Termios For Windows
Name
Termius is more than a mere SSH client – it’s a complete command-line solution that’s redefining remote access for sysadmins and network engineers. Securely access Linux or IoT devices and quickly fix issues from the comfort of your couch via laptop or phone. Generated: 2020-12-23 20:33:13 UTC. Generated: 2020-12-23 20:33:13 UTC. X-Windows sends key presses and releases. You can write X-Windows or Tk/Xyzzy code instead of using an xterm. That would require writing a complete GUI application. I hope you realize this is several orders of magnitude more work than an application running in a terminal. Cfgetispeed returns the input baud rate stored in the termios structure. Cfsetispeed sets the input baud rate stored in the termios structure to speed, which must be specified as one of the Bnnn constants listed above for cfsetospeed. If the input baud rate is set to zero. (no)tty - If set, Cygwin enabled extra support (i.e., termios) for UNIX-like ttys in the Windows console. This option has been removed because it can be easily replaced by using a terminal like mintty, and it does not work well with some Windows programs. (no)upcaseenv - This option could be used to convert all environment variables to. Termius for Windows. Version 7.3.2 - Released 28 December, 2020. Launched Group Sharing 2.0 introducing new features for Termius for Teams.
termios, tcgetattr, tcsetattr, tcsendbreak, tcdrain, tcflush, tcflow, cfmakeraw, cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfsetspeed - get andset terminal attributes, line control, get and set baud rate
Synopsis
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):In the descriptions below, 'not in POSIX' means that the value is not specified in POSIX.1-2001, and 'XSI' means that the value is specified in POSIX.1-2001as part of the XSI extension.
c_iflag flag constants:
IGNBRKIgnore BREAK condition on input.
BRKINT
If IGNBRK is set, a BREAK is ignored. If it is not set but BRKINT is set, then a BREAK causes the input and output queues to be flushed, andif the terminal is the controlling terminal of a foreground process group, it will cause a SIGINT to be sent to this foreground process group. Whenneither IGNBRK nor BRKINT are set, a BREAK reads as a null byte ('0'), except when PARMRK is set, in which case it reads as the sequence377 0 0.
IGNPAR
Ignore framing errors and parity errors.
PARMRK
If IGNPAR is not set, prefix a character with a parity error or framing error with 377 0. If neither IGNPAR nor PARMRK is set, read acharacter with a parity error or framing error as 0.
INPCK
Enable input parity checking.
ISTRIP
Strip off eighth bit.
INLCR
Translate NL to CR on input.
IGNCR
Ignore carriage return on input.
ICRNL
Translate carriage return to newline on input (unless IGNCR is set).
IUCLC
(not in POSIX) Map uppercase characters to lowercase on input.
IXON
Enable XON/XOFF flow control on output.
IXANY
(XSI) Typing any character will restart stopped output. (The default is to allow just the START character to restart output.)
IXOFF
Enable XON/XOFF flow control on input.
Enable implementation-defined output processing.
(not in POSIX) Map lowercase characters to uppercase on output.
ONLCR
(XSI) Map NL to CR-NL on output.
OCRNL
Map CR to NL on output.
ONOCR
Don't output CR at column 0.
ONLRET
Don't output CR.
OFILL
Send fill characters for a delay, rather than using a timed delay.
OFDEL
(not in POSIX) Fill character is ASCII DEL (0177). If unset, fill character is ASCII NUL ('0'). (Not implemented on Linux.)
NLDLY
Newline delay mask. Values are NL0 and NL1. [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
CRDLY
Carriage return delay mask. Values are CR0, CR1, CR2, or CR3. [requires _BSD_SOURCE or _SVID_SOURCE or_XOPEN_SOURCE]
TABDLY
Horizontal tab delay mask. Values are TAB0, TAB1, TAB2, TAB3 (or XTABS). A value of TAB3, that is, XTABS, expands tabs tospaces (with tab stops every eight columns). [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
BSDLY
Backspace delay mask. Values are BS0 or BS1. (Has never been implemented.) [requires _BSD_SOURCE or _SVID_SOURCE or_XOPEN_SOURCE]
VTDLY
Vertical tab delay mask. Values are VT0 or VT1.
