Annotation of src/usr.bin/ssh/sshd.8, Revision 1.6
1.1 deraadt 1: .\" -*- nroff -*-
2: .\"
3: .\" sshd.8.in
4: .\"
5: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
6: .\"
7: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
8: .\" All rights reserved
9: .\"
10: .\" Created: Sat Apr 22 21:55:14 1995 ylo
11: .\"
1.6 ! aaron 12: .\" $Id: sshd.8,v 1.5 1999/10/02 13:10:26 deraadt Exp $
1.1 deraadt 13: .\"
1.2 deraadt 14: .Dd September 25, 1999
15: .Dt SSHD 8
16: .Os
17: .Sh NAME
18: .Nm sshd
19: .Nd secure shell daemon
20: .Sh SYNOPSIS
21: .Nm sshd
22: .Op Fl diq
23: .Op Fl b Ar bits
24: .Op Fl f Ar config_file
25: .Op Fl g Ar login_grace_time
26: .Op Fl h Ar host_key_file
27: .Op Fl k Ar key_gen_time
28: .Op Fl p Ar port
29: .Sh DESCRIPTION
30: .Nm
1.1 deraadt 31: (Secure Shell Daemon) is the daemon program for
1.2 deraadt 32: .Xr ssh 1 .
1.1 deraadt 33: Together these programs replace rlogin and rsh programs, and
34: provide secure encrypted communications between two untrusted hosts
35: over an insecure network. The programs are intended to be as easy to
36: install and use as possible.
1.2 deraadt 37: .Pp
38: .Nm
1.1 deraadt 39: is the daemon that listens for connections from clients. It is
40: normally started at boot from
1.2 deraadt 41: .Pa /etc/rc .
42: It forks a new
1.1 deraadt 43: daemon for each incoming connection. The forked daemons handle
44: key exchange, encryption, authentication, command execution,
45: and data exchange.
1.2 deraadt 46: .Pp
47: .Nm
48: works as follows. Each host has a host-specific RSA key
1.1 deraadt 49: (normally 1024 bits) used to identify the host. Additionally, when
50: the daemon starts, it generates a server RSA key (normally 768 bits).
51: This key is normally regenerated every hour if it has been used, and
52: is never stored on disk.
1.2 deraadt 53: .Pp
1.1 deraadt 54: Whenever a client connects the daemon, the daemon sends its host
55: and server public keys to the client. The client compares the
56: host key against its own database to verify that it has not changed.
57: The client then generates a 256 bit random number. It encrypts this
58: random number using both the host key and the server key, and sends
59: the encrypted number to the server. Both sides then start to use this
60: random number as a session key which is used to encrypt all further
61: communications in the session. The rest of the session is encrypted
1.5 deraadt 62: using a conventional cipher, currently Blowfish and 3DES, with 3DES
63: being is used by default. The client selects the encryption algorithm
64: to use from those offered by the server.
1.2 deraadt 65: .Pp
1.1 deraadt 66: Next, the server and the client enter an authentication dialog. The
1.2 deraadt 67: client tries to authenticate itself using
68: .Pa .rhosts
69: authentication,
70: .Pa .rhosts
71: authentication combined with RSA host
1.1 deraadt 72: authentication, RSA challenge-response authentication, or password
73: based authentication.
1.2 deraadt 74: .Pp
1.1 deraadt 75: Rhosts authentication is normally disabled
76: because it is fundamentally insecure, but can be enabled in the server
77: configuration file if desired. System security is not improved unless
1.2 deraadt 78: .Xr rshd 8 ,
79: .Xr rlogind 8 ,
80: .Xr rexecd 8 ,
81: and
82: .Xr rexd 8
1.1 deraadt 83: are disabled (thus completely disabling
1.2 deraadt 84: .Xr rlogin 1
1.1 deraadt 85: and
1.2 deraadt 86: .Xr rsh 1
1.1 deraadt 87: into that machine).
