| 1 | .\" $OpenBSD: ssh-agent.1,v 1.35 2002/06/24 13:12:23 markus Exp $ |
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| 2 | .\" |
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| 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
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| 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
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| 5 | .\" All rights reserved |
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| 6 | .\" |
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| 7 | .\" As far as I am concerned, the code I have written for this software |
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| 8 | .\" can be used freely for any purpose. Any derived versions of this |
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| 9 | .\" software must be clearly marked as such, and if the derived work is |
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| 10 | .\" incompatible with the protocol description in the RFC file, it must be |
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| 11 | .\" called by a name other than "ssh" or "Secure Shell". |
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| 12 | .\" |
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| 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
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| 14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. |
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| 15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. |
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| 16 | .\" |
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| 17 | .\" Redistribution and use in source and binary forms, with or without |
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| 18 | .\" modification, are permitted provided that the following conditions |
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| 19 | .\" are met: |
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| 20 | .\" 1. Redistributions of source code must retain the above copyright |
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| 21 | .\" notice, this list of conditions and the following disclaimer. |
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| 22 | .\" 2. Redistributions in binary form must reproduce the above copyright |
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| 23 | .\" notice, this list of conditions and the following disclaimer in the |
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| 24 | .\" documentation and/or other materials provided with the distribution. |
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| 25 | .\" |
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| 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
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| 27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
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| 28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
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| 29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
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| 30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
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| 31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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| 32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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| 33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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| 34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
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| 35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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| 36 | .\" |
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| 37 | .Dd September 25, 1999 |
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| 38 | .Dt SSH-AGENT 1 |
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| 39 | .Os |
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| 40 | .Sh NAME |
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| 41 | .Nm ssh-agent |
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| 42 | .Nd authentication agent |
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| 43 | .Sh SYNOPSIS |
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| 44 | .Nm ssh-agent |
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| 45 | .Op Fl a Ar bind_address |
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| 46 | .Op Fl c Li | Fl s |
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| 47 | .Op Fl d |
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| 48 | .Op Ar command Op Ar args ... |
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| 49 | .Nm ssh-agent |
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| 50 | .Op Fl c Li | Fl s |
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| 51 | .Fl k |
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| 52 | .Sh DESCRIPTION |
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| 53 | .Nm |
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| 54 | is a program to hold private keys used for public key authentication |
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| 55 | (RSA, DSA). |
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| 56 | The idea is that |
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| 57 | .Nm |
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| 58 | is started in the beginning of an X-session or a login session, and |
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| 59 | all other windows or programs are started as clients to the ssh-agent |
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| 60 | program. |
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| 61 | Through use of environment variables the agent can be located |
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| 62 | and automatically used for authentication when logging in to other |
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| 63 | machines using |
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| 64 | .Xr ssh 1 . |
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| 65 | .Pp |
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| 66 | The options are as follows: |
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| 67 | .Bl -tag -width Ds |
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| 68 | .It Fl a Ar bind_address |
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| 69 | Bind the agent to the unix-domain socket |
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| 70 | .Ar bind_address . |
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| 71 | The default is |
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| 72 | .Pa /tmp/ssh-XXXXXXXX/agent.<ppid> . |
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| 73 | .It Fl c |
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| 74 | Generate C-shell commands on |
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| 75 | .Dv stdout . |
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| 76 | This is the default if |
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| 77 | .Ev SHELL |
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| 78 | looks like it's a csh style of shell. |
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| 79 | .It Fl s |
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| 80 | Generate Bourne shell commands on |
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| 81 | .Dv stdout . |
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| 82 | This is the default if |
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| 83 | .Ev SHELL |
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| 84 | does not look like it's a csh style of shell. |
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| 85 | .It Fl k |
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| 86 | Kill the current agent (given by the |
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| 87 | .Ev SSH_AGENT_PID |
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| 88 | environment variable). |
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| 89 | .It Fl d |
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| 90 | Debug mode. When this option is specified |
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| 91 | .Nm |
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| 92 | will not fork. |
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| 93 | .El |
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| 94 | .Pp |
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| 95 | If a commandline is given, this is executed as a subprocess of the agent. |
