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 1.193 2002/09/24 20:59:44 todd Exp $ 38.\" $FreeBSD: src/crypto/openssh/sshd.8,v 1.5.2.11 2003/02/05 19:31:31 trhodes Exp $ 39.\" $DragonFly: src/crypto/openssh/Attic/sshd.8,v 1.2 2003/06/17 04:24:36 dillon Exp $ 40.Dd September 25, 1999 41.Dt SSHD 8 42.Os 43.Sh NAME 44.Nm sshd 45.Nd OpenSSH SSH daemon 46.Sh SYNOPSIS 47.Nm sshd 48.Op Fl deiqtD46 49.Op Fl b Ar bits 50.Op Fl f Ar config_file 51.Op Fl g Ar login_grace_time 52.Op Fl h Ar host_key_file 53.Op Fl k Ar key_gen_time 54.Op Fl o Ar option 55.Op Fl p Ar port 56.Op Fl u Ar len 57.Sh DESCRIPTION 58.Nm 59(SSH Daemon) is the daemon program for 60.Xr ssh 1 . 61Together these programs replace rlogin and rsh, and 62provide secure encrypted communications between two untrusted hosts 63over an insecure network. 64The programs are intended to be as easy to 65install and use as possible. 66.Pp 67.Nm 68is the daemon that listens for connections from clients. 69It is normally started at boot from 70.Pa /etc/rc.d/sshd . 71It forks a new 72daemon for each incoming connection. 73The forked daemons handle 74key exchange, encryption, authentication, command execution, 75and data exchange. 76This implementation of 77.Nm 78supports both SSH protocol version 1 and 2 simultaneously. 79.Nm 80works as follows. 81.Pp 82.Ss SSH protocol version 1 83.Pp 84Each host has a host-specific RSA key 85(normally 1024 bits) used to identify the host. 86Additionally, when 87the daemon starts, it generates a server RSA key (normally 768 bits). 88This key is normally regenerated every hour if it has been used, and 89is never stored on disk. 90.Pp 91Whenever a client connects the daemon responds with its public 92host and server keys. 93The client compares the 94RSA host key against its own database to verify that it has not changed. 95The client then generates a 256 bit random number. 96It encrypts this 97random number using both the host key and the server key, and sends 98the encrypted number to the server. 99Both sides then use this 100random number as a session key which is used to encrypt all further 101communications in the session. 102The rest of the session is encrypted 103using a conventional cipher, currently Blowfish or 3DES, with 3DES 104being used by default. 105The client selects the encryption algorithm 106to use from those offered by the server. 107.Pp 108Next, the server and the client enter an authentication dialog. 109The client tries to authenticate itself using 110.Pa .rhosts 111authentication, 112.Pa .rhosts 113authentication combined with RSA host 114authentication, RSA challenge-response authentication, or password 115based authentication. 116.Pp 117Rhosts authentication is normally disabled 118because it is fundamentally insecure, but can be enabled in the server 119configuration file if desired. 120System security is not improved unless 121.Nm rshd , 122.Nm rlogind , 123and 124.Xr rexecd 125are disabled (thus completely disabling 126.Xr rlogin 127and 128.Xr rsh 129into the machine). 130.Pp 131.Ss SSH protocol version 2 132.Pp 133Version 2 works similarly: 134Each host has a host-specific key (RSA or DSA) used to identify the host. 135However, when the daemon starts, it does not generate a server key. 136Forward security is provided through a Diffie-Hellman key agreement. 137This key agreement results in a shared session key. 138.Pp 139The rest of the session is encrypted using a symmetric cipher, currently 140128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES. 141The client selects the encryption algorithm 142to use from those offered by the server. 143Additionally, session integrity is provided 144through a cryptographic message authentication code 145(hmac-sha1 or hmac-md5). 146.Pp 147Protocol version 2 provides a public key based 148user (PubkeyAuthentication) or 149client host (HostbasedAuthentication) authentication method, 150conventional password authentication and challenge response based methods. 151.Pp 152.Ss Command execution and data forwarding 153.Pp 154If the client successfully authenticates itself, a dialog for 155preparing the session is entered. 156At this time the client may request 157things like allocating a pseudo-tty, forwarding X11 connections, 158forwarding TCP/IP connections, or forwarding the authentication agent 159connection over the secure channel. 160.Pp 161Finally, the client either requests a shell or execution of a command. 