1SSH-AGENT(1) BSD General Commands Manual SSH-AGENT(1)
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4 ssh-agent — authentication agent
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7 ssh-agent [-c | -s] [-d] [-a bind_address] [-t life] [command [arg ...]]
8 ssh-agent [-c | -s] -k
9
11 ssh-agent is a program to hold private keys used for public key authenti‐
12 cation (RSA, DSA, ECDSA). The idea is that ssh-agent is started in the
13 beginning of an X-session or a login session, and all other windows or
14 programs 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 The options are as follows:
19 -a bind_address
21 Bind the agent to the unix-domain socket bind_address. The
22 default is /tmp/ssh-XXXXXXXXXX/agent.<ppid>.
23 -c Generate C-shell commands on stdout. This is the default if
25 SHELL looks like it's a csh style of shell.
26 -d Debug mode. When this option is specified ssh-agent will not
28 fork.
29 -k Kill the current agent (given by the SSH_AGENT_PID environment
31 variable).
32 -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 -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 If a commandline is given, this is executed as a subprocess of the agent.
44 When the command dies, so does the agent.
45 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, ~/.ssh/id_ecdsa and ~/.ssh/identity. If
49 the identity has a passphrase, ssh-add(1) asks for the passphrase (using
50 a small X11 application if running under X11, or from the terminal if
51 running without X). It then sends the identity to the agent. Several
52 identities can be stored in the agent; the agent can automatically use
53 any of these identities. ssh-add -l displays the identities currently
54 held by the agent.
55 The idea is that the agent is run in the user's local PC, laptop, or ter‐
57 minal. Authentication data need not be stored on any other machine, and
58 authentication passphrases never go over the network. However, the con‐
59 nection to the agent is forwarded over SSH remote logins, and the user
60 can thus use the privileges given by the identities anywhere in the net‐
61 work in a secure way.
62 There are two main ways to get an agent set up: The first is that the
64 agent starts a new subcommand into which some environment variables are
65 exported, eg ssh-agent xterm &. The second is that the agent prints the
66 needed shell commands (either sh(1) or csh(1) syntax can be generated)
67 which can be evaluated in the calling shell, eg eval `ssh-agent -s` for
68 Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for
69 csh(1) and derivatives.
70 Later ssh(1) looks at these variables and uses them to establish a con‐
72 nection to the agent.
73 The agent will never send a private key over its request channel.
75 Instead, operations that require a private key will be performed by the
76 agent, and the result will be returned to the requester. This way, pri‐
77 vate keys are not exposed to clients using the agent.
78 A unix-domain socket is created and the name of this socket is stored in
80 the SSH_AUTH_SOCK environment variable. The socket is made accessible
81 only to the current user. This method is easily abused by root or
82 another instance of the same user.
83 The SSH_AGENT_PID environment variable holds the agent's process ID.
85 The agent exits automatically when the command given on the command line
87 terminates.
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90 ~/.ssh/identity
91 Contains the protocol version 1 RSA authentication identity of
92 the user.
93 ~/.ssh/id_dsa
95 Contains the protocol version 2 DSA authentication identity of
96 the user.
97 ~/.ssh/id_ecdsa
99 Contains the protocol version 2 ECDSA authentication identity of
100 the user.
101 ~/.ssh/id_rsa
103 Contains the protocol version 2 RSA authentication identity of
104 the user.
105 /tmp/ssh-XXXXXXXXXX/agent.<ppid>
107 Unix-domain sockets used to contain the connection to the authen‐
108 tication agent. These sockets should only be readable by the
109 owner. The sockets should get automatically removed when the
110 agent exits.
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113 SSH_USE_STRONG_RNG
114 The reseeding of the OpenSSL random generator is usually done
115 from /dev/urandom. If the SSH_USE_STRONG_RNG environment vari‐
116 able is set to value other than 0 the OpenSSL random generator is
117 reseeded from /dev/random. The number of bytes read is defined
118 by the SSH_USE_STRONG_RNG value. Minimum is 14 bytes. This set‐
119 ting is not recommended on the computers without the hardware
120 random generator because insufficient entropy causes the connec‐
121 tion to be blocked until enough entropy is available.
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124 ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)
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127 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
128 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
129 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
130 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
131 versions 1.5 and 2.0.
132BSD June 21, 2019 BSD