1 | SSH-AGENT(1) OpenBSD Reference Manual SSH-AGENT(1) |
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2 | |
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3 | NAME |
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4 | ssh-agent - authentication agent |
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5 | |
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6 | SYNOPSIS |
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7 | ssh-agent [-a bind_address] [-c | -s] [-t life] [-d] [command [args ...]] |
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8 | ssh-agent [-c | -s] -k |
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9 | |
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10 | DESCRIPTION |
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11 | ssh-agent is a program to hold private keys used for public key authenti- |
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12 | cation (RSA, DSA). The idea is that ssh-agent is started in the begin- |
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13 | ning of an X-session or a login session, and all other windows or pro- |
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14 | grams are started as clients to the ssh-agent program. Through use of |
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15 | environment variables the agent can be located and automatically used for |
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16 | authentication when logging in to other machines using ssh(1). |
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17 | |
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18 | The options are as follows: |
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19 | |
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20 | -a bind_address |
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21 | Bind the agent to the unix-domain socket bind_address. The de- |
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22 | fault is /tmp/ssh-XXXXXXXX/agent.<ppid>. |
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23 | |
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24 | -c Generate C-shell commands on stdout. This is the default if |
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25 | SHELL looks like it's a csh style of shell. |
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26 | |
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27 | -s Generate Bourne shell commands on stdout. This is the default if |
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28 | SHELL does not look like it's a csh style of shell. |
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29 | |
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30 | -k Kill the current agent (given by the SSH_AGENT_PID environment |
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31 | variable). |
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32 | |
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33 | -t life |
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34 | Set a default value for the maximum lifetime of identities added |
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35 | to the agent. The lifetime may be specified in seconds or in a |
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36 | time format specified in sshd(8). A lifetime specified for an |
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37 | identity with ssh-add(1) overrides this value. Without this op- |
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38 | tion the default maximum lifetime is forever. |
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39 | |
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40 | -d Debug mode. When this option is specified ssh-agent will not |
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41 | fork. |
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42 | |
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43 | If a commandline is given, this is executed as a subprocess of the agent. |
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44 | When the command dies, so does the agent. |
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45 | |
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46 | The agent initially does not have any private keys. Keys are added using |
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47 | ssh-add(1). When executed without arguments, ssh-add(1) adds the files |
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48 | ~/.ssh/id_rsa, ~/.ssh/id_dsa and ~/.ssh/identity. If the identity has a |
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49 | passphrase, ssh-add(1) asks for the passphrase (using a small X11 appli- |
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50 | cation if running under X11, or from the terminal if running without X). |
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51 | It then sends the identity to the agent. Several identities can be |
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52 | stored in the agent; the agent can automatically use any of these identi- |
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53 | ties. ssh-add -l displays the identities currently held by the agent. |
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54 | |
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55 | The idea is that the agent is run in the user's local PC, laptop, or ter- |
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56 | minal. Authentication data need not be stored on any other machine, and |
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57 | authentication passphrases never go over the network. However, the con- |
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58 | nection to the agent is forwarded over SSH remote logins, and the user |
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59 | can thus use the privileges given by the identities anywhere in the net- |
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60 | work in a secure way. |
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61 | |
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62 | There are two main ways to get an agent set up: The first is that the |
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63 | agent starts a new subcommand into which some environment variables are |
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64 | exported, eg ssh-agent xterm &. The second is that the agent prints the |
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65 | needed shell commands (either sh(1) or csh(1) syntax can be generated) |
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66 | which can be evalled in the calling shell, eg eval `ssh-agent -s` for |
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67 | Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for |
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68 | csh(1) and derivatives. |
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69 | |
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70 | Later ssh(1) looks at these variables and uses them to establish a con- |
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71 | nection to the agent. |
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72 | |
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73 | The agent will never send a private key over its request channel. In- |
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74 | stead, operations that require a private key will be performed by the |
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75 | agent, and the result will be returned to the requester. This way, pri- |
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76 | vate keys are not exposed to clients using the agent. |
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77 | |
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78 | A unix-domain socket is created and the name of this socket is stored in |
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79 | the SSH_AUTH_SOCK environment variable. The socket is made accessible |
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80 | only to the current user. This method is easily abused by root or anoth- |
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81 | er instance of the same user. |
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82 | |
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83 | The SSH_AGENT_PID environment variable holds the agent's process ID. |
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84 | |
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85 | The agent exits automatically when the command given on the command line |
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86 | terminates. |
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87 | |
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88 | FILES |
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89 | ~/.ssh/identity |
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90 | Contains the protocol version 1 RSA authentication identity of |
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91 | the user. |
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92 | |
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93 | ~/.ssh/id_dsa |
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94 | Contains the protocol version 2 DSA authentication identity of |
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95 | the user. |
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96 | |
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97 | ~/.ssh/id_rsa |
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98 | Contains the protocol version 2 RSA authentication identity of |
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99 | the user. |
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100 | |
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101 | /tmp/ssh-XXXXXXXX/agent.<ppid> |
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102 | Unix-domain sockets used to contain the connection to the authen- |
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103 | tication agent. These sockets should only be readable by the |
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104 | owner. The sockets should get automatically removed when the |
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105 | agent exits. |
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106 | |
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107 | SEE ALSO |
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108 | ssh(1), ssh-add(1), ssh-keygen(1), sshd(8) |
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109 | |
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110 | AUTHORS |
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111 | OpenSSH is a derivative of the original and free ssh 1.2.12 release by |
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112 | Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo |
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113 | de Raadt and Dug Song removed many bugs, re-added newer features and cre- |
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114 | ated OpenSSH. Markus Friedl contributed the support for SSH protocol |
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115 | versions 1.5 and 2.0. |
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116 | |
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117 | OpenBSD 3.8 September 25, 1999 2 |
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