162The sides then enter session mode. 163In this mode, either side may send 164data at any time, and such data is forwarded to/from the shell or 165command on the server side, and the user terminal in the client side. 166.Pp 167When the user program terminates and all forwarded X11 and other 168connections have been closed, the server sends command exit status to 169the client, and both sides exit. 170.Pp 171.Nm 172can be configured using command-line options or a configuration 173file. 174Command-line options override values specified in the 175configuration file. 176.Pp 177.Nm 178rereads its configuration file when it receives a hangup signal, 179.Dv SIGHUP , 180by executing itself with the name it was started as, i.e., 181.Pa /usr/sbin/sshd . 182.Pp 183The options are as follows: 184.Bl -tag -width Ds 185.It Fl b Ar bits 186Specifies the number of bits in the ephemeral protocol version 1 187server key (default 768). 188.It Fl d 189Debug mode. 190The server sends verbose debug output to the system 191log, and does not put itself in the background. 192The server also will not fork and will only process one connection. 193This option is only intended for debugging for the server. 194Multiple -d options increase the debugging level. 195Maximum is 3. 196.It Fl e 197When this option is specified, 198.Nm 199will send the output to the standard error instead of the system log. 200.It Fl f Ar configuration_file 201Specifies the name of the configuration file. 202The default is 203.Pa /etc/ssh/sshd_config . 204.Nm 205refuses to start if there is no configuration file. 206.It Fl g Ar login_grace_time 207Gives the grace time for clients to authenticate themselves (default 208120 seconds). 209If the client fails to authenticate the user within 210this many seconds, the server disconnects and exits. 211A value of zero indicates no limit. 212.It Fl h Ar host_key_file 213Specifies a file from which a host key is read. 214This option must be given if 215.Nm 216is not run as root (as the normal 217host key files are normally not readable by anyone but root). 218The default is 219.Pa /etc/ssh/ssh_host_key 220for protocol version 1, and 221.Pa /etc/ssh/ssh_host_dsa_key 222for protocol version 2. 223It is possible to have multiple host key files for 224the different protocol versions and host key algorithms. 225.It Fl i 226Specifies that 227.Nm 228is being run from inetd. 229.Nm 230is normally not run 231from inetd because it needs to generate the server key before it can 232respond to the client, and this may take tens of seconds. 233Clients would have to wait too long if the key was regenerated every time. 234However, with small key sizes (e.g., 512) using 235.Nm 236from inetd may 237be feasible. 238.It Fl k Ar key_gen_time 239Specifies how often the ephemeral protocol version 1 server key is 240regenerated (default 3600 seconds, or one hour). 241The motivation for regenerating the key fairly 242often is that the key is not stored anywhere, and after about an hour, 243it becomes impossible to recover the key for decrypting intercepted 244communications even if the machine is cracked into or physically 245seized. 246A value of zero indicates that the key will never be regenerated. 247.It Fl o Ar option 248Can be used to give options in the format used in the configuration file. 249This is useful for specifying options for which there is no separate 250command-line flag. 251.It Fl p Ar port 252Specifies the port on which the server listens for connections 253(default 22). 254Multiple port options are permitted. 255Ports specified in the configuration file are ignored when a 256command-line port is specified. 257.It Fl q 258Quiet mode. 259Nothing is sent to the system log. 260Normally the beginning, 261authentication, and termination of each connection is logged. 262.It Fl t 263Test mode. 264Only check the validity of the configuration file and sanity of the keys. 265This is useful for updating 266.Nm 267reliably as configuration options may change. 268.It Fl u Ar len 269This option is used to specify the size of the field 270in the 271.Li utmp 272structure that holds the remote host name. 273If the resolved host name is longer than 274.Ar len , 275the dotted decimal value will be used instead. 276This allows hosts with very long host names that 277overflow this field to still be uniquely identified. 