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.\" 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.\" 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. 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. 25.\" 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. 36.\" 37.\" $OpenBSD: sshd.8,v 1.186 2002/06/22 16:45:29 stevesk Exp $ 38.\" $FreeBSD$ 39.Dd September 25, 1999 40.Dt SSHD 8 41.Os 42.Sh NAME 43.Nm sshd 44.Nd OpenSSH SSH daemon 45.Sh SYNOPSIS 46.Nm sshd 47.Op Fl deiqtD46 48.Op Fl b Ar bits 49.Op Fl f Ar config_file 50.Op Fl g Ar login_grace_time 51.Op Fl h Ar host_key_file 52.Op Fl k Ar key_gen_time 53.Op Fl o Ar option 54.Op Fl p Ar port 55.Op Fl u Ar len 56.Sh DESCRIPTION 57.Nm 58(SSH Daemon) is the daemon program for 59.Xr ssh 1 . 60Together these programs replace rlogin and rsh, and 61provide secure encrypted communications between two untrusted hosts 62over an insecure network. 63The programs are intended to be as easy to 64install and use as possible. 65.Pp 66.Nm 67is the daemon that listens for connections from clients. 68It is normally started at boot from 69.Pa /etc/rc.d/sshd . 70It forks a new 71daemon for each incoming connection. 72The forked daemons handle 73key exchange, encryption, authentication, command execution, 74and data exchange. 75This implementation of 76.Nm 77supports both SSH protocol version 1 and 2 simultaneously. 78.Nm 79works as follows. 80.Pp 81.Ss SSH protocol version 1 82.Pp 83Each host has a host-specific RSA key 84(normally 1024 bits) used to identify the host. 85Additionally, when 86the daemon starts, it generates a server RSA key (normally 768 bits). 87This key is normally regenerated every hour if it has been used, and 88is never stored on disk. 89.Pp 90Whenever a client connects the daemon responds with its public 91host and server keys. 92The client compares the 93RSA host key against its own database to verify that it has not changed. 94The client then generates a 256 bit random number. 95It encrypts this 96random number using both the host key and the server key, and sends 97the encrypted number to the server. 98Both sides then use this 99random number as a session key which is used to encrypt all further 100communications in the session. 101The rest of the session is encrypted 102using a conventional cipher, currently Blowfish or 3DES, with 3DES 103being used by default. 104The client selects the encryption algorithm 105to use from those offered by the server. 106.Pp 107Next, the server and the client enter an authentication dialog. 108The client tries to authenticate itself using 109.Pa .rhosts 110authentication, 111.Pa .rhosts 112authentication combined with RSA host 113authentication, RSA challenge-response authentication, or password 114based authentication. 115.Pp 116Rhosts authentication is normally disabled 117because it is fundamentally insecure, but can be enabled in the server 118configuration file if desired. 119System security is not improved unless 120.Nm rshd , 121.Nm rlogind , 122and 123.Xr rexecd 124are disabled (thus completely disabling 125.Xr rlogin 126and 127.Xr rsh 128into the machine). 129.Pp 130.Ss SSH protocol version 2 131.Pp 132Version 2 works similarly: 133Each host has a host-specific key (RSA or DSA) used to identify the host. 134However, when the daemon starts, it does not generate a server key. 135Forward security is provided through a Diffie-Hellman key agreement. 136This key agreement results in a shared session key. 137.Pp 138The rest of the session is encrypted using a symmetric cipher, currently 139128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES. 140The client selects the encryption algorithm 141to use from those offered by the server. 142Additionally, session integrity is provided 143through a cryptographic message authentication code 144(hmac-sha1 or hmac-md5). 145.Pp 146Protocol version 2 provides a public key based 147user (PubkeyAuthentication) or 148client host (HostbasedAuthentication) authentication method, 149conventional password authentication and challenge response based methods. 150.Pp 151.Ss Command execution and data forwarding 152.Pp 153If the client successfully authenticates itself, a dialog for 154preparing the session is entered. 155At this time the client may request 156things like allocating a pseudo-tty, forwarding X11 connections, 157forwarding TCP/IP connections, or forwarding the authentication agent 158connection over the secure channel. 