1.2 deraadt 88: .Pp
1.1 deraadt 89: If the client successfully authenticates itself, a dialog for
90: preparing the session is entered. At this time the client may request
91: things like allocating a pseudo-tty, forwarding X11 connections,
92: forwarding TCP/IP connections, or forwarding the authentication agent
93: connection over the secure channel.
1.2 deraadt 94: .Pp
1.1 deraadt 95: Finally, the client either requests a shell or execution of a command.
96: The sides then enter session mode. In this mode, either side may send
97: data at any time, and such data is forwarded to/from the shell or
98: command on the server side, and the user terminal in the client side.
1.2 deraadt 99: .Pp
1.1 deraadt 100: When the user program terminates and all forwarded X11 and other
101: connections have been closed, the server sends command exit status to
102: the client, and both sides exit.
1.2 deraadt 103: .Pp
104: .Nm
1.1 deraadt 105: can be configured using command-line options or a configuration
106: file. Command-line options override values specified in the
107: configuration file.
1.2 deraadt 108: .Sh OPTIONS
109: .Bl -tag -width Ds
110: .It Fl b Ar bits
1.1 deraadt 111: Specifies the number of bits in the server key (default 768).
1.2 deraadt 112: .Pp
113: .It Fl d
1.1 deraadt 114: Debug mode. The server sends verbose debug output to the system
115: log, and does not put itself in the background. The server also will
116: not fork and will only process one connection. This option is only
117: intended for debugging for the server.
1.2 deraadt 118: .It Fl f Ar configuration_file
1.1 deraadt 119: Specifies the name of the configuration file. The default is
1.2 deraadt 120: .Pa /etc/sshd_config .
121: .It Fl g Ar login_grace_time
1.1 deraadt 122: Gives the grace time for clients to authenticate themselves (default
123: 300 seconds). If the client fails to authenticate the user within
124: this many seconds, the server disconnects and exits. A value of zero
125: indicates no limit.
1.2 deraadt 126: .It Fl h Ar host_key_file
1.1 deraadt 127: Specifies the file from which the host key is read (default
1.2 deraadt 128: .Pa /etc/ssh_host_key ) .
1.1 deraadt 129: This option must be given if sshd is not run as root (as the normal
130: host file is normally not readable by anyone but root).
1.2 deraadt 131: .It Fl i
1.1 deraadt 132: Specifies that sshd is being run from inetd. Sshd is normally not run
133: from inetd because it needs to generate the server key before it can
134: respond to the client, and this may take tens of seconds. Clients
135: would have to wait too long if the key was regenerated every time.
136: However, with small key sizes (e.g. 512) using sshd from inetd may
137: be feasible.
1.2 deraadt 138: .It Fl k Ar key_gen_time
1.1 deraadt 139: Specifies how often the server key is regenerated (default 3600
140: seconds, or one hour). The motivation for regenerating the key fairly
141: often is that the key is not stored anywhere, and after about an hour,
142: it becomes impossible to recover the key for decrypting intercepted
143: communications even if the machine is cracked into or physically
144: seized. A value of zero indicates that the key will never be regenerated.
1.2 deraadt 145: .It Fl p Ar port
1.1 deraadt 146: Specifies the port on which the server listens for connections
147: (default 22).
1.2 deraadt 148: .It Fl q
1.1 deraadt 149: Quiet mode. Nothing is sent to the system log. Normally the beginning,
150: authentication, and termination of each connection is logged.
1.2 deraadt 151: .El
152: .Sh CONFIGURATION FILE
153: .Nm
1.1 deraadt 154: reads configuration data from
1.2 deraadt 155: .Pa /etc/sshd_config
156: (or the file specified with
157: .Fl f
158: on the command line). The file
159: contains keyword-value pairs, one per line. Lines starting with
160: .Ql #
1.1 deraadt 161: and empty lines are interpreted as comments.
1.2 deraadt 162: .Pp
1.1 deraadt 163: The following keywords are possible.
1.2 deraadt 164: .Bl -tag -width Ds
165: .It Cm AFSTokenPassing
1.3 dugsong 166: Specifies whether an AFS token may be forwarded to the server. Default is
1.2 deraadt 167: .Dq yes .
