| 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><ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports the use of virtual serial ports in a virtual machine with an x86 architecture. Serial ports are not available on Arm VMs.</p>
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| 8 | <p>Ever since the original IBM PC, personal computers have been equipped with one or two serial ports, also called
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| 9 | COM ports by DOS and Windows. Serial ports were commonly used with modems, and some computer mice used to be
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| 10 | connected to serial ports before USB became commonplace. </p>
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| 11 | <p>While serial ports are no longer as common as they used to be, there are still some important uses left for them.
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| 12 | For example, serial ports can be used to set up a primitive network over a null-modem cable, in case Ethernet is
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| 13 | not available. Also, serial ports are indispensable for system programmers needing to do kernel debugging, since
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| 14 | kernel debugging software usually interacts with developers over a serial port. With virtual serial ports, system
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| 15 | programmers can do kernel debugging on a virtual machine instead of needing a real computer to connect to. </p>
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| 16 | <p>If a virtual serial port is enabled, the guest OS sees a standard 16550A compatible UART device. Other UART types
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| 17 | can be configured using the <userinput>VBoxManage modifyvm</userinput> command. Both receiving and transmitting
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| 18 | data is supported. How this virtual serial port is then connected to the host is configurable, and the details
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| 19 | depend on your host OS. </p>
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| 20 | <p>You can use either the Settings tabs or the <userinput>VBoxManage</userinput> command to set up virtual serial
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| 21 | ports. For the latter, see <xref href="vboxmanage-modifyvm.dita"/> for information on the <codeph>--uart</codeph>,
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| 22 | <codeph>--uart-mode</codeph> and <codeph>--uart-type</codeph> options. </p>
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| 23 | <p>You can configure up to four virtual serial ports per virtual machine. For each device, you must set the
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| 24 | following: </p>
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| 25 | <ol>
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| 26 | <li>
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| 27 | <p><b outputclass="bold">Port Number:</b> This determines
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| 28 | the serial port that the virtual machine should see. For best
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| 29 | results, use the traditional values as follows:
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| 30 | </p>
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| 31 | <ul>
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| 32 | <li>
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| 33 | <p>
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| 34 | COM1: I/O base 0x3F8, IRQ 4
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| 35 | </p>
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| 36 | </li>
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| 37 | <li>
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| 38 | <p>
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| 39 | COM2: I/O base 0x2F8, IRQ 3
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| 40 | </p>
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| 41 | </li>
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| 42 | <li>
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| 43 | <p>
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| 44 | COM3: I/O base 0x3E8, IRQ 4
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| 45 | </p>
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| 46 | </li>
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| 47 | <li>
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| 48 | <p>
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| 49 | COM4: I/O base 0x2E8, IRQ 3
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| 50 | </p>
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| 51 | </li>
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| 52 | </ul>
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| 53 | <p>
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| 54 | You can also configure a user-defined serial port. Enter an
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| 55 | I/O base address and interrupt (IRQ).
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| 56 | </p>
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| 57 | </li>
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| 58 | <li>
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| 59 | <p><b outputclass="bold">Port Mode:</b> What the virtual
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| 60 | port is connected to. For each virtual serial port, you have
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| 61 | the following options:
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| 62 | </p>
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| 63 | <ul>
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| 64 | <li>
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| 65 | <p><b outputclass="bold">Disconnected:</b> The guest
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| 66 | will see the device, but it will behave as if no cable had
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| 67 | been connected to it.
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| 68 | </p>
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| 69 | </li>
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| 70 | <li>
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| 71 | <p><b outputclass="bold">Host Device:</b> Connects the
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| 72 | virtual serial port to a physical serial port on your
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| 73 | host. On a Windows host, this will be a name like
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| 74 | <codeph>COM1</codeph>. On Linux or Oracle Solaris hosts,
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| 75 | it will be a device node like
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| 76 | <filepath>/dev/ttyS0</filepath>. <ph conkeyref="vbox-conkeyref-phrases/product-name"/> will then
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| 77 | simply redirect all data received from and sent to the
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| 78 | virtual serial port to the physical device.
