Annotation of src/usr.bin/ssh/sshd.8, Revision 1.112
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,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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: .\"
1.111 stevesk 37: .\" $OpenBSD: sshd.8,v 1.110 2001/04/08 16:01:36 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
1.85 markus 46: .Op Fl diqD46
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 .
1.26 markus 266: .It Fl V Ar client_protocol_id
1.68 markus 267: SSH-2 compatibility mode.
1.42 hugh 268: When this option is specified
1.26 markus 269: .Nm
1.42 hugh 270: assumes the client has sent the supplied version string
1.26 markus 271: and skips the
272: Protocol Version Identification Exchange.
1.68 markus 273: This option is not intended to be called directly.
1.29 markus 274: .It Fl 4
275: Forces
276: .Nm
277: to use IPv4 addresses only.
278: .It Fl 6
279: Forces
280: .Nm
281: to use IPv6 addresses only.
1.2 deraadt 282: .El
283: .Sh CONFIGURATION FILE
284: .Nm
1.40 aaron 285: reads configuration data from
1.2 deraadt 286: .Pa /etc/sshd_config
287: (or the file specified with
288: .Fl f
1.36 aaron 289: on the command line).
290: The file contains keyword-value pairs, one per line.
291: Lines starting with
1.2 deraadt 292: .Ql #
1.1 deraadt 293: and empty lines are interpreted as comments.
1.2 deraadt 294: .Pp
1.1 deraadt 295: The following keywords are possible.
1.2 deraadt 296: .Bl -tag -width Ds
297: .It Cm AFSTokenPassing
1.36 aaron 298: Specifies whether an AFS token may be forwarded to the server.
299: Default is
1.2 deraadt 300: .Dq yes .
1.11 markus 301: .It Cm AllowGroups
1.92 deraadt 302: This keyword can be followed by a list of group names, separated
1.36 aaron 303: by spaces.
304: If specified, login is allowed only for users whose primary
1.81 markus 305: group or supplementary group list matches one of the patterns.
1.11 markus 306: .Ql \&*
307: and
308: .Ql ?
309: can be used as
1.36 aaron 310: wildcards in the patterns.
1.58 deraadt 311: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 312: By default login is allowed regardless of the group list.
1.3 dugsong 313: .Pp
1.69 markus 314: .It Cm AllowTcpForwarding
315: Specifies whether TCP forwarding is permitted.
316: The default is
317: .Dq yes .
318: Note that disabling TCP forwarding does not improve security unless
319: users are also denied shell access, as they can always install their
320: own forwarders.
321: .Pp
1.11 markus 322: .It Cm AllowUsers
1.92 deraadt 323: This keyword can be followed by a list of user names, separated
1.36 aaron 324: by spaces.
325: If specified, login is allowed only for users names that
1.11 markus 326: match one of the patterns.
327: .Ql \&*
328: and
329: .Ql ?
330: can be used as
1.36 aaron 331: wildcards in the patterns.
1.58 deraadt 332: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 333: By default login is allowed regardless of the user name.
1.80 markus 334: .Pp
335: .It Cm Banner
336: In some jurisdictions, sending a warning message before authentication
337: may be relevant for getting legal protection.
338: The contents of the specified file are sent to the remote user before
339: authentication is allowed.
340: This option is only available for protocol version 2.
1.11 markus 341: .Pp
1.104 deraadt 342: .It Cm ChallengeResponseAuthentication
343: Specifies whether
344: challenge response
345: authentication is allowed.
346: Currently there is only support for
347: .Xr skey 1
348: authentication.
349: The default is
350: .Dq yes .
1.41 markus 351: .It Cm Ciphers
352: Specifies the ciphers allowed for protocol version 2.
353: Multiple ciphers must be comma-separated.
354: The default is
1.105 deraadt 355: .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
1.8 markus 356: .It Cm CheckMail
357: Specifies whether
358: .Nm
359: should check for new mail for interactive logins.
360: The default is
361: .Dq no .
1.11 markus 362: .It Cm DenyGroups
363: This keyword can be followed by a number of group names, separated
1.36 aaron 364: by spaces.
1.81 markus 365: Users whose primary group or supplementary group list matches
366: one of the patterns aren't allowed to log in.
1.11 markus 367: .Ql \&*
368: and
369: .Ql ?
370: can be used as
1.36 aaron 371: wildcards in the patterns.
1.58 deraadt 372: Only group names are valid; a numerical group ID isn't recognized.
1.81 markus 373: By default login is allowed regardless of the group list.
1.11 markus 374: .Pp
375: .It Cm DenyUsers
376: This keyword can be followed by a number of user names, separated
1.36 aaron 377: by spaces.
378: Login is disallowed for user names that match one of the patterns.
1.11 markus 379: .Ql \&*
380: and
381: .Ql ?
