Annotation of src/usr.bin/ssh/sshd.8, Revision 1.143
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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34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 36: .\"
1.143 ! stevesk 37: .\" $OpenBSD: sshd.8,v 1.142 2001/08/21 21:47:42 stevesk 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: and
1.143 ! stevesk 122: .Xr rexecd 8
1.1 deraadt 123: are disabled (thus completely disabling
1.2 deraadt 124: .Xr rlogin 1
1.1 deraadt 125: and
1.2 deraadt 126: .Xr rsh 1
1.42 hugh 127: into the machine).
1.2 deraadt 128: .Pp
1.49 markus 129: .Ss SSH protocol version 2
130: .Pp
1.58 deraadt 131: Version 2 works similarly:
1.138 markus 132: Each host has a host-specific key (RSA or DSA) used to identify the host.
1.49 markus 133: However, when the daemon starts, it does not generate a server key.
134: Forward security is provided through a Diffie-Hellman key agreement.
135: This key agreement results in a shared session key.
1.120 markus 136: .Pp
1.103 deraadt 137: The rest of the session is encrypted using a symmetric cipher, currently
1.120 markus 138: 128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 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
1.120 markus 146: user (PubkeyAuthentication) or
147: client host (HostbasedAuthentication) authentication method,
148: conventional password authentication and challenge response based methods.
1.49 markus 149: .Pp
150: .Ss Command execution and data forwarding
151: .Pp
1.1 deraadt 152: If the client successfully authenticates itself, a dialog for
1.36 aaron 153: preparing the session is entered.
154: At this time the client may request
1.1 deraadt 155: things like allocating a pseudo-tty, forwarding X11 connections,
156: forwarding TCP/IP connections, or forwarding the authentication agent
157: connection over the secure channel.
1.2 deraadt 158: .Pp
1.1 deraadt 159: Finally, the client either requests a shell or execution of a command.
1.36 aaron 160: The sides then enter session mode.
161: In this mode, either side may send
1.1 deraadt 162: data at any time, and such data is forwarded to/from the shell or
163: command on the server side, and the user terminal in the client side.
1.2 deraadt 164: .Pp
1.1 deraadt 165: When the user program terminates and all forwarded X11 and other
166: connections have been closed, the server sends command exit status to
167: the client, and both sides exit.
1.2 deraadt 168: .Pp
169: .Nm
1.1 deraadt 170: can be configured using command-line options or a configuration
1.36 aaron 171: file.
172: Command-line options override values specified in the
1.1 deraadt 173: configuration file.
1.25 markus 174: .Pp
175: .Nm
176: rereads its configuration file when it receives a hangup signal,
1.97 deraadt 177: .Dv SIGHUP ,
1.128 mpech 178: by executing itself with the name it was started as, i.e.,
1.97 deraadt 179: .Pa /usr/sbin/sshd .
1.18 aaron 180: .Pp
181: The options are as follows:
1.2 deraadt 182: .Bl -tag -width Ds
183: .It Fl b Ar bits
1.120 markus 184: Specifies the number of bits in the ephemeral protocol version 1
185: server key (default 768).
1.2 deraadt 186: .It Fl d
1.36 aaron 187: Debug mode.
188: The server sends verbose debug output to the system
189: log, and does not put itself in the background.
190: The server also will not fork and will only process one connection.
191: This option is only intended for debugging for the server.
1.120 markus 192: Multiple -d options increase the debugging level.
1.67 aaron 193: Maximum is 3.
1.120 markus 194: .It Fl e
195: When this option is specified,
196: .Nm
197: will send the output to the standard error instead of the system log.
1.2 deraadt 198: .It Fl f Ar configuration_file
1.36 aaron 199: Specifies the name of the configuration file.
200: The default is
1.2 deraadt 201: .Pa /etc/sshd_config .
1.16 markus 202: .Nm
203: refuses to start if there is no configuration file.
1.2 deraadt 204: .It Fl g Ar login_grace_time
1.1 deraadt 205: Gives the grace time for clients to authenticate themselves (default
1.77 markus 206: 600 seconds).
1.36 aaron 207: If the client fails to authenticate the user within
208: this many seconds, the server disconnects and exits.
209: A value of zero indicates no limit.
1.2 deraadt 210: .It Fl h Ar host_key_file
1.75 markus 211: Specifies the file from which the host key is read (default
1.2 deraadt 212: .Pa /etc/ssh_host_key ) .
1.7 markus 213: This option must be given if
214: .Nm
215: is not run as root (as the normal
1.1 deraadt 216: host file is normally not readable by anyone but root).
1.75 markus 217: It is possible to have multiple host key files for
1.120 markus 218: the different protocol versions and host key algorithms.
1.2 deraadt 219: .It Fl i
1.7 markus 220: Specifies that
221: .Nm
1.40 aaron 222: is being run from inetd.
1.7 markus 223: .Nm
224: is normally not run
1.1 deraadt 225: from inetd because it needs to generate the server key before it can
1.36 aaron 226: respond to the client, and this may take tens of seconds.
227: Clients would have to wait too long if the key was regenerated every time.
1.35 aaron 228: However, with small key sizes (e.g., 512) using
1.7 markus 229: .Nm
230: from inetd may
1.1 deraadt 231: be feasible.
1.2 deraadt 232: .It Fl k Ar key_gen_time
1.120 markus 233: Specifies how often the ephemeral protocol version 1 server key is
234: regenerated (default 3600 seconds, or one hour).
1.36 aaron 235: The motivation for regenerating the key fairly
1.1 deraadt 236: often is that the key is not stored anywhere, and after about an hour,
237: it becomes impossible to recover the key for decrypting intercepted
238: communications even if the machine is cracked into or physically
1.36 aaron 239: seized.
240: A value of zero indicates that the key will never be regenerated.
1.2 deraadt 241: .It Fl p Ar port
1.1 deraadt 242: Specifies the port on which the server listens for connections
243: (default 22).
1.2 deraadt 244: .It Fl q
1.36 aaron 245: Quiet mode.
246: Nothing is sent to the system log.
247: Normally the beginning,
1.1 deraadt 248: authentication, and termination of each connection is logged.
1.137 stevesk 249: .It Fl t
250: Test mode.
