Annotation of src/usr.bin/ssh/sshd.8, Revision 1.110
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: .\"
1.110 ! stevesk 37: .\" $OpenBSD: sshd.8,v 1.109 2001/04/02 14:15:31 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
1.7 markus 489: .Nm
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
! 496: host|IPv4_addr|IPv6_addr
! 497: .It
! 498: .Cm ListenAddress
! 499: host|IPv4_addr:port
! 500: .It
! 501: .Cm ListenAddress
! 502: [host|IPv6_addr]:port
! 503: .El
! 504: .Pp
! 505: If
! 506: .Dq :port
! 507: is not specified,
! 508: .Nm
! 509: will listen on the address and all prior
! 510: .Cm Port
! 511: options specified. The default is to listen on all local
! 512: addresses. Multiple
! 513: .Cm ListenAddress
! 514: options are permitted. Additionally, any
! 515: .Cm Port
! 516: options must precede this option for non port qualified addresses.
1.2 deraadt 517: .It Cm LoginGraceTime
1.1 deraadt 518: The server disconnects after this time if the user has not
1.36 aaron 519: successfully logged in.
520: If the value is 0, there is no time limit.
1.1 deraadt 521: The default is 600 (seconds).
1.23 markus 522: .It Cm LogLevel
523: Gives the verbosity level that is used when logging messages from
524: .Nm sshd .
525: The possible values are:
1.82 markus 526: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
527: The default is INFO.
1.23 markus 528: Logging with level DEBUG violates the privacy of users
529: and is not recommended.
1.93 markus 530: .It Cm MACs
531: Specifies the available MAC (message authentication code) algorithms.
532: The MAC algorithm is used in protocol version 2
533: for data integrity protection.
534: Multiple algorithms must be comma-separated.
535: The default is
536: .Pp
537: .Bd -literal
1.105 deraadt 538: ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
1.93 markus 539: hmac-sha1-96,hmac-md5-96''
540: .Ed
1.55 markus 541: .It Cm MaxStartups
542: Specifies the maximum number of concurrent unauthenticated connections to the
543: .Nm
544: daemon.
545: Additional connections will be dropped until authentication succeeds or the
546: .Cm LoginGraceTime
547: expires for a connection.
548: The default is 10.
1.57 markus 549: .Pp
550: Alternatively, random early drop can be enabled by specifying
551: the three colon separated values
552: .Dq start:rate:full
1.67 aaron 553: (e.g., "10:30:60").
1.57 markus 554: .Nm
1.86 stevesk 555: will refuse connection attempts with a probability of
1.57 markus 556: .Dq rate/100
557: (30%)
558: if there are currently
559: .Dq start
560: (10)
561: unauthenticated connections.
1.86 stevesk 562: The probability increases linearly and all connection attempts
1.57 markus 563: are refused if the number of unauthenticated connections reaches
564: .Dq full
565: (60).
1.2 deraadt 566: .It Cm PasswordAuthentication
1.1 deraadt 567: Specifies whether password authentication is allowed.
1.2 deraadt 568: The default is
569: .Dq yes .
1.58 deraadt 570: Note that this option applies to both protocol versions 1 and 2.
1.2 deraadt 571: .It Cm PermitEmptyPasswords
1.1 deraadt 572: When password authentication is allowed, it specifies whether the
1.36 aaron 573: server allows login to accounts with empty password strings.
574: The default is
1.34 markus 575: .Dq no .
1.2 deraadt 576: .It Cm PermitRootLogin
1.100 stevesk 577: Specifies whether root can login using
1.2 deraadt 578: .Xr ssh 1 .
1.15 markus 579: The argument must be
580: .Dq yes ,
1.94 markus 581: .Dq without-password ,
582: .Dq forced-commands-only
1.15 markus 583: or
584: .Dq no .
1.2 deraadt 585: The default is
586: .Dq yes .
1.94 markus 587: .Pp
588: If this option is set to
1.15 markus 589: .Dq without-password
1.94 markus 590: password authentication is disabled for root.