1.36 aaron 382: can be used as wildcards in the patterns.
1.58 deraadt 383: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 384: By default login is allowed regardless of the user name.
1.47 markus 385: .It Cm GatewayPorts
386: Specifies whether remote hosts are allowed to connect to ports
387: forwarded for the client.
388: The argument must be
389: .Dq yes
390: or
391: .Dq no .
392: The default is
393: .Dq no .
1.2 deraadt 394: .It Cm HostKey
1.72 markus 395: Specifies the file containing the private host keys (default
1.46 markus 396: .Pa /etc/ssh_host_key )
1.72 markus 397: used by SSH protocol versions 1 and 2.
1.9 markus 398: Note that
399: .Nm
1.83 markus 400: will refuse to use a file if it is group/world-accessible.
1.72 markus 401: It is possible to have multiple host key files.
402: .Dq rsa1
403: keys are used for version 1 and
404: .Dq dsa
405: or
406: .Dq rsa
407: are used for version 2 of the SSH protocol.
1.2 deraadt 408: .It Cm IgnoreRhosts
1.34 markus 409: Specifies that
410: .Pa .rhosts
1.40 aaron 411: and
1.34 markus 412: .Pa .shosts
413: files will not be used in authentication.
1.2 deraadt 414: .Pa /etc/hosts.equiv
1.1 deraadt 415: and
1.40 aaron 416: .Pa /etc/shosts.equiv
1.36 aaron 417: are still used.
1.40 aaron 418: The default is
1.34 markus 419: .Dq yes .
1.24 markus 420: .It Cm IgnoreUserKnownHosts
421: Specifies whether
422: .Nm
423: should ignore the user's
424: .Pa $HOME/.ssh/known_hosts
1.45 markus 425: during
1.24 markus 426: .Cm RhostsRSAAuthentication .
427: The default is
1.2 deraadt 428: .Dq no .
429: .It Cm KeepAlive
1.1 deraadt 430: Specifies whether the system should send keepalive messages to the
1.36 aaron 431: other side.
432: If they are sent, death of the connection or crash of one
433: of the machines will be properly noticed.
434: However, this means that
1.1 deraadt 435: connections will die if the route is down temporarily, and some people
1.36 aaron 436: find it annoying.
1.51 hugh 437: On the other hand, if keepalives are not sent,
1.2 deraadt 438: sessions may hang indefinitely on the server, leaving
439: .Dq ghost
440: users and consuming server resources.
441: .Pp
442: The default is
443: .Dq yes
444: (to send keepalives), and the server will notice
1.36 aaron 445: if the network goes down or the client host reboots.
446: This avoids infinitely hanging sessions.
1.2 deraadt 447: .Pp
448: To disable keepalives, the value should be set to
449: .Dq no
450: in both the server and the client configuration files.
451: .It Cm KerberosAuthentication
1.36 aaron 452: Specifies whether Kerberos authentication is allowed.
453: This can be in the form of a Kerberos ticket, or if
1.7 markus 454: .Cm PasswordAuthentication
1.1 deraadt 455: is yes, the password provided by the user will be validated through
1.67 aaron 456: the Kerberos KDC.
457: To use this option, the server needs a
1.59 provos 458: Kerberos servtab which allows the verification of the KDC's identity.
1.36 aaron 459: Default is
1.60 provos 460: .Dq yes .
1.2 deraadt 461: .It Cm KerberosOrLocalPasswd
1.1 deraadt 462: If set then if password authentication through Kerberos fails then
463: the password will be validated via any additional local mechanism
1.2 deraadt 464: such as
1.66 markus 465: .Pa /etc/passwd .
1.36 aaron 466: Default is
1.20 dugsong 467: .Dq yes .
1.2 deraadt 468: .It Cm KerberosTgtPassing
1.1 deraadt 469: Specifies whether a Kerberos TGT may be forwarded to the server.
1.40 aaron 470: Default is
1.3 dugsong 471: .Dq no ,
472: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 473: .It Cm KerberosTicketCleanup
1.7 markus 474: Specifies whether to automatically destroy the user's ticket cache
1.36 aaron 475: file on logout.
476: Default is
1.3 dugsong 477: .Dq yes .
1.2 deraadt 478: .It Cm KeyRegenerationInterval
1.1 deraadt 479: The server key is automatically regenerated after this many seconds
1.36 aaron 480: (if it has been used).
481: The purpose of regeneration is to prevent
1.1 deraadt 482: decrypting captured sessions by later breaking into the machine and
1.36 aaron 483: stealing the keys.
484: The key is never stored anywhere.
485: If the value is 0, the key is never regenerated.
486: The default is 3600 (seconds).
1.7 markus 487: .It Cm ListenAddress
1.110 stevesk 488: Specifies the local addresses
1.112 ! stevesk 489: .Xr sshd 8
1.7 markus 490: should listen on.
