1.\" $OpenBSD: ssh-agent.1,v 1.29 2001/11/19 18:40:46 stevesk Exp $ 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.Dd September 25, 1999 38.Dt SSH-AGENT 1 39.Os 40.Sh NAME 41.Nm ssh-agent 42.Nd authentication agent 43.Sh SYNOPSIS 44.Nm ssh-agent 45.Op Fl c Li | Fl s 46.Op Fl d 47.Op Ar command Op Ar args ... 48.Nm ssh-agent 49.Op Fl c Li | Fl s 50.Fl k 51.Sh DESCRIPTION 52.Nm 53is a program to hold private keys used for public key authentication 54(RSA, DSA). 55The idea is that 56.Nm 57is started in the beginning of an X-session or a login session, and 58all other windows or programs are started as clients to the ssh-agent 59program. 60Through use of environment variables the agent can be located 61and automatically used for authentication when logging in to other 62machines using 63.Xr ssh 1 . 64.Pp 65The options are as follows: 66.Bl -tag -width Ds 67.It Fl c 68Generate C-shell commands on 69.Dv stdout . 70This is the default if 71.Ev SHELL 72looks like it's a csh style of shell. 73.It Fl s 74Generate Bourne shell commands on 75.Dv stdout . 76This is the default if 77.Ev SHELL 78does not look like it's a csh style of shell. 79.It Fl k 80Kill the current agent (given by the 81.Ev SSH_AGENT_PID 82environment variable). 83.It Fl d 84Debug mode. When this option is specified 85.Nm 86will not fork. 87.El 88.Pp 89If a commandline is given, this is executed as a subprocess of the agent. 90When the command dies, so does the agent. 91.Pp 92The agent initially does not have any private keys. 93Keys are added using 94.Xr ssh-add 1 . 95When executed without arguments, 96.Xr ssh-add 1 97adds the 98.Pa $HOME/.ssh/identity 99file. 100If the identity has a passphrase, 101.Xr ssh-add 1 102asks for the passphrase (using a small X11 application if running 103under X11, or from the terminal if running without X). 104It then sends the identity to the agent. 105Several identities can be stored in the 106agent; the agent can automatically use any of these identities. 107.Ic ssh-add -l 108displays the identities currently held by the agent. 109.Pp 110The idea is that the agent is run in the user's local PC, laptop, or 111terminal. 112Authentication data need not be stored on any other 113machine, and authentication passphrases never go over the network. 114However, the connection to the agent is forwarded over SSH 115remote logins, and the user can thus use the privileges given by the 116identities anywhere in the network in a secure way. 117.Pp 118There are two main ways to get an agent setup: 119Either the agent starts a new subcommand into which some environment 120variables are exported, or the agent prints the needed shell commands 121(either 122.Xr sh 1 123or 124.Xr csh 1 125syntax can be generated) which can be evalled in the calling shell. 126Later 127.Xr ssh 1 128looks at these variables and uses them to establish a connection to the agent. 129.Pp 130The agent will never send a private key over its request channel. 131Instead, operations that require a private key will be performed 132by the agent, and the result will be returned to the requester. 133This way, private keys are not exposed to clients using the agent. 134.Pp 135A unix-domain socket is created 136.Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> , 137and the name of this socket is stored in the 138.Ev SSH_AUTH_SOCK 139environment 140variable. 141The socket is made accessible only to the current user. 142This method is easily abused by root or another instance of the same 143user. 144.Pp 145The 146.Ev SSH_AGENT_PID 147environment variable holds the agent's PID. 148.Pp 149The agent exits automatically when the command given on the command 150line terminates. 151.Sh FILES 152.Bl -tag -width Ds 153.It Pa $HOME/.ssh/identity 154Contains the protocol version 1 RSA authentication identity of the user. 155This file should not be readable by anyone but the user. 156It is possible to 157specify a passphrase when generating the key; that passphrase will be 158used to encrypt the private part of this file. 159This file is not used by 160.Nm 161but is normally added to the agent using 162.Xr ssh-add 1 163at login time. 164.It Pa $HOME/.ssh/id_dsa 165Contains the protocol version 2 DSA authentication identity of the user. 166.It Pa $HOME/.ssh/id_rsa 167Contains the protocol version 2 RSA authentication identity of the user. 168.It Pa /tmp/ssh-XXXXXXXX/agent.<pid> 169Unix-domain sockets used to contain the connection to the 170authentication agent. 171These sockets should only be readable by the owner. 172The sockets should get automatically removed when the agent exits. 173.El 174.Sh AUTHORS 175OpenSSH is a derivative of the original and free 176ssh 1.2.12 release by Tatu Ylonen. 177Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 178Theo de Raadt and Dug Song 179removed many bugs, re-added newer features and 180created OpenSSH. 181Markus Friedl contributed the support for SSH 182protocol versions 1.5 and 2.0. 183.Sh SEE ALSO 184.Xr ssh 1 , 185.Xr ssh-add 1 , 186.Xr ssh-keygen 1 , 187.Xr sshd 8 188