What do pty and tty mean

Question

I noticed many mentions of pty and tty in some open source projects  could someone tell me what do they mean and what is the difference between them

User · Answer

A tty is a terminal  it stands for teletype - the original terminals used a line printer for output and a keyboard for input     A terminal is a basically just a user interface device that uses text for input and output   A pty is a pseudo-terminal - it s a software implementation that appears to the attached program like a terminal  but instead of communicating directly with a  real  terminal  it transfers the input and output to another program   For example  when you ssh in to a machine and run ls  the ls command is sending its output to a pseudo-terminal  the other side of which is attached to the SSH daemon

User · Answer

tty  originally meant  teletype  and  pty  means  pseudo-teletype    In UNIX   dev tty  is any device that acts like a  teletype   ie  a terminal    Called teletype because that s what we had for terminals in those benighted days    A pty is a pseudotty  a device entry that acts like a terminal to the process reading and writing there  but is managed by something else  They first appeared  as I recall  for X Window and screen and the like  where you needed something that acted like a terminal but could be used from another program

User · Answer

A tty is a physical terminal-teletype port on a computer  usually a serial port    The word teletype is a shorting of the telegraph typewriter  or teletypewriter device from the 1930s - itself an electromagnetic device which replaced the telegraph encoding machines of the 1830s and 1840s    TTY - Teletypewriter 1930s  A pty is a pseudo-teletype port provided by a computer Operating System Kernel to connect software programs emulating terminals  such as ssh  xterm  or screen    PTY - PseudoTeletype  A terminal is simply a computer s user interface that uses text for input and output       OS Implementations  These use pseudo-teletype ports however  their naming and implementations have diverged a little     Linux mounts a special file system devpts on  dev  the  s  presumably standing for serial  that creates a corresponding entry in  dev pts for every new terminal window you open  e g   dev pts 0   macOS FreeBSD also use the  dev file structure however  they use a numbered TTY naming convention ttys for every new terminal window you open e g   dev ttys002   Microsoft Windows still has the concept of an LPT port for Line Printer Terminals within it s Command Shell for output to a printer

User · Answer

If you run the mount command with no command-line arguments  which displays the file systems mounted on your system  you   ll notice a line that looks something like this  none on  dev pts type devpts  rw gid 5 mode 620  This indicates that a special type of file system  devpts   is mounted at  dev pts  This file system  which isn   t associated with any hardware device  is a    magic    file system that is created by the Linux kernel  It   s similar to the  proc file system  Like the  dev directory   dev pts contains entries corresponding to devices  But unlike  dev   which is an ordinary directory   dev pts is a special directory that is cre- ated dynamically by the Linux kernel The contents of the directory vary with time and reflect the state of the running system  The entries in  dev pts correspond to pseudo-terminals  or pseudo-TTYs  or PTYs    Linux creates a PTY for every new terminal window you open and displays a corre- sponding entry in  dev pts  The PTY device acts like a terminal device   it accepts input from the keyboard and displays text output from the programs that run in it  PTYs are numbered  and the PTY number is the name of the corresponding entry in  dev pts    For example  if the new terminal window   s PTY number is 7  invoke this command from another window    echo    I am a virtual di        dev pts 7 The output appears in the new terminal window

User · Answer

tty  teletype   Usually refers to the serial ports of a computer  to which terminals were attached   pty  pseudoteletype   Kernel provided pseudoserial port connected to programs emulating terminals  such as xterm  or screen

[c] What do pty and tty mean?

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