1.3 dugsong 168: .Pp
1.2 deraadt 169: .It Cm AllowHosts
1.1 deraadt 170: This keyword can be followed by any number of host name patterns,
171: separated by spaces. If specified, login is allowed only from hosts
1.2 deraadt 172: whose name matches one of the patterns.
173: .Ql \&*
174: and
175: .Ql ?
176: can be used as
1.1 deraadt 177: wildcards in the patterns. Normal name servers are used to map the
178: client's host into a canonical host name. If the name cannot be
179: mapped, its IP-address is used as the host name. By default all hosts
180: are allowed to connect.
1.2 deraadt 181: .Pp
1.1 deraadt 182: Note that
1.2 deraadt 183: .Nm
184: can also be configured to use tcp_wrappers using the
1.6 ! aaron 185: .Fl LIBWARP
! 186: compile-time option.
1.2 deraadt 187: .It Cm DenyHosts
1.1 deraadt 188: This keyword can be followed by any number of host name patterns,
189: separated by spaces. If specified, login is disallowed from the hosts
190: whose name matches any of the patterns.
1.2 deraadt 191: .It Cm FascistLogging
1.1 deraadt 192: Specifies whether to use verbose logging. Verbose logging violates
193: the privacy of users and is not recommended. The argument must be
1.2 deraadt 194: .Dq yes
195: or
196: .Dq no .
197: The default is
198: .Dq no .
199: .It Cm HostKey
1.1 deraadt 200: Specifies the file containing the private host key (default
1.2 deraadt 201: .Pa /etc/ssh_host_key ) .
202: .It Cm IgnoreRhosts
1.1 deraadt 203: Specifies that rhosts and shosts files will not be used in
204: authentication.
1.2 deraadt 205: .Pa /etc/hosts.equiv
1.1 deraadt 206: and
1.2 deraadt 207: .Pa /etc/shosts.equiv
208: are still used. The default is
209: .Dq no .
210: .It Cm KeepAlive
1.1 deraadt 211: Specifies whether the system should send keepalive messages to the
212: other side. If they are sent, death of the connection or crash of one
213: of the machines will be properly noticed. However, this means that
214: connections will die if the route is down temporarily, and some people
215: find it annoying. On the other hand, if keepalives are not send,
1.2 deraadt 216: sessions may hang indefinitely on the server, leaving
217: .Dq ghost
218: users and consuming server resources.
219: .Pp
220: The default is
221: .Dq yes
222: (to send keepalives), and the server will notice
1.1 deraadt 223: if the network goes down or the client host reboots. This avoids
224: infinitely hanging sessions.
1.2 deraadt 225: .Pp
226: To disable keepalives, the value should be set to
227: .Dq no
228: in both the server and the client configuration files.
229: .It Cm KerberosAuthentication
1.1 deraadt 230: Specifies whether Kerberos authentication is allowed. This can
231: be in the form of a Kerberos ticket, or if PasswordAuthentication
232: is yes, the password provided by the user will be validated through
1.3 dugsong 233: the Kerberos KDC. Default is
234: .Dq yes .
1.2 deraadt 235: .It Cm KerberosOrLocalPasswd
1.1 deraadt 236: If set then if password authentication through Kerberos fails then
237: the password will be validated via any additional local mechanism
1.2 deraadt 238: such as
239: .Pa /etc/passwd
240: or SecurID. Default is
241: .Dq no .
242: .It Cm KerberosTgtPassing
1.1 deraadt 243: Specifies whether a Kerberos TGT may be forwarded to the server.
1.3 dugsong 244: Default is
245: .Dq no ,
246: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 247: .It Cm KerberosTicketCleanup
1.1 deraadt 248: Specifies whether to automatically destroy the user's
1.3 dugsong 249: ticket cache file on logout. Default is
250: .Dq yes .
1.2 deraadt 251: .It Cm KeyRegenerationInterval
1.1 deraadt 252: The server key is automatically regenerated after this many seconds
253: (if it has been used). The purpose of regeneration is to prevent
254: decrypting captured sessions by later breaking into the machine and
255: stealing the keys. The key is never stored anywhere. If the value is
256: 0, the key is never regenerated. The default is 3600
257: (seconds).
