1 SSH-AGENT(1) OpenBSD Reference Manual SSH-AGENT(1) 2 3 NAME 4 ssh-agent - authentication agent 5 6 SYNOPSIS 7 ssh-agent [-c | -s] [-d] [-a bind_address] [-t life] [command [arg ...]] 8 ssh-agent [-c | -s] -k 9 10 DESCRIPTION 11 ssh-agent is a program to hold private keys used for public key 12 authentication (RSA, DSA, ECDSA). The idea is that ssh-agent is started 13 in the beginning of an X-session or a login session, and all other 14 windows or programs are started as clients to the ssh-agent program. 15 Through use of environment variables the agent can be located and 16 automatically used for authentication when logging in to other machines 17 using ssh(1). 18 19 The options are as follows: 20 21 -a bind_address 22 Bind the agent to the UNIX-domain socket bind_address. The 23 default is $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>. 24 25 -c Generate C-shell commands on stdout. This is the default if 26 SHELL looks like it's a csh style of shell. 27 28 -d Debug mode. When this option is specified ssh-agent will not 29 fork. 30 31 -k Kill the current agent (given by the SSH_AGENT_PID environment 32 variable). 33 34 -s Generate Bourne shell commands on stdout. This is the default if 35 SHELL does not look like it's a csh style of shell. 36 37 -t life 38 Set a default value for the maximum lifetime of identities added 39 to the agent. The lifetime may be specified in seconds or in a 40 time format specified in sshd_config(5). A lifetime specified 41 for an identity with ssh-add(1) overrides this value. Without 42 this option the default maximum lifetime is forever. 43 44 If a commandline is given, this is executed as a subprocess of the agent. 45 When the command dies, so does the agent. 46 47 The agent initially does not have any private keys. Keys are added using 48 ssh-add(1). When executed without arguments, ssh-add(1) adds the files 49 ~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and ~/.ssh/identity. If 50 the identity has a passphrase, ssh-add(1) asks for the passphrase on the 51 terminal if it has one or from a small X11 program if running under X11. 52 If neither of these is the case then the authentication will fail. It 53 then sends the identity to the agent. Several identities can be stored 54 in the agent; the agent can automatically use any of these identities. 55 ssh-add -l displays the identities currently held by the agent. 56 57 The idea is that the agent is run in the user's local PC, laptop, or 58 terminal. Authentication data need not be stored on any other machine, 59 and authentication passphrases never go over the network. However, the 60 connection to the agent is forwarded over SSH remote logins, and the user 61 can thus use the privileges given by the identities anywhere in the 62 network in a secure way. 63 64 There are two main ways to get an agent set up: The first is that the 65 agent starts a new subcommand into which some environment variables are 66 exported, eg ssh-agent xterm &. The second is that the agent prints the 67 needed shell commands (either sh(1) or csh(1) syntax can be generated) 68 which can be evaluated in the calling shell, eg eval `ssh-agent -s` for 69 Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for 70 csh(1) and derivatives. 71 72 Later ssh(1) looks at these variables and uses them to establish a 73 connection to the agent. 74 75 The agent will never send a private key over its request channel. 76 Instead, operations that require a private key will be performed by the 77 agent, and the result will be returned to the requester. This way, 78 private keys are not exposed to clients using the agent. 79 80 A UNIX-domain socket is created and the name of this socket is stored in 81 the SSH_AUTH_SOCK environment variable. The socket is made accessible 82 only to the current user. This method is easily abused by root or 83 another instance of the same user. 84 85 The SSH_AGENT_PID environment variable holds the agent's process ID. 86 87 The agent exits automatically when the command given on the command line 88 terminates. 89 90 FILES 91 ~/.ssh/identity 92 Contains the protocol version 1 RSA authentication identity of 93 the user. 94 95 ~/.ssh/id_dsa 96 Contains the protocol version 2 DSA authentication identity of 97 the user. 98 99 ~/.ssh/id_ecdsa 100 Contains the protocol version 2 ECDSA authentication identity of 101 the user. 102 103 ~/.ssh/id_rsa 104 Contains the protocol version 2 RSA authentication identity of 105 the user. 106 107 $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid> 108 UNIX-domain sockets used to contain the connection to the 109 authentication agent. These sockets should only be readable by 110 the owner. The sockets should get automatically removed when the 111 agent exits. 112 113 SEE ALSO 114 ssh(1), ssh-add(1), ssh-keygen(1), sshd(8) 115 116 AUTHORS 117 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 118 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 119 de Raadt and Dug Song removed many bugs, re-added newer features and 120 created OpenSSH. Markus Friedl contributed the support for SSH protocol 121 versions 1.5 and 2.0. 122 123 OpenBSD 5.0 November 21, 2010 OpenBSD 5.0 124