FFDLY
Form feed delay mask. Values are FF0 or FF1. [requires _BSD_SOURCE or _SVID_SOURCE or _XOPEN_SOURCE]
(not in POSIX) Baud speed mask (4+1 bits). [requires _BSD_SOURCE or _SVID_SOURCE]
(POSIX says that the baud speed is stored in the termios structure without specifying where precisely, and provides cfgetispeed() andcfsetispeed() for getting at it. Some systems use bits selected by CBAUD in c_cflag, other systems use separate fields, for example,sg_ispeed and sg_ospeed.)
CSIZECharacter size mask. Values are CS5, CS6, CS7, or CS8.
CSTOPB
Set two stop bits, rather than one.
CREAD
Enable receiver.
PARENB
Enable parity generation on output and parity checking for input.
PARODD
If set, then parity for input and output is odd; otherwise even parity is used.
HUPCL
Lower modem control lines after last process closes the device (hang up).
CLOCAL
Ignore modem control lines.
LOBLK
(not in POSIX) Block output from a noncurrent shell layer. For use by shl (shell layers). (Not implemented on Linux.)
CIBAUD
(not in POSIX) Mask for input speeds. The values for the CIBAUD bits are the same as the values for the CBAUD bits, shifted leftIBSHIFT bits. [requires _BSD_SOURCE or _SVID_SOURCE] (Not implemented on Linux.)
CMSPAR
(not in POSIX) Use 'stick' (mark/space) parity (supported on certain serial devices): if PARODD is set, the parity bit is always 1; if PARODDis not set, then the parity bit is always 0). [requires _BSD_SOURCE or _SVID_SOURCE]
When any of the characters INTR, QUIT, SUSP, or DSUSP are received, generate the corresponding signal.
ICANON
Enable canonical mode (described below).
XCASE
(not in POSIX; not supported under Linux) If ICANON is also set, terminal is uppercase only. Input is converted to lowercase, except for characterspreceded by . On output, uppercase characters are preceded by and lowercase characters are converted to uppercase. [requires _BSD_SOURCE or _SVID_SOURCE or_XOPEN_SOURCE]
ECHO
Echo input characters.
ECHOE
If ICANON is also set, the ERASE character erases the preceding input character, and WERASE erases the preceding word.
ECHOK
If ICANON is also set, the KILL character erases the current line.
ECHONL
If ICANON is also set, echo the NL character even if ECHO is not set.
(not in POSIX) If ICANON is also set, KILL is echoed by erasing each character on the line, as specified by ECHOE and ECHOPRT.[requires _BSD_SOURCE or _SVID_SOURCE]
(not in POSIX; not supported under Linux) Output is being flushed. This flag is toggled by typing the DISCARD character. [requires _BSD_SOURCE or_SVID_SOURCE]
NOFLSH
Disable flushing the input and output queues when generating signals for the INT, QUIT, and SUSP characters.
TOSTOP
Send the SIGTTOU signal to the process group of a background process which tries to write to its controlling terminal.
PENDIN
(not in POSIX; not supported under Linux) All characters in the input queue are reprinted when the next character is read. (bash(1) handles typeaheadthis way.) [requires _BSD_SOURCE or _SVID_SOURCE]
IEXTEN
Enable implementation-defined input processing. This flag, as well as ICANON must be enabled for the special characters EOL2, LNEXT, REPRINT, WERASEto be interpreted, and for the IUCLC flag to be effective.
(not in POSIX; not supported under Linux; 031, EM, Ctrl-Y) Delayed suspend character (DSUSP): send SIGTSTP signal when the character is read by theuser program. Recognized when IEXTEN and ISIG are set, and the system supports job control, and then not passed as input.
VEOF
(004, EOT, Ctrl-D) End-of-file character (EOF). More precisely: this character causes the pending tty buffer to be sent to the waiting user program withoutwaiting for end-of-line. If it is the first character of the line, the read(2) in the user program returns 0, which signifies end-of-file. Recognizedwhen ICANON is set, and then not passed as input.
VEOL
(0, NUL) Additional end-of-line character (EOL). Recognized when ICANON is set.
VEOL2
(not in POSIX; 0, NUL) Yet another end-of-line character (EOL2). Recognized when ICANON is set.