251: Only check the validity of the configuration file and sanity of the keys.
252: This is useful for updating
253: .Nm
254: reliably as configuration options may change.
1.61 markus 255: .It Fl u Ar len
256: This option is used to specify the size of the field
257: in the
258: .Li utmp
259: structure that holds the remote host name.
260: If the resolved host name is longer than
261: .Ar len ,
262: the dotted decimal value will be used instead.
263: This allows hosts with very long host names that
264: overflow this field to still be uniquely identified.
265: Specifying
266: .Fl u0
267: indicates that only dotted decimal addresses
268: should be put into the
269: .Pa utmp
270: file.
1.74 markus 271: .It Fl D
272: When this option is specified
273: .Nm
274: will not detach and does not become a daemon.
275: This allows easy monitoring of
1.76 markus 276: .Nm sshd .
1.29 markus 277: .It Fl 4
278: Forces
279: .Nm
280: to use IPv4 addresses only.
281: .It Fl 6
282: Forces
283: .Nm
284: to use IPv6 addresses only.
1.2 deraadt 285: .El
286: .Sh CONFIGURATION FILE
287: .Nm
1.40 aaron 288: reads configuration data from
1.2 deraadt 289: .Pa /etc/sshd_config
290: (or the file specified with
291: .Fl f
1.36 aaron 292: on the command line).
1.141 stevesk 293: The file contains keyword-argument pairs, one per line.
1.36 aaron 294: Lines starting with
1.2 deraadt 295: .Ql #
1.1 deraadt 296: and empty lines are interpreted as comments.
1.2 deraadt 297: .Pp
1.141 stevesk 298: The possible
299: keywords and their meanings are as follows (note that
300: keywords are case-insensitive and arguments are case-sensitive):
1.2 deraadt 301: .Bl -tag -width Ds
302: .It Cm AFSTokenPassing
1.36 aaron 303: Specifies whether an AFS token may be forwarded to the server.
304: Default is
1.2 deraadt 305: .Dq yes .
1.11 markus 306: .It Cm AllowGroups
1.92 deraadt 307: This keyword can be followed by a list of group names, separated
1.36 aaron 308: by spaces.
309: If specified, login is allowed only for users whose primary
1.81 markus 310: group or supplementary group list matches one of the patterns.
1.11 markus 311: .Ql \&*
312: and
313: .Ql ?
314: can be used as
1.36 aaron 315: wildcards in the patterns.
1.58 deraadt 316: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 317: By default login is allowed regardless of the group list.
1.3 dugsong 318: .Pp
1.69 markus 319: .It Cm AllowTcpForwarding
320: Specifies whether TCP forwarding is permitted.
321: The default is
322: .Dq yes .
323: Note that disabling TCP forwarding does not improve security unless
324: users are also denied shell access, as they can always install their
325: own forwarders.
326: .Pp
1.11 markus 327: .It Cm AllowUsers
1.92 deraadt 328: This keyword can be followed by a list of user names, separated
1.36 aaron 329: by spaces.
330: If specified, login is allowed only for users names that
1.11 markus 331: match one of the patterns.
332: .Ql \&*
333: and
334: .Ql ?
335: can be used as
1.36 aaron 336: wildcards in the patterns.
1.58 deraadt 337: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 338: By default login is allowed regardless of the user name.
1.135 markus 339: If the pattern takes the form USER@HOST then USER and HOST
340: are separately checked, allowing you to restrict logins to particular
341: users from particular hosts.
1.80 markus 342: .Pp
1.125 markus 343: .It Cm AuthorizedKeysFile
1.138 markus 344: Specifies the file that contains the public keys that can be used
345: for user authentication.
1.125 markus 346: .Cm AuthorizedKeysFile
347: may contain tokens of the form %T which are substituted during connection
1.142 stevesk 348: set-up. The following tokens are defined: %% is replaced by a literal '%',
1.125 markus 349: %h is replaced by the home directory of the user being authenticated and
350: %u is replaced by the username of that user.
351: After expansion,
352: .Cm AuthorizedKeysFile
1.126 markus 353: is taken to be an absolute path or one relative to the user's home
1.125 markus 354: directory.
355: The default is
356: .Dq .ssh/authorized_keys
1.80 markus 357: .It Cm Banner
358: In some jurisdictions, sending a warning message before authentication
359: may be relevant for getting legal protection.
360: The contents of the specified file are sent to the remote user before
361: authentication is allowed.
362: This option is only available for protocol version 2.
1.11 markus 363: .Pp
1.104 deraadt 364: .It Cm ChallengeResponseAuthentication
1.136 markus 365: Specifies whether challenge response authentication is allowed.
366: All authentication styles from
367: .Xr login.conf 5
368: are supported.
1.104 deraadt 369: The default is
370: .Dq yes .
1.122 markus 371: .It Cm Ciphers
372: Specifies the ciphers allowed for protocol version 2.
373: Multiple ciphers must be comma-separated.
374: The default is
375: .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
1.115 beck 376: .It Cm ClientAliveInterval
377: Sets a timeout interval in seconds after which if no data has been received
1.133 itojun 378: from the client,
1.115 beck 379: .Nm
380: will send a message through the encrypted
1.116 stevesk 381: channel to request a response from the client.
382: The default
1.115 beck 383: is 0, indicating that these messages will not be sent to the client.
1.116 stevesk 384: This option applies to protocol version 2 only.
1.115 beck 385: .It Cm ClientAliveCountMax
386: Sets the number of client alive messages (see above) which may be
387: sent without
388: .Nm
389: receiving any messages back from the client. If this threshold is
1.133 itojun 390: reached while client alive messages are being sent,
1.115 beck 391: .Nm
392: will disconnect the client, terminating the session. It is important
1.133 itojun 393: to note that the use of client alive messages is very different from
1.116 stevesk 394: .Cm Keepalive
395: (below). The client alive messages are sent through the
1.115 beck 396: encrypted channel and therefore will not be spoofable. The TCP keepalive
1.116 stevesk 397: option enabled by
398: .Cm Keepalive
399: is spoofable. You want to use the client
1.115 beck 400: alive mechanism when you are basing something important on
401: clients having an active connection to the server.
