1.\" $OpenBSD: ssh-agent.1,v 1.64 2016/11/30 06:54:26 jmc Exp $ 2.\" $FreeBSD$ 3.\" 4.\" Author: Tatu Ylonen <ylo@cs.hut.fi> 5.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland 6.\" All rights reserved 7.\" 8.\" As far as I am concerned, the code I have written for this software 9.\" can be used freely for any purpose. Any derived versions of this 10.\" software must be clearly marked as such, and if the derived work is 11.\" incompatible with the protocol description in the RFC file, it must be 12.\" called by a name other than "ssh" or "Secure Shell". 13.\" 14.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. 15.\" Copyright (c) 1999 Aaron Campbell. All rights reserved. 16.\" Copyright (c) 1999 Theo de Raadt. All rights reserved. 17.\" 18.\" Redistribution and use in source and binary forms, with or without 19.\" modification, are permitted provided that the following conditions 20.\" are met: 21.\" 1. Redistributions of source code must retain the above copyright 22.\" notice, this list of conditions and the following disclaimer. 23.\" 2. Redistributions in binary form must reproduce the above copyright 24.\" notice, this list of conditions and the following disclaimer in the 25.\" documentation and/or other materials provided with the distribution. 26.\" 27.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 28.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 29.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 30.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 31.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 32.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 33.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 34.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 35.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 36.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 37.\" 38.Dd $Mdocdate: November 30 2016 $ 39.Dt SSH-AGENT 1 40.Os 41.Sh NAME 42.Nm ssh-agent 43.Nd authentication agent 44.Sh SYNOPSIS 45.Nm ssh-agent 46.Op Fl c | s 47.Op Fl \&Ddx 48.Op Fl a Ar bind_address 49.Op Fl E Ar fingerprint_hash 50.Op Fl P Ar pkcs11_whitelist 51.Op Fl t Ar life 52.Op Ar command Op Ar arg ... 53.Nm ssh-agent 54.Op Fl c | s 55.Fl k 56.Sh DESCRIPTION 57.Nm 58is a program to hold private keys used for public key authentication 59(RSA, DSA, ECDSA, Ed25519). 60.Nm 61is usually started in the beginning of an X-session or a login session, and 62all other windows or programs are started as clients to the ssh-agent 63program. 64Through use of environment variables the agent can be located 65and automatically used for authentication when logging in to other 66machines using 67.Xr ssh 1 . 68.Pp 69The agent initially does not have any private keys. 70Keys are added using 71.Xr ssh 1 72(see 73.Cm AddKeysToAgent 74in 75.Xr ssh_config 5 76for details) 77or 78.Xr ssh-add 1 . 79Multiple identities may be stored in 80.Nm 81concurrently and 82.Xr ssh 1 83will automatically use them if present. 84.Xr ssh-add 1 85is also used to remove keys from 86.Nm 87and to query the keys that are held in one. 88.Pp 89The options are as follows: 90.Bl -tag -width Ds 91.It Fl a Ar bind_address 92Bind the agent to the 93.Ux Ns -domain 94socket 95.Ar bind_address . 96The default is 97.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 98.It Fl c 99Generate C-shell commands on 100.Dv stdout . 101This is the default if 102.Ev SHELL 103looks like it's a csh style of shell. 104.It Fl D 105Foreground mode. 106When this option is specified 107.Nm 108will not fork. 109.It Fl d 110Debug mode. 111When this option is specified 112.Nm 113will not fork and will write debug information to standard error. 114.It Fl E Ar fingerprint_hash 115Specifies the hash algorithm used when displaying key fingerprints. 116Valid options are: 117.Dq md5 118and 119.Dq sha256 . 120The default is 121.Dq sha256 . 122.It Fl k 123Kill the current agent (given by the 124.Ev SSH_AGENT_PID 125environment variable). 126.It Fl P Ar pkcs11_whitelist 127Specify a pattern-list of acceptable paths for PKCS#11 shared libraries 128that may be added using the 129.Fl s 130option to 131.Xr ssh-add 1 . 132The default is to allow loading PKCS#11 libraries from 133.Dq /usr/lib/*,/usr/local/lib/* . 134PKCS#11 libraries that do not match the whitelist will be refused. 135See PATTERNS in 136.Xr ssh_config 5 137for a description of pattern-list syntax. 138.It Fl s 139Generate Bourne shell commands on 140.Dv stdout . 141This is the default if 142.Ev SHELL 143does not look like it's a csh style of shell. 144.It Fl t Ar life 145Set a default value for the maximum lifetime of identities added to the agent. 146The lifetime may be specified in seconds or in a time format specified in 147.Xr sshd_config 5 . 148A lifetime specified for an identity with 149.Xr ssh-add 1 150overrides this value. 151Without this option the default maximum lifetime is forever. 152.It Fl x 153Exit after the last client has disconnected. 154.El 155.Pp 156If a command line is given, this is executed as a subprocess of the agent. 157When the command dies, so does the agent. 158.Pp 159The idea is that the agent is run in the user's local PC, laptop, or 160terminal. 161Authentication data need not be stored on any other 162machine, and authentication passphrases never go over the network. 163However, the connection to the agent is forwarded over SSH 164remote logins, and the user can thus use the privileges given by the 165identities anywhere in the network in a secure way. 166.Pp 167There are two main ways to get an agent set up: 168The first is that the agent starts a new subcommand into which some environment 169variables are exported, eg 170.Cm ssh-agent xterm & . 171The second is that the agent prints the needed shell commands (either 172.Xr sh 1 173or 174.Xr csh 1 175syntax can be generated) which can be evaluated in the calling shell, eg 176.Cm eval `ssh-agent -s` 177for Bourne-type shells such as 178.Xr sh 1 179or 180.Xr ksh 1 181and 182.Cm eval `ssh-agent -c` 183for 184.Xr csh 1 185and derivatives. 186.Pp 187Later 188.Xr ssh 1 189looks at these variables and uses them to establish a connection to the agent. 190.Pp 191The agent will never send a private key over its request channel. 192Instead, operations that require a private key will be performed 193by the agent, and the result will be returned to the requester. 194This way, private keys are not exposed to clients using the agent. 195.Pp 196A 197.Ux Ns -domain 198socket is created and the name of this socket is stored in the 199.Ev SSH_AUTH_SOCK 200environment 201variable. 202The socket is made accessible only to the current user. 203This method is easily abused by root or another instance of the same 204user. 205.Pp 206The 207.Ev SSH_AGENT_PID 208environment variable holds the agent's process ID. 209.Pp 210The agent exits automatically when the command given on the command 211line terminates. 212.Sh FILES 213.Bl -tag -width Ds 214.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid> 215.Ux Ns -domain 216sockets used to contain the connection to the authentication agent. 217These sockets should only be readable by the owner. 218The sockets should get automatically removed when the agent exits. 219.El 220.Sh SEE ALSO 221.Xr ssh 1 , 222.Xr ssh-add 1 , 223.Xr ssh-keygen 1 , 224.Xr sshd 8 225.Sh AUTHORS 226.An -nosplit 227OpenSSH is a derivative of the original and free ssh 1.2.12 release by 228.An Tatu Ylonen . 229.An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt 230and 231.An Dug Song 232removed many bugs, re-added newer features and created OpenSSH. 233.An Markus Friedl 234contributed the support for SSH protocol versions 1.5 and 2.0. 235