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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 | ||