c3270 man page

c3270 — curses-based  IBM host access tool


c3270 [options] [host]

c3270 [options] session-file.c3270


c3270 opens a telnet connection to an IBM host in a console window. It implements RFCs 2355 (TN3270E), 1576 (TN3270) and 1646 (LU name selection), and supports IND$FILE file transfer. If the console is capable of displaying colors, then c3270 emulates an IBM 3279.  Otherwise, it emulates a 3278. The full syntax for host is:


Prepending a P: onto hostname causes the connection to go through the telnet-passthru service rather than directly to the host. See Passthru below.

Prepending an S: onto hostname removes the "extended data stream" option reported to the host. See -tn below for further information.

Prepending an N: onto hostname turns off TN3270E support for the session.

Prepending an L: onto hostname causes c3270 to first create an SSL tunnel to the host, and then create a TN3270 session inside the tunnel.  (This function is supported only if c3270 was built with SSL/TLS support). Note that TLS-encrypted sessions using the TELNET START-TLS option are negotiated with the host automatically; for these sessions the L: prefix should not be used.

Prepending a B: onto hostname changes the interaction of scripts and the host BIND-IMAGE message. Without B:, c3270 will unlock the keyboard as soon as a BIND-IMAGE is received. With B:, it will wait for a Write command that explicitly unlocks the keyboard.

A specific Logical Unit (LU) name to use may be specified by prepending it to the hostname with an `@'. Multiple LU names to try can be separated by commas. An empty LU can be placed in the list with an extra comma. (Note that the LU name is used for different purposes by different kinds of hosts. For example, CICS uses the LU name as the Terminal ID.)

The hostname may optionally be placed inside square-bracket characters `[' and `]'. This will prevent any colon `:' characters in the hostname from being interpreted as indicating option prefixes or port numbers. This allows numeric IPv6 addresses to be used as hostnames.

On systems that support the forkpty library call, the hostname may be replaced with -e and a command string. This will cause c3270 to connect to a local child process, such as a shell.

The port to connect to defaults to telnet. This can be overridden with the -port option, or by appending a port to the hostname with a colon `:'. (For compatability with previous versions of c3270 and with tn3270(1), the port may also be specified as a second, separate argument.)


c3270 understands the following options:

-accepthostname spec

Specifies a particular hostname to accept when validating the name presented in the host's SSL certificate, instead of comparing to the name or address used to make the connection. spec can either be any, which disables name validation, DNS:hostname, which matches a particular DNS hostname, or IP:address, which matches a particular numeric IPv4 or IPv6 address.


Forces all characters to be displayed in bold. This helps with PC consoles which display non-bold characters in unreadably dim colors. All-bold mode is the default for color displays, but not for monochrome displays.

-altscreen rowsxcols=init_string

Defines the dimensions and escape sequence for the alternate (132-column) screen mode. See Screen Size Switching, below.

-cadir directory

Specifies a directory containing CA (root) certificates to use when verifying a certificate provided by the host.

-cafile filename

Specifies a PEM-format file containing CA (root) certificates to use when verifying a certificate provided by the host.


Causes c3270 to operate in cbreak mode, instead of raw mode. In cbreak mode, the TTY driver will properly process XOFF and XON characters, which are required by some terminals for proper operation. However, those characters (usually ^S and ^Q), as well as the characters for interrupt, quit, and lnext (usually ^C, ^\ and ^V respectively) will be seen by c3270 only if preceded by the lnext character. The susp character (usually ^Z) cannot be seen by c3270 at all.

-certfile filename

Specifies a file containing a certificate to provide to the host, if requested. The default file type is PEM.

-certfiletype type

Specifies the type of the certificate file specified by -certfile. Type can be pem or asn1.

-chainfile filename

Specifies a certificate chain file in PEM format, containing a certificate to provide to the host if requested, as well as one or more intermediate certificates and the CA certificate used to sign that certificate. If -chainfile is specified, it overrides -certfile.

-charset name

Specifies an EBCDIC host character set.

-clear toggle

Sets the initial value of toggle to false.

-connecttimeout seconds

Specifies the time that c3270 will wait for a host connection to complete.