1.116 stevesk 402: .Pp
403: The default value is 3. If you set
404: .Cm ClientAliveInterval
1.115 beck 405: (above) to 15, and leave this value at the default, unresponsive ssh clients
1.133 itojun 406: will be disconnected after approximately 45 seconds.
1.11 markus 407: .It Cm DenyGroups
408: This keyword can be followed by a number of group names, separated
1.36 aaron 409: by spaces.
1.81 markus 410: Users whose primary group or supplementary group list matches
411: one of the patterns aren't allowed to log in.
1.11 markus 412: .Ql \&*
413: and
414: .Ql ?
415: can be used as
1.36 aaron 416: wildcards in the patterns.
1.58 deraadt 417: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 418: By default login is allowed regardless of the group list.
1.11 markus 419: .Pp
420: .It Cm DenyUsers
421: This keyword can be followed by a number of user names, separated
1.36 aaron 422: by spaces.
423: Login is disallowed for user names that match one of the patterns.
1.11 markus 424: .Ql \&*
425: and
426: .Ql ?
1.36 aaron 427: can be used as wildcards in the patterns.
1.58 deraadt 428: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 429: By default login is allowed regardless of the user name.
1.47 markus 430: .It Cm GatewayPorts
431: Specifies whether remote hosts are allowed to connect to ports
432: forwarded for the client.
433: The argument must be
434: .Dq yes
435: or
436: .Dq no .
437: The default is
438: .Dq no .
1.120 markus 439: .It Cm HostbasedAuthentication
440: Specifies whether rhosts or /etc/hosts.equiv authentication together
441: with successful public key client host authentication is allowed
442: (hostbased authentication).
443: This option is similar to
444: .Cm RhostsRSAAuthentication
445: and applies to protocol version 2 only.
446: The default is
447: .Dq no .
1.2 deraadt 448: .It Cm HostKey
1.72 markus 449: Specifies the file containing the private host keys (default
1.46 markus 450: .Pa /etc/ssh_host_key )
1.72 markus 451: used by SSH protocol versions 1 and 2.
1.9 markus 452: Note that
453: .Nm
1.83 markus 454: will refuse to use a file if it is group/world-accessible.
1.72 markus 455: It is possible to have multiple host key files.
456: .Dq rsa1
457: keys are used for version 1 and
458: .Dq dsa
459: or
460: .Dq rsa
461: are used for version 2 of the SSH protocol.
1.2 deraadt 462: .It Cm IgnoreRhosts
1.34 markus 463: Specifies that
464: .Pa .rhosts
1.40 aaron 465: and
1.34 markus 466: .Pa .shosts
1.120 markus 467: files will not be used in
468: .Cm RhostsAuthentication ,
469: .Cm RhostsRSAAuthentication
470: or
471: .Cm HostbasedAuthentication .
472: .Pp
1.2 deraadt 473: .Pa /etc/hosts.equiv
1.1 deraadt 474: and
1.40 aaron 475: .Pa /etc/shosts.equiv
1.36 aaron 476: are still used.
1.40 aaron 477: The default is
1.34 markus 478: .Dq yes .
1.24 markus 479: .It Cm IgnoreUserKnownHosts
480: Specifies whether
481: .Nm
482: should ignore the user's
483: .Pa $HOME/.ssh/known_hosts
1.45 markus 484: during
1.120 markus 485: .Cm RhostsRSAAuthentication
486: or
487: .Cm HostbasedAuthentication .
1.24 markus 488: The default is
1.2 deraadt 489: .Dq no .
490: .It Cm KeepAlive
1.1 deraadt 491: Specifies whether the system should send keepalive messages to the
1.36 aaron 492: other side.
493: If they are sent, death of the connection or crash of one
494: of the machines will be properly noticed.
495: However, this means that
1.1 deraadt 496: connections will die if the route is down temporarily, and some people
1.36 aaron 497: find it annoying.
1.51 hugh 498: On the other hand, if keepalives are not sent,
1.2 deraadt 499: sessions may hang indefinitely on the server, leaving
500: .Dq ghost
501: users and consuming server resources.
502: .Pp
503: The default is
504: .Dq yes
505: (to send keepalives), and the server will notice
1.36 aaron 506: if the network goes down or the client host reboots.
507: This avoids infinitely hanging sessions.
1.2 deraadt 508: .Pp
509: To disable keepalives, the value should be set to
510: .Dq no
511: in both the server and the client configuration files.
512: .It Cm KerberosAuthentication
1.36 aaron 513: Specifies whether Kerberos authentication is allowed.
514: This can be in the form of a Kerberos ticket, or if
1.7 markus 515: .Cm PasswordAuthentication
1.1 deraadt 516: is yes, the password provided by the user will be validated through
1.67 aaron 517: the Kerberos KDC.
518: To use this option, the server needs a
1.59 provos 519: Kerberos servtab which allows the verification of the KDC's identity.
1.36 aaron 520: Default is
1.60 provos 521: .Dq yes .
1.2 deraadt 522: .It Cm KerberosOrLocalPasswd
1.1 deraadt 523: If set then if password authentication through Kerberos fails then
524: the password will be validated via any additional local mechanism
1.2 deraadt 525: such as
1.66 markus 526: .Pa /etc/passwd .
1.36 aaron 527: Default is
1.20 dugsong 528: .Dq yes .
1.2 deraadt 529: .It Cm KerberosTgtPassing
1.1 deraadt 530: Specifies whether a Kerberos TGT may be forwarded to the server.
1.40 aaron 531: Default is
1.3 dugsong 532: .Dq no ,
533: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 534: .It Cm KerberosTicketCleanup
1.7 markus 535: Specifies whether to automatically destroy the user's ticket cache
1.36 aaron 536: file on logout.
537: Default is
1.3 dugsong 538: .Dq yes .
1.2 deraadt 539: .It Cm KeyRegenerationInterval
1.120 markus 540: In protocol version 1, the ephemeral server key is automatically regenerated
541: after this many seconds (if it has been used).
1.36 aaron 542: The purpose of regeneration is to prevent
1.1 deraadt 543: decrypting captured sessions by later breaking into the machine and
1.36 aaron 544: stealing the keys.
