| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="serialports">
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| 4 | <title>Serial Ports</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>
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| 8 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports the use of virtual serial ports in a
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| 9 | virtual machine.
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| 10 | </p>
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| 11 | <p>
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| 12 | Ever since the original IBM PC, personal computers have been
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| 13 | equipped with one or two serial ports, also called COM ports by
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| 14 | DOS and Windows. Serial ports were commonly used with modems, and
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| 15 | some computer mice used to be connected to serial ports before USB
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| 16 | became commonplace.
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| 17 | </p>
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| 18 | <p>
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| 19 | While serial ports are no longer as common as they used to be,
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| 20 | there are still some important uses left for them. For example,
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| 21 | serial ports can be used to set up a primitive network over a
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| 22 | null-modem cable, in case Ethernet is not available. Also, serial
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| 23 | ports are indispensable for system programmers needing to do
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| 24 | kernel debugging, since kernel debugging software usually
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| 25 | interacts with developers over a serial port. With virtual serial
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| 26 | ports, system programmers can do kernel debugging on a virtual
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| 27 | machine instead of needing a real computer to connect to.
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| 28 | </p>
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| 29 | <p>
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| 30 | If a virtual serial port is enabled, the guest OS sees a standard
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| 31 | 16550A compatible UART device. Other UART types can be configured
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| 32 | using the <userinput>VBoxManage modifyvm</userinput> command. Both
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| 33 | receiving and transmitting data is supported. How this virtual
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| 34 | serial port is then connected to the host is configurable, and the
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| 35 | details depend on your host OS.
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| 36 | </p>
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| 37 | <p>
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| 38 | You can use either the Settings tabs or the <userinput>VBoxManage</userinput> command to set
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| 39 | up virtual serial ports. For the latter, see <xref href="vboxmanage-modifyvm.dita"/> for
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| 40 | information on the <codeph>--uart</codeph>, <codeph>--uart-mode</codeph> and
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| 41 | <codeph>--uart-type</codeph> options.
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| 42 | </p>
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| 43 | <p>
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| 44 | You can configure up to four virtual serial ports per virtual
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| 45 | machine. For each device, you must set the following:
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| 46 | </p>
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| 47 | <ol>
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| 48 | <li>
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| 49 | <p><b outputclass="bold">Port Number:</b> This determines
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| 50 | the serial port that the virtual machine should see. For best
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| 51 | results, use the traditional values as follows:
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| 52 | </p>
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| 53 | <ul>
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| 54 | <li>
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| 55 | <p>
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| 56 | COM1: I/O base 0x3F8, IRQ 4
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| 57 | </p>
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| 58 | </li>
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| 59 | <li>
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| 60 | <p>
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| 61 | COM2: I/O base 0x2F8, IRQ 3
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| 62 | </p>
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| 63 | </li>
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| 64 | <li>
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| 65 | <p>
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| 66 | COM3: I/O base 0x3E8, IRQ 4
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| 67 | </p>
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| 68 | </li>
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| 69 | <li>
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| 70 | <p>
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| 71 | COM4: I/O base 0x2E8, IRQ 3
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| 72 | </p>
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| 73 | </li>
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| 74 | </ul>
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| 75 | <p>
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| 76 | You can also configure a user-defined serial port. Enter an
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| 77 | I/O base address and interrupt (IRQ).
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| 78 | </p>
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| 79 | </li>
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| 80 | <li>
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| 81 | <p><b outputclass="bold">Port Mode:</b> What the virtual
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| 82 | port is connected to. For each virtual serial port, you have
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| 83 | the following options:
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| 84 | </p>
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| 85 | <ul>
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| 86 | <li>
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| 87 | <p><b outputclass="bold">Disconnected:</b> The guest
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| 88 | will see the device, but it will behave as if no cable had
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| 89 | been connected to it.
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| 90 | </p>
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| 91 | </li>
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| 92 | <li>
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| 93 | <p><b outputclass="bold">Host Device:</b> Connects the
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| 94 | virtual serial port to a physical serial port on your
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| 95 | host. On a Windows host, this will be a name like
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| 96 | <codeph>COM1</codeph>. On Linux or Oracle Solaris hosts,
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| 97 | it will be a device node like
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| 98 | <filepath>/dev/ttyS0</filepath>. <ph conkeyref="vbox-conkeyref-phrases/product-name"/> will then
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| 99 | simply redirect all data received from and sent to the
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| 100 | virtual serial port to the physical device.