1.110 stevesk 491: The following forms may be used:
492: .Pp
493: .Bl -item -offset indent -compact
494: .It
495: .Cm ListenAddress
1.112 ! stevesk 496: .Sm off
! 497: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
! 498: .Sm on
1.110 stevesk 499: .It
500: .Cm ListenAddress
1.112 ! stevesk 501: .Sm off
! 502: .Ar host No | Ar IPv4_addr No : Ar port
! 503: .Sm on
1.110 stevesk 504: .It
505: .Cm ListenAddress
1.112 ! stevesk 506: .Sm off
! 507: .Oo
! 508: .Ar host No | Ar IPv6_addr Oc : Ar port
! 509: .Sm on
1.110 stevesk 510: .El
511: .Pp
512: If
1.112 ! stevesk 513: .Ar port
1.110 stevesk 514: is not specified,
1.112 ! stevesk 515: .Xr sshd 8
1.110 stevesk 516: will listen on the address and all prior
517: .Cm Port
518: options specified. The default is to listen on all local
519: addresses. Multiple
520: .Cm ListenAddress
521: options are permitted. Additionally, any
522: .Cm Port
523: options must precede this option for non port qualified addresses.
1.2 deraadt 524: .It Cm LoginGraceTime
1.1 deraadt 525: The server disconnects after this time if the user has not
1.36 aaron 526: successfully logged in.
527: If the value is 0, there is no time limit.
1.1 deraadt 528: The default is 600 (seconds).
1.23 markus 529: .It Cm LogLevel
530: Gives the verbosity level that is used when logging messages from
531: .Nm sshd .
532: The possible values are:
1.82 markus 533: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
534: The default is INFO.
1.23 markus 535: Logging with level DEBUG violates the privacy of users
536: and is not recommended.
1.93 markus 537: .It Cm MACs
538: Specifies the available MAC (message authentication code) algorithms.
539: The MAC algorithm is used in protocol version 2
540: for data integrity protection.
541: Multiple algorithms must be comma-separated.
542: The default is
543: .Pp
544: .Bd -literal
1.105 deraadt 545: ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
1.93 markus 546: hmac-sha1-96,hmac-md5-96''
547: .Ed
1.55 markus 548: .It Cm MaxStartups
549: Specifies the maximum number of concurrent unauthenticated connections to the
550: .Nm
551: daemon.
552: Additional connections will be dropped until authentication succeeds or the
553: .Cm LoginGraceTime
554: expires for a connection.
555: The default is 10.
1.57 markus 556: .Pp
557: Alternatively, random early drop can be enabled by specifying
558: the three colon separated values
559: .Dq start:rate:full
1.67 aaron 560: (e.g., "10:30:60").
1.57 markus 561: .Nm
1.86 stevesk 562: will refuse connection attempts with a probability of
1.57 markus 563: .Dq rate/100
564: (30%)
565: if there are currently
566: .Dq start
567: (10)
568: unauthenticated connections.
1.86 stevesk 569: The probability increases linearly and all connection attempts
1.57 markus 570: are refused if the number of unauthenticated connections reaches
571: .Dq full
572: (60).
1.2 deraadt 573: .It Cm PasswordAuthentication
1.1 deraadt 574: Specifies whether password authentication is allowed.
1.2 deraadt 575: The default is
576: .Dq yes .
1.58 deraadt 577: Note that this option applies to both protocol versions 1 and 2.
1.2 deraadt 578: .It Cm PermitEmptyPasswords
1.1 deraadt 579: When password authentication is allowed, it specifies whether the
1.36 aaron 580: server allows login to accounts with empty password strings.
581: The default is
1.34 markus 582: .Dq no .
1.2 deraadt 583: .It Cm PermitRootLogin
1.100 stevesk 584: Specifies whether root can login using
1.2 deraadt 585: .Xr ssh 1 .
1.15 markus 586: The argument must be
587: .Dq yes ,
1.94 markus 588: .Dq without-password ,
589: .Dq forced-commands-only
1.15 markus 590: or
591: .Dq no .
1.2 deraadt 592: The default is
593: .Dq yes .
1.94 markus 594: .Pp
595: If this option is set to
1.15 markus 596: .Dq without-password
1.94 markus 597: password authentication is disabled for root.
1.2 deraadt 598: .Pp
1.94 markus 599: If this option is set to
600: .Dq forced-commands-only
601: root login with public key authentication will be allowed,
602: but only if the
1.2 deraadt 603: .Ar command
1.94 markus 604: option has been specified
1.1 deraadt 605: (which may be useful for taking remote backups even if root login is
1.94 markus 606: normally not allowed). All other authentication methods are disabled
607: for root.
1.100 stevesk 608: .Pp
609: If this option is set to
610: .Dq no
611: root is not allowed to login.
