1.\" $OpenBSD: ssh-agent.1,v 1.26 2001/07/15 16:57:21 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.Ar command 46.Ar args ... 47.Nm ssh-agent 48.Op Fl c Li | Fl s 49.Nm ssh-agent 50.Fl k 51.Nm ssh-agent 52.Fl d 53.Sh DESCRIPTION 54.Nm 55is a program to hold private keys used for public key authentication 56(RSA, DSA). 57The idea is that 58.Nm 59is started in the beginning of an X-session or a login session, and 60all other windows or programs are started as clients to the ssh-agent 61program. 62Through use of environment variables the agent can be located 63and automatically used for authentication when logging in to other 64machines using 65.Xr ssh 1 . 66.Pp 67The options are as follows: 68.Bl -tag -width Ds 69.It Fl c 70Generate C-shell commands on 71.Dv stdout . 72This is the default if 73.Ev SHELL 74looks like it's a csh style of shell. 75.It Fl s 76Generate Bourne shell commands on 77.Dv stdout . 78This is the default if 79.Ev SHELL 80does not look like it's a csh style of shell. 81.It Fl k 82Kill the current agent (given by the 83.Ev SSH_AGENT_PID 84environment variable). 85.It Fl d 86Debug mode. When this option is specified 87.Nm 88will not fork. 89.El 90.Pp 91If a commandline is given, this is executed as a subprocess of the agent. 92When the command dies, so does the agent. 93.Pp 94The agent initially does not have any private keys. 95Keys are added using 96.Xr ssh-add 1 . 97When executed without arguments, 98.Xr ssh-add 1 99adds the 100.Pa $HOME/.ssh/identity 101file. 102If the identity has a passphrase, 103.Xr ssh-add 1 104asks for the passphrase (using a small X11 application if running 105under X11, or from the terminal if running without X). 106It then sends the identity to the agent. 107Several identities can be stored in the 108agent; the agent can automatically use any of these identities. 109.Ic ssh-add -l 110displays the identities currently held by the agent. 111.Pp 112The idea is that the agent is run in the user's local PC, laptop, or 113terminal. 114Authentication data need not be stored on any other 115machine, and authentication passphrases never go over the network. 116However, the connection to the agent is forwarded over SSH 117remote logins, and the user can thus use the privileges given by the 118identities anywhere in the network in a secure way. 119.Pp 120There are two main ways to get an agent setup: 121Either you let the agent 122start a new subcommand into which some environment variables are exported, or 123you let the agent print the needed shell commands (either 124.Xr sh 1 125or 126.Xr csh 1 127syntax can be generated) which can be evalled in the calling shell. 128Later 129.Xr ssh 1 130looks at these variables and uses them to establish a connection to the agent. 131.Pp 132A unix-domain socket is created 133.Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> , 134and the name of this socket is stored in the 135.Ev SSH_AUTH_SOCK 136environment 137variable. 138The socket is made accessible only to the current user. 139This method is easily abused by root or another instance of the same 140user. 141.Pp 142The 143.Ev SSH_AGENT_PID 144environment variable holds the agent's PID. 145.Pp 146The agent exits automatically when the command given on the command 147line terminates. 148.Sh FILES 149.Bl -tag -width Ds 150.It Pa $HOME/.ssh/identity 151Contains the protocol version 1 RSA authentication identity of the user. 152This file should not be readable by anyone but the user. 153It is possible to 154specify a passphrase when generating the key; that passphrase will be 155used to encrypt the private part of this file. 156This file is not used by 157.Nm 158but is normally added to the agent using 159.Xr ssh-add 1 160at login time. 161.It Pa $HOME/.ssh/id_dsa 162Contains the protocol version 2 DSA authentication identity of the user. 163.It Pa $HOME/.ssh/id_rsa 164Contains the protocol version 2 RSA authentication identity of the user. 165.It Pa /tmp/ssh-XXXXXXXX/agent.<pid> 166Unix-domain sockets used to contain the connection to the 167authentication agent. 168These sockets should only be readable by the owner. 169The sockets should get automatically removed when the agent exits. 170.El 171.Sh AUTHORS 172OpenSSH is a derivative of the original and free 173ssh 1.2.12 release by Tatu Ylonen. 174Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 175Theo de Raadt and Dug Song 176removed many bugs, re-added newer features and 177created OpenSSH. 178Markus Friedl contributed the support for SSH 179protocol versions 1.5 and 2.0. 180.Sh SEE ALSO 181.Xr ssh 1 , 182.Xr ssh-add 1 , 183.Xr ssh-keygen 1 , 184.Xr sshd 8 185