--- name: "cu" section: "1" platform: "freebsd" package: "base" version: "16.0-CURRENT-20261027-61c70dc16a79" release: "FreeBSD 16.0-CURRENT (2026-10-27)" platforms: ["linux", "freebsd", "openbsd", "macos"] url: "https://new.carta.tech/cu" --- # cu(1) call UNIX over a serial line ## NAME **cu** – call UNIX over a serial line ## SYNOPSIS **cu** \[**-ehot**\] \[**-a** *acu*\] \[**-l** *line*\] \[**-s** *speed* \| **-***speed*\] \[*phone-number*\] ## DESCRIPTION The **cu** utility establishes a full-duplex connection to another machine, giving the appearance of being logged in directly on the remote CPU. It goes without saying that you must have a login on the machine (or equivalent) to which you wish to connect. The options are as follows: - **-a** *acu* Set the acu. - **-e** Use even parity. If both **-e** and **-o** are given, then no parity is used (the default). - **-h** Echo characters locally (half-duplex mode). - **-l** *line* Specify the line to use. Either of the forms like *cuau0* or */dev/cuau0* are permitted. - **-o** Use odd parity. If both **-e** and **-o** are given, then no parity is used (the default). - **-s** *speed* \| **-***speed* Set the speed of the connection. The default is 9600. - **-t** Connect via a hard-wired connection to a host on a dial-up line. Typed characters are normally transmitted directly to the remote machine (which does the echoing as well). A tilde (‘~’) appearing as the first character of a line is an escape signal; the following are recognized: - **~^D** or **~.** Drop the connection and exit. Only the connection is dropped – the login session is not terminated. - **~c** \[*name*\] Change directory to *name* (no argument implies change to home directory). - **~!** Escape to a shell (exiting the shell will return to **cu**). - **~\>** Copy file from local to remote. The **cu** utility prompts for the name of a local file to transmit. - **~\<** Copy file from remote to local. The **cu** utility prompts first for the name of the file to be sent, then for a command to be executed on the remote machine. - **~p** *from* \[*to*\] Send a file to a remote UNIX host. This command causes the remote UNIX system to run the following command string, sending it the *from* file: ``` stty -echo; cat > 'to'; stty echo ``` If the *to* file is not specified, the *from* file name is used. This command is actually a UNIX specific version of the **~\>** command. - **~t** *from* \[*to*\] Take a file from a remote UNIX host. As in the **~p** command, the *to* file defaults to the *from* file name if it is not specified. The remote host executes the following command string to send the file to **cu**: ``` cat 'from'; echo '' | tr '\012' '\01' ``` - **~\|** Pipe the output from a remote command to a local UNIX process. The command string sent to the local UNIX system is processed by the shell. - **~$** Pipe the output from a local UNIX process to the remote host. The command string sent to the local UNIX system is processed by the shell. - **~C** Fork a child process on the local system to perform special protocols such as XMODEM. The child program will be run with the following arrangement of file descriptors: ``` 0 <-> remote tty in 1 <-> remote tty out 2 <-> local tty stderr ``` - **~#** Send a BREAK to the remote system. For systems which do not support the necessary **ioctl**() call, the break is simulated by a sequence of line speed changes and DEL characters. - **~s** Set a variable (see the discussion below). - **~v** List all variables and their values (if set). - **~^Z** Stop **cu** (only available with job control). - **~^Y** Stop only the “local side” of **cu** (only available with job control); the “remote side” of **cu**, the side that displays output from the remote host, is left running. - **~?** Get a summary of the tilde escapes. When **cu** prompts for an argument, for example during setup of a file transfer, the line typed may be edited with the standard erase and kill characters. A null line in response to a prompt, or an interrupt, will abort the dialogue and return the user to the remote machine. The **cu** utility guards against multiple users connecting to a remote system by opening modems and terminal lines with exclusive access, and by honoring the locking protocol used by [uucico(8)](/uucico/8.md) (*ports/net/freebsd-uucp*). During file transfers **cu** provides a running count of the number of lines transferred. When using the **~\>** and **~\<** commands, the *eofread* and *eofwrite* variables are used to recognize end-of-file when reading, and specify end-of-file when writing (see below). File transfers normally depend on hardwareflow or tandem mode for flow control. If the remote system does not support hardwareflow or tandem mode, *echocheck* may be set to indicate that **cu** should synchronize with the remote system on the echo of each transmitted character. When **cu** must dial a phone number to connect to a system, it will print various messages indicating its actions. The **cu** utility supports a variety of auto-call units and modems with the *at* capability in system descriptions. Support for Ventel 212+ (ventel), Hayes AT-style (hayes), USRobotics Courier (courier), Telebit T3000 (t3000) and Racal-Vadic 831 (vadic) units is enabled by default. Support for Bizcomp 1031\[fw\] (biz31\[fw\]), Bizcomp 1022\[fw\] (biz22\[fw\]), DEC DF0\[23\]-AC (df0\[23\]), DEC DN-11 (dn11) and