159.Pp 160Finally, the client either requests a shell or execution of a command. 161The sides then enter session mode. 162In this mode, either side may send 163data at any time, and such data is forwarded to/from the shell or 164command on the server side, and the user terminal in the client side. 165.Pp 166When the user program terminates and all forwarded X11 and other 167connections have been closed, the server sends command exit status to 168the client, and both sides exit. 169.Pp 170.Nm 171can be configured using command-line options or a configuration 172file. 173Command-line options override values specified in the 174configuration file. 175.Pp 176.Nm 177rereads its configuration file when it receives a hangup signal, 178.Dv SIGHUP , 179by executing itself with the name it was started as, i.e., 180.Pa /usr/sbin/sshd . 181.Pp 182The options are as follows: 183.Bl -tag -width Ds 184.It Fl b Ar bits 185Specifies the number of bits in the ephemeral protocol version 1 186server key (default 768). 187.It Fl d 188Debug mode. 189The server sends verbose debug output to the system 190log, and does not put itself in the background. 191The server also will not fork and will only process one connection. 192This option is only intended for debugging for the server. 193Multiple -d options increase the debugging level. 194Maximum is 3. 195.It Fl e 196When this option is specified, 197.Nm 198will send the output to the standard error instead of the system log. 199.It Fl f Ar configuration_file 200Specifies the name of the configuration file. 201The default is 202.Pa /etc/ssh/sshd_config . 203.Nm 204refuses to start if there is no configuration file. 205.It Fl g Ar login_grace_time 206Gives the grace time for clients to authenticate themselves (default 207600 seconds). 208If the client fails to authenticate the user within 209this many seconds, the server disconnects and exits. 210A value of zero indicates no limit. 211.It Fl h Ar host_key_file 212Specifies a file from which a host key is read. 213This option must be given if 214.Nm 215is not run as root (as the normal 216host key files are normally not readable by anyone but root). 217The default is 218.Pa /etc/ssh/ssh_host_key 219for protocol version 1, and 220.Pa /etc/ssh/ssh_host_dsa_key 221for protocol version 2. 222It is possible to have multiple host key files for 223the different protocol versions and host key algorithms. 224.It Fl i 225Specifies that 226.Nm 227is being run from inetd. 228.Nm 229is normally not run 230from inetd because it needs to generate the server key before it can 231respond to the client, and this may take tens of seconds. 232Clients would have to wait too long if the key was regenerated every time. 233However, with small key sizes (e.g., 512) using 234.Nm 235from inetd may 236be feasible. 237.It Fl k Ar key_gen_time 238Specifies how often the ephemeral protocol version 1 server key is 239regenerated (default 3600 seconds, or one hour). 240The motivation for regenerating the key fairly 241often is that the key is not stored anywhere, and after about an hour, 242it becomes impossible to recover the key for decrypting intercepted 243communications even if the machine is cracked into or physically 244seized. 245A value of zero indicates that the key will never be regenerated. 246.It Fl o Ar option 247Can be used to give options in the format used in the configuration file. 248This is useful for specifying options for which there is no separate 249command-line flag. 250.It Fl p Ar port 251Specifies the port on which the server listens for connections 252(default 22). 253Multiple port options are permitted. 254Ports specified in the configuration file are ignored when a 255command-line port is specified. 256.It Fl q 257Quiet mode. 258Nothing is sent to the system log. 259Normally the beginning, 260authentication, and termination of each connection is logged. 261.It Fl t 262Test mode. 263Only check the validity of the configuration file and sanity of the keys. 264This is useful for updating 265.Nm 266reliably as configuration options may change. 267.It Fl u Ar len 268This option is used to specify the size of the field 269in the 270.Li utmp 271structure that holds the remote host name. 272If the resolved host name is longer than 273.Ar len , 274the dotted decimal value will be used instead. 275This allows hosts with very long host names that 276overflow this field to still be uniquely identified. 