278Specifying 279.Fl u0 280indicates that only dotted decimal addresses 281should be put into the 282.Pa utmp 283file. 284.Fl u0 285is also be used to prevent 286.Nm 287from making DNS requests unless the authentication 288mechanism or configuration requires it. 289Authentication mechanisms that may require DNS include 290.Cm RhostsAuthentication , 291.Cm RhostsRSAAuthentication , 292.Cm HostbasedAuthentication 293and using a 294.Cm from="pattern-list" 295option in a key file. 296Configuration options that require DNS include using a 297USER@HOST pattern in 298.Cm AllowUsers 299or 300.Cm DenyUsers . 301.It Fl D 302When this option is specified 303.Nm 304will not detach and does not become a daemon. 305This allows easy monitoring of 306.Nm sshd . 307.It Fl 4 308Forces 309.Nm 310to use IPv4 addresses only. 311.It Fl 6 312Forces 313.Nm 314to use IPv6 addresses only. 315.El 316.Sh CONFIGURATION FILE 317.Nm 318reads configuration data from 319.Pa /etc/ssh/sshd_config 320(or the file specified with 321.Fl f 322on the command line). 323The file format and configuration options are described in 324.Xr sshd_config 5 . 325.Sh LOGIN PROCESS 326When a user successfully logs in, 327.Nm 328does the following: 329.Bl -enum -offset indent 330.It 331If the login is on a tty, and no command has been specified, 332prints last login time and 333.Pa /etc/motd 334(unless prevented in the configuration file or by 335.Pa $HOME/.hushlogin ; 336see the 337.Sx FILES 338section). 339.It 340If the login is on a tty, records login time. 341.It 342Checks 343.Pa /etc/nologin and 344.Pa /var/run/nologin ; 345if one exists, it prints the contents and quits 346(unless root). 347.It 348Changes to run with normal user privileges. 349.It 350Sets up basic environment. 351.It 352Reads 353.Pa $HOME/.ssh/environment 354if it exists and users are allowed to change their environment. 355See the 356.Cm PermitUserEnvironment 357option in 358.Xr sshd_config 5 . 359.It 360Changes to user's home directory. 361.It 362If 363.Pa $HOME/.ssh/rc 364exists, runs it; else if 365.Pa /etc/ssh/sshrc 366exists, runs 367it; otherwise runs 368.Xr xauth 1 . 369The 370.Dq rc 371files are given the X11 372authentication protocol and cookie (if applicable) in standard input. 373.It 374Runs user's shell or command. 375.El 376.Sh AUTHORIZED_KEYS FILE FORMAT 377.Pa $HOME/.ssh/authorized_keys 378is the default file that lists the public keys that are 379permitted for RSA authentication in protocol version 1 380and for public key authentication (PubkeyAuthentication) 381in protocol version 2. 382.Cm AuthorizedKeysFile 383may be used to specify an alternative file. 384.Pp 385Each line of the file contains one 386key (empty lines and lines starting with a 387.Ql # 388are ignored as 389comments). 390Each RSA public key consists of the following fields, separated by 391spaces: options, bits, exponent, modulus, comment. 392Each protocol version 2 public key consists of: 393options, keytype, base64 encoded key, comment. 394The options field 395is optional; its presence is determined by whether the line starts 396with a number or not (the options field never starts with a number). 397The bits, exponent, modulus and comment fields give the RSA key for 398protocol version 1; the 399comment field is not used for anything (but may be convenient for the 400user to identify the key). 401For protocol version 2 the keytype is 402.Dq ssh-dss 403or 404.Dq ssh-rsa . 405.Pp 406Note that lines in this file are usually several hundred bytes long 407(because of the size of the public key encoding). 408You don't want to type them in; instead, copy the 409.Pa identity.pub , 410.Pa id_dsa.pub 411or the 412.Pa id_rsa.pub 413file and edit it. 414.Pp 415.Nm 416enforces a minimum RSA key modulus size for protocol 1 417and protocol 2 keys of 768 bits. 418.Pp 419The options (if present) consist of comma-separated option 420specifications. 421No spaces are permitted, except within double quotes. 422The following option specifications are supported (note 423that option keywords are case-insensitive): 424.Bl -tag -width Ds 425.It Cm from="pattern-list" 426Specifies that in addition to public key authentication, the canonical name 427of the remote host must be present in the comma-separated list of 428patterns 429.Pf ( Ql * 430and 431.Ql ? 432serve as wildcards). 433The list may also contain 434patterns negated by prefixing them with 435.Ql ! ; 436if the canonical host name matches a negated pattern, the key is not accepted. 437The purpose 438of this option is to optionally increase security: public key authentication 439by itself does not trust the network or name servers or anything (but 440the key); however, if somebody somehow steals the key, the key 441permits an intruder to log in from anywhere in the world. 