1.43 markus 612: .It Cm PidFile
613: Specifies the file that contains the process identifier of the
614: .Nm
615: daemon.
616: The default is
617: .Pa /var/run/sshd.pid .
1.2 deraadt 618: .It Cm Port
1.1 deraadt 619: Specifies the port number that
1.2 deraadt 620: .Nm
1.36 aaron 621: listens on.
622: The default is 22.
1.28 markus 623: Multiple options of this type are permitted.
1.108 stevesk 624: .It Cm PrintLastLog
625: Specifies whether
626: .Nm
627: should print the date and time when the user last logged in.
628: The default is
629: .Dq yes .
1.2 deraadt 630: .It Cm PrintMotd
1.1 deraadt 631: Specifies whether
1.2 deraadt 632: .Nm
1.40 aaron 633: should print
1.2 deraadt 634: .Pa /etc/motd
1.36 aaron 635: when a user logs in interactively.
636: (On some systems it is also printed by the shell,
1.2 deraadt 637: .Pa /etc/profile ,
1.36 aaron 638: or equivalent.)
639: The default is
1.2 deraadt 640: .Dq yes .
1.41 markus 641: .It Cm Protocol
642: Specifies the protocol versions
643: .Nm
644: should support.
645: The possible values are
646: .Dq 1
647: and
648: .Dq 2 .
649: Multiple versions must be comma-separated.
650: The default is
651: .Dq 1 .
1.104 deraadt 652: .It Cm PubkeyAuthentication
653: Specifies whether public key authentication is allowed.
654: The default is
655: .Dq yes .
656: Note that this option applies to protocol version 2 only.
1.87 markus 657: .It Cm ReverseMappingCheck
658: Specifies whether
659: .Nm
660: should try to verify the remote host name and check that
661: the resolved host name for the remote IP address maps back to the
662: very same IP address.
663: The default is
664: .Dq no .
1.2 deraadt 665: .It Cm RhostsAuthentication
1.1 deraadt 666: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 667: files is sufficient.
668: Normally, this method should not be permitted because it is insecure.
1.7 markus 669: .Cm RhostsRSAAuthentication
670: should be used
1.1 deraadt 671: instead, because it performs RSA-based host authentication in addition
672: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 673: The default is
674: .Dq no .
675: .It Cm RhostsRSAAuthentication
1.1 deraadt 676: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 677: with successful RSA host authentication is allowed.
678: The default is
1.34 markus 679: .Dq no .
1.2 deraadt 680: .It Cm RSAAuthentication
1.36 aaron 681: Specifies whether pure RSA authentication is allowed.
682: The default is
1.2 deraadt 683: .Dq yes .
1.49 markus 684: Note that this option applies to protocol version 1 only.
1.2 deraadt 685: .It Cm ServerKeyBits
1.36 aaron 686: Defines the number of bits in the server key.
687: The minimum value is 512, and the default is 768.
1.2 deraadt 688: .It Cm StrictModes
1.12 markus 689: Specifies whether
690: .Nm
691: should check file modes and ownership of the
1.36 aaron 692: user's files and home directory before accepting login.
693: This is normally desirable because novices sometimes accidentally leave their
694: directory or files world-writable.
695: The default is
1.7 markus 696: .Dq yes .
1.54 jakob 697: .It Cm Subsystem
1.67 aaron 698: Configures an external subsystem (e.g., file transfer daemon).
699: Arguments should be a subsystem name and a command to execute upon subsystem
700: request.
1.63 markus 701: The command
702: .Xr sftp-server 8
703: implements the
704: .Dq sftp
705: file transfer subsystem.
1.54 jakob 706: By default no subsystems are defined.
707: Note that this option applies to protocol version 2 only.
1.2 deraadt 708: .It Cm SyslogFacility
1.1 deraadt 709: Gives the facility code that is used when logging messages from
1.2 deraadt 710: .Nm sshd .
1.1 deraadt 711: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 712: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
713: The default is AUTH.
1.10 markus 714: .It Cm UseLogin
715: Specifies whether
716: .Xr login 1
1.53 markus 717: is used for interactive login sessions.
718: Note that
719: .Xr login 1
1.58 deraadt 720: is never used for remote command execution.
1.36 aaron 721: The default is
1.10 markus 722: .Dq no .
1.6 aaron 723: .It Cm X11DisplayOffset
724: Specifies the first display number available for
725: .Nm sshd Ns 's
1.36 aaron 726: X11 forwarding.
727: This prevents
1.6 aaron 728: .Nm
729: from interfering with real X11 servers.
1.34 markus 730: The default is 10.
1.30 markus 731: .It Cm X11Forwarding
1.36 aaron 732: Specifies whether X11 forwarding is permitted.
733: The default is
1.34 markus 734: .Dq no .