VERASE
(0177, DEL, rubout, or 010, BS, Ctrl-H, or also #) Erase character (ERASE). This erases the previous not-yet-erased character, but does not erase past EOFor beginning-of-line. Recognized when ICANON is set, and then not passed as input.
VINTR
(003, ETX, Ctrl-C, or also 0177, DEL, rubout) Interrupt character (INTR). Send a SIGINT signal. Recognized when ISIG is set, and then notpassed as input.
VKILL
(025, NAK, Ctrl-U, or Ctrl-X, or also @) Kill character (KILL). This erases the input since the last EOF or beginning-of-line. Recognized when ICANONis set, and then not passed as input.
VLNEXT
(not in POSIX; 026, SYN, Ctrl-V) Literal next (LNEXT). Quotes the next input character, depriving it of a possible special meaning. Recognized whenIEXTEN is set, and then not passed as input.
VMIN
Minimum number of characters for noncanonical read (MIN).
VQUIT
(034, FS, Ctrl-) Quit character (QUIT). Send SIGQUIT signal. Recognized when ISIG is set, and then not passed as input.
(021, DC1, Ctrl-Q) Start character (START). Restarts output stopped by the Stop character. Recognized when IXON is set, and then not passed asinput.
(023, DC3, Ctrl-S) Stop character (STOP). Stop output until Start character typed. Recognized when IXON is set, and then not passed as input.
VSUSP
(032, SUB, Ctrl-Z) Suspend character (SUSP). Send SIGTSTP signal. Recognized when ISIG is set, and then not passed as input.
VSWTCH
(not in POSIX; not supported under Linux; 0, NUL) Switch character (SWTCH). Used in System V to switch shells in shell layers, a predecessor to shelljob control.
VTIME
Timeout in deciseconds for noncanonical read (TIME).
The above symbolic subscript values are all different, except that VTIME, VMIN may have the same value as VEOL, VEOF,respectively. In noncanonical mode the special character meaning is replaced by the timeout meaning. For an explanation of VMIN and VTIME, seethe description of noncanonical mode below.
Retrieving and changing terminal settings
tcgetattr() gets the parameters associated with the object referred by fd and stores them in the termios structure referenced bytermios_p. This function may be invoked from a background process; however, the terminal attributes may be subsequently changed by a foreground process.tcsetattr() sets the parameters associated with the terminal (unless support is required from the underlying hardware that is not available) from thetermios structure referred to by termios_p. optional_actions specifies when the changes take effect:
Canonical and noncanonical mode
The setting of the ICANON canon flag in c_lflag determines whether the terminal is operating in canonical mode (ICANON set) ornoncanonical mode (ICANON unset). By default, ICANON set.In canonical mode:
*Input is made available line by line. An input line is available when one of the line delimiters is typed (NL, EOL, EOL2; or EOF at the start of line).Except in the case of EOF, the line delimiter is included in the buffer returned by read(2).
*
Line editing is enabled (ERASE, KILL; and if the IEXTEN flag is set: WERASE, REPRINT, LNEXT). A read(2) returns at most one line of input; ifthe read(2) requested fewer bytes than are available in the current line of input, then only as many bytes as requested are read, and the remainingcharacters will be available for a future read(2).
MIN 0; TIME 0: If data is available, read(2) returns immediately, with the lesser of the number of bytes available, or the number of bytesrequested. If no data is available, read(2) returns 0.
*
MIN > 0; TIME 0: read(2) blocks until the lesser of MIN bytes or the number of bytes requested are available, and returns the lesser of thesetwo values.
*
MIN 0; TIME > 0: TIME specifies the limit for a timer in tenths of a second. The timer is started when read(2) is called. read(2)returns either when at least one byte of data is available, or when the timer expires. If the timer expires without any input becoming available,read(2) returns 0.
*
MIN > 0; TIME > 0: TIME specifies the limit for a timer in tenths of a second. Once an initial byte of input becomes available, the timer is restartedafter each further byte is received. read(2) returns either when the lesser of the number of bytes requested or MIN byte have been read, or when theinter-byte timeout expires. Because the timer is only started after the initial byte becomes available, at least one byte will be read.
