1.\" $OpenBSD: ssh-agent.1,v 1.44 2006/07/18 08:03:09 jmc 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 a Ar bind_address 46.Op Fl c Li | Fl s 47.Op Fl t Ar life 48.Op Fl d 49.Op Ar command Op Ar args ... 50.Nm ssh-agent 51.Op Fl c Li | Fl s 52.Fl k 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 a Ar bind_address 70Bind the agent to the unix-domain socket 71.Ar bind_address . 72The default is 73.Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 74.It Fl c 75Generate C-shell commands on 76.Dv stdout . 77This is the default if 78.Ev SHELL 79looks like it's a csh style of shell. 80.It Fl s 81Generate Bourne shell commands on 82.Dv stdout . 83This is the default if 84.Ev SHELL 85does not look like it's a csh style of shell. 86.It Fl k 87Kill the current agent (given by the 88.Ev SSH_AGENT_PID 89environment variable). 90.It Fl t Ar life 91Set a default value for the maximum lifetime of identities added to the agent. 92The lifetime may be specified in seconds or in a time format specified in 93.Xr sshd_config 5 . 94A lifetime specified for an identity with 95.Xr ssh-add 1 96overrides this value. 97Without this option the default maximum lifetime is forever. 98.It Fl d 99Debug mode. 100When this option is specified 101.Nm 102will not fork. 103.El 104.Pp 105If a commandline is given, this is executed as a subprocess of the agent. 106When the command dies, so does the agent. 107.Pp 108The agent initially does not have any private keys. 109Keys are added using 110.Xr ssh-add 1 . 111When executed without arguments, 112.Xr ssh-add 1 113adds the files 114.Pa ~/.ssh/id_rsa , 115.Pa ~/.ssh/id_dsa 116and 117.Pa ~/.ssh/identity . 118If the identity has a passphrase, 119.Xr ssh-add 1 120asks for the passphrase (using a small X11 application if running 121under X11, or from the terminal if running without X). 122It then sends the identity to the agent. 123Several identities can be stored in the 124agent; the agent can automatically use any of these identities. 125.Ic ssh-add -l 126displays the identities currently held by the agent. 127.Pp 128The idea is that the agent is run in the user's local PC, laptop, or 129terminal. 130Authentication data need not be stored on any other 131machine, and authentication passphrases never go over the network. 132However, the connection to the agent is forwarded over SSH 133remote logins, and the user can thus use the privileges given by the 134identities anywhere in the network in a secure way. 135.Pp 136There are two main ways to get an agent set up: 137The first is that the agent starts a new subcommand into which some environment 138variables are exported, eg 139.Cm ssh-agent xterm & . 140The second is that the agent prints the needed shell commands (either 141.Xr sh 1 142or 143.Xr csh 1 144syntax can be generated) which can be evalled in the calling shell, eg 145.Cm eval `ssh-agent -s` 146for Bourne-type shells such as 147.Xr sh 1 148or 149.Xr ksh 1 150and 151.Cm eval `ssh-agent -c` 152for 153.Xr csh 1 154and derivatives. 155.Pp 156Later 157.Xr ssh 1 158looks at these variables and uses them to establish a connection to the agent. 159.Pp 160The agent will never send a private key over its request channel. 161Instead, operations that require a private key will be performed 162by the agent, and the result will be returned to the requester. 163This way, private keys are not exposed to clients using the agent. 164.Pp 165A unix-domain socket is created 166and the name of this socket is stored in the 167.Ev SSH_AUTH_SOCK 168environment 169variable. 170The socket is made accessible only to the current user. 171This method is easily abused by root or another instance of the same 172user. 173.Pp 174The 175.Ev SSH_AGENT_PID 176environment variable holds the agent's process ID. 177.Pp 178The agent exits automatically when the command given on the command 179line terminates. 180.Sh FILES 181.Bl -tag -width Ds 182.It Pa ~/.ssh/identity 183Contains the protocol version 1 RSA authentication identity of the user. 184.It Pa ~/.ssh/id_dsa 185Contains the protocol version 2 DSA authentication identity of the user. 186.It Pa ~/.ssh/id_rsa 187Contains the protocol version 2 RSA authentication identity of the user. 188.It Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt 189Unix-domain sockets used to contain the connection to the 190authentication agent. 191These sockets should only be readable by the owner. 192The sockets should get automatically removed when the agent exits. 193.El 194.Sh SEE ALSO 195.Xr ssh 1 , 196.Xr ssh-add 1 , 197.Xr ssh-keygen 1 , 198.Xr sshd 8 199.Sh AUTHORS 200OpenSSH is a derivative of the original and free 201ssh 1.2.12 release by Tatu Ylonen. 202Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 203Theo de Raadt and Dug Song 204removed many bugs, re-added newer features and 205created OpenSSH. 206Markus Friedl contributed the support for SSH 207protocol versions 1.5 and 2.0. 208