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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
12 authentication (RSA, DSA, ECDSA, ED25519). The idea is that ssh-agent is
13 started in the beginning of an X-session or a login session, and all
14 other windows or programs are started as clients to the ssh-agent
15 program. Through use of environment variables the agent can be located
16 and automatically used for authentication when logging in to other
17 machines 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, ~/.ssh/id_ed25519 and
50 ~/.ssh/identity. If the identity has a passphrase, ssh-add(1) asks for
51 the passphrase on the terminal if it has one or from a small X11 program
52 if running under X11. If neither of these is the case then the
53 authentication will fail. It then sends the identity to the agent.
54 Several identities can be stored in the agent; the agent can
55 automatically use any of these identities. ssh-add -l displays the
56 identities currently held by the agent.
57
58 The idea is that the agent is run in the user's local PC, laptop, or
59 terminal. Authentication data need not be stored on any other machine,
60 and authentication passphrases never go over the network. However, the
61 connection to the agent is forwarded over SSH remote logins, and the user
62 can thus use the privileges given by the identities anywhere in the
63 network in a secure way.
64
65 There are two main ways to get an agent set up: The first is that the
66 agent starts a new subcommand into which some environment variables are
67 exported, eg ssh-agent xterm &. The second is that the agent prints the
68 needed shell commands (either sh(1) or csh(1) syntax can be generated)
69 which can be evaluated in the calling shell, eg eval `ssh-agent -s` for
70 Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for
71 csh(1) and derivatives.
72
73 Later ssh(1) looks at these variables and uses them to establish a
74 connection to the agent.
75
76 The agent will never send a private key over its request channel.
77 Instead, operations that require a private key will be performed by the
78 agent, and the result will be returned to the requester. This way,
79 private keys are not exposed to clients using the agent.
80
81 A UNIX-domain socket is created and the name of this socket is stored in
82 the SSH_AUTH_SOCK environment variable. The socket is made accessible
83 only to the current user. This method is easily abused by root or
84 another instance of the same user.
85
86 The SSH_AGENT_PID environment variable holds the agent's process ID.
87
88 The agent exits automatically when the command given on the command line
89 terminates.
90
91FILES
92 ~/.ssh/identity
93 Contains the protocol version 1 RSA authentication identity of
94 the user.
95
96 ~/.ssh/id_dsa
97 Contains the protocol version 2 DSA authentication identity of
98 the user.
99
100 ~/.ssh/id_ecdsa
101 Contains the protocol version 2 ECDSA authentication identity of
102 the user.
103
104 ~/.ssh/id_ed25519
105 Contains the protocol version 2 ED25519 authentication identity
106 of the user.
107
108 ~/.ssh/id_rsa
109 Contains the protocol version 2 RSA authentication identity of
110 the user.
111
112 $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
113 UNIX-domain sockets used to contain the connection to the
114 authentication agent. These sockets should only be readable by
115 the owner. The sockets should get automatically removed when the
116 agent exits.
117
118SEE ALSO
119 ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)
120
121AUTHORS
122 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
123 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
124 de Raadt and Dug Song removed many bugs, re-added newer features and
125 created OpenSSH. Markus Friedl contributed the support for SSH protocol
126 versions 1.5 and 2.0.
127
128OpenBSD 5.4 December 7, 2013 OpenBSD 5.4