Causes c3270 to use the terminal's default foreground color instead of the curses color black, and the terminal's default background color instead of the curses color white. This is helpful for emulators such as gnome-terminal whose representation of a black background is a murky gray, and for emulators configured to use black text on a white background. It is set automatically if the environment variable COLORTERM is set to gnome-terminal. It is available only if c3270 was compiled with a version of ncurses that supports default colors, if the emulator supports default colors, and if the termcap/terminfo entry indicates this capability.

-defscreen rowsxcols=init_string

Defines the dimensions and escape sequence for the default (80-column) screen mode. See Screen Size Switching, below.

-devname name

Specifies a device name (workstation ID) for RFC 4777 support.

-hostsfile file

Uses file as the hosts file, which allows aliases for host names and scripts to be executed at login. See ibm_hosts(1) for details.

-httpd [addr:]port

Specifies a port and optional address to listen on for HTTP connections. Addr can be specified as `*' to indicate; the default is IPv6 numeric addresses must be specified inside of square brackets, e.g., [::1]:4080 to specify the IPv6 loopback address and TCP port 4080.

Note that this option is mutually-exclusive with the -scriptport option

-keyfile filename

Specifies a file containing the private key for the certificate file (specified via -certfile or -chainfile). The default file type is PEM.

-keyfiletype type

Specifies the type of the private key file specified by -keyfile. Type can be pem or asn1.

-keypasswd type:value

Specifies the password for the private key file, if it is encrypted. The argument can be file:filename, specifying that the password is in a file, or string:string, specifying the password on the command-line directly. If the private key file is encrypted and no -keypasswd option is given, the password will be prompted for interactively.

-keymap name

Specifies a keyboard map to be found in the resource c3270.keymap.name or the file name. See Keymaps below for details.

-km name

Specifies the local encoding method for multi-byte text. name is an encoding name recognized by the ICU library. (Supported only when c3270 is compiled with DBCS support, and necessary only when c3270 cannot figure it out from the locale.)

-loginmacro Action(arg...) ...

Specifies a macro to run at login time.

-model name

The model of 3270 display to be emulated. The model name is in two parts, either of which may be omitted:

The first part is the base model, which is either 3278 or 3279. 3278 specifies a monochrome (green on black) 3270 display; 3279 specifies a color 3270 display.

The second part is the model number, which specifies the number of rows and columns. Model 4 is the default.

Model Number Columns Rows
2 80 24
3 80 32
4 80 43
5 132 27

Note: Technically, there is no such 3270 display as a 3279-4 or 3279-5, but most hosts seem to work with them anyway.

The default model for a color display is 3279-4. For a monochrome display, it is 3278-4.


Prevents c3270 from using color, ignoring any color capabilities reported by the terminal.


An alias for -secure.


Start in NVT mode instead of waiting for the host to send data, and make the default terminal type xterm.

-oversize colsxrows

Makes the screen larger than the default for the chosen model number. This option has effect only in combination with extended data stream support (controlled by the "c3270.extended" resource), and only if the host supports the Query Reply structured field. The number of columns multiplied by the number of rows must not exceed 16383 (3fff hex), the limit of 14-bit 3270 buffer addressing.

It can also be specified as auto, which causes c3270 to fill the entire terminal or console window.

-port n

Specifies a different TCP port to connect to. n can be a name from /etc/services like telnet, or a number. This option changes the default port number used for all connections. (The positional parameter affects only the initial connection.)

-proxy type:host[:port]

Causes c3270 to connect via the specified proxy, instead of using a direct connection. The host can be an IP address or hostname. The optional port can be a number or a service name. For a list of supported proxy types, see Proxy below.

-printerlu luname

Causes c3270 to automatically start a pr3287 printer session. If luname is ".", then the printer session will be associated with the interactive terminal session (this requires that the host support TN3270E). Otherwise, the value is used as the explicit LU name to associate with the printer session.


Causes c3270 to automatically reconnect to the host if it ever disconnects. This option has effect only if a hostname is specified on the command line.


Switches c3270 from a white-on-black display to a black-on-white display.

-sl n

Specifies that n lines should be saved for scrolling back. The default is 4096.

-scriptport [addr:]port

Specifies a port and optional address to listen on for scripting connections. Addr can be specified as `*' to indicate; the default is IPv6 numeric addresses must be specified inside of square brackets, e.g., [::1]:4081 to specify the IPv6 loopback address and TCP port 4081.