1.2 deraadt 591: .Pp
1.94 markus 592: If this option is set to
593: .Dq forced-commands-only
594: root login with public key authentication will be allowed,
595: but only if the
1.2 deraadt 596: .Ar command
1.94 markus 597: option has been specified
1.1 deraadt 598: (which may be useful for taking remote backups even if root login is
1.94 markus 599: normally not allowed). All other authentication methods are disabled
600: for root.
1.100 stevesk 601: .Pp
602: If this option is set to
603: .Dq no
604: root is not allowed to login.
1.43 markus 605: .It Cm PidFile
606: Specifies the file that contains the process identifier of the
607: .Nm
608: daemon.
609: The default is
610: .Pa /var/run/sshd.pid .
1.2 deraadt 611: .It Cm Port
1.1 deraadt 612: Specifies the port number that
1.2 deraadt 613: .Nm
1.36 aaron 614: listens on.
615: The default is 22.
1.28 markus 616: Multiple options of this type are permitted.
1.108 stevesk 617: .It Cm PrintLastLog
618: Specifies whether
619: .Nm
620: should print the date and time when the user last logged in.
621: The default is
622: .Dq yes .
1.2 deraadt 623: .It Cm PrintMotd
1.1 deraadt 624: Specifies whether
1.2 deraadt 625: .Nm
1.40 aaron 626: should print
1.2 deraadt 627: .Pa /etc/motd
1.36 aaron 628: when a user logs in interactively.
629: (On some systems it is also printed by the shell,
1.2 deraadt 630: .Pa /etc/profile ,
1.36 aaron 631: or equivalent.)
632: The default is
1.2 deraadt 633: .Dq yes .
1.41 markus 634: .It Cm Protocol
635: Specifies the protocol versions
636: .Nm
637: should support.
638: The possible values are
639: .Dq 1
640: and
641: .Dq 2 .
642: Multiple versions must be comma-separated.
643: The default is
644: .Dq 1 .
1.104 deraadt 645: .It Cm PubkeyAuthentication
646: Specifies whether public key authentication is allowed.
647: The default is
648: .Dq yes .
649: Note that this option applies to protocol version 2 only.
1.87 markus 650: .It Cm ReverseMappingCheck
651: Specifies whether
652: .Nm
653: should try to verify the remote host name and check that
654: the resolved host name for the remote IP address maps back to the
655: very same IP address.
656: The default is
657: .Dq no .
1.2 deraadt 658: .It Cm RhostsAuthentication
1.1 deraadt 659: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 660: files is sufficient.
661: Normally, this method should not be permitted because it is insecure.
1.7 markus 662: .Cm RhostsRSAAuthentication
663: should be used
1.1 deraadt 664: instead, because it performs RSA-based host authentication in addition
665: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 666: The default is
667: .Dq no .
668: .It Cm RhostsRSAAuthentication
1.1 deraadt 669: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 670: with successful RSA host authentication is allowed.
671: The default is
1.34 markus 672: .Dq no .
1.2 deraadt 673: .It Cm RSAAuthentication
1.36 aaron 674: Specifies whether pure RSA authentication is allowed.
675: The default is
1.2 deraadt 676: .Dq yes .
1.49 markus 677: Note that this option applies to protocol version 1 only.
1.2 deraadt 678: .It Cm ServerKeyBits
1.36 aaron 679: Defines the number of bits in the server key.
680: The minimum value is 512, and the default is 768.
1.2 deraadt 681: .It Cm StrictModes
1.12 markus 682: Specifies whether
683: .Nm
684: should check file modes and ownership of the
1.36 aaron 685: user's files and home directory before accepting login.
686: This is normally desirable because novices sometimes accidentally leave their
687: directory or files world-writable.
688: The default is
1.7 markus 689: .Dq yes .
1.54 jakob 690: .It Cm Subsystem
1.67 aaron 691: Configures an external subsystem (e.g., file transfer daemon).
692: Arguments should be a subsystem name and a command to execute upon subsystem
693: request.
1.63 markus 694: The command
695: .Xr sftp-server 8
696: implements the
697: .Dq sftp
698: file transfer subsystem.
