1.\" $OpenBSD: ssh-agent.1,v 1.71 2020/06/19 07:21:42 dtucker 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 $Mdocdate: June 19 2020 $ 38.Dt SSH-AGENT 1 39.Os 40.Sh NAME 41.Nm ssh-agent 42.Nd OpenSSH authentication agent 43.Sh SYNOPSIS 44.Nm ssh-agent 45.Op Fl c | s 46.Op Fl \&Dd 47.Op Fl a Ar bind_address 48.Op Fl E Ar fingerprint_hash 49.Op Fl P Ar provider_whitelist 50.Op Fl t Ar life 51.Nm ssh-agent 52.Op Fl a Ar bind_address 53.Op Fl E Ar fingerprint_hash 54.Op Fl P Ar provider_whitelist 55.Op Fl t Ar life 56.Ar command Op Ar arg ... 57.Nm ssh-agent 58.Op Fl c | s 59.Fl k 60.Sh DESCRIPTION 61.Nm 62is a program to hold private keys used for public key authentication. 63Through use of environment variables the agent can be located 64and automatically used for authentication when logging in to other 65machines using 66.Xr ssh 1 . 67.Pp 68The options are as follows: 69.Bl -tag -width Ds 70.It Fl a Ar bind_address 71Bind the agent to the 72.Ux Ns -domain 73socket 74.Ar bind_address . 75The default is 76.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt . 77.It Fl c 78Generate C-shell commands on 79.Dv stdout . 80This is the default if 81.Ev SHELL 82looks like it's a csh style of shell. 83.It Fl D 84Foreground mode. 85When this option is specified 86.Nm 87will not fork. 88.It Fl d 89Debug mode. 90When this option is specified 91.Nm 92will not fork and will write debug information to standard error. 93.It Fl E Ar fingerprint_hash 94Specifies the hash algorithm used when displaying key fingerprints. 95Valid options are: 96.Dq md5 97and 98.Dq sha256 . 99The default is 100.Dq sha256 . 101.It Fl k 102Kill the current agent (given by the 103.Ev SSH_AGENT_PID 104environment variable). 105.It Fl P Ar provider_whitelist 106Specify a pattern-list of acceptable paths for PKCS#11 and FIDO authenticator 107shared libraries that may be used with the 108.Fl S 109or 110.Fl s 111options to 112.Xr ssh-add 1 . 113Libraries that do not match the whitelist will be refused. 114See PATTERNS in 115.Xr ssh_config 5 116for a description of pattern-list syntax. 117The default whitelist is 118.Dq /usr/lib/*,/usr/local/lib/* . 119.It Fl s 120Generate Bourne shell commands on 121.Dv stdout . 122This is the default if 123.Ev SHELL 124does not look like it's a csh style of shell. 125.It Fl t Ar life 126Set a default value for the maximum lifetime of identities added to the agent. 127The lifetime may be specified in seconds or in a time format specified in 128.Xr sshd_config 5 . 129A lifetime specified for an identity with 130.Xr ssh-add 1 131overrides this value. 132Without this option the default maximum lifetime is forever. 133.It Ar command Op Ar arg ... 134If a command (and optional arguments) is given, 135this is executed as a subprocess of the agent. 136The agent exits automatically when the command given on the command 137line terminates. 138.El 139.Pp 140There are two main ways to get an agent set up. 141The first is at the start of an X session, 142where all other windows or programs are started as children of the 143.Nm 144program. 145The agent starts a command under which its environment 146variables are exported, for example 147.Cm ssh-agent xterm & . 148When the command terminates, so does the agent. 149.Pp 150The second method is used for a login session. 151When 152.Nm 153is started, 154it prints the shell commands required to set its environment variables, 155which in turn can be evaluated in the calling shell, for example 156.Cm eval `ssh-agent -s` . 157.Pp 158In both cases, 159.Xr ssh 1 160looks at these environment variables and uses them to establish a connection to the agent. 161.Pp 162The agent initially does not have any private keys. 163Keys are added using 164.Xr ssh-add 1 165or by 166.Xr ssh 1 167when 168.Cm AddKeysToAgent 169is set in 170.Xr ssh_config 5 . 171Multiple identities may be stored in 172.Nm 173concurrently and 174.Xr ssh 1 175will automatically use them if present. 176.Xr ssh-add 1 177is also used to remove keys from 178.Nm 179and to query the keys that are held in one. 180.Pp 181Connections to 182.Nm 183may be forwarded from further remote hosts using the 184.Fl A 185option to 186.Xr ssh 1 187(but see the caveats documented therein), 188avoiding the need for authentication data to be stored on other machines. 189Authentication passphrases and private keys never go over the network: 190the connection to the agent is forwarded over SSH remote connections 191and the result is returned to the requester, 192allowing the user access to their identities anywhere in the network 193in a secure fashion. 194.Sh ENVIRONMENT 195.Bl -tag -width "SSH_AGENT_PID" 196.It Ev SSH_AGENT_PID 197When 198.Nm 199starts, it stores the name of the agent's process ID (PID) in this variable. 200.It Ev SSH_AUTH_SOCK 201When 202.Nm 203starts, it creates a 204.Ux Ns -domain 205socket and stores its pathname in this variable. 206It is accessible only to the current user, 207but is easily abused by root or another instance of the same user. 208.El 209.Sh FILES 210.Bl -tag -width Ds 211.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid> 212.Ux Ns -domain 213sockets used to contain the connection to the authentication agent. 214These sockets should only be readable by the owner. 215The sockets should get automatically removed when the agent exits. 216.El 217.Sh SEE ALSO 218.Xr ssh 1 , 219.Xr ssh-add 1 , 220.Xr ssh-keygen 1 , 221.Xr ssh_config 5 , 222.Xr sshd 8 223.Sh AUTHORS 224.An -nosplit 225OpenSSH is a derivative of the original and free ssh 1.2.12 release by 226.An Tatu Ylonen . 227.An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt 228and 229.An Dug Song 230removed many bugs, re-added newer features and created OpenSSH. 231.An Markus Friedl 232contributed the support for SSH protocol versions 1.5 and 2.0. 233