Note that this option is mutually-exclusive with the -httpd option


Allows c3270 to accept only one script connection. When that connection is broken, c3270 will exit.


Disables the interactive c3270> prompt. When used, a hostname must be provided on the command line.


When verifying a host SSL certificate, allow it to be self-signed.

-set toggle

Sets the initial value of toggle to true.


Causes the emulator to create a Unix-domain socket when it starts, for use by script processes to send commands to the emulator. The socket is named /tmp/x3sck.pid. The -p option of x3270if causes it to use this socket, instead of pipes specified by environment variables.

-tn name

Specifies the terminal name to be transmitted over the telnet connection. The default name is IBM-model_name-E, for example, IBM-3279-4-E  for a color display, or IBM-3278-4-E for a monochrome display.

Some hosts are confused by the -E suffix on the terminal name, and will ignore the extra screen area on models 3, 4 and 5. Prepending an s: on the hostname, or setting the "c3270.extended" resource to "false", removes the -E from the terminal name when connecting to such hosts.

The name can also be specified with the "c3270.termName" resource.


Turns on data stream and event tracing at startup. The default trace file name is /tmp/x3trc.

-tracefile file

Specifies a file to save data stream and event traces into. If the name starts with `>>', data will be appended to the file.

-tracefilesize size

Places a limit on the size of a trace file. If this option is not specified, or is specified as 0 or none, the trace file size will be unlimited. The minimum size is 64 Kbytes. The value of size can have a K or M suffix, indicating kilobytes or megabytes respectively. When the trace file reaches the size limit, it will be renamed with a  `-' appended and a new file started.

-user name

Specifies the user name for RFC 4777 support.


Forces the local codeset to be UTF-8, ignoring the locale or Windows codepage.


Display the version and build options for c3270 and exit.


For SSL or SSL/TLS connections, verify the host certificate, and do not allow the connection to complete unless it can be validated.

-xrm "c3270.resource: value"

Sets the value of the named resource to value. Resources control less common c3270 options, and are defined under Resources below.

Status Line

If the terminal that c3270 is running on has at least one more row that the 3270 model requires (e.g., 25 rows for a model 2), c3270 will display a status line. The c3270 status line contains a variety of information. From left to right, the fields are:

comm status

The first symbol is always a 4. If c3270 is in TN3270E mode, the second symbol is a B; otherwise it is an A. If  c3270 is in SSCP-LU mode, the third symbol is an S. Otherwise it is blank.

keyboard lock

If the keyboard is locked, an "X" symbol and a message field indicate the reason for the keyboard lock.


The letter "T" indicates that one or more keystrokes are in the typeahead buffer.

temporary keymap

The letter "K" indicates that a temporary keymap is in effect.


The letter "R" indicates that the keyboard is in reverse field entry mode.

insert mode

The  letter "I" indicates that the keyboard is in insert mode.

printer session

The letter "P" indicates that a pr3287 session is active.

secure connection

A green letter "S" indicates that the connection is secured via SSL/TLS.

LU name

The LU name associated with the session, if there is one.

cursor position

The cursor row and column are optionally displayed, zero padded and separated by a "/". Location 001/001 is at the upper left, which is different from the row and columns parameters used with various actions, where the upper left corner is row 0, column 0.


Here is a complete list of basic c3270 actions. Script-specific actions are described on the x3270-script(1) manual page. ).PP Actions marked with an asterisk (*) may block, sending data to the host and possibly waiting for a response.


attention key


move cursor left (or send ASCII BS)


tab to start of previous input field


input "^" in NVT mode, or "notsign" in 3270 mode


clear screen


next two keys form a special symbol


connect to host


Cursor Select AID


delete character under cursor (or send ASCII DEL)


delete the entire field


delete the current or previous word


disconnect from host


move cursor down


duplicate field


Enter AID (or send ASCII CR)


erase previous character (or send ASCII BS)


erase to end of current field


erase all input fields


escape to c3270> prompt


execute a command in a shell


move cursor to end of field


mark field


insert control-character string


move cursor to first input field


set insert mode


send TELNET IP to host


Display pop-up keypad


insert key keysym


insert key with character code xx


move cursor left


move cursor left 2 positions


Display menu bar


toggle uppercase-only mode

MoveCursor(row, col)

move cursor to zero-origin (row,col)


move cursor to first field on next line (or send ASCII LF)


move cursor to next word


Program Attention AID (n from 1 to 3)