1.2 deraadt 258: .It Cm LoginGraceTime
1.1 deraadt 259: The server disconnects after this time if the user has not
260: successfully logged in. If the value is 0, there is no time limit.
261: The default is 600 (seconds).
1.2 deraadt 262: .It Cm PasswordAuthentication
1.1 deraadt 263: Specifies whether password authentication is allowed.
1.2 deraadt 264: The default is
265: .Dq yes .
266: .It Cm PermitEmptyPasswords
1.1 deraadt 267: When password authentication is allowed, it specifies whether the
268: server allows login to accounts with empty password strings. The default
1.2 deraadt 269: is
270: .Dq yes .
271: .It Cm PermitRootLogin
1.1 deraadt 272: Specifies whether the root can log in using
1.2 deraadt 273: .Xr ssh 1 .
274: The default is
275: .Dq yes .
276: .Pp
277: Root login with RSA authentication when the
278: .Ar command
279: option has been
1.1 deraadt 280: specified will be allowed regardless of the value of this setting
281: (which may be useful for taking remote backups even if root login is
282: normally not allowed).
1.2 deraadt 283: .It Cm Port
1.1 deraadt 284: Specifies the port number that
1.2 deraadt 285: .Nm
1.1 deraadt 286: listens on. The default is 22.
1.2 deraadt 287: .It Cm PrintMotd
1.1 deraadt 288: Specifies whether
1.2 deraadt 289: .Nm
1.1 deraadt 290: should print
1.2 deraadt 291: .Pa /etc/motd
1.1 deraadt 292: when a user logs in interactively. (On some systems it is also
1.2 deraadt 293: printed by the shell,
294: .Pa /etc/profile ,
295: or equivalent.) The default is
296: .Dq yes .
297: .It Cm QuietMode
1.1 deraadt 298: Specifies whether the system runs in quiet mode. In quiet mode,
299: nothing is logged in the system log, except fatal errors. The default
1.2 deraadt 300: is
301: .Dq no .
302: .It Cm RandomSeed
1.4 deraadt 303: Obsolete. Random number generation uses other techniques.
1.2 deraadt 304: .It Cm RhostsAuthentication
1.1 deraadt 305: Specifies whether authentication using rhosts or /etc/hosts.equiv
306: files is sufficient. Normally, this method should not be permitted
307: because it is insecure. RhostsRSAAuthentication should be used
308: instead, because it performs RSA-based host authentication in addition
309: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 310: The default is
311: .Dq no .
312: .It Cm RhostsRSAAuthentication
1.1 deraadt 313: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.2 deraadt 314: with successful RSA host authentication is allowed. The default is
315: .Dq yes .
316: .It Cm RSAAuthentication
317: Specifies whether pure RSA authentication is allowed. The default is
318: .Dq yes .
319: .It Cm ServerKeyBits
1.1 deraadt 320: Defines the number of bits in the server key. The minimum value is
321: 512, and the default is 768.
1.2 deraadt 322: .It Cm StrictModes
323: Specifies whether SSH should check file modes and ownership of the
1.1 deraadt 324: user's home directory and rhosts files before accepting login. This
325: is normally desirable because novices sometimes accidentally leave their
326: directory or files world-writable. The default is "yes".
1.2 deraadt 327: .It Cm SyslogFacility
1.1 deraadt 328: Gives the facility code that is used when logging messages from
1.2 deraadt 329: .Nm sshd .
1.1 deraadt 330: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
331: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is DAEMON.
1.2 deraadt 332: .It Cm X11Forwarding
333: Specifies whether X11 forwarding is permitted. The default is
334: .Dq yes .
1.1 deraadt 335: Note that disabling X11 forwarding does not improve security in any
336: way, as users can always install their own forwarders.
1.6 ! aaron 337: .It Cm X11DisplayOffset
! 338: Specifies the first display number available for
! 339: .Nm sshd Ns 's
! 340: X11 forwarding. This prevents
! 341: .Nm
! 342: from interfering with real X11 servers.