442This additional option makes using a stolen key more difficult (name 443servers and/or routers would have to be compromised in addition to 444just the key). 445.It Cm command="command" 446Specifies that the command is executed whenever this key is used for 447authentication. 448The command supplied by the user (if any) is ignored. 449The command is run on a pty if the client requests a pty; 450otherwise it is run without a tty. 451If a 8-bit clean channel is required, 452one must not request a pty or should specify 453.Cm no-pty . 454A quote may be included in the command by quoting it with a backslash. 455This option might be useful 456to restrict certain public keys to perform just a specific operation. 457An example might be a key that permits remote backups but nothing else. 458Note that the client may specify TCP/IP and/or X11 459forwarding unless they are explicitly prohibited. 460Note that this option applies to shell, command or subsystem execution. 461.It Cm environment="NAME=value" 462Specifies that the string is to be added to the environment when 463logging in using this key. 464Environment variables set this way 465override other default environment values. 466Multiple options of this type are permitted. 467Environment processing is disabled by default and is 468controlled via the 469.Cm PermitUserEnvironment 470option. 471This option is automatically disabled if 472.Cm UseLogin 473is enabled. 474.It Cm no-port-forwarding 475Forbids TCP/IP forwarding when this key is used for authentication. 476Any port forward requests by the client will return an error. 477This might be used, e.g., in connection with the 478.Cm command 479option. 480.It Cm no-X11-forwarding 481Forbids X11 forwarding when this key is used for authentication. 482Any X11 forward requests by the client will return an error. 483.It Cm no-agent-forwarding 484Forbids authentication agent forwarding when this key is used for 485authentication. 486.It Cm no-pty 487Prevents tty allocation (a request to allocate a pty will fail). 488.It Cm permitopen="host:port" 489Limit local 490.Li ``ssh -L'' 491port forwarding such that it may only connect to the specified host and 492port. 493IPv6 addresses can be specified with an alternative syntax: 494.Ar host/port . 495Multiple 496.Cm permitopen 497options may be applied separated by commas. No pattern matching is 498performed on the specified hostnames, they must be literal domains or 499addresses. 500.El 501.Ss Examples 5021024 33 12121.\|.\|.\|312314325 ylo@foo.bar 503.Pp 504from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula 505.Pp 506command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi 507.Pp 508permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323 509.Sh SSH_KNOWN_HOSTS FILE FORMAT 510The 511.Pa /etc/ssh/ssh_known_hosts 512and 513.Pa $HOME/.ssh/known_hosts 514files contain host public keys for all known hosts. 515The global file should 516be prepared by the administrator (optional), and the per-user file is 517maintained automatically: whenever the user connects from an unknown host 518its key is added to the per-user file. 519.Pp 520Each line in these files contains the following fields: hostnames, 521bits, exponent, modulus, comment. 522The fields are separated by spaces. 523.Pp 524Hostnames is a comma-separated list of patterns ('*' and '?' act as 525wildcards); each pattern in turn is matched against the canonical host 526name (when authenticating a client) or against the user-supplied 527name (when authenticating a server). 528A pattern may also be preceded by 529.Ql ! 530to indicate negation: if the host name matches a negated 531pattern, it is not accepted (by that line) even if it matched another 532pattern on the line. 533.Pp 534Bits, exponent, and modulus are taken directly from the RSA host key; they 535can be obtained, e.g., from 536.Pa /etc/ssh/ssh_host_key.pub . 537The optional comment field continues to the end of the line, and is not used. 538.Pp 539Lines starting with 540.Ql # 541and empty lines are ignored as comments. 542.Pp 543When performing host authentication, authentication is accepted if any 544matching line has the proper key. 545It is thus permissible (but not 546recommended) to have several lines or different host keys for the same 547names. 548This will inevitably happen when short forms of host names 549from different domains are put in the file. 550It is possible 551that the files contain conflicting information; authentication is 552accepted if valid information can be found from either file. 553.Pp 554Note that the lines in these files are typically hundreds of characters 555long, and you definitely don't want to type in the host keys by hand. 556Rather, generate them by a script 557or by taking 558.Pa /etc/ssh/ssh_host_key.pub 559and adding the host names at the front. 