1.\" $OpenBSD: ssh-agent.1,v 1.37 2003/03/28 10:11:43 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-XXXXXXXX/agent.<ppid> . 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 8 . 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 $HOME/.ssh/id_rsa , 115.Pa $HOME/.ssh/id_dsa 116and 117.Pa $HOME/.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 setup: 137Either the agent starts a new subcommand into which some environment 138variables are exported, or the agent prints the needed shell commands 139(either 140.Xr sh 1 141or 142.Xr csh 1 143syntax can be generated) which can be evalled in the calling shell. 144Later 145.Xr ssh 1 146looks at these variables and uses them to establish a connection to the agent. 147.Pp 148The agent will never send a private key over its request channel. 149Instead, operations that require a private key will be performed 150by the agent, and the result will be returned to the requester. 151This way, private keys are not exposed to clients using the agent. 152.Pp 153A unix-domain socket is created 154and the name of this socket is stored in the 155.Ev SSH_AUTH_SOCK 156environment 157variable. 158The socket is made accessible only to the current user. 159This method is easily abused by root or another instance of the same 160user. 161.Pp 162The 163.Ev SSH_AGENT_PID 164environment variable holds the agent's process ID. 165.Pp 166The agent exits automatically when the command given on the command 167line terminates. 168.Sh FILES 169.Bl -tag -width Ds 170.It Pa $HOME/.ssh/identity 171Contains the protocol version 1 RSA authentication identity of the user. 172.It Pa $HOME/.ssh/id_dsa 173Contains the protocol version 2 DSA authentication identity of the user. 174.It Pa $HOME/.ssh/id_rsa 175Contains the protocol version 2 RSA authentication identity of the user. 176.It Pa /tmp/ssh-XXXXXXXX/agent.<ppid> 177Unix-domain sockets used to contain the connection to the 178authentication agent. 179These sockets should only be readable by the owner. 180The sockets should get automatically removed when the agent exits. 181.El 182.Sh AUTHORS 183OpenSSH is a derivative of the original and free 184ssh 1.2.12 release by Tatu Ylonen. 185Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, 186Theo de Raadt and Dug Song 187removed many bugs, re-added newer features and 188created OpenSSH. 189Markus Friedl contributed the support for SSH 190protocol versions 1.5 and 2.0. 191.Sh SEE ALSO 192.Xr ssh 1 , 193.Xr ssh-add 1 , 194.Xr ssh-keygen 1 , 195.Xr sshd 8 196