545: The key is never stored anywhere.
546: If the value is 0, the key is never regenerated.
547: The default is 3600 (seconds).
1.7 markus 548: .It Cm ListenAddress
1.110 stevesk 549: Specifies the local addresses
1.120 markus 550: .Nm
1.7 markus 551: should listen on.
1.110 stevesk 552: The following forms may be used:
553: .Pp
554: .Bl -item -offset indent -compact
555: .It
556: .Cm ListenAddress
1.112 stevesk 557: .Sm off
558: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
559: .Sm on
1.110 stevesk 560: .It
561: .Cm ListenAddress
1.112 stevesk 562: .Sm off
563: .Ar host No | Ar IPv4_addr No : Ar port
564: .Sm on
1.110 stevesk 565: .It
566: .Cm ListenAddress
1.112 stevesk 567: .Sm off
568: .Oo
569: .Ar host No | Ar IPv6_addr Oc : Ar port
570: .Sm on
1.110 stevesk 571: .El
572: .Pp
573: If
1.112 stevesk 574: .Ar port
1.110 stevesk 575: is not specified,
1.120 markus 576: .Nm
1.110 stevesk 577: will listen on the address and all prior
578: .Cm Port
579: options specified. The default is to listen on all local
580: addresses. Multiple
581: .Cm ListenAddress
582: options are permitted. Additionally, any
583: .Cm Port
584: options must precede this option for non port qualified addresses.
1.2 deraadt 585: .It Cm LoginGraceTime
1.1 deraadt 586: The server disconnects after this time if the user has not
1.36 aaron 587: successfully logged in.
588: If the value is 0, there is no time limit.
1.1 deraadt 589: The default is 600 (seconds).
1.23 markus 590: .It Cm LogLevel
591: Gives the verbosity level that is used when logging messages from
592: .Nm sshd .
593: The possible values are:
1.82 markus 594: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
595: The default is INFO.
1.23 markus 596: Logging with level DEBUG violates the privacy of users
597: and is not recommended.
1.93 markus 598: .It Cm MACs
599: Specifies the available MAC (message authentication code) algorithms.
600: The MAC algorithm is used in protocol version 2
601: for data integrity protection.
602: Multiple algorithms must be comma-separated.
603: The default is
1.123 markus 604: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
1.55 markus 605: .It Cm MaxStartups
606: Specifies the maximum number of concurrent unauthenticated connections to the
607: .Nm
608: daemon.
609: Additional connections will be dropped until authentication succeeds or the
610: .Cm LoginGraceTime
611: expires for a connection.
612: The default is 10.
1.57 markus 613: .Pp
614: Alternatively, random early drop can be enabled by specifying
615: the three colon separated values
616: .Dq start:rate:full
1.67 aaron 617: (e.g., "10:30:60").
1.57 markus 618: .Nm
1.86 stevesk 619: will refuse connection attempts with a probability of
1.57 markus 620: .Dq rate/100
621: (30%)
622: if there are currently
623: .Dq start
624: (10)
625: unauthenticated connections.
1.86 stevesk 626: The probability increases linearly and all connection attempts
1.57 markus 627: are refused if the number of unauthenticated connections reaches
628: .Dq full
629: (60).
1.2 deraadt 630: .It Cm PasswordAuthentication
1.1 deraadt 631: Specifies whether password authentication is allowed.
1.2 deraadt 632: The default is
633: .Dq yes .
634: .It Cm PermitEmptyPasswords
1.1 deraadt 635: When password authentication is allowed, it specifies whether the
1.36 aaron 636: server allows login to accounts with empty password strings.
637: The default is
1.34 markus 638: .Dq no .
1.2 deraadt 639: .It Cm PermitRootLogin
1.100 stevesk 640: Specifies whether root can login using
1.2 deraadt 641: .Xr ssh 1 .
1.15 markus 642: The argument must be
643: .Dq yes ,
1.94 markus 644: .Dq without-password ,
645: .Dq forced-commands-only
1.15 markus 646: or
647: .Dq no .
1.2 deraadt 648: The default is
649: .Dq yes .
1.94 markus 650: .Pp
651: If this option is set to
1.15 markus 652: .Dq without-password
1.94 markus 653: password authentication is disabled for root.
1.2 deraadt 654: .Pp
1.94 markus 655: If this option is set to
656: .Dq forced-commands-only
657: root login with public key authentication will be allowed,
658: but only if the
1.2 deraadt 659: .Ar command
1.94 markus 660: option has been specified
1.1 deraadt 661: (which may be useful for taking remote backups even if root login is
1.94 markus 662: normally not allowed). All other authentication methods are disabled
663: for root.
1.100 stevesk 664: .Pp
665: If this option is set to
666: .Dq no
667: root is not allowed to login.
1.43 markus 668: .It Cm PidFile
669: Specifies the file that contains the process identifier of the
670: .Nm
671: daemon.
672: The default is
673: .Pa /var/run/sshd.pid .
1.2 deraadt 674: .It Cm Port
1.1 deraadt 675: Specifies the port number that
1.2 deraadt 676: .Nm
1.36 aaron 677: listens on.
678: The default is 22.
1.28 markus 679: Multiple options of this type are permitted.
1.120 markus 680: See also
681: .Cm ListenAddress .
1.108 stevesk 682: .It Cm PrintLastLog
683: Specifies whether
684: .Nm
685: should print the date and time when the user last logged in.
686: The default is
687: .Dq yes .
1.2 deraadt 688: .It Cm PrintMotd
1.1 deraadt 689: Specifies whether
1.2 deraadt 690: .Nm
1.40 aaron 691: should print
1.2 deraadt 692: .Pa /etc/motd
1.36 aaron 693: when a user logs in interactively.
694: (On some systems it is also printed by the shell,
1.2 deraadt 695: .Pa /etc/profile ,
1.36 aaron 696: or equivalent.)
697: The default is
1.2 deraadt 698: .Dq yes .
1.41 markus 699: .It Cm Protocol
700: Specifies the protocol versions
701: .Nm
702: should support.
703: The possible values are
704: .Dq 1
705: and
706: .Dq 2 .
707: Multiple versions must be comma-separated.