Program Function AID (n from 1 to 24)


move cursor to previous word


start or stop printer session


print screen text on printer


exit c3270


redraw window


reset locked keyboard


move cursor right


move cursor right 2 positions


run a script


scroll screen


insert string (simple macro facility)


move cursor to next input field


toggle an option


toggle insert mode


toggle reverse-input mode


file transfer


move cursor up


do nothing

Any of the above actions may be entered at the c3270> prompt; these commands are also available for use in keymaps (see Keymaps). Command names are case-insensitive. Parameters can be specified with parentheses and commas, e.g.:


or with spaces, e.g.:

PF 1

Parameters can be quoted with double-quote characters, to allow spaces, commas, and parentheses to be used.

c3270 also supports the following interactive commands:


Displays a list of available commands.


Turns screen tracing (saving screen images to a file) on or off. The command screentrace on enables screen tracing; the command screentrace off disables it. After on, a filename may be specified to override the default trace file name of /tmp/x3scr.pid. The keyaord on can also be followed by the keyword printer and an optional print command to direct screen traces directly to the printer.


Displays statistics and settings.


Turns tracing on or off. The command trace on enables data stream and keyboard event tracing; the command trace off disables it. The qualifier data or keyboard can be specified before on or off to enable or disable a particular trace. After on, a filename may be specified to override the default trace file name of /tmp/x3trc.pid.

Note that certain parameters to c3270 actions (such as the names of files and keymaps) are subject to substitutions:

The character ~ at the beginning of a string is replaced with the user's home directory. A ~ character followed by a username is replaced with that user's home directory.

Environment variables are substituted using the Unix shell convention of $name or ${name}.

Two special pseudo-environment variables are supported. ${TIMESTAMP} is replaced with a microsecond-resolution timestamp; ${UNIQUE} is replaced with a string guaranteed to make a unique filename (the process ID optionally followed by a dash and a string of digits). ${UNIQUE} is used to form trace file names.


The -keymap option or the c3270.keymap resource allow a custom keymap to be specified. If the option -keymap xxx is given (or the c3270.keymap resource has the value xxx), c3270 will look for a resource named c3270.keymap.xxx. If no resource definition is found, it will look for a file named xxx.

Multiple keymaps may be specified be separating their names with commas. Definitions in later keymaps supercede those in earlier keymaps.

In addition, separate keymaps may be defined that apply only in 3270 mode or NVT mode. For example, the resource definition c3270.keymap.xxx.nvt or the file xxx.nvt will augment the definition of keymap xxx in NVT mode. Similarly, the resource definition c3270.keymap.xxx.3270 or the file xxx.3270 will augment the definition of keymap xxx in 3270 mode.

Temporary keymaps can also be added or removed while c3270 is running with the Keymap action. See x3270-script(1) for details.

Each line (rule) in a keymap specifies actions to perform when a particular key or sequence of keys is pressed. Keymap rules have the following syntax:

[Meta][Ctrl]<Key>key...: action[(param[,...])] ...

Here is a sample keymap definition from a file:

! Lines beginning with ! are ignored and can
! occur anywhere.
! Definition of keymap xxx
!  When Alt-c is pressed, clear the screen.
Alt<Key>c: Clear()
!  When PageUp is pressed, send PF7 to the host.
<Key>PPAGE: PF(7)
!  When Ctrl-a is pressed, then F1, send PF13
!  to the host.
Ctrl<Key>a <Key>F1: PF(13)

Here is the same definition as a resource:

! Lines beginning with ! are ignored, but NOT
! within a definition.
! Note that the \ is required at the end of the
! first line, and \n\ is
! required at the end of every other line except
! the last.
! Definition of keymap xxx
c3270.keymap.xxx: \
 Alt<Key>c: Clear() \n\
 <Key>PPAGE: PF(7) \n\
 Ctrl<Key>A <Key>F1: PF(13)

The optional Alt or Ctrl modifiers specify that the Alt and Ctrl keys are pressed along with the specified key, respectively. Key is either an ISO 8859-1 symbol name, such as equal for `=' and a for `a', or a symbolic ncurses key name, such as UP. More than one key can be specified, indicating that a sequence of keys must be pressed in order for the rule to be matched. The action is an action from the Actions list above. More than one action may be specified; they will be executed in order.