1.2 deraadt 343: .El
344: .Sh LOGIN PROCESS
1.1 deraadt 345: When a user successfully logs in,
1.2 deraadt 346: .Nm
1.1 deraadt 347: does the following:
1.2 deraadt 348: .Bl -enum -offset indent
349: .It
1.1 deraadt 350: If the login is on a tty, and no command has been specified,
351: prints last login time and
1.2 deraadt 352: .Pa /etc/motd
1.1 deraadt 353: (unless prevented in the configuration file or by
1.2 deraadt 354: .Pa $HOME/.hushlogin ;
355: see the
356: .Sx FILES
357: section).
358: .It
1.1 deraadt 359: If the login is on a tty, records login time.
1.2 deraadt 360: .It
361: Checks
362: .Pa /etc/nologin ;
363: if it exists, prints contents and quits
1.1 deraadt 364: (unless root).
1.2 deraadt 365: .It
1.1 deraadt 366: Changes to run with normal user privileges.
1.2 deraadt 367: .It
1.1 deraadt 368: Sets up basic environment.
1.2 deraadt 369: .It
370: Reads
371: .Pa $HOME/.ssh/environment
372: if it exists.
373: .It
1.1 deraadt 374: Changes to user's home directory.
1.2 deraadt 375: .It
376: If
377: .Pa $HOME/.ssh/rc
378: exists, runs it; else if
379: .Pa /etc/sshrc
380: exists, runs
381: it; otherwise runs xauth. The
382: .Dq rc
383: files are given the X11
1.1 deraadt 384: authentication protocol and cookie in standard input.
1.2 deraadt 385: .It
1.1 deraadt 386: Runs user's shell or command.
1.2 deraadt 387: .El
388: .Sh AUTHORIZED_KEYS FILE FORMAT
1.1 deraadt 389: The
1.2 deraadt 390: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 391: file lists the RSA keys that are
392: permitted for RSA authentication. Each line of the file contains one
1.2 deraadt 393: key (empty lines and lines starting with a
394: .Ql #
395: are ignored as
1.1 deraadt 396: comments). Each line consists of the following fields, separated by
397: spaces: options, bits, exponent, modulus, comment. The options field
398: is optional; its presence is determined by whether the line starts
399: with a number or not (the option field never starts with a number).
400: The bits, exponent, modulus and comment fields give the RSA key; the
401: comment field is not used for anything (but may be convenient for the
402: user to identify the key).
1.2 deraadt 403: .Pp
1.1 deraadt 404: Note that lines in this file are usually several hundred bytes long
405: (because of the size of the RSA key modulus). You don't want to type
406: them in; instead, copy the
1.2 deraadt 407: .Pa identity.pub
1.1 deraadt 408: file and edit it.
1.2 deraadt 409: .Pp
1.1 deraadt 410: The options (if present) consists of comma-separated option
411: specifications. No spaces are permitted, except within double quotes.
412: The following option specifications are supported:
1.2 deraadt 413: .Bl -tag -width Ds
414: .It Cm from="pattern-list"
1.1 deraadt 415: Specifies that in addition to RSA authentication, the canonical name
416: of the remote host must be present in the comma-separated list of
417: patterns ('*' and '?' serve as wildcards). The list may also contain
418: patterns negated by prefixing them with '!'; if the canonical host
419: name matches a negated pattern, the key is not accepted. The purpose
420: of this option is to optionally increase security: RSA authentication
421: by itself does not trust the network or name servers or anything (but
422: the key); however, if somebody somehow steals the key, the key
423: permits an intruder to log in from anywhere in the world. This
424: additional option makes using a stolen key more difficult (name
425: servers and/or routers would have to be compromised in addition to
426: just the key).
1.2 deraadt 427: .It Cm command="command"
1.1 deraadt 428: Specifies that the command is executed whenever this key is used for
429: authentication. The command supplied by the user (if any) is ignored.