708: The default is
1.118 deraadt 709: .Dq 2,1 .
1.104 deraadt 710: .It Cm PubkeyAuthentication
711: Specifies whether public key authentication is allowed.
712: The default is
713: .Dq yes .
714: Note that this option applies to protocol version 2 only.
1.87 markus 715: .It Cm ReverseMappingCheck
716: Specifies whether
717: .Nm
718: should try to verify the remote host name and check that
719: the resolved host name for the remote IP address maps back to the
720: very same IP address.
721: The default is
722: .Dq no .
1.2 deraadt 723: .It Cm RhostsAuthentication
1.1 deraadt 724: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 725: files is sufficient.
726: Normally, this method should not be permitted because it is insecure.
1.7 markus 727: .Cm RhostsRSAAuthentication
728: should be used
1.1 deraadt 729: instead, because it performs RSA-based host authentication in addition
730: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 731: The default is
732: .Dq no .
1.120 markus 733: This option applies to protocol version 1 only.
1.2 deraadt 734: .It Cm RhostsRSAAuthentication
1.1 deraadt 735: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 736: with successful RSA host authentication is allowed.
737: The default is
1.34 markus 738: .Dq no .
1.120 markus 739: This option applies to protocol version 1 only.
1.2 deraadt 740: .It Cm RSAAuthentication
1.36 aaron 741: Specifies whether pure RSA authentication is allowed.
742: The default is
1.2 deraadt 743: .Dq yes .
1.120 markus 744: This option applies to protocol version 1 only.
1.2 deraadt 745: .It Cm ServerKeyBits
1.120 markus 746: Defines the number of bits in the ephemeral protocol version 1 server key.
1.36 aaron 747: The minimum value is 512, and the default is 768.
1.2 deraadt 748: .It Cm StrictModes
1.12 markus 749: Specifies whether
750: .Nm
751: should check file modes and ownership of the
1.36 aaron 752: user's files and home directory before accepting login.
753: This is normally desirable because novices sometimes accidentally leave their
754: directory or files world-writable.
755: The default is
1.7 markus 756: .Dq yes .
1.54 jakob 757: .It Cm Subsystem
1.67 aaron 758: Configures an external subsystem (e.g., file transfer daemon).
759: Arguments should be a subsystem name and a command to execute upon subsystem
760: request.
1.63 markus 761: The command
762: .Xr sftp-server 8
763: implements the
764: .Dq sftp
765: file transfer subsystem.
1.54 jakob 766: By default no subsystems are defined.
767: Note that this option applies to protocol version 2 only.
1.2 deraadt 768: .It Cm SyslogFacility
1.1 deraadt 769: Gives the facility code that is used when logging messages from
1.2 deraadt 770: .Nm sshd .
1.1 deraadt 771: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 772: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
773: The default is AUTH.
1.10 markus 774: .It Cm UseLogin
775: Specifies whether
776: .Xr login 1
1.53 markus 777: is used for interactive login sessions.
1.127 markus 778: The default is
779: .Dq no .
1.53 markus 780: Note that
781: .Xr login 1
1.58 deraadt 782: is never used for remote command execution.
1.133 itojun 783: Note also, that if this is enabled,
784: .Cm X11Forwarding
1.127 markus 785: will be disabled because
786: .Xr login 1
787: does not know how to handle
1.133 itojun 788: .Xr xauth 1
1.127 markus 789: cookies.
1.6 aaron 790: .It Cm X11DisplayOffset
791: Specifies the first display number available for
792: .Nm sshd Ns 's
1.36 aaron 793: X11 forwarding.
794: This prevents
1.6 aaron 795: .Nm
796: from interfering with real X11 servers.
1.34 markus 797: The default is 10.
1.30 markus 798: .It Cm X11Forwarding
1.36 aaron 799: Specifies whether X11 forwarding is permitted.
800: The default is
1.34 markus 801: .Dq no .
1.30 markus 802: Note that disabling X11 forwarding does not improve security in any
803: way, as users can always install their own forwarders.
1.133 itojun 804: X11 forwarding is automatically disabled if
805: .Cm UseLogin
806: is enabled.
1.52 markus 807: .It Cm XAuthLocation
808: Specifies the location of the
809: .Xr xauth 1
810: program.
811: The default is
812: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 813: .El
1.124 stevesk 814: .Ss Time Formats
815: .Pp
816: .Nm
817: command-line arguments and configuration file options that specify time
818: may be expressed using a sequence of the form:
819: .Sm off
820: .Ar time Oo Ar qualifier Oc ,
821: .Sm on
822: where
823: .Ar time
824: is a positive integer value and
825: .Ar qualifier
826: is one of the following:
827: .Pp
828: .Bl -tag -width Ds -compact -offset indent
829: .It Cm <none>
830: seconds
831: .It Cm s | Cm S
832: seconds
833: .It Cm m | Cm M
834: minutes
835: .It Cm h | Cm H
836: hours
837: .It Cm d | Cm D
838: days
839: .It Cm w | Cm W
840: weeks
841: .El
842: .Pp
843: Each member of the sequence is added together to calculate
844: the total time value.
845: .Pp
846: Time format examples:
847: .Pp
848: .Bl -tag -width Ds -compact -offset indent
849: .It 600
850: 600 seconds (10 minutes)
851: .It 10m
852: 10 minutes
853: .It 1h30m
854: 1 hour 30 minutes (90 minutes)
855: .El
1.2 deraadt 856: .Sh LOGIN PROCESS
1.1 deraadt 857: When a user successfully logs in,
1.2 deraadt 858: .Nm
1.1 deraadt 859: does the following:
1.2 deraadt 860: .Bl -enum -offset indent
861: .It
1.1 deraadt 862: If the login is on a tty, and no command has been specified,
1.40 aaron 863: prints last login time and
1.2 deraadt 864: .Pa /etc/motd
1.1 deraadt 865: (unless prevented in the configuration file or by
1.2 deraadt 866: .Pa $HOME/.hushlogin ;
867: see the
1.40 aaron 868: .Sx FILES
1.2 deraadt 869: section).
870: .It
1.1 deraadt 871: If the login is on a tty, records login time.