Keymap entries are case-sensitive and modifier-specific. This means that a keymap for the b key will match only a lowercase b. Actions for uppercase B, or for Alt-B, must be specified separately.

The base keymap is:

Key Action
Ctrl<Key>] Escape
Ctrl<Key>a Ctrl<Key>a Key(0x01)
Ctrl<Key>a Ctrl<Key>] Key(0x1d)
Ctrl<Key>a <Key>Tab BackTab
Ctrl<Key>a <Key>c Clear
Ctrl<Key>a <Key>e Escape
Ctrl<Key>a <Key>r Reset
Ctrl<Key>a <Key>k Keypad
Ctrl<Key>a <Key>l Redraw
Ctrl<Key>a <Key>m Compose
Ctrl<Key>a <Key>n Menu
Ctrl<Key>a <Key>p PrintText
Ctrl<Key>a <Key>^ Key(notsign)
Ctrl<Key>k Keypad
Ctrl<Key>n Menu
<Key>UP Up
<Key>DOWN Down
<Key>LEFT Left
<Key>RIGHT Right
<Key>F(n) PF(n)
Ctrl<Key>a <Key>F(n) PF(n+12)
Ctrl<Key>a <Key>1 PA(1)
Ctrl<Key>a <Key>2 PA(2)
Ctrl<Key>a <Key>3 PA(3)
<Key>PPAGE Scroll(Backward)
<Key>NPAGE Scroll(Forward)

The base 3270-mode keymap adds:

Key Action
Ctrl<Key>c Clear
Ctrl<Key>d Dup
Ctrl<Key>f FieldMark
Ctrl<Key>i Tab
Ctrl<Key>l Redraw
Ctrl<Key>r Reset
Ctrl<Key>u DeleteField
<Key>BackSpace BackSpace
<Key>Return Enter
<Key>Tab Tab
<Key>Linefeed Newline
<Key>BACKSPACE BackSpace
<Key>DC Delete
<Key>HOME Home
<Key>IC ToggleInsert

The Meta or Alt Key

Some keyboards do not have a Meta key. Instead, they have an Alt key. Sometimes this key acts as a proper Meta key, that is, it is a modifier key that sets the high-order bit (0x80) in the code that is transmitted for each key. Other keyboards send a two-character sequence when the Alt key is pressed with another key: the Escape character (0x1b), followed by the code for the other key.

The resource c3270.metaEscape and the termcap km attribute control how c3270 will interpret these sequences. When c3270.metaEscape is set to true, or when c3270.metaEscape is set to auto and the termcap km attribute is set, the keyboard is assumed to have a separate Meta key. The Escape key can be used as an ordinary data key and has no special meaning.

When c3270.metaEscape is set to true, or when c3270.metaEscape is set to auto and the termcap km attribute is not set, the keyboard is assumed to use the Escape character as a prefix to indicate that the following character is supposed to have the high-order bit set. When c3270 sees an Escape character from the keyboard, it sets a short timeout. If another character arrives before the timeout expires, then c3270 will combine the two characters, setting the high-order bit of the second. In an event trace file, the combined character is listed as derived. In a keymap, only the combined character or the Meta prefix may be used. The Escape key can still be used by itself, but only if there is a short pause before pressing another key.

The default value for c3270.metaEscape is auto.

File Transfer

The Transfer action implements IND$FILE file transfer. This action requires that the IND$FILE program be installed on the IBM host, and that the 3270 cursor be located in a field that will accept a TSO or VM/CMS command.

The Transfer action can be entered at the command prompt with no parameters, which will cause it to prompt interactively for the file names and options. It can also be invoked with parameters to define the entire transfer.

Because of the complexity and number of options for file transfer, the parameters to the Transfer action take the unique form of option=value, and can appear in any order. Note that if the value contains spaces (such as a VM/CMS file name), then the entire parameter must be quoted, e.g., "HostFile=xxx foo a". The options are:

Option Required? Default Other Values
Direction No receive send
HostFile Yes    
LocalFile Yes    
Host No tso vm, cics
Mode No ascii binary
Cr No remove add, keep
Remap No yes no
Exist No keep replace, append
Recfm No   fixed, variable, undefined
Lrecl No    
Blksize No    
Allocation No   tracks, cylinders, avblock
PrimarySpace Sometimes    
SecondarySpace No    
Avblock Sometimes    
BufferSize No 4096  

The option details are as follows.


send to send a file to the host, receive to receive a file from the host.