1.30 markus 735: Note that disabling X11 forwarding does not improve security in any
736: way, as users can always install their own forwarders.
1.52 markus 737: .It Cm XAuthLocation
738: Specifies the location of the
739: .Xr xauth 1
740: program.
741: The default is
742: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 743: .El
744: .Sh LOGIN PROCESS
1.1 deraadt 745: When a user successfully logs in,
1.2 deraadt 746: .Nm
1.1 deraadt 747: does the following:
1.2 deraadt 748: .Bl -enum -offset indent
749: .It
1.1 deraadt 750: If the login is on a tty, and no command has been specified,
1.40 aaron 751: prints last login time and
1.2 deraadt 752: .Pa /etc/motd
1.1 deraadt 753: (unless prevented in the configuration file or by
1.2 deraadt 754: .Pa $HOME/.hushlogin ;
755: see the
1.40 aaron 756: .Sx FILES
1.2 deraadt 757: section).
758: .It
1.1 deraadt 759: If the login is on a tty, records login time.
1.2 deraadt 760: .It
761: Checks
762: .Pa /etc/nologin ;
763: if it exists, prints contents and quits
1.1 deraadt 764: (unless root).
1.2 deraadt 765: .It
1.1 deraadt 766: Changes to run with normal user privileges.
1.2 deraadt 767: .It
1.1 deraadt 768: Sets up basic environment.
1.2 deraadt 769: .It
770: Reads
771: .Pa $HOME/.ssh/environment
772: if it exists.
773: .It
1.1 deraadt 774: Changes to user's home directory.
1.2 deraadt 775: .It
776: If
777: .Pa $HOME/.ssh/rc
778: exists, runs it; else if
779: .Pa /etc/sshrc
780: exists, runs
1.36 aaron 781: it; otherwise runs xauth.
782: The
1.2 deraadt 783: .Dq rc
784: files are given the X11
1.1 deraadt 785: authentication protocol and cookie in standard input.
1.2 deraadt 786: .It
1.1 deraadt 787: Runs user's shell or command.
1.2 deraadt 788: .El
789: .Sh AUTHORIZED_KEYS FILE FORMAT
1.40 aaron 790: The
1.2 deraadt 791: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 792: file lists the RSA keys that are
1.44 deraadt 793: permitted for RSA authentication in SSH protocols 1.3 and 1.5
1.51 hugh 794: Similarly, the
1.44 deraadt 795: .Pa $HOME/.ssh/authorized_keys2
1.75 markus 796: file lists the DSA and RSA keys that are
797: permitted for public key authentication (PubkeyAuthentication)
798: in SSH protocol 2.0.
799: .Pp
1.36 aaron 800: Each line of the file contains one
1.2 deraadt 801: key (empty lines and lines starting with a
802: .Ql #
803: are ignored as
1.36 aaron 804: comments).
1.75 markus 805: Each RSA public key consists of the following fields, separated by
1.36 aaron 806: spaces: options, bits, exponent, modulus, comment.
1.75 markus 807: Each protocol version 2 public key consists of:
808: options, keytype, base64 encoded key, comment.
809: The options fields
810: are optional; its presence is determined by whether the line starts
1.1 deraadt 811: with a number or not (the option field never starts with a number).
1.75 markus 812: The bits, exponent, modulus and comment fields give the RSA key for
813: protocol version 1; the
1.1 deraadt 814: comment field is not used for anything (but may be convenient for the
815: user to identify the key).
1.75 markus 816: For protocol version 2 the keytype is
817: .Dq ssh-dss
818: or
819: .Dq ssh-rsa .
1.2 deraadt 820: .Pp
1.1 deraadt 821: Note that lines in this file are usually several hundred bytes long
1.36 aaron 822: (because of the size of the RSA key modulus).
823: You don't want to type them in; instead, copy the
1.2 deraadt 824: .Pa identity.pub
1.75 markus 825: or the
826: .Pa id_dsa.pub
1.1 deraadt 827: file and edit it.
1.2 deraadt 828: .Pp
1.58 deraadt 829: The options (if present) consist of comma-separated option
1.36 aaron 830: specifications.
831: No spaces are permitted, except within double quotes.
1.1 deraadt 832: The following option specifications are supported:
1.2 deraadt 833: .Bl -tag -width Ds
834: .It Cm from="pattern-list"
1.1 deraadt 835: Specifies that in addition to RSA authentication, the canonical name
836: of the remote host must be present in the comma-separated list of
1.36 aaron 837: patterns
838: .Pf ( Ql *
839: and
840: .Ql ?
841: serve as wildcards).
842: The list may also contain
843: patterns negated by prefixing them with
844: .Ql ! ;
845: if the canonical host name matches a negated pattern, the key is not accepted.