1.2 deraadt 872: .It
873: Checks
874: .Pa /etc/nologin ;
875: if it exists, prints contents and quits
1.1 deraadt 876: (unless root).
1.2 deraadt 877: .It
1.1 deraadt 878: Changes to run with normal user privileges.
1.2 deraadt 879: .It
1.1 deraadt 880: Sets up basic environment.
1.2 deraadt 881: .It
882: Reads
883: .Pa $HOME/.ssh/environment
884: if it exists.
885: .It
1.1 deraadt 886: Changes to user's home directory.
1.2 deraadt 887: .It
888: If
889: .Pa $HOME/.ssh/rc
890: exists, runs it; else if
891: .Pa /etc/sshrc
892: exists, runs
1.36 aaron 893: it; otherwise runs xauth.
894: The
1.2 deraadt 895: .Dq rc
896: files are given the X11
1.1 deraadt 897: authentication protocol and cookie in standard input.
1.2 deraadt 898: .It
1.1 deraadt 899: Runs user's shell or command.
1.2 deraadt 900: .El
901: .Sh AUTHORIZED_KEYS FILE FORMAT
902: .Pa $HOME/.ssh/authorized_keys
1.130 markus 903: is the default file that lists the public keys that are
904: permitted for RSA authentication in protocol version 1
905: and for public key authentication (PubkeyAuthentication)
906: in protocol version 2.
1.125 markus 907: .Cm AuthorizedKeysFile
908: may be used to specify an alternative file.
1.75 markus 909: .Pp
1.36 aaron 910: Each line of the file contains one
1.2 deraadt 911: key (empty lines and lines starting with a
912: .Ql #
913: are ignored as
1.36 aaron 914: comments).
1.75 markus 915: Each RSA public key consists of the following fields, separated by
1.36 aaron 916: spaces: options, bits, exponent, modulus, comment.
1.75 markus 917: Each protocol version 2 public key consists of:
918: options, keytype, base64 encoded key, comment.
919: The options fields
920: are optional; its presence is determined by whether the line starts
1.1 deraadt 921: with a number or not (the option field never starts with a number).
1.75 markus 922: The bits, exponent, modulus and comment fields give the RSA key for
923: protocol version 1; the
1.1 deraadt 924: comment field is not used for anything (but may be convenient for the
925: user to identify the key).
1.75 markus 926: For protocol version 2 the keytype is
927: .Dq ssh-dss
928: or
929: .Dq ssh-rsa .
1.2 deraadt 930: .Pp
1.1 deraadt 931: Note that lines in this file are usually several hundred bytes long
1.36 aaron 932: (because of the size of the RSA key modulus).
933: You don't want to type them in; instead, copy the
1.113 itojun 934: .Pa identity.pub ,
935: .Pa id_dsa.pub
1.75 markus 936: or the
1.113 itojun 937: .Pa id_rsa.pub
1.1 deraadt 938: file and edit it.
1.2 deraadt 939: .Pp
1.58 deraadt 940: The options (if present) consist of comma-separated option
1.36 aaron 941: specifications.
942: No spaces are permitted, except within double quotes.
1.141 stevesk 943: The following option specifications are supported (note
944: that option keywords are case-insensitive):
1.2 deraadt 945: .Bl -tag -width Ds
946: .It Cm from="pattern-list"
1.1 deraadt 947: Specifies that in addition to RSA authentication, the canonical name
948: of the remote host must be present in the comma-separated list of
1.36 aaron 949: patterns
950: .Pf ( Ql *
951: and
952: .Ql ?
953: serve as wildcards).
954: The list may also contain
955: patterns negated by prefixing them with
956: .Ql ! ;
957: if the canonical host name matches a negated pattern, the key is not accepted.
958: The purpose
1.1 deraadt 959: of this option is to optionally increase security: RSA authentication
960: by itself does not trust the network or name servers or anything (but
961: the key); however, if somebody somehow steals the key, the key
1.36 aaron 962: permits an intruder to log in from anywhere in the world.
963: This additional option makes using a stolen key more difficult (name
1.1 deraadt 964: servers and/or routers would have to be compromised in addition to
965: just the key).
1.2 deraadt 966: .It Cm command="command"
1.1 deraadt 967: Specifies that the command is executed whenever this key is used for
1.36 aaron 968: authentication.
969: The command supplied by the user (if any) is ignored.
1.1 deraadt 970: The command is run on a pty if the connection requests a pty;
1.36 aaron 971: otherwise it is run without a tty.
1.89 markus 972: Note that if you want a 8-bit clean channel,
973: you must not request a pty or should specify
974: .Cm no-pty .
1.36 aaron 975: A quote may be included in the command by quoting it with a backslash.
976: This option might be useful
977: to restrict certain RSA keys to perform just a specific operation.
978: An example might be a key that permits remote backups but nothing else.
1.51 hugh 979: Note that the client may specify TCP/IP and/or X11
980: forwarding unless they are explicitly prohibited.
1.2 deraadt 981: .It Cm environment="NAME=value"
1.1 deraadt 982: Specifies that the string is to be added to the environment when
1.36 aaron 983: logging in using this key.
984: Environment variables set this way
985: override other default environment values.
986: Multiple options of this type are permitted.
1.2 deraadt 987: .It Cm no-port-forwarding
1.1 deraadt 988: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 989: Any port forward requests by the client will return an error.
990: This might be used, e.g., in connection with the
1.2 deraadt 991: .Cm command
1.1 deraadt 992: option.
1.2 deraadt 993: .It Cm no-X11-forwarding
1.1 deraadt 994: Forbids X11 forwarding when this key is used for authentication.
995: Any X11 forward requests by the client will return an error.
1.2 deraadt 996: .It Cm no-agent-forwarding
1.1 deraadt 997: Forbids authentication agent forwarding when this key is used for
998: authentication.
1.2 deraadt 999: .It Cm no-pty
1.1 deraadt 1000: Prevents tty allocation (a request to allocate a pty will fail).
1.107 djm 1001: .It Cm permitopen="host:port"
1.133 itojun 1002: Limit local
1.107 djm 1003: .Li ``ssh -L''
1.111 stevesk 1004: port forwarding such that it may only connect to the specified host and
1.133 itojun 1005: port. Multiple
1.107 djm 1006: .Cm permitopen
1.133 itojun 1007: options may be applied separated by commas. No pattern matching is
1008: performed on the specified hostnames, they must be literal domains or
1.107 djm 1009: addresses.
