ssh-agent.0 revision 180746
1SSH-AGENT(1) OpenBSD Reference Manual SSH-AGENT(1) 2 3NAME 4 ssh-agent - authentication agent 5 6SYNOPSIS 7 ssh-agent [-c | -s] [-d] [-a bind_address] [-t life] [command [arg ...]] 8 ssh-agent [-c | -s] -k 9 10DESCRIPTION 11 ssh-agent is a program to hold private keys used for public key authenti- 12 cation (RSA, DSA). The idea is that ssh-agent is started in the begin- 13 ning of an X-session or a login session, and all other windows or pro- 14 grams are started as clients to the ssh-agent program. Through use of 15 environment variables the agent can be located and automatically used for 16 authentication when logging in to other machines using ssh(1). 17 18 The options are as follows: 19 20 -a bind_address 21 Bind the agent to the unix-domain socket bind_address. The de- 22 fault is /tmp/ssh-XXXXXXXXXX/agent.<ppid>. 23 24 -c Generate C-shell commands on stdout. This is the default if 25 SHELL looks like it's a csh style of shell. 26 27 -d Debug mode. When this option is specified ssh-agent will not 28 fork. 29 30 -k Kill the current agent (given by the SSH_AGENT_PID environment 31 variable). 32 33 -s Generate Bourne shell commands on stdout. This is the default if 34 SHELL does not look like it's a csh style of shell. 35 36 -t life 37 Set a default value for the maximum lifetime of identities added 38 to the agent. The lifetime may be specified in seconds or in a 39 time format specified in sshd_config(5). A lifetime specified 40 for an identity with ssh-add(1) overrides this value. Without 41 this option the default maximum lifetime is forever. 42 43 If a commandline is given, this is executed as a subprocess of the agent. 44 When the command dies, so does the agent. 45 46 The agent initially does not have any private keys. Keys are added using 47 ssh-add(1). When executed without arguments, ssh-add(1) adds the files 48 ~/.ssh/id_rsa, ~/.ssh/id_dsa and ~/.ssh/identity. If the identity has a 49 passphrase, ssh-add(1) asks for the passphrase (using a small X11 appli- 50 cation if running under X11, or from the terminal if running without X). 51 It then sends the identity to the agent. Several identities can be 52 stored in the agent; the agent can automatically use any of these identi- 53 ties. ssh-add -l displays the identities currently held by the agent. 54 55 The idea is that the agent is run in the user's local PC, laptop, or ter- 56 minal. Authentication data need not be stored on any other machine, and 57 authentication passphrases never go over the network. However, the con- 58 nection to the agent is forwarded over SSH remote logins, and the user 59 can thus use the privileges given by the identities anywhere in the net- 60 work in a secure way. 61 62 There are two main ways to get an agent set up: The first is that the 63 agent starts a new subcommand into which some environment variables are 64 exported, eg ssh-agent xterm &. The second is that the agent prints the 65 needed shell commands (either sh(1) or csh(1) syntax can be generated) 66 which can be evalled in the calling shell, eg eval `ssh-agent -s` for 67 Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for 68 csh(1) and derivatives. 69 70 Later ssh(1) looks at these variables and uses them to establish a con- 71 nection to the agent. 72 73 The agent will never send a private key over its request channel. In- 74 stead, operations that require a private key will be performed by the 75 agent, and the result will be returned to the requester. This way, pri- 76 vate keys are not exposed to clients using the agent. 77 78 A unix-domain socket is created and the name of this socket is stored in 79 the SSH_AUTH_SOCK environment variable. The socket is made accessible 80 only to the current user. This method is easily abused by root or anoth- 81 er instance of the same user. 82 83 The SSH_AGENT_PID environment variable holds the agent's process ID. 84 85 The agent exits automatically when the command given on the command line 86 terminates. 87 88FILES 89 ~/.ssh/identity 90 Contains the protocol version 1 RSA authentication identity of 91 the user. 92 93 ~/.ssh/id_dsa 94 Contains the protocol version 2 DSA authentication identity of 95 the user. 96 97 ~/.ssh/id_rsa 98 Contains the protocol version 2 RSA authentication identity of 99 the user. 100 101 /tmp/ssh-XXXXXXXXXX/agent.<ppid> 102 Unix-domain sockets used to contain the connection to the authen- 103 tication agent. These sockets should only be readable by the 104 owner. The sockets should get automatically removed when the 105 agent exits. 106 107SEE ALSO 108 ssh(1), ssh-add(1), ssh-keygen(1), sshd(8) 109 110AUTHORS 111 OpenSSH is a derivative of the original and free ssh 1.2.12 release by 112 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo 113 de Raadt and Dug Song removed many bugs, re-added newer features and cre- 114 ated OpenSSH. Markus Friedl contributed the support for SSH protocol 115 versions 1.5 and 2.0. 116 117OpenBSD 4.3 September 17, 2007 2 118