Racal-Vadic 3451 (v3451) units can be added by recompiling **cu** with the appropriate defines. Note that if support for both the Racal-Vadic 831 and 3451 is enabled, they are referred to as the v831 and v3451, respectively. If only one of the two is supported, it is referred to as vadic. ### Variables The **cu** utility maintains a set of variables which control its operation. Some of these variables are read-only to normal users (root is allowed to change anything of interest). Variables may be displayed and set through the **~s** escape. The syntax for variables is patterned after [vi(1)](/vi/1.md) and [Mail(1)](/Mail/1.md). Supplying “all” as an argument to the set command displays all variables readable by the user. Alternatively, the user may request display of a particular variable by attaching a ‘?’ to the end. For example, “escape?” displays the current escape character. Variables are numeric, string, character, or boolean values. Boolean variables are set merely by specifying their name; they may be reset by prepending a ‘!’ to the name. Other variable types are set by concatenating an ‘=’ and the value. The entire assignment must not have any blanks in it. A single set command may be used to interrogate as well as set a number of variables. Certain common variables have abbreviations. The following is a list of common variables, their abbreviations, and their default values: - *baudrate* (*num*) The baud rate at which the connection was established; abbreviated *ba*. - *beautify* (*bool*) Discard unprintable characters when a session is being scripted; abbreviated *be*. - *dialtimeout* (*num*) When dialing a phone number, the time (in seconds) to wait for a connection to be established; abbreviated *dial*. - *echocheck* (*bool*) Synchronize with the remote host during file transfer by waiting for the echo of the last character transmitted; default is **off**. - *eofread* (*str*) The set of characters which signify an end-of-transmission during a **~\<** file transfer command; abbreviated *eofr*. - *eofwrite* (*str*) The string sent to indicate end-of-transmission during a **~\>** file transfer command; abbreviated *eofw*. - *eol* (*str*) The set of characters which indicate an end-of-line. The **cu** utility will recognize escape characters only after an end-of-line. - *escape* (*char*) The command prefix (escape) character; abbreviated *es*; default value is ‘~’. - *exceptions* (*str*) The set of characters which should not be discarded due to the beautification switch; abbreviated *ex*; default value is “\\t\\n\\f\\b”. - *force* (*char*) The character used to force literal data transmission; abbreviated *fo*; default value is ‘^P’. - *framesize* (*num*) The amount of data (in bytes) to buffer between file system writes when receiving files; abbreviated *fr*. - *hardwareflow* (*bool*) Whether hardware flow control (CRTSCTS) is enabled for the connection; abbreviated *hf*; default value is **off**. - *host* (*str*) The name of the host to which you are connected; abbreviated *ho*. - *linedisc* (*num*) The line discipline to use; abbreviated *ld*. - *prompt* (*char*) The character which indicates an end-of-line on the remote host; abbreviated *pr*; default value is ‘\\n’. This value is used to synchronize during data transfers. The count of lines transferred during a file transfer command is based on receipt of this character. - *raise* (*bool*) Upper case mapping mode; abbreviated *ra*; default value is **off**. When this mode is enabled, all lowercase letters will be mapped to uppercase by **cu** for transmission to the remote machine. - *raisechar* (*char*) The input character used to toggle uppercase mapping mode; abbreviated *rc*; not set by default. - *record* (*str*) The name of the file in which a session script is recorded; abbreviated *rec*. - *script* (*bool*) Session scripting mode; abbreviated *sc*; default is **off**. When *script* is **true**, **cu** will record everything transmitted by the remote machine in the script record file specified in *record*. If the *beautify* switch is on, only printable ASCII characters will be included in the script file (those characters between 040 and 0177). The variable *exceptions* is used to indicate characters which are an exception to the normal beautification rules. - *tabexpand* (*bool*) Expand tabs to spaces during file transfers; abbreviated *tab*; default value is **false**. Each tab is expanded to 8 spaces. - *tandem* (*bool*) Use XON/XOFF flow control to throttle data from the remote host; abbreviated *ta*. The default value is **true**. - *verbose* (*bool*) Verbose mode; abbreviated *verb*; default is **true**. When verbose mode is enabled, **cu** prints messages while dialing, shows the current number of lines transferred during a file transfer operations, and more. ## ENVIRONMENT - HOME The home directory to use for the **~c** command. - SHELL The name of the shell to use for the **~!** command; default value is “/bin/sh”. ## FILES - */var/log/aculog* line access log - */var/spool/lock/LCK..\** lock file to avoid conflicts with [uucp(1)](/uucp/1.md) (*ports/net/freebsd-uucp*) ## EXAMPLES Connect to the first USB serial port at the speed of 115200 baud: ``` cu -s 115200 -l /dev/cuaU0 ``` ## SEE ALSO [tip(1)](/tip/1.md) ## HISTORY The **cu** command appeared in 4.2BSD. ## BUGS The full set of variables is undocumented and should, probably, be pared down.