1.54 jakob 699: By default no subsystems are defined.
700: Note that this option applies to protocol version 2 only.
1.2 deraadt 701: .It Cm SyslogFacility
1.1 deraadt 702: Gives the facility code that is used when logging messages from
1.2 deraadt 703: .Nm sshd .
1.1 deraadt 704: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 705: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
706: The default is AUTH.
1.10 markus 707: .It Cm UseLogin
708: Specifies whether
709: .Xr login 1
1.53 markus 710: is used for interactive login sessions.
711: Note that
712: .Xr login 1
1.58 deraadt 713: is never used for remote command execution.
1.36 aaron 714: The default is
1.10 markus 715: .Dq no .
1.6 aaron 716: .It Cm X11DisplayOffset
717: Specifies the first display number available for
718: .Nm sshd Ns 's
1.36 aaron 719: X11 forwarding.
720: This prevents
1.6 aaron 721: .Nm
722: from interfering with real X11 servers.
1.34 markus 723: The default is 10.
1.30 markus 724: .It Cm X11Forwarding
1.36 aaron 725: Specifies whether X11 forwarding is permitted.
726: The default is
1.34 markus 727: .Dq no .
1.30 markus 728: Note that disabling X11 forwarding does not improve security in any
729: way, as users can always install their own forwarders.
1.52 markus 730: .It Cm XAuthLocation
731: Specifies the location of the
732: .Xr xauth 1
733: program.
734: The default is
735: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 736: .El
737: .Sh LOGIN PROCESS
1.1 deraadt 738: When a user successfully logs in,
1.2 deraadt 739: .Nm
1.1 deraadt 740: does the following:
1.2 deraadt 741: .Bl -enum -offset indent
742: .It
1.1 deraadt 743: If the login is on a tty, and no command has been specified,
1.40 aaron 744: prints last login time and
1.2 deraadt 745: .Pa /etc/motd
1.1 deraadt 746: (unless prevented in the configuration file or by
1.2 deraadt 747: .Pa $HOME/.hushlogin ;
748: see the
1.40 aaron 749: .Sx FILES
1.2 deraadt 750: section).
751: .It
1.1 deraadt 752: If the login is on a tty, records login time.
1.2 deraadt 753: .It
754: Checks
755: .Pa /etc/nologin ;
756: if it exists, prints contents and quits
1.1 deraadt 757: (unless root).
1.2 deraadt 758: .It
1.1 deraadt 759: Changes to run with normal user privileges.
1.2 deraadt 760: .It
1.1 deraadt 761: Sets up basic environment.
1.2 deraadt 762: .It
763: Reads
764: .Pa $HOME/.ssh/environment
765: if it exists.
766: .It
1.1 deraadt 767: Changes to user's home directory.
1.2 deraadt 768: .It
769: If
770: .Pa $HOME/.ssh/rc
771: exists, runs it; else if
772: .Pa /etc/sshrc
773: exists, runs
1.36 aaron 774: it; otherwise runs xauth.
775: The
1.2 deraadt 776: .Dq rc
777: files are given the X11
1.1 deraadt 778: authentication protocol and cookie in standard input.
1.2 deraadt 779: .It
1.1 deraadt 780: Runs user's shell or command.
1.2 deraadt 781: .El
782: .Sh AUTHORIZED_KEYS FILE FORMAT
1.40 aaron 783: The
1.2 deraadt 784: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 785: file lists the RSA keys that are
1.44 deraadt 786: permitted for RSA authentication in SSH protocols 1.3 and 1.5
1.51 hugh 787: Similarly, the
1.44 deraadt 788: .Pa $HOME/.ssh/authorized_keys2
1.75 markus 789: file lists the DSA and RSA keys that are
790: permitted for public key authentication (PubkeyAuthentication)
791: in SSH protocol 2.0.
792: .Pp
1.36 aaron 793: Each line of the file contains one
1.2 deraadt 794: key (empty lines and lines starting with a
795: .Ql #
796: are ignored as
1.36 aaron 797: comments).