1.2 deraadt 1010: .El
1011: .Ss Examples
1.1 deraadt 1012: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 1013: .Pp
1.1 deraadt 1014: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 1015: .Pp
1.1 deraadt 1016: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.107 djm 1017: .Pp
1018: permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
1.2 deraadt 1019: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 1020: The
1.44 deraadt 1021: .Pa /etc/ssh_known_hosts ,
1.40 aaron 1022: and
1.131 markus 1023: .Pa $HOME/.ssh/known_hosts
1.36 aaron 1024: files contain host public keys for all known hosts.
1025: The global file should
1.37 brad 1026: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 1027: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 1028: its key is added to the per-user file.
1.2 deraadt 1029: .Pp
1.1 deraadt 1030: Each line in these files contains the following fields: hostnames,
1.36 aaron 1031: bits, exponent, modulus, comment.
1032: The fields are separated by spaces.
1.2 deraadt 1033: .Pp
1.1 deraadt 1034: Hostnames is a comma-separated list of patterns ('*' and '?' act as
1035: wildcards); each pattern in turn is matched against the canonical host
1036: name (when authenticating a client) or against the user-supplied
1.36 aaron 1037: name (when authenticating a server).
1038: A pattern may also be preceded by
1.2 deraadt 1039: .Ql !
1040: to indicate negation: if the host name matches a negated
1.1 deraadt 1041: pattern, it is not accepted (by that line) even if it matched another
1042: pattern on the line.
1.2 deraadt 1043: .Pp
1.49 markus 1044: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 1045: can be obtained, e.g., from
1046: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 1047: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 1048: .Pp
1049: Lines starting with
1050: .Ql #
1051: and empty lines are ignored as comments.
1052: .Pp
1.1 deraadt 1053: When performing host authentication, authentication is accepted if any
1.36 aaron 1054: matching line has the proper key.
1055: It is thus permissible (but not
1.1 deraadt 1056: recommended) to have several lines or different host keys for the same
1.36 aaron 1057: names.
1058: This will inevitably happen when short forms of host names
1059: from different domains are put in the file.
1060: It is possible
1.1 deraadt 1061: that the files contain conflicting information; authentication is
1062: accepted if valid information can be found from either file.
1.2 deraadt 1063: .Pp
1.1 deraadt 1064: Note that the lines in these files are typically hundreds of characters
1065: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 1066: Rather, generate them by a script
1.40 aaron 1067: or by taking
1.2 deraadt 1068: .Pa /etc/ssh_host_key.pub
1.1 deraadt 1069: and adding the host names at the front.
1.2 deraadt 1070: .Ss Examples
1.120 markus 1071: .Bd -literal
1072: closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1073: cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....=
1074: .Ed
1.2 deraadt 1075: .Sh FILES
1076: .Bl -tag -width Ds
1077: .It Pa /etc/sshd_config
1.1 deraadt 1078: Contains configuration data for
1.2 deraadt 1079: .Nm sshd .
1.1 deraadt 1080: This file should be writable by root only, but it is recommended
1081: (though not necessary) that it be world-readable.
1.98 deraadt 1082: .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
1.120 markus 1083: These three files contain the private parts of the host keys.
1.98 deraadt 1084: These files should only be owned by root, readable only by root, and not
1.1 deraadt 1085: accessible to others.
1.14 markus 1086: Note that
1087: .Nm
1088: does not start if this file is group/world-accessible.
1.98 deraadt 1089: .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1.120 markus 1090: These three files contain the public parts of the host keys.
1.98 deraadt 1091: These files should be world-readable but writable only by
1.36 aaron 1092: root.
1.98 deraadt 1093: Their contents should match the respective private parts.
1094: These files are not
1095: really used for anything; they are provided for the convenience of
1096: the user so their contents can be copied to known hosts files.
1097: These files are created using
1.7 markus 1098: .Xr ssh-keygen 1 .
1.129 provos 1099: .It Pa /etc/moduli
1.73 provos 1100: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 1101: .It Pa /var/run/sshd.pid
1102: Contains the process ID of the
1103: .Nm
1.1 deraadt 1104: listening for connections (if there are several daemons running
1105: concurrently for different ports, this contains the pid of the one
1.36 aaron 1106: started last).
1.58 deraadt 1107: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 1108: .It Pa $HOME/.ssh/authorized_keys
1.120 markus 1109: Lists the public keys (RSA or DSA) that can be used to log into the user's account.
1.44 deraadt 1110: This file must be readable by root (which may on some machines imply
1111: it being world-readable if the user's home directory resides on an NFS
1112: volume).
1113: It is recommended that it not be accessible by others.
1114: The format of this file is described above.
1115: Users will place the contents of their
1.130 markus 1116: .Pa identity.pub ,
1.44 deraadt 1117: .Pa id_dsa.pub
1.113 itojun 1118: and/or
1119: .Pa id_rsa.pub
1.44 deraadt 1120: files into this file, as described in
1121: .Xr ssh-keygen 1 .
1.22 markus 1122: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1123: These files are consulted when using rhosts with RSA host
1.131 markus 1124: authentication or protocol version 2 hostbased authentication
1125: to check the public key of the host.
1.36 aaron 1126: The key must be listed in one of these files to be accepted.
1.22 markus 1127: The client uses the same files
1.96 markus 1128: to verify that it is connecting to the correct remote host.
1.36 aaron 1129: These files should be writable only by root/the owner.
1.2 deraadt 1130: .Pa /etc/ssh_known_hosts
1131: should be world-readable, and
1132: .Pa $HOME/.ssh/known_hosts
1.120 markus 1133: can but need not be world-readable.
1.6 aaron 1134: .It Pa /etc/nologin
1.40 aaron 1135: If this file exists,
1.2 deraadt 1136: .Nm
1.36 aaron 1137: refuses to let anyone except root log in.
1138: The contents of the file
1.1 deraadt 1139: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 1140: refused.
1141: The file should be world-readable.