277Specifying 278.Fl u0 279indicates that only dotted decimal addresses 280should be put into the 281.Pa utmp 282file. 283.Fl u0 284is also be used to prevent 285.Nm 286from making DNS requests unless the authentication 287mechanism or configuration requires it. 288Authentication mechanisms that may require DNS include 289.Cm RhostsAuthentication , 290.Cm RhostsRSAAuthentication , 291.Cm HostbasedAuthentication 292and using a 293.Cm from="pattern-list" 294option in a key file. 295Configuration options that require DNS include using a 296USER@HOST pattern in 297.Cm AllowUsers 298or 299.Cm DenyUsers . 300.It Fl D 301When this option is specified 302.Nm 303will not detach and does not become a daemon. 304This allows easy monitoring of 305.Nm sshd . 306.It Fl 4 307Forces 308.Nm 309to use IPv4 addresses only. 310.It Fl 6 311Forces 312.Nm 313to use IPv6 addresses only. 314.El 315.Sh CONFIGURATION FILE 316.Nm 317reads configuration data from 318.Pa /etc/ssh/sshd_config 319(or the file specified with 320.Fl f 321on the command line). 322The file format and configuration options are described in 323.Xr sshd_config 5 . 324.Sh LOGIN PROCESS 325When a user successfully logs in, 326.Nm 327does the following: 328.Bl -enum -offset indent 329.It 330If the login is on a tty, and no command has been specified, 331prints last login time and 332.Pa /etc/motd 333(unless prevented in the configuration file or by 334.Pa $HOME/.hushlogin ; 335see the 336.Sx FILES 337section). 338.It 339If the login is on a tty, records login time. 340.It 341Checks 342.Pa /etc/nologin and 343.Pa /var/run/nologin ; 344if one exists, it prints the contents and quits 345(unless root). 346.It 347Changes to run with normal user privileges. 348.It 349Sets up basic environment. 350.It 351Reads 352.Pa $HOME/.ssh/environment 353if it exists. 354.It 355Changes to user's home directory. 356.It 357If 358.Pa $HOME/.ssh/rc 359exists, runs it; else if 360.Pa /etc/ssh/sshrc 361exists, runs 362it; otherwise runs 363.Xr xauth 1 . 364The 365.Dq rc 366files are given the X11 367authentication protocol and cookie (if applicable) in standard input. 368.It 369Runs user's shell or command. 370.El 371.Sh AUTHORIZED_KEYS FILE FORMAT 372.Pa $HOME/.ssh/authorized_keys 373is the default file that lists the public keys that are 374permitted for RSA authentication in protocol version 1 375and for public key authentication (PubkeyAuthentication) 376in protocol version 2. 377.Cm AuthorizedKeysFile 378may be used to specify an alternative file. 379.Pp 380Each line of the file contains one 381key (empty lines and lines starting with a 382.Ql # 383are ignored as 384comments). 385Each RSA public key consists of the following fields, separated by 386spaces: options, bits, exponent, modulus, comment. 387Each protocol version 2 public key consists of: 388options, keytype, base64 encoded key, comment. 389The options fields 390are optional; its presence is determined by whether the line starts 391with a number or not (the option field never starts with a number). 392The bits, exponent, modulus and comment fields give the RSA key for 393protocol version 1; the 394comment field is not used for anything (but may be convenient for the 395user to identify the key). 396For protocol version 2 the keytype is 397.Dq ssh-dss 398or 399.Dq ssh-rsa . 400.Pp 401Note that lines in this file are usually several hundred bytes long 402(because of the size of the RSA key modulus). 403You don't want to type them in; instead, copy the 404.Pa identity.pub , 405.Pa id_dsa.pub 406or the 407.Pa id_rsa.pub 408file and edit it. 409.Pp 410.Nm 411enforces a minimum RSA key modulus size for protocol 1 412and protocol 2 keys of 768 bits. 413.Pp 414The options (if present) consist of comma-separated option 415specifications. 416No spaces are permitted, except within double quotes. 417The following option specifications are supported (note 418that option keywords are case-insensitive): 419.Bl -tag -width Ds 420.It Cm from="pattern-list" 421Specifies that in addition to RSA authentication, the canonical name 422of the remote host must be present in the comma-separated list of 423patterns 424.Pf ( Ql * 425and 426.Ql ? 427serve as wildcards). 428The list may also contain 429patterns negated by prefixing them with 430.Ql ! ; 431if the canonical host name matches a negated pattern, the key is not accepted. 432The purpose 433of this option is to optionally increase security: RSA authentication 434by itself does not trust the network or name servers or anything (but 435the key); however, if somebody somehow steals the key, the key 436permits an intruder to log in from anywhere in the world. 