1.75 markus 798: Each RSA public key consists of the following fields, separated by
1.36 aaron 799: spaces: options, bits, exponent, modulus, comment.
1.75 markus 800: Each protocol version 2 public key consists of:
801: options, keytype, base64 encoded key, comment.
802: The options fields
803: are optional; its presence is determined by whether the line starts
1.1 deraadt 804: with a number or not (the option field never starts with a number).
1.75 markus 805: The bits, exponent, modulus and comment fields give the RSA key for
806: protocol version 1; the
1.1 deraadt 807: comment field is not used for anything (but may be convenient for the
808: user to identify the key).
1.75 markus 809: For protocol version 2 the keytype is
810: .Dq ssh-dss
811: or
812: .Dq ssh-rsa .
1.2 deraadt 813: .Pp
1.1 deraadt 814: Note that lines in this file are usually several hundred bytes long
1.36 aaron 815: (because of the size of the RSA key modulus).
816: You don't want to type them in; instead, copy the
1.2 deraadt 817: .Pa identity.pub
1.75 markus 818: or the
819: .Pa id_dsa.pub
1.1 deraadt 820: file and edit it.
1.2 deraadt 821: .Pp
1.58 deraadt 822: The options (if present) consist of comma-separated option
1.36 aaron 823: specifications.
824: No spaces are permitted, except within double quotes.
1.1 deraadt 825: The following option specifications are supported:
1.2 deraadt 826: .Bl -tag -width Ds
827: .It Cm from="pattern-list"
1.1 deraadt 828: Specifies that in addition to RSA authentication, the canonical name
829: of the remote host must be present in the comma-separated list of
1.36 aaron 830: patterns
831: .Pf ( Ql *
832: and
833: .Ql ?
834: serve as wildcards).
835: The list may also contain
836: patterns negated by prefixing them with
837: .Ql ! ;
838: if the canonical host name matches a negated pattern, the key is not accepted.
839: The purpose
1.1 deraadt 840: of this option is to optionally increase security: RSA authentication
841: by itself does not trust the network or name servers or anything (but
842: the key); however, if somebody somehow steals the key, the key
1.36 aaron 843: permits an intruder to log in from anywhere in the world.
844: This additional option makes using a stolen key more difficult (name
1.1 deraadt 845: servers and/or routers would have to be compromised in addition to
846: just the key).
1.2 deraadt 847: .It Cm command="command"
1.1 deraadt 848: Specifies that the command is executed whenever this key is used for
1.36 aaron 849: authentication.
850: The command supplied by the user (if any) is ignored.
1.1 deraadt 851: The command is run on a pty if the connection requests a pty;
1.36 aaron 852: otherwise it is run without a tty.
1.89 markus 853: Note that if you want a 8-bit clean channel,
854: you must not request a pty or should specify
855: .Cm no-pty .
1.36 aaron 856: A quote may be included in the command by quoting it with a backslash.
857: This option might be useful
858: to restrict certain RSA keys to perform just a specific operation.
859: An example might be a key that permits remote backups but nothing else.
1.51 hugh 860: Note that the client may specify TCP/IP and/or X11
861: forwarding unless they are explicitly prohibited.
1.2 deraadt 862: .It Cm environment="NAME=value"
1.1 deraadt 863: Specifies that the string is to be added to the environment when
1.36 aaron 864: logging in using this key.
865: Environment variables set this way
866: override other default environment values.
867: Multiple options of this type are permitted.
1.2 deraadt 868: .It Cm no-port-forwarding
1.1 deraadt 869: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 870: Any port forward requests by the client will return an error.
871: This might be used, e.g., in connection with the
1.2 deraadt 872: .Cm command
1.1 deraadt 873: option.
1.2 deraadt 874: .It Cm no-X11-forwarding
1.1 deraadt 875: Forbids X11 forwarding when this key is used for authentication.
876: Any X11 forward requests by the client will return an error.
1.2 deraadt 877: .It Cm no-agent-forwarding
1.1 deraadt 878: Forbids authentication agent forwarding when this key is used for
879: authentication.