430: The command is run on a pty if the connection requests a pty;
431: otherwise it is run without a tty. A quote may be included in the
432: command by quoting it with a backslash. This option might be useful
433: to restrict certain RSA keys to perform just a specific operation. An
434: example might be a key that permits remote backups but nothing
435: else. Notice that the client may specify TCP/IP and/or X11
436: forwardings unless they are explicitly prohibited.
1.2 deraadt 437: .It Cm environment="NAME=value"
1.1 deraadt 438: Specifies that the string is to be added to the environment when
439: logging in using this key. Environment variables set this way
440: override other default environment values. Multiple options of this
441: type are permitted.
1.2 deraadt 442: .It Cm no-port-forwarding
1.1 deraadt 443: Forbids TCP/IP forwarding when this key is used for authentication.
444: Any port forward requests by the client will return an error. This
1.2 deraadt 445: might be used, e.g., in connection with the
446: .Cm command
1.1 deraadt 447: option.
1.2 deraadt 448: .It Cm no-X11-forwarding
1.1 deraadt 449: Forbids X11 forwarding when this key is used for authentication.
450: Any X11 forward requests by the client will return an error.
1.2 deraadt 451: .It Cm no-agent-forwarding
1.1 deraadt 452: Forbids authentication agent forwarding when this key is used for
453: authentication.
1.2 deraadt 454: .It Cm no-pty
1.1 deraadt 455: Prevents tty allocation (a request to allocate a pty will fail).
1.2 deraadt 456: .El
457: .Ss Examples
1.1 deraadt 458: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 459: .Pp
1.1 deraadt 460: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 461: .Pp
1.1 deraadt 462: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.2 deraadt 463: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.1 deraadt 464: The
1.2 deraadt 465: .Pa /etc/ssh_known_hosts
1.1 deraadt 466: and
1.2 deraadt 467: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 468: files contain host public keys for all known hosts. The global file should
469: be prepared by the admistrator (optional), and the per-user file is
470: maintained automatically: whenever the user connects an unknown host
1.6 ! aaron 471: its key is added to the per-user file.
1.2 deraadt 472: .Pp
1.1 deraadt 473: Each line in these files contains the following fields: hostnames,
474: bits, exponent, modulus, comment. The fields are separated by spaces.
1.2 deraadt 475: .Pp
1.1 deraadt 476: Hostnames is a comma-separated list of patterns ('*' and '?' act as
477: wildcards); each pattern in turn is matched against the canonical host
478: name (when authenticating a client) or against the user-supplied
479: name (when authenticating a server). A pattern may also be preceded
1.2 deraadt 480: by
481: .Ql !
482: to indicate negation: if the host name matches a negated
1.1 deraadt 483: pattern, it is not accepted (by that line) even if it matched another
484: pattern on the line.
1.2 deraadt 485: .Pp
1.1 deraadt 486: Bits, exponent, and modulus are taken directly from the host key; they
1.2 deraadt 487: can be obtained, e.g., from
488: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 489: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 490: .Pp
491: Lines starting with
492: .Ql #
493: and empty lines are ignored as comments.
494: .Pp
1.1 deraadt 495: When performing host authentication, authentication is accepted if any
496: matching line has the proper key. It is thus permissible (but not
497: recommended) to have several lines or different host keys for the same
498: names. This will inevitably happen when short forms of host names
499: from different domains are put in the file. It is possible
500: that the files contain conflicting information; authentication is
501: accepted if valid information can be found from either file.
1.2 deraadt 502: .Pp
1.1 deraadt 503: Note that the lines in these files are typically hundreds of characters
504: long, and you definitely don't want to type in the host keys by hand.
1.6 ! aaron 505: Rather, generate them by a script
1.1 deraadt 506: or by taking
1.2 deraadt 507: .Pa /etc/ssh_host_key.pub
1.1 deraadt 508: and adding the host names at the front.
1.2 deraadt 509: .Ss Examples
1.1 deraadt 510: closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1.2 deraadt 511: .Sh FILES
512: .Bl -tag -width Ds
513: .It Pa /etc/sshd_config
1.1 deraadt 514: Contains configuration data for
1.2 deraadt 515: .Nm sshd .