The name of the file on the host.


The name of the file on the local workstation.


The type of host (which dictates the form of the IND$FILE command): tso (the default), vm or cics.


Use ascii (the default) for a text file, which will be translated between EBCDIC and ASCII as necessary. Use binary for non-text files.


Controls how Newline characters are handled when transferring Mode=ascii files. remove (the default) strips Newline characters in local files before transferring them to the host. add adds Newline characters to each host file record before transferring it to the local workstation. keep preserves Newline characters when transferring a local file to the host.


Controls text translation for Mode=ascii files. The value yes (the default) causes c3270 to remap the text to ensure maximum compatibility between the workstation's character set and encoding and the host's EBCDIC code page. The value no causes c3270 to pass the text to or from the host as-is, leaving all translation to the IND$FILE program on the host.


Controls what happens when the destination file already exists. keep (the default) preserves the file, causing the Transfer action to fail. replace overwrites the destination file with the source file. append appends the source file to the destination file.


Controls the record format of files created on the host. (TSO and VM hosts only.) fixed creates a file with fixed-length records. variable creates a file with variable-length records. undefined creates a file with undefined-length records (TSO hosts only). The Lrecl option controls the record length or maximum record length for Recfm=fixed and Recfm=variable files, respectively.


Specifies the record length (or maximum record length) for files created on the host. (TSO and VM hosts only.)


Specifies the block size for files created on the host. (TSO and VM hosts only.)


Specifies the units for the PrimarySpace and SecondarySpace options: tracks, cylinders or avblock. (TSO hosts only.)


Primary allocation for a file. The units are given by the Allocation option. Required when the Allocation is specified as something other than default. (TSO hosts only.)


Secondary allocation for a file. The units are given by the Allocation option. (TSO hosts only.)


Average block size, required when Allocation specifies avblock. (TSO hosts only.)


Buffer size for DFT-mode transfers. Can range from 256 to 32768. Larger values give better performance, but some hosts may not be able to support them.

There are also resources that control the default values for each of the file transfer parameters. These resources have the same names as the Transfer keywords, but with ft prepended. E.g., the default for the Mode keyword is the c3270.ftMode resource.

The Printtext Action

The PrintText produces screen snapshots in a number of different forms. The default form wth no arguments sends a copy of the screen to the default printer. A single argument is the command to use to print, e.g., lpr.

Multiple arguments can include keywords to control the output of PrintText:

file filename

Save the output in a file.


Save the output as HTML.  This option implies file.


Save the output as RichText.  This option implies file. The font defaults to Courier New and the point size defaults to 8. These can be overridden by the printTextFont and printTextSize resources, respectively.


Return the output as a string.  This can only be used from scripts.


Render modified fields in italics.

caption text

Add the specified text as a caption above the output. Within text, the special sequence %T% will be replaced with a timestamp.

command command

Directs the output to a command. This allows one or more of the other keywords to be specified, while still sending the output to the printer.


There are several types of script functions available.

The String Action

The simplest method for scripting is provided via the String action. The arguments to String are one or more double-quoted strings which are inserted directly as if typed. The C backslash conventions are honored as follows. (Entries marked * mean that after sending the AID code to the host, c3270 will wait for the host to unlock the keyboard before further processing the string.)

\b Left
\exxxx EBCDIC character in hex
\f Clear*
\n Enter*
\pan PA(n)*
\pfnn PF(nn)*
\r Newline
\t Tab
\T BackTab
\uxxxx Unicode character in hex
\xxxxx Unicode character in hex

Note that the numeric values for the \e, \u and \x sequences can be abbreviated to 2 digits. Note also that EBCDIC codes greater than 255 and some Unicode character codes represent DBCS characters, which will work only if c3270 is built with DBCS support and the host allows DBCS input in the current field.

An example keymap entry would be:

Meta<Key>p: String("probs clearrdr\n")

Note: The strings are in ASCII and converted to EBCDIC, so beware of inserting control codes.