1.2 deraadt 880: .It Cm no-pty
1.1 deraadt 881: Prevents tty allocation (a request to allocate a pty will fail).
1.107 djm 882: .It Cm permitopen="host:port"
883: Limit local
884: .Li ``ssh -L''
885: port-forwading such that it may only connect to the specified host and
886: port. Multiple
887: .Cm permitopen
888: options may be applied seperated by commas. No pattern matching is
889: performed on the specified hostnames, they must be literal domains or
890: addresses.
1.2 deraadt 891: .El
892: .Ss Examples
1.1 deraadt 893: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 894: .Pp
1.1 deraadt 895: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 896: .Pp
1.1 deraadt 897: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.107 djm 898: .Pp
899: permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
1.2 deraadt 900: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 901: The
1.44 deraadt 902: .Pa /etc/ssh_known_hosts ,
903: .Pa /etc/ssh_known_hosts2 ,
904: .Pa $HOME/.ssh/known_hosts ,
1.40 aaron 905: and
1.44 deraadt 906: .Pa $HOME/.ssh/known_hosts2
1.36 aaron 907: files contain host public keys for all known hosts.
908: The global file should
1.37 brad 909: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 910: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 911: its key is added to the per-user file.
1.2 deraadt 912: .Pp
1.1 deraadt 913: Each line in these files contains the following fields: hostnames,
1.36 aaron 914: bits, exponent, modulus, comment.
915: The fields are separated by spaces.
1.2 deraadt 916: .Pp
1.1 deraadt 917: Hostnames is a comma-separated list of patterns ('*' and '?' act as
918: wildcards); each pattern in turn is matched against the canonical host
919: name (when authenticating a client) or against the user-supplied
1.36 aaron 920: name (when authenticating a server).
921: A pattern may also be preceded by
1.2 deraadt 922: .Ql !
923: to indicate negation: if the host name matches a negated
1.1 deraadt 924: pattern, it is not accepted (by that line) even if it matched another
925: pattern on the line.
1.2 deraadt 926: .Pp
1.49 markus 927: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 928: can be obtained, e.g., from
929: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 930: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 931: .Pp
932: Lines starting with
933: .Ql #
934: and empty lines are ignored as comments.
935: .Pp
1.1 deraadt 936: When performing host authentication, authentication is accepted if any
1.36 aaron 937: matching line has the proper key.
938: It is thus permissible (but not
1.1 deraadt 939: recommended) to have several lines or different host keys for the same
1.36 aaron 940: names.
941: This will inevitably happen when short forms of host names
942: from different domains are put in the file.
943: It is possible
1.1 deraadt 944: that the files contain conflicting information; authentication is
945: accepted if valid information can be found from either file.
1.2 deraadt 946: .Pp
1.1 deraadt 947: Note that the lines in these files are typically hundreds of characters
948: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 949: Rather, generate them by a script
1.40 aaron 950: or by taking
1.2 deraadt 951: .Pa /etc/ssh_host_key.pub
1.1 deraadt 952: and adding the host names at the front.
1.2 deraadt 953: .Ss Examples
1.1 deraadt 954: closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1.2 deraadt 955: .Sh FILES
956: .Bl -tag -width Ds
957: .It Pa /etc/sshd_config
1.1 deraadt 958: Contains configuration data for
1.2 deraadt 959: .Nm sshd .
1.1 deraadt 960: This file should be writable by root only, but it is recommended
961: (though not necessary) that it be world-readable.
1.98 deraadt 962: .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
963: These three files contain the private parts of the
964: (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
965: These files should only be owned by root, readable only by root, and not
1.1 deraadt 966: accessible to others.
1.14 markus 967: Note that
968: .Nm
969: does not start if this file is group/world-accessible.
1.98 deraadt 970: .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1.109 stevesk 971: These three files contain the public parts of the
1.98 deraadt 972: (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
973: These files should be world-readable but writable only by
1.36 aaron 974: root.
1.98 deraadt 975: Their contents should match the respective private parts.
976: These files are not
977: really used for anything; they are provided for the convenience of
978: the user so their contents can be copied to known hosts files.