Raw mode
Line control
tcsendbreak() transmits a continuous stream of zero-valued bits for a specific duration, if the terminal is using asynchronous serial datatransmission. If duration is zero, it transmits zero-valued bits for at least 0.25 seconds, and not more that 0.5 seconds. If duration is notzero, it sends zero-valued bits for some implementation-defined length of time.If the terminal is not using asynchronous serial data transmission, tcsendbreak() returns without taking any action.
tcdrain() waits until all output written to the object referred to by fd has been transmitted.
tcflush() discards data written to the object referred to by fd but not transmitted, or data received but not read, depending on the value ofqueue_selector:
suspends output.
TCOON
restarts suspended output.
TCIOFF
transmits a STOP character, which stops the terminal device from transmitting data to the system.
TCION
transmits a START character, which starts the terminal device transmitting data to the system.
Line speed
The baud rate functions are provided for getting and setting the values of the input and output baud rates in the termios structure. The new valuesdo not take effect until tcsetattr() is successfully called.Setting the speed to B0 instructs the modem to 'hang up'. The actual bit rate corresponding to B38400 may be altered with setserial(8).
The input and output baud rates are stored in the termios structure.
cfgetospeed() returns the output baud rate stored in the termios structure pointed to by termios_p.
cfsetospeed() sets the output baud rate stored in the termios structure pointed to by termios_p to speed, which must be one ofthese constants:
B0B50
B75
B110
B134
B150
B200
B300
B600
B1200
B1800
B2400
B4800
B9600
B19200
B38400
B57600
B115200
B230400
The zero baud rate, B0, is used to terminate the connection. If B0 is specified, the modem control lines shall no longer be asserted. Normally, thiswill disconnect the line. CBAUDEXTerminus Download For Windows 10
is a mask for the speeds beyond those defined in POSIX.1 (57600 and above). Thus, B57600 & CBAUDEXis nonzero.cfgetispeed() returns the input baud rate stored in the termios structure.
cfsetispeed() sets the input baud rate stored in the termios structure to speed, which must be specified as one of the Bnnnconstants listed above for cfsetospeed(). If the input baud rate is set to zero, the input baud rate will be equal to the output baud rate.
cfsetspeed() is a 4.4BSD extension. It takes the same arguments as cfsetispeed(), and sets both input and output speed.
Return Value
cfgetispeed() returns the input baud rate stored in the termios structure.
cfgetospeed() returns the output baud rate stored in the termios structure.
All other functions return:
0on success.
-1
on failure and set errno to indicate the error.
Conforming To
tcgetattr(), tcsetattr(), tcsendbreak(), tcdrain(), tcflush(), tcflow(), cfgetispeed(),cfgetospeed(), cfsetispeed(), and cfsetospeed() are specified in POSIX.1-2001.
cfmakeraw() and cfsetspeed() are nonstandard, but available on the BSDs.
Notes
UNIX V7 and several later systems have a list of baud rates where after the fourteen values B0, .., B9600 one finds the two constants EXTA, EXTB ('ExternalA' and 'External B'). Many systems extend the list with much higher baud rates.
The effect of a nonzero duration with tcsendbreak() varies. SunOS specifies a break of duration * N seconds, where N is at least0.25, and not more than 0.5. Linux, AIX, DU, Tru64 send a break of duration milliseconds. FreeBSD and NetBSD and HP-UX and MacOS ignore the value ofduration. Under Solaris and UnixWare, tcsendbreak() with nonzero duration behaves like tcdrain().
See Also
stty(1), console_ioctl(4), tty_ioctl(4), setserial(8)
Referenced By
exit(2),getpass(3),perlopentut(1),pty(7),setpgrp(2),stdin(3),termio(7),tty(4)(This is part two of a multi-part introduction to termios and terminalemulation on UNIX. Read part 1 if you’re new here)
In this entry, we’ll look at the interfaces that are used to controlthe behavior of the “termios” box sitting between the master andslave pty. The behaviors I described last time are fine if you have acompletely dumb program talking to the terminal, but if the programover on the right is using curses (like emacs or vim), or even justreadline (like bash), it will want to disable or customize some of thebehaviors.