1.19 dugsong 1142: .It Pa /etc/hosts.allow, /etc/hosts.deny
1143: If compiled with
1144: .Sy LIBWRAP
1145: support, tcp-wrappers access controls may be defined here as described in
1146: .Xr hosts_access 5 .
1.6 aaron 1147: .It Pa $HOME/.rhosts
1.1 deraadt 1148: This file contains host-username pairs, separated by a space, one per
1.36 aaron 1149: line.
1150: The given user on the corresponding host is permitted to log in
1151: without password.
1152: The same file is used by rlogind and rshd.
1.6 aaron 1153: The file must
1.1 deraadt 1154: be writable only by the user; it is recommended that it not be
1155: accessible by others.
1.2 deraadt 1156: .Pp
1.36 aaron 1157: If is also possible to use netgroups in the file.
1158: Either host or user
1.1 deraadt 1159: name may be of the form +@groupname to specify all hosts or all users
1160: in the group.
1.2 deraadt 1161: .It Pa $HOME/.shosts
1162: For ssh,
1163: this file is exactly the same as for
1164: .Pa .rhosts .
1165: However, this file is
1166: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 1167: .It Pa /etc/hosts.equiv
1.2 deraadt 1168: This file is used during
1169: .Pa .rhosts
1.36 aaron 1170: authentication.
1171: In the simplest form, this file contains host names, one per line.
1172: Users on
1.1 deraadt 1173: those hosts are permitted to log in without a password, provided they
1.36 aaron 1174: have the same user name on both machines.
1175: The host name may also be
1.1 deraadt 1176: followed by a user name; such users are permitted to log in as
1.2 deraadt 1177: .Em any
1.36 aaron 1178: user on this machine (except root).
1179: Additionally, the syntax
1.2 deraadt 1180: .Dq +@group
1.36 aaron 1181: can be used to specify netgroups.
1182: Negated entries start with
1.2 deraadt 1183: .Ql \&- .
1184: .Pp
1.1 deraadt 1185: If the client host/user is successfully matched in this file, login is
1186: automatically permitted provided the client and server user names are the
1.36 aaron 1187: same.
1188: Additionally, successful RSA host authentication is normally required.
1189: This file must be writable only by root; it is recommended
1.1 deraadt 1190: that it be world-readable.
1.2 deraadt 1191: .Pp
1.6 aaron 1192: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1193: .Pa hosts.equiv .
1.1 deraadt 1194: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1195: .Em anybody ,
1.1 deraadt 1196: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1197: binaries and directories.
1198: Using a user name practically grants the user root access.
1199: The only valid use for user names that I can think
1.1 deraadt 1200: of is in negative entries.
1.2 deraadt 1201: .Pp
1202: Note that this warning also applies to rsh/rlogin.
1203: .It Pa /etc/shosts.equiv
1.1 deraadt 1204: This is processed exactly as
1.2 deraadt 1205: .Pa /etc/hosts.equiv .
1.1 deraadt 1206: However, this file may be useful in environments that want to run both
1.2 deraadt 1207: rsh/rlogin and ssh.
1.6 aaron 1208: .It Pa $HOME/.ssh/environment
1.36 aaron 1209: This file is read into the environment at login (if it exists).
1210: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1211: .Ql # ) ,
1.36 aaron 1212: and assignment lines of the form name=value.
1213: The file should be writable
1.6 aaron 1214: only by the user; it need not be readable by anyone else.
1.2 deraadt 1215: .It Pa $HOME/.ssh/rc
1.1 deraadt 1216: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1217: environment files but before starting the user's shell or command.
1218: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1219: standard input (and
1220: .Ev DISPLAY
1.36 aaron 1221: in environment).
1222: This must call
1.2 deraadt 1223: .Xr xauth 1
1224: in that case.
1225: .Pp
1.1 deraadt 1226: The primary purpose of this file is to run any initialization routines
1227: which may be needed before the user's home directory becomes
1228: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1229: .Pp
1.1 deraadt 1230: This file will probably contain some initialization code followed by
1.120 markus 1231: something similar to:
1232: .Bd -literal
1233: if read proto cookie; then
1234: echo add $DISPLAY $proto $cookie | xauth -q -
1235: fi
1236: .Ed
1.2 deraadt 1237: .Pp
1238: If this file does not exist,
1239: .Pa /etc/sshrc
1240: is run, and if that
1.1 deraadt 1241: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1242: .Pp
1.1 deraadt 1243: This file should be writable only by the user, and need not be
1244: readable by anyone else.
1.2 deraadt 1245: .It Pa /etc/sshrc
1246: Like
1247: .Pa $HOME/.ssh/rc .
1248: This can be used to specify
1.36 aaron 1249: machine-specific login-time initializations globally.
1250: This file should be writable only by root, and should be world-readable.
1.56 aaron 1251: .El
1.71 aaron 1252: .Sh AUTHORS
1.84 markus 1253: OpenSSH is a derivative of the original and free
1254: ssh 1.2.12 release by Tatu Ylonen.
1255: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1256: Theo de Raadt and Dug Song
1257: removed many bugs, re-added newer features and
1258: created OpenSSH.
1259: Markus Friedl contributed the support for SSH
1260: protocol versions 1.5 and 2.0.
1.2 deraadt 1261: .Sh SEE ALSO
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 ,
1.136 markus 1268: .Xr login.conf 5 ,
1269: .Xr moduli 5 ,
1.128 mpech 1270: .Xr sftp-server 8
1.119 markus 1271: .Rs
1272: .%A T. Ylonen
1273: .%A T. Kivinen
1274: .%A M. Saarinen
1275: .%A T. Rinne
1276: .%A S. Lehtinen
1277: .%T "SSH Protocol Architecture"
1.139 markus 1278: .%N draft-ietf-secsh-architecture-09.txt
1279: .%D July 2001
1.120 markus 1280: .%O work in progress material
1281: .Re
1282: .Rs
1283: .%A M. Friedl
1284: .%A N. Provos
1285: .%A W. A. Simpson
1286: .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol"
1.132 markus 1287: .%N draft-ietf-secsh-dh-group-exchange-01.txt
1288: .%D April 2001
1.119 markus 1289: .%O work in progress material
1290: .Re
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