560.Ss Examples 561.Bd -literal 562closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi 563cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= 564.Ed 565.Sh FILES 566.Bl -tag -width Ds 567.It Pa /etc/ssh/sshd_config 568Contains configuration data for 569.Nm sshd . 570The file format and configuration options are described in 571.Xr sshd_config 5 . 572.It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key 573These two files contain the private parts of the host keys. 574These files should only be owned by root, readable only by root, and not 575accessible to others. 576Note that 577.Nm 578does not start if this file is group/world-accessible. 579.It Pa /etc/ssh/ssh_host_key.pub, /etc/ssh/ssh_host_dsa_key.pub 580These two files contain the public parts of the host keys. 581These files should be world-readable but writable only by 582root. 583Their contents should match the respective private parts. 584These files are not 585really used for anything; they are provided for the convenience of 586the user so their contents can be copied to known hosts files. 587These files are created using 588.Xr ssh-keygen 1 . 589.It Pa /etc/ssh/moduli 590Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". 591The file format is described in 592.Xr moduli 5 . 593.It Pa /var/empty 594.Xr chroot 2 595directory used by 596.Nm 597during privilege separation in the pre-authentication phase. 598The directory should not contain any files and must be owned by root 599and not group or world-writable. 600.It Pa /var/run/sshd.pid 601Contains the process ID of the 602.Nm 603listening for connections (if there are several daemons running 604concurrently for different ports, this contains the process ID of the one 605started last). 606The content of this file is not sensitive; it can be world-readable. 607.It Pa $HOME/.ssh/authorized_keys 608Lists the public keys (RSA or DSA) that can be used to log into the user's account. 609This file must be readable by root (which may on some machines imply 610it being world-readable if the user's home directory resides on an NFS 611volume). 612It is recommended that it not be accessible by others. 613The format of this file is described above. 614Users will place the contents of their 615.Pa identity.pub , 616.Pa id_dsa.pub 617and/or 618.Pa id_rsa.pub 619files into this file, as described in 620.Xr ssh-keygen 1 . 621.It Pa "/etc/ssh/ssh_known_hosts" and "$HOME/.ssh/known_hosts" 622These files are consulted when using rhosts with RSA host 623authentication or protocol version 2 hostbased authentication 624to check the public key of the host. 625The key must be listed in one of these files to be accepted. 626The client uses the same files 627to verify that it is connecting to the correct remote host. 628These files should be writable only by root/the owner. 629.Pa /etc/ssh/ssh_known_hosts 630should be world-readable, and 631.Pa $HOME/.ssh/known_hosts 632can but need not be world-readable. 633.It Pa /etc/nologin 634If this file exists, 635.Nm 636refuses to let anyone except root log in. 637The contents of the file 638are displayed to anyone trying to log in, and non-root connections are 639refused. 640The file should be world-readable. 641.It Pa /etc/hosts.allow, /etc/hosts.deny 642Access controls that should be enforced by tcp-wrappers are defined here. 643Further details are described in 644.Xr hosts_access 5 . 645.It Pa $HOME/.rhosts 646This file contains host-username pairs, separated by a space, one per 647line. 648The given user on the corresponding host is permitted to log in 649without password. 650The same file is used by rlogind and rshd. 651The file must 652be writable only by the user; it is recommended that it not be 653accessible by others. 654.Pp 655If is also possible to use netgroups in the file. 656Either host or user 657name may be of the form +@groupname to specify all hosts or all users 658in the group. 659.It Pa $HOME/.shosts 660For ssh, 661this file is exactly the same as for 662.Pa .rhosts . 663However, this file is 664not used by rlogin and rshd, so using this permits access using SSH only. 665.It Pa /etc/hosts.equiv 666This file is used during 667.Pa .rhosts 668authentication. 