There is also an alternate form of the String action, HexString, which is used to enter non-printing data. The argument to HexString is a string of hexadecimal digits, two per character.  A leading 0x or 0X is optional. In 3270 mode, the hexadecimal data represent EBCDIC characters, which are entered into the current field. In NVT mode, the hexadecimal data represent ASCII characters, which are sent directly to the host.

The Script Action

This action causes c3270 to start a child process which can execute c3270 actions. Standard input and output from the child process are piped back to c3270. The Script action is fully documented in x3270-script(1).

Composite Characters

c3270 allows the direct entry of accented letters and special symbols. Pressing and releasing the "Compose" key, followed by two other keys, causes entry of the symbol combining those two keys. For example, "Compose" followed by the "C" key and the "," (comma) key, enters the "C-cedilla" symbol. A C on the status line indicates a pending composite character.

The mappings between these pairs of ordinary keys and the symbols they represent is controlled by the "c3270.composeMap" resource; it gives the name of the map to use. The maps themselves are named "c3270.composeMap.name". The default is "latin1", which gives mappings for most of the symbols in the ISO 8859-1 Latin-1 character set that are not in the 7-bit ASCII character set.

Note: The default keymap defines Meta<Key>m as the "Compose" key. You may set up your own "Compose" key with a keymap that maps some other keysym onto the Compose action.

Printer Session Support

c3270 supports associated printer sessions via the pr3287(1) program. The Printer action is used to start or stop a pr3287 session.

The action Printer Start starts a printer session, associated with the current LU.  (This works only if the host supports TN3270E.)

The action Printer Start lu starts a printer session, associated with a specific lu.

The action Printer Stop stops a printer session.

The resource c3270.printer.options specifies extra options, such as -trace to pass to pr3287.

See pr3287(1) for further details.

The resource c3270.printerLu controls automatic printer session start-up.  If it is set to `.', then whenever a login session is started, a printer session will automatically be started, associated with the login session.  If it is set an LU name, then the automatic printer session will be associated with the specified LU.


c3270 supports the Sun telnet-passthru service provided by the in.telnet-gw server. This allows outbound telnet connections through a firewall machine. When a p: is prepended to a hostname, c3270 acts much like the itelnet(1) command. It contacts the machine named internet-gateway at the port defined in /etc/services as telnet-passthru (which defaults to 3514). It then passes the requested hostname and port to the in.telnet-gw server.


The -proxy option or the c3270.proxy resource causes c3270 to use a proxy server to connect to the host. The syntax of the option or resource is:


The supported values for type are:

Proxy Type Protocol Default Port
http RFC 2817 HTTP tunnel (squid) 3128
passthru Sun in.telnet-gw none
socks4 SOCKS version 4 1080
socks5 SOCKS version 5 (RFC 1928) 1080
telnet No protocol (just send connect host port) none

The special types socks4a and socks5d can also be used to force the proxy server to do the hostname resolution for the SOCKS protocol.

Screen Size Switching

When running as a 3270 Model 5, c3270 can take advantage of terminals that can switch between 80 and 132 column modes.

Because the curses library does not support mode switching, the escape sequences and resulting screen dimensions must be specified explicitly to c3270. These are specified with the -altscreen and -defscreen command-line options, or the altScreen and defScreen resources. -altscreen or altScreen defines the alternate (132-column) mode; -defscreen or defScreen defines the default (80-column) mode.

The syntax for the options and resources is rowsxcols=init_string, where rows and cols give the screen dimensions, and init_string is the escape sequence to transmit to the terminal to enter that mode. For defscreen, the minimum dimensions are 24 rows and 80 columns. For altscreen, the minimum dimensions are 27 rows and 132 columns. Within init_string, the usual escape sequences are supported (\E for escape, \r, \b, etc.). For example, the init string for a 132-column xterm is:


Note: When defscreen and altscreen are specified, the model number is always set to 5.