1.1 deraadt 516: This file should be writable by root only, but it is recommended
517: (though not necessary) that it be world-readable.
1.2 deraadt 518: .It Pa /etc/ssh_host_key
1.1 deraadt 519: Contains the private part of the host key. This file is normally
520: created automatically by "make install", but can also be created
521: manually using
1.2 deraadt 522: .Xr ssh-keygen 1 .
1.1 deraadt 523: This file should only be owned by root, readable only by root, and not
524: accessible to others.
1.2 deraadt 525: .It Pa /etc/ssh_host_key.pub
1.1 deraadt 526: Contains the public part of the host key. This file is normally
527: created automatically by "make install", but can also be created
528: manually. This file should be world-readable but writable only by
529: root. Its contents should match the private part. This file is not
530: really used for anything; it is only provided for the convenience of
531: the user so its contents can be copied to known hosts files.
1.2 deraadt 532: .It Pa /var/run/sshd.pid
533: Contains the process ID of the
534: .Nm
1.1 deraadt 535: listening for connections (if there are several daemons running
536: concurrently for different ports, this contains the pid of the one
537: started last). The contents of this file are not sensitive; it can be
538: world-readable.
1.2 deraadt 539: .It Pa $HOME/.ssh/authorized_keys
1.1 deraadt 540: Lists the RSA keys that can be used to log into the user's account.
541: This file must be readable by root (which may on some machines imply
542: it being world-readable if the user's home directory resides on an NFS
543: volume). It is recommended that it not be accessible by others. The
544: format of this file is described above.
1.6 ! aaron 545: .It Pa /etc/ssh_known_hosts
! 546: This file is consulted when using rhosts with RSA host
1.1 deraadt 547: authentication to check the public key of the host. The key must be
1.6 ! aaron 548: listed in this file to be accepted.
! 549: .It Pa $HOME/.ssh/known_hosts
! 550: The client uses this file
! 551: and
! 552: .Pa /etc/ssh_known_hosts
! 553: to verify that the remote host is the one we intended to
! 554: connect. These files should be writable only by root/the owner.
1.2 deraadt 555: .Pa /etc/ssh_known_hosts
556: should be world-readable, and
557: .Pa $HOME/.ssh/known_hosts
558: can but need not be world-readable.
1.6 ! aaron 559: .It Pa /etc/nologin
1.1 deraadt 560: If this file exists,
1.2 deraadt 561: .Nm
1.1 deraadt 562: refuses to let anyone except root log in. The contents of the file
563: are displayed to anyone trying to log in, and non-root connections are
564: refused. The file should be world-readable.
1.6 ! aaron 565: .It Pa $HOME/.rhosts
1.1 deraadt 566: This file contains host-username pairs, separated by a space, one per
567: line. The given user on the corresponding host is permitted to log in
568: without password. The same file is used by rlogind and rshd.
1.6 ! aaron 569: The file must
1.1 deraadt 570: be writable only by the user; it is recommended that it not be
571: accessible by others.
1.2 deraadt 572: .Pp
1.1 deraadt 573: If is also possible to use netgroups in the file. Either host or user
574: name may be of the form +@groupname to specify all hosts or all users
575: in the group.
1.2 deraadt 576: .It Pa $HOME/.shosts
577: For ssh,
578: this file is exactly the same as for
579: .Pa .rhosts .
580: However, this file is
581: not used by rlogin and rshd, so using this permits access using SSH only.
582: .Pa /etc/hosts.equiv
583: This file is used during
584: .Pa .rhosts
585: authentication. In the
1.1 deraadt 586: simplest form, this file contains host names, one per line. Users on
587: those hosts are permitted to log in without a password, provided they
588: have the same user name on both machines. The host name may also be
589: followed by a user name; such users are permitted to log in as
1.2 deraadt 590: .Em any
591: user on this machine (except root). Additionally, the syntax
592: .Dq +@group
593: can be used to specify netgroups. Negated entries start with
594: .Ql \&- .
595: .Pp
1.1 deraadt 596: If the client host/user is successfully matched in this file, login is
597: automatically permitted provided the client and server user names are the
598: same. Additionally, successful RSA host authentication is normally
599: required. This file must be writable only by root; it is recommended
600: that it be world-readable.