846: The purpose
1.1 deraadt 847: of this option is to optionally increase security: RSA authentication
848: by itself does not trust the network or name servers or anything (but
849: the key); however, if somebody somehow steals the key, the key
1.36 aaron 850: permits an intruder to log in from anywhere in the world.
851: This additional option makes using a stolen key more difficult (name
1.1 deraadt 852: servers and/or routers would have to be compromised in addition to
853: just the key).
1.2 deraadt 854: .It Cm command="command"
1.1 deraadt 855: Specifies that the command is executed whenever this key is used for
1.36 aaron 856: authentication.
857: The command supplied by the user (if any) is ignored.
1.1 deraadt 858: The command is run on a pty if the connection requests a pty;
1.36 aaron 859: otherwise it is run without a tty.
1.89 markus 860: Note that if you want a 8-bit clean channel,
861: you must not request a pty or should specify
862: .Cm no-pty .
1.36 aaron 863: A quote may be included in the command by quoting it with a backslash.
864: This option might be useful
865: to restrict certain RSA keys to perform just a specific operation.
866: An example might be a key that permits remote backups but nothing else.
1.51 hugh 867: Note that the client may specify TCP/IP and/or X11
868: forwarding unless they are explicitly prohibited.
1.2 deraadt 869: .It Cm environment="NAME=value"
1.1 deraadt 870: Specifies that the string is to be added to the environment when
1.36 aaron 871: logging in using this key.
872: Environment variables set this way
873: override other default environment values.
874: Multiple options of this type are permitted.
1.2 deraadt 875: .It Cm no-port-forwarding
1.1 deraadt 876: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 877: Any port forward requests by the client will return an error.
878: This might be used, e.g., in connection with the
1.2 deraadt 879: .Cm command
1.1 deraadt 880: option.
1.2 deraadt 881: .It Cm no-X11-forwarding
1.1 deraadt 882: Forbids X11 forwarding when this key is used for authentication.
883: Any X11 forward requests by the client will return an error.
1.2 deraadt 884: .It Cm no-agent-forwarding
1.1 deraadt 885: Forbids authentication agent forwarding when this key is used for
886: authentication.
1.2 deraadt 887: .It Cm no-pty
1.1 deraadt 888: Prevents tty allocation (a request to allocate a pty will fail).
1.107 djm 889: .It Cm permitopen="host:port"
890: Limit local
891: .Li ``ssh -L''
1.111 stevesk 892: port forwarding such that it may only connect to the specified host and
1.107 djm 893: port. Multiple
894: .Cm permitopen
1.111 stevesk 895: options may be applied separated by commas. No pattern matching is
1.107 djm 896: performed on the specified hostnames, they must be literal domains or
897: addresses.
1.2 deraadt 898: .El
899: .Ss Examples
1.1 deraadt 900: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 901: .Pp
1.1 deraadt 902: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 903: .Pp
1.1 deraadt 904: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.107 djm 905: .Pp
906: permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
1.2 deraadt 907: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 908: The
1.44 deraadt 909: .Pa /etc/ssh_known_hosts ,
910: .Pa /etc/ssh_known_hosts2 ,
911: .Pa $HOME/.ssh/known_hosts ,
1.40 aaron 912: and
1.44 deraadt 913: .Pa $HOME/.ssh/known_hosts2
1.36 aaron 914: files contain host public keys for all known hosts.
915: The global file should
1.37 brad 916: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 917: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 918: its key is added to the per-user file.
1.2 deraadt 919: .Pp
1.1 deraadt 920: Each line in these files contains the following fields: hostnames,
1.36 aaron 921: bits, exponent, modulus, comment.
922: The fields are separated by spaces.
1.2 deraadt 923: .Pp
1.1 deraadt 924: Hostnames is a comma-separated list of patterns ('*' and '?' act as
925: wildcards); each pattern in turn is matched against the canonical host
926: name (when authenticating a client) or against the user-supplied
1.36 aaron 927: name (when authenticating a server).
928: A pattern may also be preceded by
1.2 deraadt 929: .Ql !
930: to indicate negation: if the host name matches a negated
1.1 deraadt 931: pattern, it is not accepted (by that line) even if it matched another
932: pattern on the line.
1.2 deraadt 933: .Pp
1.49 markus 934: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 935: can be obtained, e.g., from
936: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 937: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 938: .Pp
939: Lines starting with
940: .Ql #
941: and empty lines are ignored as comments.
942: .Pp
1.1 deraadt 943: When performing host authentication, authentication is accepted if any
1.36 aaron 944: matching line has the proper key.
945: It is thus permissible (but not
1.1 deraadt 946: recommended) to have several lines or different host keys for the same
1.36 aaron 947: names.
948: This will inevitably happen when short forms of host names
949: from different domains are put in the file.