Certain c3270 options can be configured via resources. Resources are defined in the file .c3270pro in the user's home directory, and by -xrm options. The definitions are similar to X11 resources, and use a similar syntax. The resources available in c3270 are:

Resource Default Option Purpose
allBold Auto -allbold Display all characters bold
altScreen   -altscreen 132-col screen definition
blankFill False -set blankFill Blank Fill mode
charset bracket -charset EBCDIC character set
composeMap latin1   Name of composed-character map
cursesColorForHostColorn (note 6)   Color mapping
cursesColorForDefault green   Default color mapping
cursesColorForIntensified red   Default color mapping
cursesColorForProtected blue   Default color mapping
cursesColorForProtectedIntensified white   Default color mapping
cursesKeymap True   Set curses keymap option
defScreen   -defscreen 80-col screen definition
dbcsCgcsgid     Override DBCS CGCSGID
dsTrace False -trace Data stream tracing
eof ^D   NVT-mode EOF character
erase ^H   NVT-mode erase character
extended True   Use 3270 extended data stream
eventTrace False -trace Event tracing
hostsFile   -hostsfile Host alias/macro file
icrnl False   Map CR to NL on NVT-mode input
inlcr False   Map NL to CR in NVT-mode input
intr ^C   NVT-mode interrupt character
keymap   -keymap Keyboard map name
keymap.foo     Definition of keymap foo
kill ^U   NVT-mode kill character
lineWrap False -set lineWrap NVT line wrap mode
lnext ^V   NVT-mode lnext character
m3279 (note 1) -model 3279 (color) emulation
metaEscape Auto   Interpret ESC-x as Meta-x
mono (note 5) -mono Ignore terminal color capabilities
monoCase False -set monoCase Mono-case mode
noPrompt False -noprompt Disable command-prompt mode
numericLock False   Lock keyboard for numeric field error
oerrLock True   Lock keyboard for input error
oversize   -oversize Oversize screen dimensions
port telnet -port Non-default TCP port
printer.* (note 4)   Printer session config
printerLu (note 4)   Printer session config
quit ^\   NVT-mode quit character
reconnect False -reconnect Automatically reconnect to host
rprnt ^R   NVT-mode reprint character
sbcsCgcsgid     Override SBCS CGCSGID
secure False   Disable "dangerous" options
termName (note 2) -tn TELNET terminal type string
traceDir /tmp   Directory for trace files
traceFile (note 3) -tracefile File for trace output
typeahead True   Allow typeahead
werase ^W   NVT-mode word-erase character

Note 1: m3279 defaults to True if the terminal supports color, False otherwise. It can be forced to False with the proper -model option.

Note 2: The default terminal type string is constructed from the model number, color emulation, and extended data stream modes. E.g., a model 2 with color emulation and the extended data stream option would be sent as IBM-3279-2-E. Note also that when TN3270E mode is used, the terminal type is always sent as 3278, but this does not affect color capabilities.

Note 3: The default trace file is x3trc.pid in the directory specified by the traceDir resource.

Note 4: See PRINTER SUPPORT for details.

Note 5: mono defaults to false if the terminal supports at least 8 colors and to true otherwise.

Note 6: The default curses color mappings for host colors 0 through 15 are: black, blue, red, magenta, green, cyan, yellow, white, black, blue, yellow, blue, green, cyan, black and white.

In .c3270pro, lines are continued with a backslash character.

-xrm options override definitions found in .c3270pro. If more than one -xrm option is given for the same resource, the last one on the command line is used.



See Also

pr3287(1), s3270(1), x3270-script(1), x3270(1), tcl3270(1), telnet(1), tn3270(1)
Data Stream Programmer's Reference, IBM GA23-0059
Character Set Reference, IBM GA27-3831
RFC 1576, TN3270 Current Practices
RFC 1646, TN3270 Extensions for LUname and Printer Selection
RFC 2355, TN3270 Enhancements


Copyright 1993-2017, Paul Mattes.
Copyright 2004-2005, Don Russell.
Copyright 2004, Dick Altenbern.
Copyright 1990, Jeff Sparkes.
Copyright 1989, Georgia Tech Research Corporation (GTRC), Atlanta, GA
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:


Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.


Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.


Neither the names of Paul Mattes, Don Russell, Dick Altenbern, Jeff Sparkes, GTRC nor the names of their contributors may be used to endorse or promote products derived from this software without specific prior written permission.



c3270 3.5ga10

Referenced By

ibm_hosts(5), pr3287(1), s3270(1), x3270(1), x3270if(1), x3270-script(1).

16 January 2017