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| 101 | </p>
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| 102 | </li>
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| 103 | <li>
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| 104 | <p><b outputclass="bold">Host Pipe:</b> Configure
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| 105 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> to connect the virtual serial port to a
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| 106 | software pipe on the host. This depends on your host OS,
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| 107 | as follows:
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| 108 | </p>
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| 109 | <ul>
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| 110 | <li>
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| 111 | <p>
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| 112 | On a Windows host, data will be sent and received
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| 113 | through a named pipe. The pipe name must be in the
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| 114 | format
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| 115 | <filepath>\\.\pipe\<varname>name</varname>
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| 116 | </filepath>
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| 117 | where <varname>name</varname> should identify
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| 118 | the virtual machine but may be freely chosen.
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| 119 | </p>
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| 120 | </li>
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| 121 | <li>
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| 122 | <p>
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| 123 | On a Mac OS, Linux, or Oracle Solaris host, a local
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| 124 | domain socket is used instead. The socket filename
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| 125 | must be chosen such that the user running
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| 126 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> has sufficient privileges to create and
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| 127 | write to it. The <filepath>/tmp</filepath> directory
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| 128 | is often a good candidate.
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| 129 | </p>
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| 130 | <p>
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| 131 | On Linux there are various tools which can connect to
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| 132 | a local domain socket or create one in server mode.
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| 133 | The most flexible tool is <userinput>socat</userinput> and
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| 134 | is available as part of many distributions.
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| 135 | </p>
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| 136 | </li>
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| 137 | </ul>
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| 138 | <p> In this case, you can configure whether <ph
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| 139 | conkeyref="vbox-conkeyref-phrases/product-name"/> should create the named pipe, or
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| 140 | the local domain socket on non-Windows hosts, itself or whether <ph
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| 141 | conkeyref="vbox-conkeyref-phrases/product-name"/> should assume that the pipe or
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| 142 | socket exists already. With the <userinput>VBoxManage</userinput> command-line
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| 143 | options, this is referred to as server mode or client mode, respectively. </p>
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| 144 | <p>
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| 145 | For a direct connection between two virtual machines,
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| 146 | corresponding to a null-modem cable, simply configure one
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| 147 | VM to create a pipe or socket and another to attach to it.
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| 148 | </p>
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| 149 | </li>
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| 150 | <li>
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| 151 | <p><b outputclass="bold">Raw File:</b> Send the
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| 152 | virtual serial port output to a file. This option is very
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| 153 | useful for capturing diagnostic output from a guest. Any
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| 154 | file may be used for this purpose, as long as the user
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| 155 | running <ph conkeyref="vbox-conkeyref-phrases/product-name"/> has sufficient privileges to create
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| 156 | and write to the file.
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| 157 | </p>
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| 158 | </li>
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| 159 | <li>
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| 160 | <p><b outputclass="bold">TCP:</b> Useful for
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| 161 | forwarding serial traffic over TCP/IP, acting as a server,
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| 162 | or it can act as a TCP client connecting to other servers.
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| 163 | This option enables a remote machine to directly connect
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| 164 | to the guest's serial port using TCP.
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| 165 | </p>
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| 166 | <ul>
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| 167 | <li>
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| 168 | <p><b outputclass="bold">TCP Server:</b> Deselect
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| 169 | the <b outputclass="bold">Connect to Existing
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| 170 | Pipe/Socket</b> check box and specify the port
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| 171 | number in the
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| 172 | <b outputclass="bold">Path/Address</b> field.
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| 173 | This is typically 23 or 2023. Note that on UNIX-like
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| 174 | systems you will have to use a port a number greater
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| 175 | than 1024 for regular users.
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| 176 | </p>
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| 177 | <p>
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| 178 | The client can use software such as
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| 179 | <userinput>PuTTY</userinput> or the
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| 180 | <userinput>telnet</userinput> command line tool to access
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| 181 | the TCP Server.
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| 182 | </p>
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| 183 | </li>
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| 184 | <li>
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| 185 | <p><b outputclass="bold">TCP Client:</b> To create
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| 186 | a virtual null-modem cable over the Internet or LAN,
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| 187 | the other side can connect using TCP by specifying
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| 188 | <codeph><varname>hostname</varname>:<varname>port</varname></codeph>
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| 189 | in the <b outputclass="bold">Path/Address</b>
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| 190 | field. The TCP socket will act in client mode if you
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| 191 | select the <b outputclass="bold">Connect to Existing
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| 192 | Pipe/Socket</b> check box.
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| 193 | </p>
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| 194 | </li>
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| 195 | </ul>
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| 196 | </li>
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| 197 | </ul>
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| 198 | </li>
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| 199 | </ol>
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| 200 | <p>
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| 201 | Up to four serial ports can be configured per virtual machine, but
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| 202 | you can pick any port numbers out of the above. However, serial
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| 203 | ports cannot reliably share interrupts. If both ports are to be
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| 204 | used at the same time, they must use different interrupt levels,
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| 205 | for example COM1 and COM2, but not COM1 and COM3.
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| 206 | </p>
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| 207 | </body>
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| 208 |
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| 209 | </topic>
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