950: It is possible
1.1 deraadt 951: that the files contain conflicting information; authentication is
952: accepted if valid information can be found from either file.
1.2 deraadt 953: .Pp
1.1 deraadt 954: Note that the lines in these files are typically hundreds of characters
955: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 956: Rather, generate them by a script
1.40 aaron 957: or by taking
1.2 deraadt 958: .Pa /etc/ssh_host_key.pub
1.1 deraadt 959: and adding the host names at the front.
1.2 deraadt 960: .Ss Examples
1.1 deraadt 961: closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1.2 deraadt 962: .Sh FILES
963: .Bl -tag -width Ds
964: .It Pa /etc/sshd_config
1.1 deraadt 965: Contains configuration data for
1.2 deraadt 966: .Nm sshd .
1.1 deraadt 967: This file should be writable by root only, but it is recommended
968: (though not necessary) that it be world-readable.
1.98 deraadt 969: .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
970: These three files contain the private parts of the
971: (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
972: These files should only be owned by root, readable only by root, and not
1.1 deraadt 973: accessible to others.
1.14 markus 974: Note that
975: .Nm
976: does not start if this file is group/world-accessible.
1.98 deraadt 977: .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1.109 stevesk 978: These three files contain the public parts of the
1.98 deraadt 979: (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
980: These files should be world-readable but writable only by
1.36 aaron 981: root.
1.98 deraadt 982: Their contents should match the respective private parts.
983: These files are not
984: really used for anything; they are provided for the convenience of
985: the user so their contents can be copied to known hosts files.
986: These files are created using
1.7 markus 987: .Xr ssh-keygen 1 .
1.73 provos 988: .It Pa /etc/primes
989: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 990: .It Pa /var/run/sshd.pid
991: Contains the process ID of the
992: .Nm
1.1 deraadt 993: listening for connections (if there are several daemons running
994: concurrently for different ports, this contains the pid of the one
1.36 aaron 995: started last).
1.58 deraadt 996: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 997: .It Pa $HOME/.ssh/authorized_keys
1.1 deraadt 998: Lists the RSA keys that can be used to log into the user's account.
999: This file must be readable by root (which may on some machines imply
1000: it being world-readable if the user's home directory resides on an NFS
1.36 aaron 1001: volume).
1002: It is recommended that it not be accessible by others.
1003: The format of this file is described above.
1.44 deraadt 1004: Users will place the contents of their
1005: .Pa identity.pub
1006: files into this file, as described in
1007: .Xr ssh-keygen 1 .
1008: .It Pa $HOME/.ssh/authorized_keys2
1009: Lists the DSA keys that can be used to log into the user's account.
1010: This file must be readable by root (which may on some machines imply
1011: it being world-readable if the user's home directory resides on an NFS
1012: volume).
1013: It is recommended that it not be accessible by others.
1014: The format of this file is described above.
1015: Users will place the contents of their
1016: .Pa id_dsa.pub
1017: files into this file, as described in
1018: .Xr ssh-keygen 1 .
1.22 markus 1019: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1020: These files are consulted when using rhosts with RSA host
1.36 aaron 1021: authentication to check the public key of the host.
1022: The key must be listed in one of these files to be accepted.
1.22 markus 1023: The client uses the same files
1.96 markus 1024: to verify that it is connecting to the correct remote host.
1.36 aaron 1025: These files should be writable only by root/the owner.
1.2 deraadt 1026: .Pa /etc/ssh_known_hosts
1027: should be world-readable, and
1028: .Pa $HOME/.ssh/known_hosts
1029: can but need not be world-readable.
1.6 aaron 1030: .It Pa /etc/nologin
1.40 aaron 1031: If this file exists,
1.2 deraadt 1032: .Nm
1.36 aaron 1033: refuses to let anyone except root log in.
1034: The contents of the file
1.1 deraadt 1035: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 1036: refused.
1037: The file should be world-readable.
1.19 dugsong 1038: .It Pa /etc/hosts.allow, /etc/hosts.deny
1039: If compiled with
1040: .Sy LIBWRAP
1041: support, tcp-wrappers access controls may be defined here as described in
1042: .Xr hosts_access 5 .
1.6 aaron 1043: .It Pa $HOME/.rhosts
1.1 deraadt 1044: This file contains host-username pairs, separated by a space, one per
1.36 aaron 1045: line.
1046: The given user on the corresponding host is permitted to log in
1047: without password.
1048: The same file is used by rlogind and rshd.
1.6 aaron 1049: The file must
1.1 deraadt 1050: be writable only by the user; it is recommended that it not be
1051: accessible by others.
1.2 deraadt 1052: .Pp
1.36 aaron 1053: If is also possible to use netgroups in the file.
1054: Either host or user
1.1 deraadt 1055: name may be of the form +@groupname to specify all hosts or all users
1056: in the group.
