided the client and server user names are the
1.36 aaron 1121: same.
1122: Additionally, successful RSA host authentication is normally required.
1123: This file must be writable only by root; it is recommended
1.1 deraadt 1124: that it be world-readable.
1.2 deraadt 1125: .Pp
1.6 aaron 1126: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1127: .Pa hosts.equiv .
1.1 deraadt 1128: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1129: .Em anybody ,
1.1 deraadt 1130: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1131: binaries and directories.
1132: Using a user name practically grants the user root access.
1133: The only valid use for user names that I can think
1.1 deraadt 1134: of is in negative entries.
1.2 deraadt 1135: .Pp
1136: Note that this warning also applies to rsh/rlogin.
1137: .It Pa /etc/shosts.equiv
1.1 deraadt 1138: This is processed exactly as
1.2 deraadt 1139: .Pa /etc/hosts.equiv .
1.1 deraadt 1140: However, this file may be useful in environments that want to run both
1.2 deraadt 1141: rsh/rlogin and ssh.
1.6 aaron 1142: .It Pa $HOME/.ssh/environment
1.36 aaron 1143: This file is read into the environment at login (if it exists).
1144: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1145: .Ql # ) ,
1.36 aaron 1146: and assignment lines of the form name=value.
1147: The file should be writable
1.6 aaron 1148: only by the user; it need not be readable by anyone else.
1.2 deraadt 1149: .It Pa $HOME/.ssh/rc
1.1 deraadt 1150: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1151: environment files but before starting the user's shell or command.
1152: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1153: standard input (and
1154: .Ev DISPLAY
1.36 aaron 1155: in environment).
1156: This must call
1.2 deraadt 1157: .Xr xauth 1
1158: in that case.
1159: .Pp
1.1 deraadt 1160: The primary purpose of this file is to run any initialization routines
1161: which may be needed before the user's home directory becomes
1162: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1163: .Pp
1.1 deraadt 1164: This file will probably contain some initialization code followed by
1165: something similar to: "if read proto cookie; then echo add $DISPLAY
1166: $proto $cookie | xauth -q -; fi".
1.2 deraadt 1167: .Pp
1168: If this file does not exist,
1169: .Pa /etc/sshrc
1170: is run, and if that
1.1 deraadt 1171: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1172: .Pp
1.1 deraadt 1173: This file should be writable only by the user, and need not be
1174: readable by anyone else.
1.2 deraadt 1175: .It Pa /etc/sshrc
1176: Like
1177: .Pa $HOME/.ssh/rc .
1178: This can be used to specify
1.36 aaron 1179: machine-specific login-time initializations globally.
1180: This file should be writable only by root, and should be world-readable.
1.56 aaron 1181: .El
1.71 aaron 1182: .Sh AUTHORS
1.84 markus 1183: OpenSSH is a derivative of the original and free
1184: ssh 1.2.12 release by Tatu Ylonen.
1185: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1186: Theo de Raadt and Dug Song
1187: removed many bugs, re-added newer features and
1188: created OpenSSH.
1189: Markus Friedl contributed the support for SSH
1190: protocol versions 1.5 and 2.0.
1.2 deraadt 1191: .Sh SEE ALSO
1192: .Xr scp 1 ,
1.90 djm 1193: .Xr sftp 1 ,
1.63 markus 1194: .Xr sftp-server 8 ,
1.2 deraadt 1195: .Xr ssh 1 ,
1.5 deraadt 1196: .Xr ssh-add 1 ,
1.2 deraadt 1197: .Xr ssh-agent 1 ,
1.5 deraadt 1198: .Xr ssh-keygen 1 ,
1.38 deraadt 1199: .Xr rlogin 1 ,
1200: .Xr rsh 1
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