437This additional option makes using a stolen key more difficult (name 438servers and/or routers would have to be compromised in addition to 439just the key). 440.It Cm command="command" 441Specifies that the command is executed whenever this key is used for 442authentication. 443The command supplied by the user (if any) is ignored. 444The command is run on a pty if the client requests a pty; 445otherwise it is run without a tty. 446If a 8-bit clean channel is required, 447one must not request a pty or should specify 448.Cm no-pty . 449A quote may be included in the command by quoting it with a backslash. 450This option might be useful 451to restrict certain RSA keys to perform just a specific operation. 452An example might be a key that permits remote backups but nothing else. 453Note that the client may specify TCP/IP and/or X11 454forwarding unless they are explicitly prohibited. 455Note that this option applies to shell, command or subsystem execution. 456.It Cm environment="NAME=value" 457Specifies that the string is to be added to the environment when 458logging in using this key. 459Environment variables set this way 460override other default environment values. 461Multiple options of this type are permitted. 462This option is automatically disabled if 463.Cm UseLogin 464is enabled. 465.It Cm no-port-forwarding 466Forbids TCP/IP forwarding when this key is used for authentication. 467Any port forward requests by the client will return an error. 468This might be used, e.g., in connection with the 469.Cm command 470option. 471.It Cm no-X11-forwarding 472Forbids X11 forwarding when this key is used for authentication. 473Any X11 forward requests by the client will return an error. 474.It Cm no-agent-forwarding 475Forbids authentication agent forwarding when this key is used for 476authentication. 477.It Cm no-pty 478Prevents tty allocation (a request to allocate a pty will fail). 479.It Cm permitopen="host:port" 480Limit local 481.Li ``ssh -L'' 482port forwarding such that it may only connect to the specified host and 483port. 484IPv6 addresses can be specified with an alternative syntax: 485.Ar host/port . 486Multiple 487.Cm permitopen 488options may be applied separated by commas. No pattern matching is 489performed on the specified hostnames, they must be literal domains or 490addresses. 491.El 492.Ss Examples 4931024 33 12121.\|.\|.\|312314325 ylo@foo.bar 494.Pp 495from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula 496.Pp 497command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi 498.Pp 499permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323 500.Sh SSH_KNOWN_HOSTS FILE FORMAT 501The 502.Pa /etc/ssh/ssh_known_hosts 503and 504.Pa $HOME/.ssh/known_hosts 505files contain host public keys for all known hosts. 506The global file should 507be prepared by the administrator (optional), and the per-user file is 508maintained automatically: whenever the user connects from an unknown host 509its key is added to the per-user file. 510.Pp 511Each line in these files contains the following fields: hostnames, 512bits, exponent, modulus, comment. 513The fields are separated by spaces. 514.Pp 515Hostnames is a comma-separated list of patterns ('*' and '?' act as 516wildcards); each pattern in turn is matched against the canonical host 517name (when authenticating a client) or against the user-supplied 518name (when authenticating a server). 519A pattern may also be preceded by 520.Ql ! 521to indicate negation: if the host name matches a negated 522pattern, it is not accepted (by that line) even if it matched another 523pattern on the line. 524.Pp 525Bits, exponent, and modulus are taken directly from the RSA host key; they 526can be obtained, e.g., from 527.Pa /etc/ssh/ssh_host_key.pub . 528The optional comment field continues to the end of the line, and is not used. 529.Pp 530Lines starting with 531.Ql # 532and empty lines are ignored as comments. 533.Pp 534When performing host authentication, authentication is accepted if any 535matching line has the proper key. 536It is thus permissible (but not 537recommended) to have several lines or different host keys for the same 538names. 