1.2 deraadt 1057: .It Pa $HOME/.shosts
1058: For ssh,
1059: this file is exactly the same as for
1060: .Pa .rhosts .
1061: However, this file is
1062: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 1063: .It Pa /etc/hosts.equiv
1.2 deraadt 1064: This file is used during
1065: .Pa .rhosts
1.36 aaron 1066: authentication.
1067: In the simplest form, this file contains host names, one per line.
1068: Users on
1.1 deraadt 1069: those hosts are permitted to log in without a password, provided they
1.36 aaron 1070: have the same user name on both machines.
1071: The host name may also be
1.1 deraadt 1072: followed by a user name; such users are permitted to log in as
1.2 deraadt 1073: .Em any
1.36 aaron 1074: user on this machine (except root).
1075: Additionally, the syntax
1.2 deraadt 1076: .Dq +@group
1.36 aaron 1077: can be used to specify netgroups.
1078: Negated entries start with
1.2 deraadt 1079: .Ql \&- .
1080: .Pp
1.1 deraadt 1081: If the client host/user is successfully matched in this file, login is
1082: automatically permitted provided the client and server user names are the
1.36 aaron 1083: same.
1084: Additionally, successful RSA host authentication is normally required.
1085: This file must be writable only by root; it is recommended
1.1 deraadt 1086: that it be world-readable.
1.2 deraadt 1087: .Pp
1.6 aaron 1088: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1089: .Pa hosts.equiv .
1.1 deraadt 1090: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1091: .Em anybody ,
1.1 deraadt 1092: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1093: binaries and directories.
1094: Using a user name practically grants the user root access.
1095: The only valid use for user names that I can think
1.1 deraadt 1096: of is in negative entries.
1.2 deraadt 1097: .Pp
1098: Note that this warning also applies to rsh/rlogin.
1099: .It Pa /etc/shosts.equiv
1.1 deraadt 1100: This is processed exactly as
1.2 deraadt 1101: .Pa /etc/hosts.equiv .
1.1 deraadt 1102: However, this file may be useful in environments that want to run both
1.2 deraadt 1103: rsh/rlogin and ssh.
1.6 aaron 1104: .It Pa $HOME/.ssh/environment
1.36 aaron 1105: This file is read into the environment at login (if it exists).
1106: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1107: .Ql # ) ,
1.36 aaron 1108: and assignment lines of the form name=value.
1109: The file should be writable
1.6 aaron 1110: only by the user; it need not be readable by anyone else.
1.2 deraadt 1111: .It Pa $HOME/.ssh/rc
1.1 deraadt 1112: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1113: environment files but before starting the user's shell or command.
1114: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1115: standard input (and
1116: .Ev DISPLAY
1.36 aaron 1117: in environment).
1118: This must call
1.2 deraadt 1119: .Xr xauth 1
1120: in that case.
1121: .Pp
1.1 deraadt 1122: The primary purpose of this file is to run any initialization routines
1123: which may be needed before the user's home directory becomes
1124: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1125: .Pp
1.1 deraadt 1126: This file will probably contain some initialization code followed by
1127: something similar to: "if read proto cookie; then echo add $DISPLAY
1128: $proto $cookie | xauth -q -; fi".
1.2 deraadt 1129: .Pp
1130: If this file does not exist,
1131: .Pa /etc/sshrc
1132: is run, and if that
1.1 deraadt 1133: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1134: .Pp
1.1 deraadt 1135: This file should be writable only by the user, and need not be
1136: readable by anyone else.
1.2 deraadt 1137: .It Pa /etc/sshrc
1138: Like
1139: .Pa $HOME/.ssh/rc .
1140: This can be used to specify
1.36 aaron 1141: machine-specific login-time initializations globally.
1142: This file should be writable only by root, and should be world-readable.
1.56 aaron 1143: .El
1.71 aaron 1144: .Sh AUTHORS
1.84 markus 1145: OpenSSH is a derivative of the original and free
1146: ssh 1.2.12 release by Tatu Ylonen.
1147: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1148: Theo de Raadt and Dug Song
1149: removed many bugs, re-added newer features and
1150: created OpenSSH.
1151: Markus Friedl contributed the support for SSH
1152: protocol versions 1.5 and 2.0.
1.2 deraadt 1153: .Sh SEE ALSO
1154: .Xr scp 1 ,
1.90 djm 1155: .Xr sftp 1 ,
1.63 markus 1156: .Xr sftp-server 8 ,
1.2 deraadt 1157: .Xr ssh 1 ,
1.5 deraadt 1158: .Xr ssh-add 1 ,
1.2 deraadt 1159: .Xr ssh-agent 1 ,
1.5 deraadt 1160: .Xr ssh-keygen 1 ,
1.38 deraadt 1161: .Xr rlogin 1 ,
1162: .Xr rsh 1
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