1.2 deraadt 601: .Pp
1.6 ! aaron 602: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 603: .Pa hosts.equiv .
1.1 deraadt 604: Beware that it really means that the named user(s) can log in as
1.2 deraadt 605: .Em anybody ,
1.1 deraadt 606: which includes bin, daemon, adm, and other accounts that own critical
607: binaries and directories. Using a user name practically grants the
608: user root access. The only valid use for user names that I can think
609: of is in negative entries.
1.2 deraadt 610: .Pp
611: Note that this warning also applies to rsh/rlogin.
612: .It Pa /etc/shosts.equiv
1.1 deraadt 613: This is processed exactly as
1.2 deraadt 614: .Pa /etc/hosts.equiv .
1.1 deraadt 615: However, this file may be useful in environments that want to run both
1.2 deraadt 616: rsh/rlogin and ssh.
1.6 ! aaron 617: .It Pa $HOME/.ssh/environment
1.1 deraadt 618: This file is read into the environment at login (if it exists). It
1.2 deraadt 619: can only contain empty lines, comment lines (that start with
620: .Ql # ) ,
1.6 ! aaron 621: and assignment lines of the form name=value. The file should be writable
! 622: only by the user; it need not be readable by anyone else.
1.2 deraadt 623: .It Pa $HOME/.ssh/rc
1.1 deraadt 624: If this file exists, it is run with /bin/sh after reading the
625: environment files but before starting the user's shell or command. If
626: X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 627: standard input (and
628: .Ev DISPLAY
629: in environment). This must call
630: .Xr xauth 1
631: in that case.
632: .Pp
1.1 deraadt 633: The primary purpose of this file is to run any initialization routines
634: which may be needed before the user's home directory becomes
635: accessible; AFS is a particular example of such an environment.
1.2 deraadt 636: .Pp
1.1 deraadt 637: This file will probably contain some initialization code followed by
638: something similar to: "if read proto cookie; then echo add $DISPLAY
639: $proto $cookie | xauth -q -; fi".
1.2 deraadt 640: .Pp
641: If this file does not exist,
642: .Pa /etc/sshrc
643: is run, and if that
1.1 deraadt 644: does not exist either, xauth is used to store the cookie.
1.2 deraadt 645: .Pp
1.1 deraadt 646: This file should be writable only by the user, and need not be
647: readable by anyone else.
1.2 deraadt 648: .It Pa /etc/sshrc
649: Like
650: .Pa $HOME/.ssh/rc .
651: This can be used to specify
1.1 deraadt 652: machine-specific login-time initializations globally. This file
653: should be writable only by root, and should be world-readable.
1.2 deraadt 654: .Sh AUTHOR
1.1 deraadt 655: Tatu Ylonen <ylo@cs.hut.fi>
1.2 deraadt 656: .Pp
1.1 deraadt 657: Information about new releases, mailing lists, and other related
1.2 deraadt 658: issues can be found from the SSH WWW home page:
659: .Pp
660: .Dl http://www.cs.hut.fi/ssh.
1.5 deraadt 661: .Pp
662: This version of
663: .Nm
664: is a derivative of the original 1.2.12 release, but with bugs removed and
665: newer features re-added. Rapidly after the 1.2.12 release, newer versions
666: bore successively more restrictive licenses. In this version, all components
667: of a restrictive nature (ie. patents) have been directly removed from the
668: source code; any licensed or patented components are chosen from external
669: libraries. The libraries described in
670: .Xr ssl 8
671: are required for proper operation.
1.2 deraadt 672: .Sh SEE ALSO
673: .Xr rlogin 1 ,
674: .Xr rsh 1 ,
675: .Xr scp 1 ,
676: .Xr ssh 1 ,
1.5 deraadt 677: .Xr ssh-add 1 ,
1.2 deraadt 678: .Xr ssh-agent 1 ,
1.5 deraadt 679: .Xr ssh-keygen 1 ,
680: .Xr ssl 8