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| 96 | When the command dies, so does the agent. |
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| 97 | .Pp |
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| 98 | The agent initially does not have any private keys. |
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| 99 | Keys are added using |
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| 100 | .Xr ssh-add 1 . |
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| 101 | When executed without arguments, |
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| 102 | .Xr ssh-add 1 |
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| 103 | adds the files |
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| 104 | .Pa $HOME/.ssh/id_rsa , |
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| 105 | .Pa $HOME/.ssh/id_dsa |
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| 106 | and |
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| 107 | .Pa $HOME/.ssh/identity . |
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| 108 | If the identity has a passphrase, |
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| 109 | .Xr ssh-add 1 |
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| 110 | asks for the passphrase (using a small X11 application if running |
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| 111 | under X11, or from the terminal if running without X). |
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| 112 | It then sends the identity to the agent. |
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| 113 | Several identities can be stored in the |
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| 114 | agent; the agent can automatically use any of these identities. |
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| 115 | .Ic ssh-add -l |
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| 116 | displays the identities currently held by the agent. |
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| 117 | .Pp |
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| 118 | The idea is that the agent is run in the user's local PC, laptop, or |
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| 119 | terminal. |
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| 120 | Authentication data need not be stored on any other |
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| 121 | machine, and authentication passphrases never go over the network. |
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| 122 | However, the connection to the agent is forwarded over SSH |
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| 123 | remote logins, and the user can thus use the privileges given by the |
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| 124 | identities anywhere in the network in a secure way. |
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| 125 | .Pp |
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| 126 | There are two main ways to get an agent setup: |
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| 127 | Either the agent starts a new subcommand into which some environment |
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| 128 | variables are exported, or the agent prints the needed shell commands |
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| 129 | (either |
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| 130 | .Xr sh 1 |
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| 131 | or |
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| 132 | .Xr csh 1 |
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| 133 | syntax can be generated) which can be evalled in the calling shell. |
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| 134 | Later |
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| 135 | .Xr ssh 1 |
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| 136 | looks at these variables and uses them to establish a connection to the agent. |
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| 137 | .Pp |
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| 138 | The agent will never send a private key over its request channel. |
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| 139 | Instead, operations that require a private key will be performed |
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| 140 | by the agent, and the result will be returned to the requester. |
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| 141 | This way, private keys are not exposed to clients using the agent. |
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| 142 | .Pp |
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| 143 | A unix-domain socket is created |
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| 144 | and the name of this socket is stored in the |
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| 145 | .Ev SSH_AUTH_SOCK |
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| 146 | environment |
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| 147 | variable. |
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| 148 | The socket is made accessible only to the current user. |
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| 149 | This method is easily abused by root or another instance of the same |
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| 150 | user. |
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| 151 | .Pp |
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| 152 | The |
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| 153 | .Ev SSH_AGENT_PID |
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| 154 | environment variable holds the agent's process ID. |
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| 155 | .Pp |
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| 156 | The agent exits automatically when the command given on the command |
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| 157 | line terminates. |
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| 158 | .Sh FILES |
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| 159 | .Bl -tag -width Ds |
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| 160 | .It Pa $HOME/.ssh/identity |
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| 161 | Contains the protocol version 1 RSA authentication identity of the user. |
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| 162 | .It Pa $HOME/.ssh/id_dsa |
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| 163 | Contains the protocol version 2 DSA authentication identity of the user. |
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| 164 | .It Pa $HOME/.ssh/id_rsa |
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| 165 | Contains the protocol version 2 RSA authentication identity of the user. |
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| 166 | .It Pa /tmp/ssh-XXXXXXXX/agent.<ppid> |
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| 167 | Unix-domain sockets used to contain the connection to the |
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| 168 | authentication agent. |
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| 169 | These sockets should only be readable by the owner. |
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| 170 | The sockets should get automatically removed when the agent exits. |
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| 171 | .El |
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| 172 | .Sh AUTHORS |
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| 173 | OpenSSH is a derivative of the original and free |
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| 174 | ssh 1.2.12 release by Tatu Ylonen. |
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| 175 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
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| 176 | Theo de Raadt and Dug Song |
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| 177 | removed many bugs, re-added newer features and |
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| 178 | created OpenSSH. |
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| 179 | Markus Friedl contributed the support for SSH |
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| 180 | protocol versions 1.5 and 2.0. |
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| 181 | .Sh SEE ALSO |
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| 182 | .Xr ssh 1 , |
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| 183 | .Xr ssh-add 1 , |
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| 184 | .Xr ssh-keygen 1 , |
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| 185 | .Xr sshd 8 |
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