The primary programmatic interface to termios is the struct termiosand two functions:
which retrieve and set the struct termios associated with a given terminal device.They are all documented in termios(3) (If you’reunfamiliar with the convention, that means document termios in section3 of the unix man pages – man 3 termios on a command-line willget it for you).
So what’s inside struct termios? POSIXspecifies that this structure contains at least the following fields:
Each “flag” field contains a number of flags (implemented as a bitmask) that can be individually enabled or disabled.c_iflag and c_oflag contain flags that affect the processingof input and output, respectively. c_cflag we will mostly ignore, asit contains settings that relate to the control of modems and seriallines that are mostly irrelevant these days. c_lflag is perhaps the most interesting of the flag values. Itcontains flags that control the broad-scale behavior of thetty. I’ll look at just a few of the interesting bits in each:
local modes 🔗︎
ICANON- Perhaps the most important bit inc_lflagis theICANONbit. Enabling it enables “canonical” mode – also known as“line editing” mode. WhenICANONis set, the terminal buffers a lineat a time, and enables line editing. WithoutICANON, input is madeavailable to programs immediately (this is also known as “cbreak”mode).ECHOinc_lflagcontrols whether input is immediately re-echoed asoutput. It is independent ofICANON, although they are often turned on and off together. Whenpasswdprompts for your password, your terminal is in canonical mode, butECHOis disabled.ISIGinc_lflagcontrols whether^Cand^Z(and friends) generate signals ornot. When unset, they are passed directly through as characters,without generating signals to the application.
input and output modes 🔗︎
There are also a few flags in c_iflag and c_oflag worth mentioning.
IXONinc_iflagenables the “flow control” mediated by^Sand^Q(by default). WithIXON, once^Shas been receivedby the master pty, the slave will not accept any output (writes to it will hang) until^Qis received by the master pty.IUTF8inc_iflagis an interesting hack. In canonical mode, backspace needs todelete the previous character in the input buffer. In non-ASCII encodings, a single character may be several bytes long, but the terminal still only sees a byte stream, and has no explicit information about the encoding or character boundaries on either end.IUTF8tells termios that the input stream is utf-8 encoded, which permits thecorrect handling of backspace. IfIUTF8is unset, and you enter amultibyte character and then press backspace, only the final byte willbe deleted, leaving you with a corrupt utf-8 stream.OLCUCinc_oflag“Map[s] lowercase characters to uppercase onoutput.” Just in CASE YOU NEED YOUR TERMINAL TO LOOK MORE LIKESHOUTING.
There are many more flags, controlling such details as newline translation and how character erase works. The full list is documented in termios(3).
c_cc 🔗︎
Next up is c_cc. This field sets the various control characters used to interact with theterminal. Characters like ^C and ^Z and delete that have special meanings to termios are not hard coded anywhere, but rather defined via the c_cc array.
c_cc is indexed by various constants for the various control characters, andthe value at any index is the character that should have that effect. Some of the notable ones are:
VINTR– Generate aSIGINT(^Cby default).VSUSP– Generate aSIGTSTP(stop the program) (^Zby default).VERASE– Erase the previous character. This tends to be one of^Hand^?(ASCII0x7f) by default – if you’ve ever pressed“backspace” and been greeted by a^H, your terminal and yourstruct termiosdisagree on the value ofVERASE.VEOF– End of file. Sends the current line to the programwithout waiting for end-of-line, or, as the first character on the line, causes the nextreadcall by the slave to return return end-of-file. (^Dby default)VSTOPandVSTART–^Sand^Qby default, stop and startoutput.
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Setting any of these to NULL (0) disables that special control character. Many of the c_cc elements are only relevant when certain modes are active – VINTR and VSUSP, for instance, only matter if ISIG is enabled in c_lflag, and VSTOP and VSTART are ignored unless IXON is set.
(A brief note on the representation of control characters – The characters ^A through ^Z, pronounced “Ctrl-FOO”, are represented by the bytes with values 1 through 26. So when I say that c_cc[VINTR] is equal to ^C by default,that’s actually just the number 3 – your terminal took the keypresses and just translated them into the byte 3 on the wire.)
stty 🔗︎
While termios(3) is the standard programmatic interface to controltermios, a much more convenient interface for experimentation is thestty program, which is just a thin wrapper around tcgetattr andtcsetattr designed to be usable from shell scripts or directly from the shell.
stty gets or sets options on a terminal device. By default, it operates on the one connected to its standard out, but you can pass it an arbitrary device using the -F option.
