pty-allocate 1 user commands nosh pty-get-tty allocate a pseudo-terminal pty-allocate next-prog pty-allocate is a chain-loading utility that allocates and opens the back end (called "master side" in older documentation) of a new pseudo-terminal, sets up environment variables appropriate to it, and then chain loads to next-prog with the execvp3 function. next-prog may contain its own command line options, which pty-allocate will ignore. pty-allocate sets the TTY environment variable to the full device filename of the pseudo-terminal front end. Programs such as open-controlling-terminal1, login-banner1 and login-process1 will make use of this environment variable. pty-allocate opens the back end of the pseudo-terminal as file descriptor number 4, closing that descriptor if it was already open. pty-run1 and console-terminal-emulator1 expect the pseudo-terminal back end on this open file descriptor. pty-allocate otherwise leaves its environment and open file descriptors unchanged. Thus next-prog will inherit the TERM7 environment variable and the (as far as the kernel is concerned anyway) original controlling terminal. To prevent a race condition in open-controlling-terminal1 (q.v.), pty-allocate calls grantpt3 to change the ownership of the front-end device to the (real, not effective) UID of the current process and set its permissions to allow only access to the owner; and then calls unlockpt3 to release the operating system interlock that prevents other processes from opening the front-end device before ownership and permissions have been set. The grantpt3 library function is only rendered a no-operation if the relevant devpts is mounted with some specific mount options. system-manager1 specifies these mount options, but that might not be what is performing system management for the machine. The grantpt3 and unlockpt3 library functions are in fact no-ops on BSD, as the front-end devices of pseudo-terminals are created with these permissions and UID in the first place. pty-run1 used to run a program attached to the newly created pseudo-terminal, passing its input and output to standard input and standard output console-terminal-emulator1 use to run a terminal emulator on the newly created pseudo-terminal, that sends and responds to the same control sequences as the kernel's built-in terminal emulator for (kernel) virtual terminals Jonathan de Boyne Pollard