669In the simplest form, this file contains host names, one per line. 670Users on 671those hosts are permitted to log in without a password, provided they 672have the same user name on both machines. 673The host name may also be 674followed by a user name; such users are permitted to log in as 675.Em any 676user on this machine (except root). 677Additionally, the syntax 678.Dq +@group 679can be used to specify netgroups. 680Negated entries start with 681.Ql \&- . 682.Pp 683If the client host/user is successfully matched in this file, login is 684automatically permitted provided the client and server user names are the 685same. 686Additionally, successful RSA host authentication is normally required. 687This file must be writable only by root; it is recommended 688that it be world-readable. 689.Pp 690.Sy "Warning: It is almost never a good idea to use user names in" 691.Pa hosts.equiv . 692Beware that it really means that the named user(s) can log in as 693.Em anybody , 694which includes bin, daemon, adm, and other accounts that own critical 695binaries and directories. 696Using a user name practically grants the user root access. 697The only valid use for user names that I can think 698of is in negative entries. 699.Pp 700Note that this warning also applies to rsh/rlogin. 701.It Pa /etc/ssh/shosts.equiv 702This is processed exactly as 703.Pa /etc/hosts.equiv . 704However, this file may be useful in environments that want to run both 705rsh/rlogin and ssh. 706.It Pa $HOME/.ssh/environment 707This file is read into the environment at login (if it exists). 708It can only contain empty lines, comment lines (that start with 709.Ql # ) , 710and assignment lines of the form name=value. 711The file should be writable 712only by the user; it need not be readable by anyone else. 713Environment processing is disabled by default and is 714controlled via the 715.Cm PermitUserEnvironment 716option. 717.It Pa $HOME/.ssh/rc 718If this file exists, it is run with 719.Pa /bin/sh 720after reading the 721environment files but before starting the user's shell or command. 722It must not produce any output on stdout; stderr must be used 723instead. 724If X11 forwarding is in use, it will receive the "proto cookie" pair in 725its standard input (and 726.Ev DISPLAY 727in its environment). 728The script must call 729.Xr xauth 1 730because 731.Nm 732will not run xauth automatically to add X11 cookies. 733.Pp 734The primary purpose of this file is to run any initialization routines 735which may be needed before the user's home directory becomes 736accessible; AFS is a particular example of such an environment. 737.Pp 738This file will probably contain some initialization code followed by 739something similar to: 740.Bd -literal 741if read proto cookie && [ -n "$DISPLAY" ]; then 742 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then 743 # X11UseLocalhost=yes 744 echo add unix:`echo $DISPLAY | 745 cut -c11-` $proto $cookie 746 else 747 # X11UseLocalhost=no 748 echo add $DISPLAY $proto $cookie 749 fi | xauth -q - 750fi 751.Ed 752.Pp 753If this file does not exist, 754.Pa /etc/ssh/sshrc 755is run, and if that 756does not exist either, xauth is used to add the cookie. 757.Pp 758This file should be writable only by the user, and need not be 759readable by anyone else. 760.It Pa /etc/ssh/sshrc 761Like 762.Pa $HOME/.ssh/rc . 763This can be used to specify 764machine-specific login-time initializations globally. 765This file should be writable only by root, and should be world-readable. 766.El 767.Sh AUTHORS 768OpenSSH is a derivative of the original and free 769ssh 1.2.12 release by Tatu Ylonen. 770Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 771Theo de Raadt and Dug Song 772removed many bugs, re-added newer features and 773created OpenSSH. 774Markus Friedl contributed the support for SSH 775protocol versions 1.5 and 2.0. 776Niels Provos and Markus Friedl contributed support 777for privilege separation. 778.Sh SEE ALSO 779.Xr scp 1 , 780.Xr sftp 1 , 781.Xr ssh 1 , 782.Xr ssh-add 1 , 783.Xr ssh-agent 1 , 784.Xr ssh-keygen 1 , 785.Xr login.conf 5 , 786.Xr moduli 5 , 787.Xr sshd_config 5 , 788.Xr sftp-server 8 789.Rs 790.%A T. Ylonen 791.%A T. Kivinen 792.%A M. Saarinen 793.%A T. Rinne 794.%A S. Lehtinen 795.%T "SSH Protocol Architecture" 796.%N draft-ietf-secsh-architecture-12.txt 797.%D January 2002 798.%O work in progress material 799.Re 800.Rs 801.%A M. Friedl 802.%A N. Provos 803.%A W. A. Simpson 804.%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" 805.%N draft-ietf-secsh-dh-group-exchange-02.txt 806.%D January 2002 807.%O work in progress material 808.Re 809