979: These files are created using
1.7 markus 980: .Xr ssh-keygen 1 .
1.73 provos 981: .It Pa /etc/primes
982: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 983: .It Pa /var/run/sshd.pid
984: Contains the process ID of the
985: .Nm
1.1 deraadt 986: listening for connections (if there are several daemons running
987: concurrently for different ports, this contains the pid of the one
1.36 aaron 988: started last).
1.58 deraadt 989: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 990: .It Pa $HOME/.ssh/authorized_keys
1.1 deraadt 991: Lists the RSA keys that can be used to log into the user's account.
992: This file must be readable by root (which may on some machines imply
993: it being world-readable if the user's home directory resides on an NFS
1.36 aaron 994: volume).
995: It is recommended that it not be accessible by others.
996: The format of this file is described above.
1.44 deraadt 997: Users will place the contents of their
998: .Pa identity.pub
999: files into this file, as described in
1000: .Xr ssh-keygen 1 .
1001: .It Pa $HOME/.ssh/authorized_keys2
1002: Lists the DSA keys that can be used to log into the user's account.
1003: This file must be readable by root (which may on some machines imply
1004: it being world-readable if the user's home directory resides on an NFS
1005: volume).
1006: It is recommended that it not be accessible by others.
1007: The format of this file is described above.
1008: Users will place the contents of their
1009: .Pa id_dsa.pub
1010: files into this file, as described in
1011: .Xr ssh-keygen 1 .
1.22 markus 1012: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1013: These files are consulted when using rhosts with RSA host
1.36 aaron 1014: authentication to check the public key of the host.
1015: The key must be listed in one of these files to be accepted.
1.22 markus 1016: The client uses the same files
1.96 markus 1017: to verify that it is connecting to the correct remote host.
1.36 aaron 1018: These files should be writable only by root/the owner.
1.2 deraadt 1019: .Pa /etc/ssh_known_hosts
1020: should be world-readable, and
1021: .Pa $HOME/.ssh/known_hosts
1022: can but need not be world-readable.
1.6 aaron 1023: .It Pa /etc/nologin
1.40 aaron 1024: If this file exists,
1.2 deraadt 1025: .Nm
1.36 aaron 1026: refuses to let anyone except root log in.
1027: The contents of the file
1.1 deraadt 1028: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 1029: refused.
1030: The file should be world-readable.
1.19 dugsong 1031: .It Pa /etc/hosts.allow, /etc/hosts.deny
1032: If compiled with
1033: .Sy LIBWRAP
1034: support, tcp-wrappers access controls may be defined here as described in
1035: .Xr hosts_access 5 .
1.6 aaron 1036: .It Pa $HOME/.rhosts
1.1 deraadt 1037: This file contains host-username pairs, separated by a space, one per
1.36 aaron 1038: line.
1039: The given user on the corresponding host is permitted to log in
1040: without password.
1041: The same file is used by rlogind and rshd.
1.6 aaron 1042: The file must
1.1 deraadt 1043: be writable only by the user; it is recommended that it not be
1044: accessible by others.
1.2 deraadt 1045: .Pp
1.36 aaron 1046: If is also possible to use netgroups in the file.
1047: Either host or user
1.1 deraadt 1048: name may be of the form +@groupname to specify all hosts or all users
1049: in the group.
1.2 deraadt 1050: .It Pa $HOME/.shosts
1051: For ssh,
1052: this file is exactly the same as for
1053: .Pa .rhosts .
1054: However, this file is
1055: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 1056: .It Pa /etc/hosts.equiv
1.2 deraadt 1057: This file is used during
1058: .Pa .rhosts
1.36 aaron 1059: authentication.
1060: In the simplest form, this file contains host names, one per line.
1061: Users on
1.1 deraadt 1062: those hosts are permitted to log in without a password, provided they
1.36 aaron 1063: have the same user name on both machines.
1064: The host name may also be
1.1 deraadt 1065: followed by a user name; such users are permitted to log in as
1.2 deraadt 1066: .Em any
1.36 aaron 1067: user on this machine (except root).