539This will inevitably happen when short forms of host names 540from different domains are put in the file. 541It is possible 542that the files contain conflicting information; authentication is 543accepted if valid information can be found from either file. 544.Pp 545Note that the lines in these files are typically hundreds of characters 546long, and you definitely don't want to type in the host keys by hand. 547Rather, generate them by a script 548or by taking 549.Pa /etc/ssh/ssh_host_key.pub 550and adding the host names at the front. 551.Ss Examples 552.Bd -literal 553closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi 554cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= 555.Ed 556.Sh FILES 557.Bl -tag -width Ds 558.It Pa /etc/ssh/sshd_config 559Contains configuration data for 560.Nm sshd . 561The file format and configuration options are described in 562.Xr sshd_config 5 . 563.It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key 564These three files contain the private parts of the host keys. 565These files should only be owned by root, readable only by root, and not 566accessible to others. 567Note that 568.Nm 569does not start if this file is group/world-accessible. 570.It Pa /etc/ssh/ssh_host_key.pub, /etc/ssh/ssh_host_dsa_key.pub 571These three files contain the public parts of the host keys. 572These files should be world-readable but writable only by 573root. 574Their contents should match the respective private parts. 575These files are not 576really used for anything; they are provided for the convenience of 577the user so their contents can be copied to known hosts files. 578These files are created using 579.Xr ssh-keygen 1 . 580.It Pa /etc/ssh/moduli 581Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". 582.It Pa /var/empty 583.Xr chroot 2 584directory used by 585.Nm 586during privilege separation in the pre-authentication phase. 587The directory should not contain any files and must be owned by root 588and not group or world-writable. 589.It Pa /var/run/sshd.pid 590Contains the process ID of the 591.Nm 592listening for connections (if there are several daemons running 593concurrently for different ports, this contains the process ID of the one 594started last). 595The content of this file is not sensitive; it can be world-readable. 596.It Pa $HOME/.ssh/authorized_keys 597Lists the public keys (RSA or DSA) that can be used to log into the user's account. 598This file must be readable by root (which may on some machines imply 599it being world-readable if the user's home directory resides on an NFS 600volume). 601It is recommended that it not be accessible by others. 602The format of this file is described above. 603Users will place the contents of their 604.Pa identity.pub , 605.Pa id_dsa.pub 606and/or 607.Pa id_rsa.pub 608files into this file, as described in 609.Xr ssh-keygen 1 . 610.It Pa "/etc/ssh/ssh_known_hosts" and "$HOME/.ssh/known_hosts" 611These files are consulted when using rhosts with RSA host 612authentication or protocol version 2 hostbased authentication 613to check the public key of the host. 614The key must be listed in one of these files to be accepted. 615The client uses the same files 616to verify that it is connecting to the correct remote host. 617These files should be writable only by root/the owner. 618.Pa /etc/ssh/ssh_known_hosts 619should be world-readable, and 620.Pa $HOME/.ssh/known_hosts 621can but need not be world-readable. 622.It Pa /etc/nologin 623If this file exists, 624.Nm 625refuses to let anyone except root log in. 626The contents of the file 627are displayed to anyone trying to log in, and non-root connections are 628refused. 629The file should be world-readable. 630.It Pa /etc/hosts.allow, /etc/hosts.deny 631Access controls that should be enforced by tcp-wrappers are defined here. 632Further details are described in 633.Xr hosts_access 5 . 634.It Pa $HOME/.rhosts 635This file contains host-username pairs, separated by a space, one per 636line. 637The given user on the corresponding host is permitted to log in 638without password. 639The same file is used by rlogind and rshd. 640The file must 641be writable only by the user; it is recommended that it not be 642accessible by others. 643.Pp 644If is also possible to use netgroups in the file. 645Either host or user 646name may be of the form +@groupname to specify all hosts or all users 647in the group. 648.It Pa $HOME/.shosts 649For ssh, 650this file is exactly the same as for 651.Pa .rhosts . 652However, this file is 653not used by rlogin and rshd, so using this permits access using SSH only. 654.It Pa /etc/hosts.equiv 655This file is used during 656.Pa .rhosts 657authentication. 