1.\" $OpenBSD: ssh-agent.1,v 1.24 2001/04/10 09:13:21 itojun 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.Ar command 46.Ar args ... 47.Nm ssh-agent 48.Op Fl c Li | Fl s 49.Nm ssh-agent 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.El 84.Pp 85If a commandline is given, this is executed as a subprocess of the agent. 86When the command dies, so does the agent. 87.Pp 88The agent initially does not have any private keys. 89Keys are added using 90.Xr ssh-add 1 . 91When executed without arguments, 92.Xr ssh-add 1 93adds the 94.Pa $HOME/.ssh/identity 95file. 96If the identity has a passphrase, 97.Xr ssh-add 1 98asks for the passphrase (using a small X11 application if running 99under X11, or from the terminal if running without X). 100It then sends the identity to the agent. 101Several identities can be stored in the 102agent; the agent can automatically use any of these identities. 103.Ic ssh-add -l 104displays the identities currently held by the agent. 105.Pp 106The idea is that the agent is run in the user's local PC, laptop, or 107terminal. 108Authentication data need not be stored on any other 109machine, and authentication passphrases never go over the network. 110However, the connection to the agent is forwarded over SSH 111remote logins, and the user can thus use the privileges given by the 112identities anywhere in the network in a secure way. 113.Pp 114There are two main ways to get an agent setup: 115Either you let the agent 116start a new subcommand into which some environment variables are exported, or 117you let the agent print the needed shell commands (either 118.Xr sh 1 119or 120.Xr csh 1 121syntax can be generated) which can be evalled in the calling shell. 122Later 123.Xr ssh 1 124looks at these variables and uses them to establish a connection to the agent. 125.Pp 126A unix-domain socket is created 127.Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> , 128and the name of this socket is stored in the 129.Ev SSH_AUTH_SOCK 130environment 131variable. 132The socket is made accessible only to the current user. 133This method is easily abused by root or another instance of the same 134user. 135.Pp 136The 137.Ev SSH_AGENT_PID 138environment variable holds the agent's PID. 139.Pp 140The agent exits automatically when the command given on the command 141line terminates. 142.Sh FILES 143.Bl -tag -width Ds 144.It Pa $HOME/.ssh/identity 145Contains the protocol version 1 RSA authentication identity of the user. 146This file should not be readable by anyone but the user. 147It is possible to 148specify a passphrase when generating the key; that passphrase will be 149used to encrypt the private part of this file. 150This file is not used by 151.Nm 152but is normally added to the agent using 153.Xr ssh-add 1 154at login time. 155.It Pa $HOME/.ssh/id_dsa 156Contains the protocol version 2 DSA authentication identity of the user. 157.It Pa $HOME/.ssh/id_rsa 158Contains the protocol version 2 RSA authentication identity of the user. 159.It Pa /tmp/ssh-XXXXXXXX/agent.<pid> 160Unix-domain sockets used to contain the connection to the 161authentication agent. 162These sockets should only be readable by the owner. 163The sockets should get automatically removed when the agent exits. 164.El 165.Sh AUTHORS 166OpenSSH is a derivative of the original and free 167ssh 1.2.12 release by Tatu Ylonen. 168Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 169Theo de Raadt and Dug Song 170removed many bugs, re-added newer features and 171created OpenSSH. 172Markus Friedl contributed the support for SSH 173protocol versions 1.5 and 2.0. 174.Sh SEE ALSO 175.Xr ssh 1 , 176.Xr ssh-add 1 , 177.Xr ssh-keygen 1 , 178.Xr sshd 8 179