1068: Additionally, the syntax
1.2 deraadt 1069: .Dq +@group
1.36 aaron 1070: can be used to specify netgroups.
1071: Negated entries start with
1.2 deraadt 1072: .Ql \&- .
1073: .Pp
1.1 deraadt 1074: If the client host/user is successfully matched in this file, login is
1075: automatically permitted provided the client and server user names are the
1.36 aaron 1076: same.
1077: Additionally, successful RSA host authentication is normally required.
1078: This file must be writable only by root; it is recommended
1.1 deraadt 1079: that it be world-readable.
1.2 deraadt 1080: .Pp
1.6 aaron 1081: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1082: .Pa hosts.equiv .
1.1 deraadt 1083: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1084: .Em anybody ,
1.1 deraadt 1085: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1086: binaries and directories.
1087: Using a user name practically grants the user root access.
1088: The only valid use for user names that I can think
1.1 deraadt 1089: of is in negative entries.
1.2 deraadt 1090: .Pp
1091: Note that this warning also applies to rsh/rlogin.
1092: .It Pa /etc/shosts.equiv
1.1 deraadt 1093: This is processed exactly as
1.2 deraadt 1094: .Pa /etc/hosts.equiv .
1.1 deraadt 1095: However, this file may be useful in environments that want to run both
1.2 deraadt 1096: rsh/rlogin and ssh.
1.6 aaron 1097: .It Pa $HOME/.ssh/environment
1.36 aaron 1098: This file is read into the environment at login (if it exists).
1099: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1100: .Ql # ) ,
1.36 aaron 1101: and assignment lines of the form name=value.
1102: The file should be writable
1.6 aaron 1103: only by the user; it need not be readable by anyone else.
1.2 deraadt 1104: .It Pa $HOME/.ssh/rc
1.1 deraadt 1105: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1106: environment files but before starting the user's shell or command.
1107: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1108: standard input (and
1109: .Ev DISPLAY
1.36 aaron 1110: in environment).
1111: This must call
1.2 deraadt 1112: .Xr xauth 1
1113: in that case.
1114: .Pp
1.1 deraadt 1115: The primary purpose of this file is to run any initialization routines
1116: which may be needed before the user's home directory becomes
1117: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1118: .Pp
1.1 deraadt 1119: This file will probably contain some initialization code followed by
1120: something similar to: "if read proto cookie; then echo add $DISPLAY
1121: $proto $cookie | xauth -q -; fi".
1.2 deraadt 1122: .Pp
1123: If this file does not exist,
1124: .Pa /etc/sshrc
1125: is run, and if that
1.1 deraadt 1126: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1127: .Pp
1.1 deraadt 1128: This file should be writable only by the user, and need not be
1129: readable by anyone else.
1.2 deraadt 1130: .It Pa /etc/sshrc
1131: Like
1132: .Pa $HOME/.ssh/rc .
1133: This can be used to specify
1.36 aaron 1134: machine-specific login-time initializations globally.
1135: This file should be writable only by root, and should be world-readable.
1.56 aaron 1136: .El
1.71 aaron 1137: .Sh AUTHORS
1.84 markus 1138: OpenSSH is a derivative of the original and free
1139: ssh 1.2.12 release by Tatu Ylonen.
1140: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1141: Theo de Raadt and Dug Song
1142: removed many bugs, re-added newer features and
1143: created OpenSSH.
1144: Markus Friedl contributed the support for SSH
1145: protocol versions 1.5 and 2.0.
1.2 deraadt 1146: .Sh SEE ALSO
1147: .Xr scp 1 ,
1.90 djm 1148: .Xr sftp 1 ,
1.63 markus 1149: .Xr sftp-server 8 ,
1.2 deraadt 1150: .Xr ssh 1 ,
1.5 deraadt 1151: .Xr ssh-add 1 ,
1.2 deraadt 1152: .Xr ssh-agent 1 ,
1.5 deraadt 1153: .Xr ssh-keygen 1 ,
1.38 deraadt 1154: .Xr rlogin 1 ,
1155: .Xr rsh 1
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