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| 79 | </p>
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| 80 | </li>
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| 81 | <li>
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| 82 | <p><b outputclass="bold">Host Pipe:</b> Configure
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| 83 | <ph conkeyref="vbox-conkeyref-phrases/product-name"/> to connect the virtual serial port to a
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| 84 | software pipe on the host. This depends on your host OS,
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| 85 | as follows:
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| 86 | </p>
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| 87 | <ul>
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| 88 | <li>
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| 89 | <p>On a Windows host, data will be sent and received through a named pipe. The pipe name must be in the
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| 90 | format <filepath>\\.\pipe\<varname>name</varname>
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| 91 | </filepath> where <varname>name</varname> should identify the virtual machine but may be freely
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| 92 | chosen. </p>
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| 93 | </li>
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| 94 | <li>
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| 95 | <p>On a Mac OS, Linux, or Oracle Solaris host, a local domain socket is used instead. The socket
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| 96 | filename must be chosen such that the user running <ph conkeyref="vbox-conkeyref-phrases/product-name"
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| 97 | /> has sufficient privileges to create and write to it. The <filepath>/tmp</filepath> directory is
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| 98 | often a good candidate. </p>
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| 99 | <p>On Linux there are various tools which can connect to a local domain socket or create one in server
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| 100 | mode. The most flexible tool is <userinput>socat</userinput> and is available as part of many
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| 101 | distributions. </p>
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| 102 | </li>
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| 103 | </ul>
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| 104 | <p>In this case, you can configure whether <ph conkeyref="vbox-conkeyref-phrases/product-name"/> should
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| 105 | create the named pipe, or the local domain socket on non-Windows hosts, itself or whether <ph
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| 106 | conkeyref="vbox-conkeyref-phrases/product-name"/> should assume that the pipe or socket exists already.
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| 107 | With the <userinput>VBoxManage</userinput> command-line options, this is referred to as server mode or
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| 108 | client mode, respectively. </p>
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| 109 | <p>For a direct connection between two virtual machines, corresponding to a null-modem cable, simply
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| 110 | configure one VM to create a pipe or socket and another to attach to it. </p>
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| 111 | </li>
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| 112 | <li>
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| 113 | <p><b outputclass="bold">Raw File:</b> Send the
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| 114 | virtual serial port output to a file. This option is very
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| 115 | useful for capturing diagnostic output from a guest. Any
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| 116 | file may be used for this purpose, as long as the user
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| 117 | running <ph conkeyref="vbox-conkeyref-phrases/product-name"/> has sufficient privileges to create
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| 118 | and write to the file.
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| 119 | </p>
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| 120 | </li>
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| 121 | <li>
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| 122 | <p><b outputclass="bold">TCP:</b> Useful for
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| 123 | forwarding serial traffic over TCP/IP, acting as a server,
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| 124 | or it can act as a TCP client connecting to other servers.
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| 125 | This option enables a remote machine to directly connect
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| 126 | to the guest's serial port using TCP.
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| 127 | </p>
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| 128 | <ul>
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| 129 | <li>
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| 130 | <p><b outputclass="bold">TCP Server:</b> Deselect
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| 131 | the <b outputclass="bold">Connect to Existing
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| 132 | Pipe/Socket</b> check box and specify the port
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| 133 | number in the
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| 134 | <b outputclass="bold">Path/Address</b> field.
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| 135 | This is typically 23 or 2023. Note that on UNIX-like
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| 136 | systems you will have to use a port a number greater
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| 137 | than 1024 for regular users.
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| 138 | </p>
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| 139 | <p>The client can use software such as <userinput>PuTTY</userinput> or the <userinput>telnet</userinput>
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| 140 | command line tool to access the TCP Server. </p>
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| 141 | </li>
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| 142 | <li>
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| 143 | <p><b outputclass="bold">TCP Client:</b> To create
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| 144 | a virtual null-modem cable over the Internet or LAN,
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| 145 | the other side can connect using TCP by specifying
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| 146 | <codeph><varname>hostname</varname>:<varname>port</varname></codeph>
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| 147 | in the <b outputclass="bold">Path/Address</b>
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| 148 | field. The TCP socket will act in client mode if you
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| 149 | select the <b outputclass="bold">Connect to Existing
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| 150 | Pipe/Socket</b> check box.
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| 151 | </p>
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| 152 | </li>
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| 153 | </ul>
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| 154 | </li>
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| 155 | </ul>
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| 156 | </li>
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| 157 | </ol>
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| 158 | <p>Up to four serial ports can be configured per virtual machine, but you can pick any port numbers out of the
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| 159 | above. However, serial ports cannot reliably share interrupts. If both ports are to be used at the same time, they
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| 160 | must use different interrupt levels, for example COM1 and COM2, but not COM1 and COM3. </p>
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| 161 | </body>
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| 162 |
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| 163 | </topic>
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