Without aguments, stty prints in what way its terminal’s settings differ from an internal set of “sane”defaults. stty -a causes it to print the value of every flag in thestruct termios in a human-readable format.
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You can toggle flags using stty flag to enable a flag, and stty-flag to disable it. So for instance, stty -isig will disablesignal generation – run a program after doing this, and you’ll findyourself unable to ^C it. In general it uses the same names as the C constants, except in lowercase, but check the man page if in doubt.
stty can also change the value of the control characters inc_cc, using stty symbolic-namecharacter. If you wanted ^G to be the interrupt character, instead of ^C, a simple stty intr ^G would suffice. You can spell 0 as undef to disable a given control character. So, if you hate flowcontrol and want to totally disable it, you could try stty -ixon stop undef – disable IXON, and then also disable the VSTOPcharacter for good measure. (You might still be foiled by screen or some other layer doing its own flow control, unfortunately).
stty's -F/ati-es1000-windows-10.html. option can be great for peeking at what some other program isdoing to its terminal. If you run tty in a shell, it will print thepath to that shell’s terminal device (usually of the form/dev/pts/N, at least under Linux). Now,from a different shell, you can run stty -a -F /dev/pts/N to see howthe first shell’s terminal is configured. You can then run programsin the first shell, and repeat the stty incant in shell two to seewhat settings are getting set. For example, if I run stty -F /dev/pts/10 right now (while I have a bash talking to a gnome-terminal via that pty), I see:
So we can see that bash/readline has disabled CR→LF translation on input (icrnl), disabled canonical mode and echo, but turned on UTF-8 mode (because bash detected a utf-8 locale). Note that if I run stty directly in that shell, I see something slightly different:
This is because bash maintains its own set of termios settings (for readline), and saves and restores settings around running programs, so that settings in place while running a program are different from those in place while you’re typing at the bash prompt.
In the next post, we’ll look at signal generation from ISIG and how it interacts with job control in your shell.
Addendum: ioctl(2) 🔗︎
This last section is a brief aside, which has very little to do with termios specifically, so you should feel free to skip it. But read on if you’re curious about some of the low-level details of how the APIs work.
Terminux Windows
If you’re familiar with man page conventions, you may have noticedthat the termios functions are in man page section 3, which meansthat they’re provided by system libraries, and are not systemcalls. But at the same time, I told you last time that termios isimplemented inside the kernel – so how are the libraries talking tothe kernel, if not through syscalls?
The answer is a single odd little catch-all system call, known asioctl. Historically, one of the “big ideas” of UNIX was that“everything is a file” – you could communicate with devices just likeyou could files, by opening files in /dev/. But a file on UNIX is also just a stream of bytes, without anyOS-imposed structure. And for a device, you may often need to sendout-of-band control data – e.g. to set the baud and parity bit settings on aserial port. And adding new system calls for every new device type wouldbe untenable for a number of reasons.
So the answer was one new new system call, ioctl (pronounced as anyof “I-O-cuddle”, “I-octal” or “I-O-C-T-L”). ioctl is prototyped as:
It takes a file descriptor, a numeric “request” code, and an unspecified number ofother arguments. ioctl looks up whatever device (or filesystem, network protcol, or whatever) is backing that file descriptor, and hands it the “request” and the argumentsto do with as they will.
So any device that needs extra control channels can define some ioctl numbers and parameters and document them somewhere, and they become the interface to control that device. So, for instance (at least on Linux), an ioctl on a tty device with a “request” of TCGETS (defined in termios.h) takes a parameter that is a pointer to a struct termios, and copies the in-kernel settings for that tty to the provided struct. So somewhere in libc, tcgetattr(fd, p) is just defined to do an ioctl(fd, TCGETS, p). Similar ioctls are defined for tcsetattr and all the functions in termios(3). On Linux, at least, the morbidly curious can find out all the gory details in tty_ioctl(4).