Terminals are one of the most important parts of how programs interact with users. Usually programs print output into them and read user input from. For example when one executes any program from a shell, the shell provides terminal peer into it, so the program output will be seen in a calling shell and a user can do additional processing (say grepping and etc).
Supported terminal types
There are wide range of terminals exist in linux world: unix98 psesudoterminals (pty), bsd terminals, virtual terminals (vt) and etc. In CRIU we support the pty completely and vt in a way full enough for work. By full support we mean complete save of pty internal state including queued data. In turn for vt only plain restoration supported which means it is complete enough to do a traditional operations with terminals after restore but if there was some data queued and not yet delivered to a terminal user it will be lost. It is worth to mention that such situation should not be treated as any kind of error - the terminal transport layer never ever be one with guaranteed data delivery.
Overall CRIU supports the following terminals:
console terminal is the most simple one. It represents
/dev/console device and its restore is just literally
current terminal is rather an abstraction over real terminal an application uses. Upon its opening the kernel simply provides back the reference to the real one thus the same way as for console its restore is just
open(/dev/tty) with one exception - it must be restored last, ie after all other terminals are restored.