658In the simplest form, this file contains host names, one per line. 659Users on 660those hosts are permitted to log in without a password, provided they 661have the same user name on both machines. 662The host name may also be 663followed by a user name; such users are permitted to log in as 664.Em any 665user on this machine (except root). 666Additionally, the syntax 667.Dq +@group 668can be used to specify netgroups. 669Negated entries start with 670.Ql \&- . 671.Pp 672If the client host/user is successfully matched in this file, login is 673automatically permitted provided the client and server user names are the 674same. 675Additionally, successful RSA host authentication is normally required. 676This file must be writable only by root; it is recommended 677that it be world-readable. 678.Pp 679.Sy "Warning: It is almost never a good idea to use user names in" 680.Pa hosts.equiv . 681Beware that it really means that the named user(s) can log in as 682.Em anybody , 683which includes bin, daemon, adm, and other accounts that own critical 684binaries and directories. 685Using a user name practically grants the user root access. 686The only valid use for user names that I can think 687of is in negative entries. 688.Pp 689Note that this warning also applies to rsh/rlogin. 690.It Pa /etc/ssh/shosts.equiv 691This is processed exactly as 692.Pa /etc/hosts.equiv . 693However, this file may be useful in environments that want to run both 694rsh/rlogin and ssh. 695.It Pa $HOME/.ssh/environment 696This file is read into the environment at login (if it exists). 697It can only contain empty lines, comment lines (that start with 698.Ql # ) , 699and assignment lines of the form name=value. 700The file should be writable 701only by the user; it need not be readable by anyone else. 702.It Pa $HOME/.ssh/rc 703If this file exists, it is run with 704.Pa /bin/sh 705after reading the 706environment files but before starting the user's shell or command. 707It must not produce any output on stdout; stderr must be used 708instead. 709If X11 forwarding is in use, it will receive the "proto cookie" pair in 710its standard input (and 711.Ev DISPLAY 712in its environment). 713The script must call 714.Xr xauth 1 715because 716.Nm 717will not run xauth automatically to add X11 cookies. 718.Pp 719The primary purpose of this file is to run any initialization routines 720which may be needed before the user's home directory becomes 721accessible; AFS is a particular example of such an environment. 722.Pp 723This file will probably contain some initialization code followed by 724something similar to: 725.Bd -literal 726if read proto cookie && [ -n "$DISPLAY" ]; then 727 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 728 # X11UseLocalhost=yes 729 xauth add unix:`echo $DISPLAY | 730 cut -c11-` $proto $cookie 731 else 732 # X11UseLocalhost=no 733 xauth add $DISPLAY $proto $cookie 734 fi 735fi 736.Ed 737.Pp 738If this file does not exist, 739.Pa /etc/ssh/sshrc 740is run, and if that 741does not exist either, xauth is used to add the cookie. 742.Pp 743This file should be writable only by the user, and need not be 744readable by anyone else. 745.It Pa /etc/ssh/sshrc 746Like 747.Pa $HOME/.ssh/rc . 748This can be used to specify 749machine-specific login-time initializations globally. 750This file should be writable only by root, and should be world-readable. 751.El 752.Sh AUTHORS 753OpenSSH is a derivative of the original and free 754ssh 1.2.12 release by Tatu Ylonen. 755Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 756Theo de Raadt and Dug Song 757removed many bugs, re-added newer features and 758created OpenSSH. 759Markus Friedl contributed the support for SSH 760protocol versions 1.5 and 2.0. 761Niels Provos and Markus Friedl contributed support 762for privilege separation. 763.Sh SEE ALSO 764.Xr scp 1 , 765.Xr sftp 1 , 766.Xr ssh 1 , 767.Xr ssh-add 1 , 768.Xr ssh-agent 1 , 769.Xr ssh-keygen 1 , 770.Xr login.conf 5 , 771.Xr moduli 5 , 772.Xr sshd_config 5 , 773.Xr sftp-server 8 774.Rs 775.%A T. Ylonen 776.%A T. Kivinen 777.%A M. Saarinen 778.%A T. Rinne 779.%A S. Lehtinen 780.%T "SSH Protocol Architecture" 781.%N draft-ietf-secsh-architecture-12.txt 782.%D January 2002 783.%O work in progress material 784.Re 785.Rs 786.%A M. Friedl 787.%A N. Provos 788.%A W. A. Simpson 789.%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" 790.%N draft-ietf-secsh-dh-group-exchange-02.txt 791.%D January 2002 792.%O work in progress material 793.Re 794